So this is a problem that I have been fighting for the last 20 years! I have a problem with my 3.4 . When the engine us cold, it runs like a carbureted engine where the choke is not closing Usually have to restart 8 - 10 times, until the engine warms up, and then it runs great!
I think I have tried just about everything, but nothing has worked, so I need help!
There are two different 3.4 engines which have been swapped into Fieros. Which one do you have?
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Originally posted by Jim Jimenez:
I think I have tried just about everything, but nothing has worked, so I need help!
What's "everything"? Have you had a scanner (or a laptop running WinALDL) connected to allow you to see what the sensors are reporting. Perhaps the MAT and/or CTS are telling the ECU that the engine is something like 250° when it's actually more like 60°.
So this is a problem that I have been fighting for the last 20 years! I have a problem with my 3.4 . When the engine us cold, it runs like a carbureted engine where the choke is not closing Usually have to restart 8 - 10 times, until the engine warms up, and then it runs great!
I think I have tried just about everything, but nothing has worked, so I need help!
If you're using the stock ECM and everything else on the engine is essentially stock other than the short-block and injectors, then my guess is that it's probably the cold start injector that's failed and / or failing. This often causes the issues you're talking about in a normal 2.8 in the Fiero.
It's my understanding that the cold start injector has no bearing on the engine once it's started. In other words, it wouldn't have anything to do with the multiple stalls.
It's my understanding that the cold start injector has no bearing on the engine once it's started. In other words, it wouldn't have anything to do with the multiple stalls.
It seems to be a constant point of discussion on Pennocks, as to whether or not it runs just while cranking, or if it provides fuel up to a certain temperature. I don't personally know or have an opinion either way. EDIT: I wonder if it's discussed in the service manual. I have one, so I'll check it out at some point tonight if I get bored.
But I figure you could rule out the cold start injector by testing it, but either way, as you say... the temperature sensor can certainly cause this behavior as well.
[This message has been edited by 82-T/A [At Work] (edited 09-20-2023).]
I think that someone should prove how the Cold start injector works by Hooking up a light to the wire that powers it- install on the dash- and then you can see when it is activated...Or you could go fishing in the computer program to see what it says......
It seems to be a constant point of discussion on Pennocks, as to whether or not it runs just while cranking, or if it provides fuel up to a certain temperature.
Keep in mind the OP has made no reference to hard starting. The problem, as reported, is the engine running rough and stalling while cold.
Another thing to check if the MAT and CTS readings proved to be satisfactory would be the fuel pressure. I suspect low fuel pressure might affect an engine more when it's cold, as it needs to be running richer.
[This message has been edited by Patrick (edited 09-20-2023).]
I would be looking at coolant temp readings, and intake air temp readings, with a scanner. This, as a first step.
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Originally posted by 82-T/A [At Work]: It seems to be a constant point of discussion on Pennocks, as to whether or not it runs just while cranking, or if it provides fuel up to a certain temperature. ...
It absolutely is only active while cranking. The big purple wire that causes the solenoid to pull in, when the key is turned to start, is the same wire that supplies power to the CS injector circuit. The temperature switch affects when it's activated when the key is turned to "start".
I would be looking at coolant temp readings, and intake air temp readings, with a scanner. This, as a first step.
It absolutely is only active while cranking. The big purple wire that causes the solenoid to pull in, when the key is turned to start, is the same wire that supplies power to the CS injector circuit. The temperature switch affects when it's activated when the key is turned to "start".
/ hijack
I totally believe you guys... it just seems like a lot of people in the archives / other (in search) seem to still think it did otherwise (as I did). I didn't look it up in the service manual last night. But odd to me why they didn't see the benefit of controlling it from the ECM via the temperature sensor. Maybe it was just too much effort to program at the time and not worth the cost?
Originally posted by 82-T/A [At Work]: I totally believe you guys... it just seems like a lot of people in the archives / other (in search) seem to still think it did otherwise (as I did). I didn't look it up in the service manual last night. But odd to me why they didn't see the benefit of controlling it from the ECM via the temperature sensor. Maybe it was just too much effort to program at the time and not worth the cost?
