4.3 V6 ECM on a V8: which way should I go?

Hello everyone! I’ve been lurking around this site for a few weeks and figured I’d introduce myself. My name is Dave, but my buddies call me DOC (“Dave-On-Call”). Five years ago I retired from St. Louis to Georgetown, Texas. I need some TBI advice and or education as I’m at a point where I’m in over my head. My project is a 1948 Chevy 1/2 PU resto-mod. I’ve owned this truck long time and did pretty much everything on it myself. I’m a gearhead. Here’s what its got: 1969 2 bolt 327 (.030 over; 10:1 forged pistons); small valve Power Pak heads and a stock cam, cast iron exhaust manifolds; Magnaflow exhaust; 700-R4 from a 1991 Z28; 3.73 Posi. I’ve been driving it about 7 years and put about 5000 miles on it. I’ve gone thru a Dualjet, then Q-jet, then a Holley carb. Quite a while back my daughter’s ex-boyfriend abandoned his clapped out 1992 GMC S-15 in my garage and so I inherited a complete running TBI 4.3 Z motor. (ECM 16144288/Prom BARL). So, looking for a challenge I decided that the 4.3 fuel injection could work on my 327. (Why can’t you use a V6 Computer/Prom on a V-8 truck?!) It took some time, but I pretty much took everything ECM related from that S15 and put it on my truck, with the exception of the distributor, of course. It’s a stock GM EST distributor, with Electronic Spark Control, from a 1990ish C10 5.7 K motor, using a TBI intake from that same generation truck.The EGR is fully functional. I’ve installed a CE lite in the dash and have a fully functional ALDL under the dash. I can monitor all of the ECM inputs and outputs using an OTC Monitor 2000. I’ve logged about 4000 miles with the TBI. But here’s the trouble: as I dialed in this computer system I gradually started experiencing a very random backfire/stalling problem from a stop, just off idle. When driving it with a scanner I’ve discovered that the scanner RPM is about 25% greater than my SunPro tach reading, which kinda makes sense, considering that the V6 ECM is interpreting a V8 RPM with 25% more cylinders. Real early on, at the throttle body, I accessed the throttle plate stop screw and manually set the idle to about 550 rpm in gear (per my tach). However, IAC/RPM on the scanner shows the engine is turning faster at around 700-800 rpm, and accordingly the ECM drives the IAC to Zero. I hit the gas from a stop and then sometimes, randomly, it will backfire and die/stall, like maybe the sudden throttle opening doesn’t support enough fuel and it goes lean; or is it getting too much fuel (rich?) and stalls. I’ve got a 1991 GMC Light Duty Truck Emissions Manual and comparing ECM Pinouts between a 4.3 Z motor and a 5.7 K motor shows that almost every terminal and circuit is identical. (EGR is different as a 4.3 uses a ported EGR valve while a 5.7 uses a negative back pressure valve). Researching this site determined that a 1227747 ECM would maybe be a good candidate for a swap as it is used on both the 4.3 and 5.7. I found one on Craigslist with an ANLW Prom. Anxiously I installed it: only to barely made it around the block (&^%$#!!). Bad ECM? (Note: I did have the vacuum supply to the EGR plugged). As of late, with the 4.3 16144288 ECM back in place, I’ve raised my minimum air rate to about 600+ RPM in gear, have driven it about 100 miles and it runs GREAT: at highway speeds. No CE light, goes Closed loop, and cycles Rich/Lean. But at around 25-35 MPH it has a bad surge. Accelerating with normal throttle from a stop I get a sag and surge also. Another issue I might add, is that my fuel economy is maybe 13 MPG combined. Which brings up another question: with the V6 ECM saying the engine is turning 25% faster than it really is, is the ECM not only closing the IAC, but is it also commanding too much fuel? Should I try another 1227747 ECM/PROM? Or is there a better ECM/Prom combination in view of the drivetrain that I’m running as described above? Or can someone burn me an appropriate prom? A prom that will work with the 4.3 V6 ECM to correct the “false” RPM reading? Or does anyone have for sale a known good ECM/Prom combo that will work with my drivetrain? Guys, sorry for the long post. I’m hoping that someone can point me in the right direction. Also, FWIW, I’m not technical enough to even begin thinking about getting into burning my own prom; I’d rather not go there. I’m at an age/stage where I just want to enjoy my old truck. And I’d really like to keep it GM TBI fuel injected. Thanks in advance. Regards, DOC

