While the chip I have currently runs my Northstar fairly well, I believe there's room for improvement. Since neither TunerCat nor GMEPro have definition files for the N* ECM yet, and I don't yet know enough about 68HC11 assembly to hack my own, I've been thinking about switching to a different computer. Aftermarket systems are nice, but expensive. If I were to spend that much money, I'd have to at least not take a step back in terms of capabilities, which means spending $1400 on an Accel DFI capable of sequential injection on a V8.

However, if there were a MUCH cheaper solution, I'd be willing to accept some reduction of capability. So I started thinking about the TPI computer, which has been hacked like no other, but is limited to batch fire injection.

The N* crank position sensors output 32x unevenly spaced analog pulses. The cam sensor outputs one pulse every other revolution. The ICM takes these signals and translates them into a 24x blip to low, a 4x signal, and a 1/2x signal, all 0-5V.

I've been told that the Caddy computer just uses the 24x for idle stability, and obviously uses the 1/2x for sequential injection. If I disregard both of these signals, I'm left with a 4x which might be similar to what a TPI ECM gets from a distributor. Because the ICM acts like an electronic distributor, the N* PCM has only one ignition output, so in this regard the TPI could also run the N*.

From what I've gleaned from service manuals, the ICM's 4x signal goes high about 5 degrees before TDC for any given cylinder, and goes low again 10 degrees after.

How compatible is this with the 4x signal the TPI ecm wants to see?
What's the maximum RPM at which a TPI computer cam control an engine?
Since I'm not currently interested in hacking up my harness, I want to build an adapter harness for the TPI computer. Does anyone have any leads on a broken N* computer for cheap? It could be smashed or burned up... I don't care as long as the connectors are intact.

Rockcrawl? TK? Darth Fiero? Dennis LaGrua? Anyone?

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

Will, according to Kenny Dutwieller, most engine computers operate in batch fire above 3000 rpm anyway regardless if they are SFI. This is because there is not enough time for the injector to pulse enough fuel in SFI mode at WOT at these engine speeds. This could or could not be true but as I have no way of testing it, I cannot deny what he has told me. If it is true, then a batch fire system would not cost you any HP or TQ at WOT anyway.

As far as the compatibility of the 7730 ECM with the N*, it is going to be a hard call. The 7730 looks for an evenly spaced 4x signal (4 pulses per crank revolution). It appears that the N* module does have a 4x ref output for the PCM so this may work with the 7730, but it is hard to tell as I don't have a scope pattern to look at from the N* module to see if this is a signal the 7730 can use.

What year N* computer are you running? If you are using the OBDI N* computer with the red, white, and blue connectors, you shouldn't need to hack anything. You could get the GM connector pak tool and pull the terminals out of the N* connectors and then insert them straight into the 7730 connectors in the proper locations. I have pinouts for both systems if you need them. I also have a complete disassembly for the $8D code (7730 ECM) which would allow you to do just about anything your heart desires; within the capabilities of the 7730.

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1987 Fiero Coupe 3800 Series II Intercooled Turbo (12.79et @ 106.6mph)
1987 Trans Am GTA 5.7L Superram 4L60-E (13.1et @ 109mph)

http://dtcc.cz28.com
GM EFI chip reprogramming & 3800 Fiero Conversions

[This message has been edited by Darth Fiero (edited 10-16-2003).]

Darth: I don't know that much about this topic, but I do know HC11 code pretty well. Would you mind sharing the 7730 disassembly? I've always wanted to look at it.

TIA

You can download it from:
http://dtcc.cz28.com/files/1227730hack.zip

It is actually for the 1227727, but that is the same computer as the 7730, just in a different case.

quote Originally posted by Darth Fiero: If it is true, then a batch fire system would not cost you any HP or TQ at WOT anyway.

I've heard that as well, and I see know reason that the code couldn't take advantage of all the time that's available, as long as it's written properly. I'm not worried about it for power, I'm after sequential for fuel economy and civility with HUGE cams.

quote As far as the compatibility of the 7730 ECM with the N*, it is going to be a hard call. The 7730 looks for an evenly spaced 4x signal (4 pulses per crank revolution). It appears that the N* module does have a 4x ref output for the PCM so this may work with the 7730, but it is hard to tell as I don't have a scope pattern to look at from the N* module to see if this is a signal the 7730 can use.

