Rough idle, Timing randomly adjusts

[ChevPasmore]

what does "fuel pressure is good" mean? what psi is it? Just because injectors are firing and the spray pattern looks good, does not mean they are good or correct. Pull out the ECU and open the small cover, the memcal will have a 4 digit code on it. Post that here and we can see what calibration is in it.

I got my first TBI vehicle was 20, 1989 Caprice ex-cop car w/ 5.7L. For starters it "ran good", but as I discovered after a year or so of owning it, it had been fixed improperly. For starters someone put a 4.3L TBI on it with 4.3L injectors. Putting the correct injectors in it made a huge difference in how it ran. Then I changed the fuel pump (this was before I got a fuel pressure gauge) and upgrade to a TPI pump, again huge difference. fastfpward about 4 years I moved to an area where annual emissions testing was required and car failed miserably. At this point I fonally invested in a fuel pressure gauge and a datalogger. Here's what I found:
- fuel pressure was 8-9 psi (technically in spec)
- the BLM were maxed out, so it was running lean

I made the fuel pressure regulator adjustable and got the pressure up to 13 psi. Made a big improvement on how it ran but still had maxed out BLM's. As a hail marry i went to the wrecker and got some injectors out of a 5.7L and threw them in. BLM'S immediately went to 128 +/- 2. Perfect. Passed enissions testing with flying colours. Car made better power, smoother idle/exhaust tone than it EVER had since I bought it. This why I always verify these things and how a fuel pressure gauge and scanner/datalogger are required for proper EFI troubleshooting.

Fuel pressure was at 12psi steady when I checked 2 weeks ago. If I recall the PSI should be between 9-13psi. I thought the throttle body was the same for the 5.0 and 5.7 engines. The 7.4 ( 454 ) I believe was different. But I could be wrong. All the information I have is that the engine came out of a 1995 Silverado, but kept the harness of the 1990. So I am assuming they slapped the intake + tbi on from the 1990 to the 95 to keep the sensors in the same location ( not sure if they are different or not ), Maybe everything on the engine is from the 95 and they didn't swap out the ECM/Prom. I will be tearing the glove box apart and will get the 4 digit code tomorrow. If it is not "calibrated". How do I go about that? I just want this damn thing to run haha. I have a 2000 quad cab dually 4x4 GMT400 that I daily but still would like this one operational.

 

[tayto]

4.3/5.0/5.7 all used the same throttle body but you need to check the part number on the injectors themselves. if you pull connectors off use a can of brake or carb cleaner and a tooth brush to clean off the tops and see if the number is still there. dont scrape with a screw driver. sometimes the tops of the injectors will be painted, usually orange and black paint identifies a 5.7L injector.

you will either need to find the correct chip or get one burned.

 

[ChevPasmore]

4.3/5.0/5.7 all used the same throttle body but you need to check the part number on the injectors themselves. if you pull connectors off use a can of brake or carb cleaner and a tooth brush to clean off the tops and see if the number is still there. dont scrape with a screw driver. sometimes the tops of the injectors will be painted, usually orange and black paint identifies a 5.7L injector.

you will either need to find the correct chip or get one burned.

I will take a look into this and report back.

Appreciate the help.

 

[Scooterwrench]

262,305 and 350 had the same throttle bodies and ran the same fuel pressures but with different injectors.
262 injectors were 45pph
305 were 54pph
350 were 61pph,65pph for police cars.

Would you happen to know the ECM#? I'm wondering if the upgraded to the 93-95 ECM and retained the external ESC. The later ECM has the ESC internally.

 

[ChevPasmore]

262,305 and 350 had the same throttle bodies and ran the same fuel pressures but with different injectors.
262 injectors were 45pph
305 were 54pph
350 were 61pph,65pph for police cars.

Would you happen to know the ECM#? I'm wondering if the upgraded to the 93-95 ECM and retained the external ESC. The later ECM has the ESC internally.

I do not know the ESM number but I will be getting that tomorrow. The ESC is plugged into the distributor correct ? Because if so mine has dual plugs on it. I was told they retained the 1990 harness and used it on the 1995 5.7. Will find out tomorrow as well if I’m running 5.7 injectors or 5.0 ones. Plus might hit up the scrap yard and pull a prom out of an 88 with a 350 just to be safe haha

 

[1998_K1500_Sub]

But now she will turn over but severe rough idle. Even after I set the timing, it would idle fine but not idle down after warm.

I don't think this is your problem, but I had a 1995 S10 Blazer once...

It had a reluctor on the distributor shaft that wasn't firmly affixed; the problem would manifest as ignition timing that would become retarded over time (typically, weeks or months). It became part of my regular service to check the ignition timing, and often "advance" it back to baseline, and for a long time (years) I couldn't figure out why this was necessary.

Anyway, one day while driving the engine suddenly started running very poorly. I got it to my shop, started poking around and just happened to compare its distributor to another I had on hand. The problem was suddenly VERY obvious.

I posted this story, with pictures, prior; the pictures really tell the tale:

1993 Chevy c1500 4.3 power issues

I’m new to this form but am in need of help and this is going to be long so please bear with me. I got the truck in may of 21 and at the time was not starting well or at all and was burning substantial amounts of coolant so I went through and replaced the head gaskets, intake gaskets, throttle...

www.gmt400.com

 

[ChevPasmore]

I don't think this is your problem, but I had a 1995 S10 Blazer once...

It had a reluctor on the distributor shaft that wasn't firmly affixed; the problem would manifest as ignition timing that would become retarded over time (typically, weeks or months). It became part of my regular service to check the ignition timing, and often "advance" it back to baseline, and for a long time (years) I couldn't figure out why this was necessary.

Anyway, one day while driving the engine suddenly started running very poorly. I limped to a nearby house, parked it, and later trailered it to our farm shop. There, I started poking around and just happened to compare its distributor to another I had on hand. The problem was suddenly VERY obvious.

I posted this story, with pictures, prior:

1993 Chevy c1500 4.3 power issues

I’m new to this form but am in need of help and this is going to be long so please bear with me. I got the truck in may of 21 and at the time was not starting well or at all and was burning substantial amounts of coolant so I went through and replaced the head gaskets, intake gaskets, throttle...

www.gmt400.com

Thanks for that,

My distributor is brand new, but sometimes new parts can be defective. I will take a look and see if this could be the culprit.

 

[Scooterwrench]

The Ignition Control Module(amplifier)is mounted on the distributor and both early and late EEC's use the same one. The early Electronic Spark Control is about a 3"X3" box normally mounted on the right side intake man. beside the TB. When retrofitting a late ECM into an early truck you would bypass the external ESC and toss it. If they didn't it may create strange ignition timing issues.

 

[tayto]

recently i went through 2 "reman" distributors before rebuilding a good core. trying to save time ended up costing me 3x the time. again, not saying you're new distributor is bad. this is is why i wait a few weeks after fixing something before returning cores.

 

[1998_K1500_Sub]

I do not know the ESM number but I will be getting that tomorrow.

In 1995 the $0D ECM code running on ECM p/n 16197427 was common. If your swap included the ECM, I would expect to see a sticker on it bearing "16197427". You might read the four digit code of the blue MEMCAL (or was it CALPAK?) and report it here; it may not be the ideal one for your application.