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Originally Posted by DOC327

Hello everyone! I’ve been lurking around this site for a few weeks and figured I’d introduce myself. My name is Dave, but my buddies call me DOC (“Dave-On-Call”). Five years ago I retired from St. Louis to Georgetown, Texas. I need some TBI advice and or education as I’m at a point where I’m in over my head. My project is a 1948 Chevy 1/2 PU resto-mod. I’ve owned this truck long time and did pretty much everything on it myself. I’m a gearhead. Here’s what its got: 1969 2 bolt 327 (.030 over; 10:1 forged pistons); small valve Power Pak heads and a stock cam, cast iron exhaust manifolds; Magnaflow exhaust; 700-R4 from a 1991 Z28; 3.73 Posi. I’ve been driving it about 7 years and put about 5000 miles on it. I’ve gone thru a Dualjet, then Q-jet, then a Holley carb. Quite a while back my daughter’s ex-boyfriend abandoned his clapped out 1992 GMC S-15 in my garage and so I inherited a complete running TBI 4.3 Z motor. (ECM 16144288/Prom BARL). So, looking for a challenge I decided that the 4.3 fuel injection could work on my 327. (Why can’t you use a V6 Computer/Prom on a V-8 truck?!) It took some time, but I pretty much took everything ECM related from that S15 and put it on my truck, with the exception of the distributor, of course. It’s a stock GM EST distributor, with Electronic Spark Control, from a 1990ish C10 5.7 K motor, using a TBI intake from that same generation truck.The EGR is fully functional. I’ve installed a CE lite in the dash and have a fully functional ALDL under the dash. I can monitor all of the ECM inputs and outputs using an OTC Monitor 2000. I’ve logged about 4000 miles with the TBI. But here’s the trouble: as I dialed in this computer system I gradually started experiencing a very random backfire/stalling problem from a stop, just off idle. When driving it with a scanner I’ve discovered that the scanner RPM is about 25% greater than my SunPro tach reading, which kinda makes sense, considering that the V6 ECM is interpreting a V8 RPM with 25% more cylinders. Real early on, at the throttle body, I accessed the throttle plate stop screw and manually set the idle to about 550 rpm in gear (per my tach). However, IAC/RPM on the scanner shows the engine is turning faster at around 700-800 rpm, and accordingly the ECM drives the IAC to Zero. I hit the gas from a stop and then sometimes, randomly, it will backfire and die/stall, like maybe the sudden throttle opening doesn’t support enough fuel and it goes lean; or is it getting too much fuel (rich?) and stalls. I’ve got a 1991 GMC Light Duty Truck Emissions Manual and comparing ECM Pinouts between a 4.3 Z motor and a 5.7 K motor shows that almost every terminal and circuit is identical. (EGR is different as a 4.3 uses a ported EGR valve while a 5.7 uses a negative back pressure valve). Researching this site determined that a 1227747 ECM would maybe be a good candidate for a swap as it is used on both the 4.3 and 5.7. I found one on Craigslist with an ANLW Prom. Anxiously I installed it: only to barely made it around the block (&^%$#!!). Bad ECM? (Note: I did have the vacuum supply to the EGR plugged). As of late, with the 4.3 16144288 ECM back in place, I’ve raised my minimum air rate to about 600+ RPM in gear, have driven it about 100 miles and it runs GREAT: at highway speeds. No CE light, goes Closed loop, and cycles Rich/Lean. But at around 25-35 MPH it has a bad surge. Accelerating with normal throttle from a stop I get a sag and surge also. Another issue I might add, is that my fuel economy is maybe 13 MPG combined. Which brings up another question: with the V6 ECM saying the engine is turning 25% faster than it really is, is the ECM not only closing the IAC, but is it also commanding too much fuel? Should I try another 1227747 ECM/PROM? Or is there a better ECM/Prom combination in view of the drivetrain that I’m running as described above? Or can someone burn me an appropriate prom? A prom that will work with the 4.3 V6 ECM to correct the “false” RPM reading? Or does anyone have for sale a known good ECM/Prom combo that will work with my drivetrain? Guys, sorry for the long post. I’m hoping that someone can point me in the right direction. Also, FWIW, I’m not technical enough to even begin thinking about getting into burning my own prom; I’d rather not go there. I’m at an age/stage where I just want to enjoy my old truck. And I’d really like to keep it GM TBI fuel injected. Thanks in advance. Regards, DOC