There's a trace in one of the shop manuals that calls out rises and falls of the signal. They are as I've told you, and I drew a bit map from these traces that describes all the signals.

The ignition signal from the N* PCM goes high when the 4x signal goes low, then goes low when the plug fires.

quote What year N* computer are you running? If you are using the OBDI N* computer with the red, white, and blue connectors, you shouldn't need to hack anything. You could get the GM connector pak tool and pull the terminals out of the N* connectors and then insert them straight into the 7730 connectors in the proper locations.

I want an adapter harness so that I can unplug the N* computer, do some tuning on the 7730, then plug the N* computer back in to drive, at least until I have the 7730 dialed in well enough to drive every day. OBDI N* computer, just like everyone else who's running a manual trans with the N*.

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

Ummm...
Not that I know anything about this at all, but how would you go about setting the base timing?

I'm not looking for a detailed technical answer as this is, presently, way out of my league.
Just curious, more than anything.

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Raydar

88 3.4 coupe. 17s, cut springs 'n all.

Will,

I don't know about the N*, but all the GM 60 degree engines with DIS act just like a distributor. With my 3.4l DOHC engine, I set up the computer as if the engine had a distributor. You will have to check if the N* DIS uses the same PWM for timing as the TPI controller. That may be your only hang up. Is your N* coil on plug? If so, how does the one wire ignition work? My DIS fires the coil for the cylinder that needs it (and waste sparks another). The DIS reads in the crank signal and outputs the reference pulse. In my case, the output is 3 square waves per revolution. A total of six pulses (3 rising, 3 falling). That is all the Haltech reads for timing and fuel. The reference of either the rising or falling edge is all that is needed.

Again, my only concern is the ignition system. My engine was evolved from a car that had a distributor. They basically made a distributor in a box to replace it. Your N* may not have used this same design since it had DIS from the beginning.

Matt

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86 GT, 5-Speed
87 GT, 3.4l DOHC Turbo
95 BMW M3
02 Nissan Altima 3.5SE

Thanx Darth. Very interesting. You have anything that's not in PDF format so I can use it in my "code writing" program. Otherwise I'll have to see if I can convert it back to text/asm.

The base timing is something to be figured out. Depending on where the HEI 4x reference pulse is relative to TDC of any particular cylinder, the TPI computer may need to have base timing added to all values of the timing table, or subtracted, or something weird. I hope there's enough "room" in the table values for doing something like that if necessary.

Matt: The N* ICM is a dizzy in a box just like yours, it just has a couple extra features that come from being on the premium V8 line. The N* is waste spark. It didn't go coil-per-plug until MY2K.

The similarity in the ignition reference signal is what makes me think it is possible to use a more standard computer on my engine.

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

Will,

It sounds like it could work. To find my base timing, I just guessed initially. Since my engine didn't have timing marks, I marked TDC and 10 degrees BTDC with a paint marker. I used a timing light to adjust the base reference until I got it right. I just recently found that my original marks were 5 degrees off, so more power is on the way. Keep me updated with this project. I am interested in doing a N* swap and if this works for you, my Haltech will also work.

Matt

Why couldn't you make a notched wheel, bolt it on the pulley and use the standard crank sensor with the ECM?

quote Originally posted by TK: Why couldn't you make a notched wheel, bolt it on the pulley and use the standard crank sensor with the ECM?

You're asking Matt, I guess?

Personally, I despise external trigger wheels. If something were to happen to it, my engine wouldn't run. Period. The factory sensor is MUCH better protected, and thus also more durable. I have a friend who was frustrated forever because of problems getting his external trigger wheel to work on his TEC2 controlled turbo Miata.

------------------
'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

quote Originally posted by Will: You're asking Matt, I guess? Personally, I despise external trigger wheels. If something were to happen to it, my engine wouldn't run. Period. The factory sensor is MUCH better protected, and thus also more durable. I have a friend who was frustrated forever because of problems getting his external trigger wheel to work on his TEC2 controlled turbo Miata.

I was just trying to make it work.

