So I want to document fuel/lean issue with my stock 3.4 swap. The swap itself is pretty straight forward with plenty of posts and website on it. The problem I ran into is which injector to use, fuel pressure, and timing. So i read a lot of posts on how their setup work fine but no aldl data to backup their claim cause it might be working fine but their BLM and INT be higher than normal.

Also fix all your exhaust leaks and intake leaks, I use both a homemade smoke machine and shop vac (as blower and connect it to the tail pipe and soapy water) to find multiple exhaust leaks and intake leaks. End up finding an EGR internal leak with the smoke machine cause an intake leak and IAC was leaking a bit too.


1) I start off with my swap with the original 2.8 injector with stock fuel pressure of 43-44 psi (key on, engine off) with 87 octane. Got lean code and a lot of pings/pre-detonation with light load. No ALDL data as I didn't have a scanner during that time. Also it didn't help that my 2.8 injector was sitting on the workbench for over a month, im pretty sure its pretty clog up.

2) Saw a post on 17# BMW injector, but later research shows its not 17lb injector but 15.8 lb (166cc/min) @43.5 (3 bar) or 17.4 lb (183cc/min) @ 50.7 psi (3.5 bar). I bought those bmw before I realized they are not 17#. The car ran lean and have pings at medium loads and have lean code sometime when it was warming up. My aldl data shows my blm was peg to 150. Also engine runs hot even on a cold day.

3) Retard the timing to 8-6 and ran 91 octane, still pings and peg to 150 BLM. engine run hot.

3) Increase the fuel pressure to 51 psi (key on, engine off), idle fuel pressure is about 42 psi, 91 octane. Using the same BMW injectors ping is gone, no lean code but my BLM still peg to 150 with some load range i can drop the BLM to 149. INT is range from 120-160.
What surprise me is the INT is trending lower than BLM but BLM still peg to 150???
Also I notice the engine run a bit weird with aldl scanner while driving with it, with couple weird buckle/hesitation. Once i took it off, the car seems to run better.

here is datalog
6/20/2018 datalog

So should I:

1) datalog couple more times and see if the ECM will re-learn and lower the BLM??
2) bump the fuel pressure even higher( maybe 55 psi key on, engine off)
3) reset the timing back 10, will that help lower the BLM?
4) clean the #15 stock injectors and run it with fuel pressure @ 51psi (key on, engine off)
5) try the 17# camaro injectors and see if it can lower the BLM


Sorry for the long post but I hope it will help someone in the future.

I would put the 3.4 injectors in it and run stock fuel pressure to get a baseline data set.

I used 19 pound Ford injectors with my turbo 3.4 and it ran pig rich with puffs of black smoke until some customized fuel tables were developed. Now everything runs well and I have a fun car to occasionally drive. This is my backup show car and it does get around periodically.

Nelson

I would try the 17# Camaro injectors and see what happens. I saw you retarded the ign. timing to get rid of the knock, but the byproduct of that is that the engine will run hot. Knocking also happens if the mixture is overriched and the timing is retarded.
Also you have to pay attention to the spray pattern of the injectors you are using, that can make a difference in how much lean or rich the engine is running.
The ideal way would be for you to get a custom chip made. Running a 2.8 program on a 3.4 with bigger injectors can get you by but it is not the ideal way, you'll have hiccups.

If I tell you the injector size I'm using you'll throw up. But they work on my engine package and power goals.

[This message has been edited by La fiera (edited 06-21-2018).]

I have been driving my 85 SE V6 w/3.4 conversion since 1999......I could not get it to run with the 3.4 injectors.....I ended up installing the original 2.8 injectors...It runs ok- does not ping......At full throttle it runs like a raped-Ape but at part-throttle it has very sensitive throttle response......I have tried injectors that others have suggested...None have worked.....I suspect everyone else is suggesting injectors that will work with an >>>88<<< computer..........

And, tho I was trained as an Avionics tech in the Navy and fixed computers at Atari for 6 months in 1982....I have basically zero understanding of computer programing.......(I keep looking for the exact spot to apply the hammer......)

So I datalog again today and still getting the same peg 150 BLM throughout the rpm. INT while idling is 160-170, while driving INT might drop below 150 -125 but BLM still peg to 150.
Initial warm up is good, no hunting idle like in the past. If I don't have an ALDL scanner, i would call it good and won't know its still running lean.

maybe i will try bump the fuel pressure to 55 psi (key on, engine off), currently with the quarter coin trick, its about 51-52 psi (key on, engine off). But some people said with higher pressure, it might lock up the injectors.