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Sounds like a great project!!!

4.3l injectors probably too small for the 327. 1227747 is expecting 350 injectors.
http://www.gearhead-efi.com/Fuel-Inj...d-part-numbers

Idk if the 4.3l ECM is programmed for async or synch that may be causing issues. Not sure if $A0 xdf has that identified.

Do you have a functional VSS?

stew86: thanks for the response! I've tried two different sets of 5.7 injectors (5235206) and even went back to the 4.3 injectors (5235279) and experienced no difference or improvement. Good thought regarding the injectors, but, but at highway speeds the system runs like a dream; around town at low speeds (<40 mph) is where it acts up, and so I'm not thinking injectors. As for the VSS, my speedometer is cable driven, and I have a 2 wire speed sensor routed in series with the cable at the transmission. At 70 mph my speedo head reads about 3-4 mph slower than what my scanner is saying. It's never set a VSS code/24. You bring up "async or sync" and "$A0 xdf"....that's not in my vocabulary, but if you want to explain I'm happy to listen. Another question: regarding the 1227747 ECM I got off of CL....is there any way to confirm an ECM is bad, or that the ANLW Prom is bad? Thanks again for your response. Dave

You're waist deep in your project and not getting feet wet meaning you're smarter than you had let on! Just to clarify, you used the bigger injectors with v6 ECM or V8 ECM? Just gonna say that it's gotta be matched with what's programmed in the PROM(chip).

Sorry for the unfamiliar jargon... http://gearhead-efi.com/Fuel-Injecti...Information-AO
Xdf is the file definition that when used in conjunction with a program such as TunerPro, you can poke around in the bin file that's programmed in the PROM. I did poke around a random '288 PROM bin and couldn't find any reference to async but it's probably not a factor. http://gearhead-efi.com/Fuel-Injecti...Asynch-fueling
I did manage to see parameter for cylinder select so with the means (PROM burner) you could change from 6 to 8 cylinders in the PROM but understood that's something you're opposed to getting into.

Do you know the specs on your 327 cam and what kind of vacuum does it produce at idle? I'm thinking something like a L79 cam is gonna require a tune as the MAP fueling tables are going to be very different than what's stock in either of the ECMs you have.

if you going fuel injection find old 350 stuff easyer to get where you want quicker.

stew86: Regarding the injectors: I probably put about 3000 miles on the V8 injectors using the V6 ECM (16144288). I put about 1000 miles on the V6 injectors while using the V6 ECM. I can't say there was any difference with the drivability either way. With the 1227747 ECM plugged in and with either the V6 or V8 injectors it surged terrible at idle and like I'd said earlier it barely made it around the block. I feel that 747 ECM was junk (or could it be the prom?). Note: I have a dash mounted fuel pressure gage and it's rock steady at 12-13 PSI. As for the cam, it's a Melling CL-CCS-1 hydraulic flat tappet: duration at .050" lift is .194int/.202exh. Advertised duration is .258int/.269exh. Valve lift with stock factory rocker arm ratio is .390int/.409exh. Their advertising said "Computer-Controlled Compatible". Vacuum at idle is 20". I went thru the engine about 4-5 months ago just to reseal it/clean it up. For what its worth, I'm looking for drivability, reliability and fuel economy. I don't have to go fast. The next Poster, "ony" said "if you going fuel injection find old 350 stuff easyer to get where you want quicker". I don't want to re-invent the wheel....maybe I should just look for another 1227747? Or can you or anyone suggest a better ECM/Prom combo?