Will, as long as the 4x signal is evenly space and produces 4 pulses per crank rev, I don't see why the 7730 would have a problem running it. Give it a try and let us know if it works.

two off the wall ideas on the computers for the N*
IRL indy race cars ran the olds version and are now just old out of date junk, surpluss, maybe very cheap, if you can find them or even get new chips from whoever made them as the work is done and the market is over now
BTW the new chevy is a cosworth {FORD} race motor that runs in IRL now

shelby also used the olds version in his S-1 cars, with a stick, some supercharged, maybe he can be a source for chips

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Question wonder and be wierd
are you kind?

Has anyone tried to run the LS-1 Vette computer to operate an N*? I tought at least someone did, but I cannot remember where...I'll try to look it up.
S.Williams

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1988 Fiero Formula T-tops
CJB 143 of 1252 "factory T-top cars"

I'm sure the Indy cars use a Motec of something similarly out of my price range.

I was looking at Shelby stuff... but www.shelbyamerican.com was down last time I checked. The new site is back up now. When did the S1 come out? If the S1 came out in '96, then it's a moot point anyway, since I'd need an OBDI computer.

I've been thinking of the LS1 computer. Both use a 24x pulse train. However, the LS1's pulse train is PWM to make it easier for the ECm to detect misfires. A PIC could translate, but that's a lot of development effort, and the editing software for the LS1 computer is still quite expensive.

How much RPM can the 7730 understand, and how high can it go and still properly control the engine?
How much "room" is in the timing tables? Could I add 10, 20, or 30 degrees to base timing if I had to?
What year should I use? I will need to use a '96 TB anyway, so I could keep the MAF on it and use a MAF computer, or I could get rid of the MAF and use a '90 computer to stay with my current MAP sensor.

quote Originally posted by htexans1: Has anyone tried to run the LS-1 Vette computer to operate an N*? I tought at least someone did, but I cannot remember where...I'll try to look it up. S.Williams

As I was reading this thread I was wondering the same thing. Has allot of similarities ( OBDII 8 cly, sfi, cam and crank sensors) this is way out of my league, but I know with LS1 edit they can manipulate allot of the controls. There are some guys over on ls1tech, that tweak just about anything not just rev limmiter and fuel tables. I would think both being GM and OBDII , it would share allot of programing. Like I said I don't know much about this, but I bet the guys over in computer/diagnoses would know at ls1tech.com. Just a thought.

The Indy cars use a special Delphi system that also is compatible with their telemetry. A year or two ago there was a pretty good article on the electronics or it at the Delphi website, but I lost the bookmark for it, if it's even still there.

I've thought about using a different computer as well and would probably use an extrnal trigger wheel for the crank sensor, although I share your conerns about them.

John Stricker

quote Originally posted by Will: I'm sure the Indy cars use a Motec of something similarly out of my price range. I was looking at Shelby stuff... but www.shelbyamerican.com was down last time I checked. The new site is back up now. When did the S1 come out? If the S1 came out in '96, then it's a moot point anyway, since I'd need an OBDI computer. I've been thinking of the LS1 computer. Both use a 24x pulse train. However, the LS1's pulse train is PWM to make it easier for the ECm to detect misfires. A PIC could translate, but that's a lot of development effort, and the editing software for the LS1 computer is still quite expensive. How much RPM can the 7730 understand, and how high can it go and still properly control the engine? How much "room" is in the timing tables? Could I add 10, 20, or 30 degrees to base timing if I had to? What year should I use? I will need to use a '96 TB anyway, so I could keep the MAF on it and use a MAF computer, or I could get rid of the MAF and use a '90 computer to stay with my current MAP sensor.

quote Originally posted by Will: How much RPM can the 7730 understand, and how high can it go and still properly control the engine? How much "room" is in the timing tables? Could I add 10, 20, or 30 degrees to base timing if I had to? What year should I use? I will need to use a '96 TB anyway, so I could keep the MAF on it and use a MAF computer, or I could get rid of the MAF and use a '90 computer to stay with my current MAP sensor.

Good question. I have had mine as high as 7000 rpm but I don't know where the "limit" is for its "understanding." As far as the timing I know you can alter initial and maximum allowible spark advance up to 90 degrees each. The main SA table is only tunable up to 5600 rpm but the PE table is tunable up to 6400 rpm. As far as the MAP and MAF issue the engine will run fine with only MAP once you get it tuned in. A MAF system would be easier to tune.