Also just order some rebuild 17# camaro injectors from ebay, will i need to reset the ECM or just run it as is and let ECM re-learn???

Thanks for all the responses.

This is what I found regarding Bosch Fuel Injectors # 0280150415. This comes from Injector Planet's website.

This is a modified pintle injector with a 4-hole nozzle. There is a pintle behind each nozzle hole. This creates a much better spray pattern for better atomization.

Bosch EV1 Fuel Injector
Jetronic port / 4 hole nozzle

Flow rates @ 43.5 psi / 3 bar
16.76 lb per hour (My Note: 17# rated injectors flow at approximately 16.666 lb/hr at 3 bar or 43.5 psi. See calculator chart below)
126.5 G per min. (N-Heptane)
176.1 cc per min

15.90 Ohm resistance

Bosch Part # 0280150415
BMW part # 13641730060

CHART FROM MOTOR MAN FUEL INJECTOR SUPPLY

Fuel Injector Size Calculator
Horsepower (at the flywheel) 160
Number of Injectors 6
B.S.F.C. *

Max Duty Cycle in % 80


Required Injector Static Flow Rate @ 43.5 psi lb/hr 16.666

cc/min

Re: Mustang 19# are equivalent to GM 22#

Re: 150-170 BLM, definitely an injector sizing issue since you are using stock 15#...

Re: Camaro injectors - only seems to work good on 88 ECMs since they are multec injectors, pre-88s need to find pintle-style.

One question, when you have the scanner plugged in, does the scanner cause the system to go into service mode?

This is injectors info I got from another site:
http://maksinjection.com/?p...p-injectors-set-of-6

15.8 lbs/hr or 166 cc/min @3 bar(43.5 psi)
17.4 lbs/hr or 183 cc/min @3.5 bar (50.75 psi)

But this site rate them higher:
http://www.gomog.com/allmor...ectorRatesBosch.html
0-280-150-415
18.1 lb/hr 190.2cc/min 136.8grams 50.75psi 3.5bar

I'm not sure which is correct??

Fierofool, did you have to bump your fuel pressure? With stock pressure, I was definitely getting pings and runs hot.

[This message has been edited by Ucycle (edited 06-22-2018).]

I didn't have to bump my pressure. It's completely stock adjustment just as it was on the 2.8 before I swapped in the 3.4. My BLM is also maxed, and I'm told that I had spark knock. (My hearing is poor).

I have been running it hard with many Run For The Hills scouting and event runs with about 30,000 miles on it, now. I did retard the timing earlier this year after being told by Sarge that he heard spark knock.

I have to say that the injectors I have in mine are not the correct injectors. They are a very light gray color. I have revised my numbers and gone back and edited my original posts and articles. It seems that the injectors have been upgraded by Bosch. The 0280150415 is the same reference number that applies to the injectors I have in my engine. But they are a very light cream color, not green.

A couple of reasons you can get different flow ratings for the same injector can be due to the duty cycle used. Don't go over 80%. 85% is beginning to max out the injector and you could begin to starve for fuel. Another variable is the fluid used to flow rate them. If you look, you will see that N-Heptane was used in my example. I believe there are about four different fluids that may be used. Each one will give a different flow rate on the same injector and same settings. The Ohm rating of these injectors is within range of the stock injectors, too. That may be part of the reason the Rochester 17# injectors perform so poorly.

quote Originally posted by fierofool: I have to say that the injectors I have in mine are not the correct injectors. They are a very light gray color. I have revised my numbers and gone back and edited my original posts and articles. It seems that the injectors have been upgraded by Bosch. The 0280150415 is the same reference number that applies to the injectors I have in my engine. But they are a very light cream color, not green. A couple of reasons you can get different flow ratings for the same injector can be due to the duty cycle used. Don't go over 80%. 85% is beginning to max out the injector and you could begin to starve for fuel. Another variable is the fluid used to flow rate them. If you look, you will see that N-Heptane was used in my example. I believe there are about four different fluids that may be used. Each one will give a different flow rate on the same injector and same settings. The Ohm rating of these injectors is within range of the stock injectors, too. That may be part of the reason the Rochester 17# injectors perform so poorly.