many moons ago I had an '89 Caprice 9C1. I would have been the age that I was interested in fixing cars but didn't know what I know now. long story short someone had swapped a 4.3L TBI (same as small block) with matching 4.3L injectors. Yes I am aware they are technically 2 different flow rates. What lead up to this repair was the throttle would actually hang open and made for some interesting stops. Did the car run? Yes. Did it run good to my standards and know how today? Hell no. I swapped in a TBI unit with less play in the throttle shaft and had 350 injectors. Did it run better. Absolutely. This is before I knew about minimum idle air adjustment and setting base timing (2 important things to check and adjust). Eventually I ran a TPI pump. It ran better. Then I figured out how to test fuel pressure and adjust the stock fuel regulator. 13.5 psi. Ran even better. Finally I couldn't pass emission, this is when I smarten'd up (~5 years after owning the car) and got an ALDL cable to datalog. Saw BLMs were high, took a chance and threw a set of junk yard 350 injectors in. BLMs came down and passed emissions with flying colours. IT ran the best it EVER had since I owned, it also made noticeably more power and had about 220,000 miles at this point (I had put on about 60,000 miles during ownership).

My advice to anyone with TBI. Size your injectors accordingly to your power output. Get your injectors (or buy them) from a place that professionally cleans injectors, ideally with flow data provided. TPI or vortec pump is a drop in for the TBI pump. adjust pressure to 13 or 14 psi or whatever is needed for your power output. NOT the Gm recommended 9-12 psi. Stop messing around with a calibration that doesn't even have the same amount of cylinders. Get a custom chip made I am sure Dave w at old school efi can hook you up.....

tayto: thanks for your input. I'll be looking for another 1227747 and appropriate prom (ACSW, AJUK, AMUR, ASDU). Does anyone have that combination for sale?

I saw this down in the for sale/wanted section
http://gearhead-efi.com/Fuel-Injecti...tes-Burn-2-etc

Hello DOC327,

Welcome to the forum. Sounds like you've done a great job on a fun truck. I think you've worked hard at experimenting and learning about computer systems and what is or is not relevant in a swap. It also seems like you've been thrifty in sourcing parts and tools as well. I think you've found the right forum to help straighten you out. Many of us here, including myself, started out with the same approach.

It's good that you've recognized problems with using the V6 program. There are many calibration values that will not be correct with a stock V6 cal and many are related to the RPM discrepancy. You may be able to work around them by changing the stock values but the easier approach is likely to be using the V8 based calibration. But your older, higher compression 327 is not very close to the stock 350 TBI engine so you should plan on working to make the calibration match the engine.

The most helpful tool to have is a scanner that records and plays back computer data. The OTC2000 (AKA Slow TC 2000) was a very early affordable scantool released during a time when $4,000 bought you a computer with a 20 Mb hard drive and 640K of internal memory. Although it was useful with many different vehicles, the speed and capability of this tool were very limited. Today folks will typically grab a laptop, and OBDI Cable, and a copy of TunerProRT to view and record ALDL data. This tool will allow you to safely record a drive then review it when its safer. It also allows you to share the recorded data with others if necessary.

As you record data and drive the vehicle you will notice issues that need addressing. For example, the ignition timing could be too far advanced at light throttle which could cause surging. Or the accelerator pump values may be more appropriate for a small volume, heated intake manifold. Or the volumetric efficiency tables might match an '80s truck engine. All of these issues are likely to create driveability bugs. Whether you work with a tuner or decide to do this yourself, you should plan to get the tools to record data.

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Also, FWIW, I’m not technical enough to even begin thinking about getting into burning my own prom; I’d rather not go there. I’m at an age/stage where I just want to enjoy my old truck.

