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

[stew86MCSS396]

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

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?

[DOC327]

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

[stew86MCSS396]

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.

[ony]

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

[DOC327]

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?

[tayto]

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.....

[DOC327]

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?

[In-Tech]

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