The later ECMs - like the 7730 - did away with the CS injector altogether. Remember, ours (and the 2.8 in the Camarobirds) were the first MPFI injected GM cars. At least that I can remember. But it's dead simple (and pretty crude) how it works. All it does is squirt gas into the lower plenum. Not into the cylinders. Not exactly "precision". It only is activated when starting. And then, only when the coolant is cold enough. When I built my 3.4, I did away with it entirely.
The later ECMs - like the 7730 - did away with the CS injector altogether. Remember, ours (and the 2.8 in the Camarobirds) were the first MPFI injected GM cars. At least that I can remember. But it's dead simple (and pretty crude) how it works. All it does is squirt gas into the lower plenum. Not into the cylinders. Not exactly "precision". It only is activated when starting. And then, only when the coolant is cold enough. When I built my 3.4, I did away with it entirely.
Yeah, that's a very good point. I'm looking at a couple of options on updating this. I've purchased a MicroSquirt and also a complete FAST EFI 2.0 system... I'm mostly planning the FAST EFI 2.0 system on my car (v6/3.4), and my daughter's car which is an 85 Duke. But I remember on my 81 TransAm... it was one of the first "computer controlled" car. It was still carbureted, but had a couple of sensors installed on the carb, had an O2 sensor, and also had spark timing control. The ECM was this gigantic box... more or less the same size of our Fiero ECM, but DOUBLE the height. It was gigantic... and that didn't even control a fuel injector.
I recall that it's a UART-compatible ECM communications channel... but only for reading data since almost everything on the ECM is simply an analog voltage signal. But regardless... the serial data speed is 180 baud... haha...
I mean, great for what it did... but damn, there's so much better out there now.
When you did away with it on your 3.4, did you use a whole new ECM? Or did you just reprogram what you had?
So this is a problem that I have been fighting for the last 20 years! I have a problem with my 3.4 . When the engine us cold, it runs like a carbureted engine where the choke is not closing Usually have to restart 8 - 10 times, until the engine warms up, and then it runs great!
Originally posted by 82-T/A [At Work]: ... When you did away with it on your 3.4, did you use a whole new ECM? Or did you just reprogram what you had?
I unplugged the wiring from the CS injector and temperature switch, and disconnected it from the starter. I plugged the hole in the corner of the fuel rail where the CS injector pipe connected. I removed the CS injector, unscrewed the other end of the pipe from it, and then reinstalled the injector in the lower intake, to block the hole. Period. I did nothing to the ECM/tune. The car ran 19# injectors to accommodate the "build". It was plenty rich enough, without the CS injector, even using a stock chip. Most of my tuning efforts were to reduce fuel, where it wasn't needed, due to the injector size. I ended up selling the car, before I had it "dialed in". But it still ran fine.
Ok guys. A little background. The 3.4 is a 3.4S out of a Camaro. The ECM is the GM replacement for the 1227730. The prom is a NOS one that I located in Florida. At one point I swapped the ECM with my other '88, 2.8 automatic car, it worked fine in there.
I would like to hook this thing to a scanner where I can see what it is doing, but I can't find anybody that has one. Me and all my friends all have tach/dwell meters (!) so that gives a clue as to our age! I do have a shop manual, I have all the covered i all the bases in there, time and time again. I just have to be missing something. I did entrust the thing to an old friend/shop owner, and he did not find anything either.
Of course I have already replaced the temp sensor for the ECM, Injectors, fuel pressure regulator , TPS, IAC and even the throttle body , It even has E3 spark plugs, a module and pick up coil.
I thought I had it a lot of times, but the next cold start it is the same thing.
So like I said, I am desperate!
Thanks guys for all your help!
P.S. I may not remember what happened 8 years ago in 2015, but we built this car in 2003, and has about 20,000 miles on it since. . Can you say running out of options???
Ok guys. A little background. The 3.4 is a 3.4S out of a Camaro. The ECM is the GM replacement for the 1227730. The prom is a NOS one that I located in Florida. At one point I swapped the ECM with my other '88, 2.8 automatic car, it worked fine in there.
I would like to hook this thing to a scanner where I can see what it is doing, but I can't find anybody that has one. Me and all my friends all have tach/dwell meters (!) so that gives a clue as to our age! I do have a shop manual, I have all the covered i all the bases in there, time and time again. I just have to be missing something. I did entrust the thing to an old friend/shop owner, and he did not find anything either.