Edit: remove wrong injector part# so I don't confuse others

Is Duty Cycle adjust from ECM/chip?? How would I know what duty cycle I'm running? thanks

[This message has been edited by Ucycle (edited 06-22-2018).]

Those aren't the injectors. Wrong body. They look just like our regular injectors, except for the color. Unfortunately, when they were installed, no numbers were recorded, so I'd have to pull the intake off to see what the numbers are. I've later been told by the vendor I bought them from that they should have the green bonnet on them, thus my remark about that in my post. I don't know how duty cycle is adjusted. Maybe your vendor or someone here can answer that.

[This message has been edited by fierofool (edited 06-22-2018).]

Fierofool, i think you are right about different fluid. Found this excel conversion chart:

Injector conversion chart (Click on it will download the excel file)

Also found this detail injector excel
KPa 300 = 43.5 psi

https://www.usrallyteam.com...ch_Injector_data.xls

Ucycle, Raydar has told me that the duty cycle is controlled by the ECM programming. He said that once the cycle is maxed in the program, the injector performance may become unstable. He had actually seen a video of the effect. It appears that if you raise the duty cycle by even 5%, the flow rate drops off. At least that's the result I got when entering data into an injector calculator program.

I'm confused by the BPW values in the log. They're in a single digit range, the highest legitimate looking value during acceleration was about 7.
I checked an old driving log of mine from 2012 and I was getting in the hundreds, my highest was 400.
I think the BPW is supposed to be the commanded injector opening time. I'm not clear on whether it includes the learned fuel trims, or if it's the calculated value without trimming.
I'm not sure what to do with this information, I just found it strange. Obviously your fuel pulses can't actually be that far off or you wouldn't get out of the driveway.

Are there any modifications other than being a 3.4L? Is this the stock 3.4L cam?
Have you confirmed that you're holding fuel pressure? With the key off, the pressurized fuel rail should only lose around 5psi in 10 minutes or so. Just wondering if there's a fuel leak that could be involved in the high BLMs.

quote What surprise me is the INT is trending lower than BLM but BLM still peg to 150??? Also I notice the engine run a bit weird with aldl scanner while driving with it, with couple weird buckle/hesitation. Once i took it off, the car seems to run better.

Unfortunately the 2.8L Fiero's 7170 ECM can only datalog in an alternate mode which doesn't run the same as normal operation. On my car this mode doesn't cause obvious drivability issues, but since your BLMs are so high that might be contributing.
In tuning my car, I've noticed some confusing behavior between the INT and BLM values. I get consistently low BLMs and high INTs. It seems like they'd meet somewhere in the middle, but they never do. I tried locking the BLM at 128 and tuning from the INTs, and as I recall this led to some contradictions from if I tuned for the BLM values, but my memory on that is vague.

Unfortunately the 7170 isn't a popular ECM so there aren't a lot of practical experiences posted about tuning it. The 7730 is way more popular (and better), but even if you are interested in that, it's probably a project for another day. And if "Bear Republic" means California, it would indirectly lead to visual inspection issues at emissions testing. So making the best of the 7170 is probably the way forward for now.

quote Also just order some rebuild 17# camaro injectors from ebay, will i need to reset the ECM or just run it as is and let ECM re-learn???

Not sure if resetting is necessary, but might as well.
I certainly expect swapping to the Camaro 3.4L injectors should get the BLMs in a better range. I *think* I have the 3.4L injectors in my 2.8L (I was too careless to write down the part number on them). My car has a surging idle with the stock chip, and I had to make a different chip to fix it. Maybe not everybody has that problem though.
Not everybody likes messing with the ECM, but if you don't loathe that, you might want to get an EPROM programmer and eraser so you can burn your own chips. But for now, see what happens with those injectors.

[This message has been edited by armos (edited 06-23-2018).]

I'm confused by the BPW values in the log. They're in a single digit range, the highest legitimate looking value during acceleration was about 7.
I checked an old driving log of mine from 2012 and I was getting in the hundreds, my highest was 400.
I think the BPW is supposed to be the commanded injector opening time. I'm not clear on whether it includes the learned fuel trims, or if it's the calculated value without trimming.
I'm not sure what to do with this information, I just found it strange. Obviously your fuel pulses can't actually be that far off or you wouldn't get out of the driveway.

I think my value is correct base on this post: aldl data stream results , i think the value unit is in M/Sec. Not sure what the "M" stand for, milsec??