Will all this work for you? I simply don't know and sitting here trying to reverse engineer the 7730 is not going to get us anywhere. I think the best way to go about seeing if this works or not is to put it on your engine and see what happens.

quote Originally posted by Darth Fiero: A MAF system would be easier to tune. Will all this work for you? I simply don't know and sitting here trying to reverse engineer the 7730 is not going to get us anywhere. I think the best way to go about seeing if this works or not is to put it on your engine and see what happens.

I know it will eventually come down to trying it, but I just don't feel like I've done enough research yet. Fortunately the GMECM list is back up, so I should be able to get some info there.

How reliable is the MAF setup? Why did GM switch away from it?

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

GM switched from MAF for one reason. Cost. It is much cheaper to produce MAP vehicles. You will see most cars going back to MAP in the next 5 years. Emission regulations caused a resurgance of the MAF sensor, but control is getting better and MAP is now viable again. Also, the MAF used in the TPI cars was very unreliable and costly to replace. Go with the MAP setup. It may take a little more tuning, but it is more robust.

Matt

If the early MAF is unreliable, what about using a modern MAF, like the LQ4 unit that F-body guys like? Or possibly the stock MAF from a '96+ Northstar, since that's a bolt on affair. I know that I'd have to redo the MAF tables in the 7730, but I'd rather invest time to do that now than retune extensively when I add headers, or redrill the cam sprockets, or change cams...
Basically, I like the idea of using a MAF for it's adaptibility, and would like pretty compelling reasons not to.

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

quote Originally posted by Will: If the early MAF is unreliable, what about using a modern MAF, like the LQ4 unit that F-body guys like? Or possibly the stock MAF from a '96+ Northstar, since that's a bolt on affair. I know that I'd have to redo the MAF tables in the 7730, but I'd rather invest time to do that now than retune extensively when I add headers, or redrill the cam sprockets, or change cams... Basically, I like the idea of using a MAF for it's adaptibility, and would like pretty compelling reasons not to.

Will, I am not aware that the 7730 is compatible with any MAF sensor, especially the newer ones like your N* has and the LS1 styles, etc. I can't say if the 7730 would be able to interperate the high frequency used by the modern MAF's.

Then what was the designation of the MAF computer used with early TPI systems? Whatever that is, that's what I meant for the MAF possibility. It sounds like it will work with some tuning, the question is now MAF or MAP.

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

In addition to the TPI v8's, the '730 ecm was also used on v6 2.8/3.1's with DIS and a frequency based MAF. This MAF might be the same signal as the Northstar's MAF. If the '730 DIS/MAF code could be tweaked to run a v8, would there be a compatable DIS unit? (It appears to me that the DIS unit on the '730 is not as complex as the Caddy one or the ones on the SFI Buick v6, doesn't the DIS brick also have the cam angle stuff in them for sequential injection?)

Ok, what was the ECM used on the MAF TPI engines?!?
With a modern 3.5" MAF sensor, couldn't the MAF tables in the ECM be remapped to work with the modern sensor? How much airflow can the code understand?

I haven't looked into other GM DIS modules, but the Caddy module is probably substantively similar. It's cam sensor output can be ignored easily enough. The other thing I'm wondering about is that the DIS module controls the timing up to a certain RPM, at which point the ECM energizes the "Hi, I'm ready to control timing" pin and takes over timing control through the ignition line. How does the start sequence work on the TPI ECM?

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

The '165 ecm was used on the F body and Vette TPI/MAF cars. The problem that you are up against there is the same one that I had when I tried to run my 3.4 with the Fiero ecm and a DIS brick- it won't work
I ran the car with a '727 ecm, TGP code and the DIS, but it ran crappy. So, I swapped back to the Fiero ecm and tried the DIS with it and all that happened was the DIS made a funny noise and the engine sputtered. Even though the wiring colors/identifications are the same (high/low/bypass/timing), the ecm signal to the distributer must be different between the two. Of course, it might be my luck was just off on that day, but I tried it and did not have any success.