Of course I have already replaced the temp sensor for the ECM, Injectors, fuel pressure regulator , TPS, IAC and even the throttle body , It even has E3 spark plugs, a module and pick up coil.
I thought I had it a lot of times, but the next cold start it is the same thing.
So like I said, I am desperate!
Thanks guys for all your help!
P.S. I may not remember what happened 8 years ago in 2015, but we built this car in 2003, and has about 20,000 miles on it since. . Can you say running out of options???
My personal opinion... if things just aren't doing really what you want them to... you might be better off really just replacing the whole ECM / system since you've made a lot of changes. Normally though, if a vehicle is running poorly on the stock ECM, it's going to run poorly with a new ECM. But in this case, you're running a modified engine on a stock 2.8 ECM and hoping it's going to work... and it will never run exactly right since the fuel map and everything else is totally not right... even if you think you've done the math right by going with bigger injectors that you think will compare to what would go with the 3.4. At that point, you really should just swap over to the 94-95 Camaro / Firebird ECM and harness.
The Microsquirt is much newer, will solve a ton of driveability issues, and allow you to tune it in a bit more. I hate to say it, but these old ECMs are not going to last forever, and the wiring harnesses get worn out, fatigued, etc. This is a big reason why I'm going this way with both my daughter's car, and my car. I bought a Microsquirt which I'll be installing on my daughter's car. My goal though is to get it running well with the factory harness and ECM (after a rebuild), because I know what to expect. It would be silly for me to swap in a new ECM when I don't even know if I've put everything together properly. But once we have her car running well, I'll take everything out "complete" and replace it with a brand new harness and ECM controller.
The wiring harness is old, and I want the car to be exceptionally reliable... so I'm going to be evaluating literally every wire from point A to point B that I won't absolutely be replacing. I'm doing the same for my V6 Fiero, but I'm going with the FAST system instead.
Ok guys. A little background. The 3.4 is a 3.4S out of a Camaro. The ECM is the GM replacement for the 1227730. The prom is a NOS one that I located in Florida. At one point I swapped the ECM with my other '88, 2.8 automatic car, it worked fine in there.
That's a whole different kettle of fish...
I'd guess the NOS prom you got is for the 7730 2.8 and why it ran fine in the '88. But that ECM was never used with a 3.4 and why the prom's tuning is wrong. The BIN likely needs to be tweaked for the 3.4's injectors. http://gafieroclub.org/ECMgood/p4xref.html#1227730
I think you'll have to message Ryan for advice on how to proceed on this one. He appears to have a very good handle on using the 7730 ECM. http://www.gmtuners.com/files/index.htm
Ok guys. A little background. The 3.4 is a 3.4S out of a Camaro. The ECM is the GM replacement for the 1227730. The prom is a NOS one that I located in Florida. At one point I swapped the ECM with my other '88, 2.8 automatic car, it worked fine in there.
This is the type of relevant info that should've been mentioned in the opening post.
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Originally posted by Jim Jimenez:
Of course I have already replaced the temp sensor for the ECM, Injectors, fuel pressure regulator , TPS, IAC and even the throttle body , It even has E3 spark plugs, a module and pick up coil.
I may not remember what happened 8 years ago in 2015...
No need to "remember", as I posted a link for you Here.
Guess what? I think you hit the nail on the head!! I installed a new set of R42-TS's, and the 3.4 now purrs like a kitty!
If anyone asks about E3 plugs, they are JUNK. I learned a very expensive lesson.
Any one (or more) of the new components you installed could be faulty... which is why you need to see what data is being sent to the ECU. However, dealing with the PROM as pointed out by fierosound might be your best first step.
The 7730 ECM is not stock to the car and I assume since you swapped it into your 88, the 88 is also running a 7730 (there are wiring changes needed to run the 7730).
When you say running a stock EPROM - stock for what car (what tune is on it)?
You stated the "other" 88 is an automatic, is the 3.4l and automatic? The code is a fair bit different between the 2 cars.
All comes back to what code are you running, what are the exact specs of the car, who rewired the 3.4l car? As other said, get a scanner on the car and see what it is doing.