Are there any modifications other than being a 3.4L? Is this the stock 3.4L cam?
Have you confirmed that you're holding fuel pressure? With the key off, the pressurized fuel rail should only lose around 5psi in 10 minutes or so. Just wondering if there's a fuel leak that could be involved in the high BLMs.

No mod at least what i was told when i bought the re-manufactured engine. It hold pressure while idling, since I increase the pressure to 42 psi during idle, 51 psi key on, engine off. I need to check what the psi is when i drive it with WOT. The INT on the datalog show during med load is trending below 128, im assuming that means its getting enough fuel. It seems like its running lean anytime except med/heavy load

Not sure if resetting is necessary, but might as well.
I certainly expect swapping to the Camaro 3.4L injectors should get the BLMs in a better range. I *think* I have the 3.4L injectors in my 2.8L (I was too careless to write down the part number on them). My car has a surging idle with the stock chip, and I had to make a different chip to fix it. Maybe not everybody has that problem though.
Not everybody likes messing with the ECM, but if you don't loathe that, you might want to get an EPROM programmer and eraser so you can burn your own chips. But for now, see what happens with those injectors.

I have another ECM that i can try. I don't know if my current ECM use stock chip/setting. It just seem weird that with higher fuel pressure didn't solve the high BLM. Using the injector calculator, i should be a high fuel injecor than the camaro 17# injectors. I also just got those 17# camaro injectors in the mail, try to get those install tonight and see what happen.
Im thinking about swapping to 7730. Been emailing Sinister Performance about getting a custom chip for stock 7170 ECM. But from what i read the 7730 will increase the performance and MPG. Might be worth to get this running good and convert it to 7730 and have Sinister Performance make me a new chip for the 7730??

[This message has been edited by Ucycle (edited 06-25-2018).]

quote Originally posted by armos:I *think* I have the 3.4L injectors in my 2.8L (I was too careless to write down the part number on them). My car has a surging idle with the stock chip, and I had to make a different chip to fix it. Maybe not everybody has that problem though.

I have a 3.4pr in an '87 GT running the stock ECM and Camaro injectors. It does everything quite well, including pass California smog. I think it runs a bit rich as fuel economy is pretty poor - worse than a very high strung XR4Ti I own - but it doesn't show in driving or a smog test.

Those # looks good. Did you set the timing to 7 degree? Seem low, did you have to retard the timing for some specific issue?? thanks

The timing is set to 10 degrees. My guess is that they don't properly short the ALDL connector before taking the reading, but I don't know. My XR4Ti also shows wacky timing - it too has a specific way to disable computer control of ignition. It should also be 10 degrees, but my last smog check shows 13. I'm guessing since both require taking tools to the car they simply aren't allowed to. I've never actually watched on these two cars, so I don't know. I think typically the rule is +/- 2 degrees but I'm not sure that applies to all cars... just the ones I've had problems with. Maybe next year I will replace the ALDL cover using some sort of security screw so they can't remove it and see what happens.

[This message has been edited by thesameguy (edited 06-25-2018).]

So i install the camaro 17# injectors and lower the fuel pressure to stock psi. Reset the ECM, start the car and got oscillating idle for the first min and setting down to a high idle of 1700-1900rpm. After it warm up(180f), it drop down to 900-1000rpm. Connected the ALDL scanner and it shows 200+ on the INT, BLM 128 during idle (i think its normal every time you reset the ECM, the BLM fuel table get reset back to 128 until it relearn) . The engine feel slugglish compare to the previous setup with the BMW injectors and 52 psi fuel pressure.
I don't get why my engine requires more fuel than other 3.4 swap i seem out there.

I took the ECM out since I want to see if it have a custom chip
07717000073320011 REMFG
DELCO APS 0168

I going to try this used ECM i got on ebay and see if it change anything
SERV. NO. 1227170
865032 M513095167
533004201235302
DELCO HWX 5184

Does anyone know if i run the HWX ecm, will it cause any issue?

Is it possible you have an air leak? Those engine speeds seem high to me. My 3.4pr's fast idle is around 1500rpm and it lasts only for a couple minutes before settling down to 700-800rpm. If yours is idling at 1000rpm, I'd suspect an air leak, and that will grow worse with revs... maybe causing a lean condition that you are correcting with more fuel.