Ok, the earlier F and Y body MAF computers were 1227165 ECMs. These are slow and work off a MAF sensor that outputed a voltage signal. There is a parameter in the 7165 ECM that would allow you to run a frequency based MAF sensor. HOWEVER, this ECM as well as the 7730 is ONLY compatible with the early frequency based Delco MAF sensors that were used on the 2.8's. These operate at a much LOWER freq than the newer MAF's like what you have. I have tryed getting the 7165 to operate with the newer MAFs but it is a feable attempt unless you buy a MAF TRANSLATOR.

As far as the 7730/7727 controlling a DIS ignition, yes it was set up to do that from the factory on 6 cyl cars so I know it will work on V8's as well. Something you need to keep in mind is there may be something else you have to change in the code to make it compatible with the DIS because the V8 programming is set up to run a distributor. If I had a disassembly of a V6 7730/7727 code I could help you figure it out but I don't. Perhaps it has something to do with the Spark latency correction table. Again it is hard to determine if this ECM will work for you. You know, it would be funny if you go to all this trouble and get the 7730 hooked up in your car and then a week later someone like TunerCat releases programming for the OBDI northstar...

you could run a '749
and tune it with programmer, tunercat or GMPCM
then datalog with DataMaster, retune and make on-the-fly changes with a laptop and a Pocket Romulator

they have been hacked (code)to run wideband O2 sens,
multiprogram chips and reconfigured to run 3 bar map sens (code) and 50 to 84 lb injectors (injector drivers)

and they cost about 40 bucks at a wrecker

I know of 1 or 2 guys on this board who have used them to run 2.8s and 3.4s

there are a lot of sbc v8s, turbo and non turbo also runing these

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84 Fiero Turbo Vortec 4300 Phantom GT
L35 block, Syclone Intake and ECM T04B H3 Turbo
www.cardomain.com/id/vortecfiero
Murphy's Constant Matter will be damaged in direct proportion to its value
Murphy's Law of Thermodynamics Things get worse under pressure.
Arthur C. Clarke "Any significantly advanced technology is indistinguishable from magic"

quote Originally posted by vortecfiero: you could run a '749 and tune it with programmer, tunercat or GMPCM then datalog with DataMaster, retune and make on-the-fly changes with a laptop and a Pocket Romulator they have been hacked (code)to run wideband O2 sens, multiprogram chips and reconfigured to run 3 bar map sens (code) and 50 to 84 lb injectors (injector drivers) and they cost about 40 bucks at a wrecker I know of 1 or 2 guys on this board who have used them to run 2.8s and 3.4s there are a lot of sbc v8s, turbo and non turbo also runing these

took the words right outa my mouth

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010010010110011000100000011110010110111101110101001000000110001101100001011011100010000001110010011001010110000101100100001000000111010001101000011010010111001100100000011110010110111101110101001000000110000101110010011001010010000001110100011011110110111100100000011001000110000101101101011011100010000001100011011011000110111101110011011001010010000000100001

code_warrior,

I guess I am too close!!

01001100010011010100000101001111

Matt

bump

Hey, code warrior, how about editing your post and removing that assinine sig of yours?

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It does decrease the readability of the thread dramatically. What does it mean?

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'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow

Will, I have had some recent thoughts about this setup. There is just one thing that didn't add up which has been bothering me.

Darth Fiero stated early in the thread that the 7730 looks for an evenly spaced 4X signal which is what the ignition module produces on standard applications. I understood what he was saying but I couldn't figure out how the ECM could figure out the crankshaft position and know which coil to fire for each signal.

After a couple days of trying to figure it out and comming up with alot of unanswered questions I finally referred to my 1992 Grand Prix service manual which I knew had DIS.

quote The system uses a magnetic crankshaft sensor which protrudes into the block, within approximately .050" of the crankshaft reluctor. The reluctor is a special wheel cast on the crankshaft that has seven machined slots, six of which are equally spaced (60* apart). The seventh slot is spaced 10* from one of the other slots. As the reluctor rotates with the crankshaft, the slots change the magnetic field of the sensor, causing an induced voltage pulse. By counting the time between pulses, the ignition module can recognize the pulse of the seventh slot (sync pulse). Based on this sync pulse, the module sends the reference signal to the ECM to calculate crankshaft position (used to fire coils in correct sequence) and engine speed.

So I am wondering now if you use an even 4x signal how will you determine crankshaft position? I ask due to interest in adapting DIS in applications which once used a distributor.

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