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I have to disagree. You've done a great job of documenting and reporting what's going on with the truck. You've been reasonable in your testing and parts replacement. And I'm sure you've solved a number of technical issue while building the truck. I'm not trying to talk you into burning your own proms but I do want to reassure you that you are likely to be successful if you try.

My advice is to stay with the 7747. Select the injectors that will support the expected power produced by the engine. Then find a tuner you feel comfortable working with who is willing to develop a calibration for you.

I don't know if it's in your budget, but EBL Flash is another more user-friendly option. with a wideband o2 self-learning is a breeze. Drive around and log, software makes a new bin form you click a few buttons and the car runs better.

EDIT: It's also plug and play for the 747

1project2many: I want to thank you for the advice and encouragement, and I can't help but feel that you are trying to coax me further down this EFI rabbit hole that I've dug myself into, and now this hole is getting DEEPER! I'm fairly committed to seeing this thru and so I'm pretty much giving up on trying to make that V6 ECM work. On that note, I sourced another used 1227747 (V8 Prom ACSU) and hooked it up today. Pulled the Set Timing connector and confirmed 0 degrees; reconnected the set timing connector. Pulled and reconnected the ECM memory fuse. It cranked and fired up instantly and ran at about 1000-1200 RPM and then gradually settled down to about 700-800 RPM and then started surging really bad, cycling from about 600-1200 RPM repeatedly about every 10 seconds. I still had the timing lite connected and timing was methodically going from 0 to about 12 degrees coinciding with the RPM fluctuation. It was undriveable. This is exactly what the other 1227747 (V8 Prom ANLW) was doing. So as to be sure the EVRV circuit wasn't triggering any EGR activity I plugged the vacuum source to the EGR Valve and the vacuum port to the EVRV. Still the same problem. I confirmed that I had the correct ESC module connected for a V8: it was correct. I've got the base idle speed at about 650. Fuel pressure is stable at 12-13 psi. The knock sensor, IAC, TPS, are new. I went back and plugged in the old V6 ECM again and took it down the road and it ran flawlessly at highway speeds, as before, but then back around town, once hot, I get mild surging and occasional backfire, again. I guess its possible I've got two bad 1227747 ECMs, but unlikely. Guys, any thoughts? Thanks, Dave

Hiya,
Just a note from the outside looking in, you seem to have a good grasp of what volumetrically is happening. If you understand a carburetor and it's limitations(very few, if you know how to tune carburetors!) You can do whatever you want with EFI. The nomenclature may not be "pump shot" or "pump cam" for example, but again, if you know what you want to change, you can :)

Of course it will require a small amount of investment to buy some equipment. Then you will be in complete control(minus the learning curve). When I got started back in the early 90's I had never heard of hexadecimal math and there was no such thing as software, we worked in hex. I had been building championship Nascar and drag race stuff as well as performance street. I got into the EFI because almost nobody else could do it and one of my builds didn't pass the "trailer it to L.A. to get tuned" crap. Long story and I won't bore ya ;)

It's a huge learning curve and I got lot's of grey hair with this and the ex-wife :thumbsup: Many people on this forum and others are willing to help. There is no "magic chip" unless someone has done the EXACT combination you have.

A bit off topic but a coin I phrased 30+ years ago in AA was, "if you can't beat or appease your demon, you're a quitter" :rockon: <<<<<< yeah that was me when I had the wig back then. :nono:

Your combination doesn't sound like something the stock tune can't handle. Can you confirm that this has been done... http://gearhead-efi.com/Fuel-Injecti...-Fuel-Pressure

Stew86: I researched that reference you made to "Min Air Adjust, TPS set..." by EagleMark and there was also a post in there by 1project2many about using the drag on a strip of paper to get the throttle plate closed the correct amount in the throttle bore to set minimum air rate. Good info! In a fashion I may have already done all this, but then again, in the heat of battle yesterday, maybe I didn't. I'll revisit setting my minimum air rate to make sure I didn't miss anything. And also, at this point I can't remember what injectors I have in the throttle body: the 4.3 set or the 5.7 set? I'll check. I'll be back................Dave