I keep thinking the same thing about intake leak or exhaust leaks. But the IAC number seems normal once the idle settle down, its around 10-12 range when fully warm up and idling. From the fierocave, if i have intake leak, i should have a lower number than 10. At the beginning of datalog from the first post, i forgot to connect a vacuum hose so the IAC is less than 10 and high idle rpm. Once i connected the vacuum hose mid way to the datalog, my IAC when back to normal value during idle and rpm drop back to normal value.

I will check with both smoke machine and shop vac again tonight.

Or my fuel pump not pump enough, but my fuel pressure while idling looks normal 35 psi and 45pis key on/engine off.

Another thing maybe my injector connector/ wiring is not good? but I don't know how to test them? I did rent noid injector test light at the beginning of my swap and confirm the injector wiring is good and firing.

As for rpm, i think its normal to be idling in 1000 when you plug into aldl scanner. I can hear the change in rpm when i disconnect the scanner plug.

Also just order Holley adj fuel pressure regulator so I don't have to keep taking off all the parts to adjust the fuel pressure.

[This message has been edited by Ucycle (edited 06-26-2018).]

Any chance you have access to an exhaust gas analyzer or even a wide band O2 sensor? I'm inherently distrustful of old computers when it comes to oddball problems, and being able to analyze your combustion outside of the 30 year old computer might prove useful. You could have something silly like a bad O2 sensor or bad MAP sensor lying to the ECM or a bad ECM not properly managing its I/O. There is no reason why a factory 2.8l ECM and factory 2.8l components can't run a 3.4l reasonably well - up to 70-80% WOT *for sure*. That you're having to resort to aftermarket equipment really suggests something in the stock configuration isn't behaving properly.

I don't have exhaust gas analyzer or wideband O2, maybe will get one. Which one is better?

I switch to HWX ecm, from my research, its a 86 4spd federal ecm. Cold starting seem to idle lower rpm then my other ecm, also seems to lower the BLM but it could be the weather effecting it. Still very high INT, in 180 range during idle.

I smoke test again and find some leak on the IAC unit, and little bit on throttle body shaft by the TPS. Got another used TB and IAC so i swap it and re-do the smoke test, the replaced TB seems to leak more than my first TB. No more IAC leak with the other unit. So i probably swap the leak-free IAC to my original TB since it have less leak on the TB shaft.

Does anyone know where i can get new seals for the TB shaft?

When i took the TB apart, i remember it only have a felt ring as the seal.

Also does anyone know how to test for internal vacuum leak for the lower intake manifold. That is the only place that i cant see if its leaking through the LIM into the crank case. I hoping that is not the case since it will be **** load of work to get it change out. thanks

[This message has been edited by Ucycle (edited 06-27-2018).]

quote Originally posted by thesameguy: I have a 3.4pr in an '87 GT running the stock ECM and Camaro injectors. It does everything quite well, including pass California smog. I think it runs a bit rich as fuel economy is pretty poor - worse than a very high strung XR4Ti I own - but it doesn't show in driving or a smog test.

Good results. The emissions test was a major roadblock with the surging idle on my car. It was clean, but as long as it was surging I couldn't take the test because I live in a "basic" testing area where we get tested at idle and 2500rpm. Ironically, if I had been in an "enhanced" area, where the car is tested at speed, this wouldn't have been a problem. The previous owner had good results from that type of test in Folsom.
In desperation, I had to retard my timing to get it to idle the first time around. But by the time of my 2nd test, I had figured out the ECM tuning issue.

So 2 of you guys have 3.4 Camaro injectors without this problem? Interesting. I wish I had written down the pn on my injectors. Maybe they're not actually the 3.4 injectors. I was only able to barely read a few digits with them already installed. That was all I had to go on, and with some web searching, found a pn that appeared to fit what I could read. I plugged in the injector "offset" values from the Camaro 3.4 ECM (which somebody posted on gearhead-efi) and it fixed the surge.

quote The timing is set to 10 degrees. My guess is that they don't properly short the ALDL connector before taking the reading, but I don't know.

If they didn't disable the ECM advance then it would have shown more advance, not less. The ECM normally adds 8 degrees of advance at idle if you don't use the jumper, so 18 BTC total.
The limit is +/- 3 degrees, so they barely let you through. Maybe they just had trouble reading the indicator.

Can you explain the surge idle?

My rpm goes up and down a little bit like from 975-1025 about 50 rpm difference once it fully closed loop and aldl scanner connected. I don't know if this count as surge idle??

Can you give me link to where to find the injector offset value?

As for the timing during smog test, i feel like they don't even bother. I never seem them do it, at least with my last three smog and I'm in the enhanced area too.

quote Originally posted by Ucycle: Can you explain the surge idle? My rpm goes up and down a little bit like from 975-1025 about 50 rpm difference once it fully closed loop and aldl scanner connected. I don't know if this count as surge idle??

No, that much fluctuation is pretty normal I think.
When I had the surging idle, it would go between like 700-1200rpm. Really irritating, and it went beyond the RPM limit for a "2 speed idle" emissions test.
What I noticed on the ALDL log is that it kept cutting the fuel trims leaner and leaner, as the surge kept getting worse. Then when it nearly stalled the ECM would panic. It would richen up the fuel and open the IAC, raising the idle to a steady ~1500rpm or whatever. Then it would settle back down to 900rpm, then start trimming the fuel again, and the cycle repeated.

quote Can you give me link to where to find the injector offset value?

I don't have it handy and I need to head off, but I'll see if I can find it later tonight and post it.

The only time i had surge similar to yours is when i plug in my old MAP sensor. The old MAP value looks correct when i plug in my aldl scanner and seems to be correct value with different vacuum pressure. I was planning to return the new autozone MAP sensor but once I plug back the new MAP sensor, the surge went away. But i only have two idle datalog on the camaro 17# injectors, who knows it might have surge idle once i start drive it a bit more.

quote Originally posted by armos: If they didn't disable the ECM advance then it would have shown more advance, not less. The ECM normally adds 8 degrees of advance at idle if you don't use the jumper, so 18 BTC total. The limit is +/- 3 degrees, so they barely let you through. Maybe they just had trouble reading the indicator.

I am virtually positive this changed, or maybe varies from car to car. I have a lot of old Saab 900s, and since they lack EGR they frequently have problems with NOx emissions as they age. It was never a problem with the idle tests, but became a real issue with the dyno tests. The solution I used to use was dial timing back from 16 to 13 and that always worked. But, starting many years ago (10?) they began failing these cars with anything more than +/-2 degrees and I had to make it work at 14 degrees. If the Fiero is still +/-3, I think the spec must vary from car to car - but IDK for sure.

Funny that you mention the surging idle.... I had an F150 with a straight six a few years ago I bought out of the foothills and the owner/seller had a devil of a time smogging it due to a surging idle - something these trucks are known for due to a complicated EGR system. He "fixed it" but the problem came back within the first few weeks of me owning it and I spent a fair amount of time & money trying to remedy it. I got it "pretty good" but never great and braced for a fail when I went to sell it. But, no problem - they threw it on the dyno and didn't even care. Those dyno tests sometimes bite you - but sometimes help you!

I think i might have figure out why I'm getting lean condition. I think i might have a internal vacuum leak (gasket??) between lower intake manifold and crankcase.

This morning I connect the smoke machine to the upper intake, plug the PVC hose, plug the brake booster hose, plug the throttle body. The only hose that is attach is cold start injector air bypass tube (i think that is correct name for it?) that goes from the lower TB to the LIM. When i peep through the oil filler hole on the valve cover, i see small trace of smoke coming out of it.

Can anyone confirm the hose goes into LIM by the CSI goes into the intake side and not the crankcase?

I going to perform another internal vacuum test and if that is positive i'm sure i have a internal leak. I'm surprised i'm not sucking in oil and getting black exhaust gas from the tail pipe.
Not looking forward to replace the LIM gasket the third time if its the case. But at least I finally figure out the issue.

[This message has been edited by Ucycle (edited 06-28-2018).]

So i don't have internal vacuum leak, after performing this test:
https://www.youtube.com/watch?v=G90ztJIaF0Y

I have positive pressure in the crankcase similar to the video.

I might have a slight vacuum leak on the brake booster hose, I try to use my hand vacuum pump but could get a vacuum on the line. i'm going to plug it and see if it improve the blm/INT.

[This message has been edited by Ucycle (edited 06-29-2018).]

quote plugged in the injector "offset" values from the Camaro 3.4 ECM (which somebody posted on gearhead-efi) and it fixed the surge.

This could be why 88ECMs work with Camaro injectors well and pre-88's don't. I have an 88 bin file but not an 87. Would be interesting to compare the values including the Camaro values.
Can you show me exactly where you made the modification?

Re: the injector offsets that I used for the 3.4L injectors
I made a post about this on the forum a few years ago but I think the way I went about changing the values wasn't quite correct, and the thread is archived so I can't edit it.

The info/files for the FBody 3.4L ECM were posted at gearhead-efi by RobertISaar (see the link).
The XDF (definition file) and BIN files from that thread can be opened in TunerPro. First select that .XDF file in TunerPro and then open the BIN.
The relevant BIN files are under the "Rev 3" folder and the "F" subdirectory (FBody). The file I used as a reference was "16203261 94 F auto federal.bin" which should be for the implied model of 3.4L Camaro.

The tables of interest (in the FBody BIN) are called "Injector Offset vs Fuel Pump Voltage" and "Injector Offset vs Low BPW". I transcribed those tables into the corresponding tables in the Fiero 7170 ECM. The tables on the 7170 are called "Injector PW Correction Vs. Battery Voltage" and "Low Pulse Width Injector Offset Vs. BPW".
Transcribing these values isn't a perfect operation. The Fiero 7170 ECM has nowhere near as much resolution or granularity in these tables. Also, it's a slower ECM so it probably doesn't time the injector pulses as accurately in any case.

code:

---

Injector PW Correction Vs. Battery Voltage
---------------------
               Edited    stock 86 auto fed (FBA)
Volts          usec      stock 88 auto fed (AKYM) and stock 88 5spd fed (AKYN)
--------------------------------------------------------------
  0.0           396.73     6591.89
  1.6           640.88     6591.89
  3.2           640.88     6591.89
  4.8           640.88     6591.89
  6.4          3082.32     6591.89
  8.0          1525.90     2868.69
  9.6           671.40     1709.01
 11.2           488.29     1251.24
 12.8           305.18      885.02
 14.4           183.11      732.43
 16.0            91.55      701.91
 17.6             0         549.32
 19.2-25.6v       0         427.25

---

code:

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Low Pulse Width Injector Offset Vs. BPW
---------------------------------
               Edited           stock 86 auto fed (FBA)
BPW(msec)      usec Added       stock 88 auto fed (AKYM) and stock 88 5spd fed (AKYN)
----------------------------------------------------------
0.488          228.88             228.88
0.732          137.33             152.59
0.976           61.04             122.07
 1.22           45.78              91.55
 1.46           30.52              76.29
 1.71           15.26              45.78
 1.95           15.26              30.52
 2.20-3.90       0.00               0.00

---

In comparing against the Fiero stock values, I didn't see a difference between the 86 and 88 BINs that I checked.
Here's a screenshot of the edited tables in TunerPro:
FBody 3.4L injector offsets used in Fiero 7170 ECM
Both of these "offset" tables are used to compensate for the non-linear behavior of the injectors. If the values are incorrect for the injectors that are in the car, it adds a source of error to the ECM's calculation of the injector pulses. This error becomes most significant at a warm idle, when the fuel pulses are the shortest.
As you can see in the graphs, the stock Fiero programming (plotted in red) adds too much compensation with the 3.4L injectors.

It's been a while, but unless I've forgotten something, I believe the values shown above are a direct, best-fit transcription of the values that GM used for the 1994 Camaro 3.4L auto w/ Federal emissions. Those edits resolved the warm hunting idle on my car, which I *think* has 3.4L Camaro injectors, but I have some doubt.


Changing the tables I mentioned will greatly impact the BLMs, and so the Base Pulse Constant (BPC) should be adjusted as needed. The BPC is a single scalar value that universally increases or decreases the amount of fuel the ECM will calculate. Increase it to get more fuel (and lower BLMs), or decrease it to get less fuel (and higher BLMs). The BPC value is the simplest way to account for differences in engine and injector size.


When I changed those 2 "offset" tables, I began to have (and still have) an occasional surge shortly after startup when it's running in open loop (no feedback from O2 sensor). But it stabilizes in closed loop, so it was a good trade. It seems something about these changes threw off my open loop tune.

In a later version, I did start tweaking the offset values a bit in the "offset vs battery voltage" table. I did that because I had a "curl" in my logged BLMs at the low MAP end of the table. It implied to me that my injector offsets were still not really correct. Based on some reading at thirdgen.org, it looked like tweaking the "offset vs battery voltage" would be a good idea. I ran into some kind of problem though and lost interest.

[This message has been edited by armos (edited 06-30-2018).]

That is stupendous... really great info!