Another TBI running rich

[opus]

Working on a 3 yr problem that no one can figure out.

1993 5.7 TBI. Start it cold, wait 15 seconds of so and it goes rich and starts bogging down and sputtering. Hold the throttle down for 30 seconds then it gets past that issue and is good to go. This of course depends on the temp. When its cold, like 0, it takes longer to reach the rich stage, but its like clock work.

I'm trying to keep this simple for you, for now. I've replaced everything, at least once. Give me some ideas. Dont spend a lot of time though because I've probably already done it. If by chance I havent, then we can go into detail.

 

[evilunclegrimace]

Working on a 3 yr problem that no one can figure out.

1993 5.7 TBI. Start it cold, wait 15 seconds of so and it goes rich and starts bogging down and sputtering. Hold the throttle down for 30 seconds then it gets past that issue and is good to go. This of course depends on the temp. When its cold, like 0, it takes longer to reach the rich stage, but its like clock work.

I'm trying to keep this simple for you, for now. I've replaced everything, at least once. Give me some ideas. Dont spend a lot of time though because I've probably already done it. If by chance I havent, then we can go into detail.

If you want us to give you ideas we need more information. What did you change and why. Does the truck have any stored codes?, have you looked at the data stream?, are there any modifications? Have you verified fuel pressure to be within specs?

 

[opus]

If you want us to give you ideas we need more information. What did you change and why. Does the truck have any stored codes?, have you looked at the data stream?, are there any modifications? Have you verified fuel pressure to be within specs?

I changed everything there is to change, out of desperation. Process of elimination is what it came to, then finances got tight, lol.

No code and I have looked at the data stream. No modifications and fuel pressure is within specs. Mind you, this is not a random thing. It happens like clock work everytime i start it. I can tel by the outside temp when its going to happen. Actually, when its 40 or so, it barely will start because its in "that mode". Which makes me think it is strictly temperature related.

Here is some data where it does its thing. The erratic rpms I think are where it tries to die, but not sure: https://drive.google.com/drive/folders/16Q3wX1Qvnb-RnP3TOunDf5LK4Fiq-Ky7?usp=sharing

 

[PlayingWithTBI]

A couple things I see, your O2 sensor is reading around stoich (450 - 500mv) the entire time. If it's accurate then, you're not running rich. If not it probably isn't getting heated enough to give proper feedback. Maybe try a 3 or 4 wire O2 sensor. Your surging (or stumbling) can be caused by, among other contributing factors, dripping injectors or a bad ICM. I know you changed everything but inferior quality parts have been known to fail. Does it idle and run right once warmed up? What is your fuel pressure? GM specs are 9 - 13PsI but 11 - 13 is preferable.

Anyone else care to step in, by all means, please do.

 

[opus]

A couple things I see, your O2 sensor is reading around stoich (450 - 500mv) the entire time. If it's accurate then, you're not running rich. If not it probably isn't getting heated enough to give proper feedback. Maybe try a 3 or 4 wire O2 sensor. Your surging (or stumbling) can be caused by, among other contributing factors, dripping injectors or a bad ICM. I know you changed everything but inferior quality parts have been known to fail. Does it idle and run right once warmed up? What is your fuel pressure? GM specs are 9 - 13PsI but 11 - 13 is preferable.

Anyone else care to step in, by all means, please do.

Its a new O2 sensor. I forget what brand everyone said to get but it was the one recommended. I think it was said not to get Bosch. New injectors, tried different ECMS and boxes. Runs good after that. It has always tried to stall now and again if you come to a stop sign, not always, but it surely shouldnt. Fuel pressure is 13 if I remember right.

I went with generic parts at first, simply because I have never had an issue with them. When I replaced, I went with OEM parts or something a majority had recommended. A lot of generic parts are just branded differently.

Whatever it is, it is electronic [programmed] of nature.....it seems to me at least.

If there were things I could bypass, I'd gladly do so for testing purposes.

 

[PlayingWithTBI]

What brand distributor did you use? The ICM (Ignition Control Module) is inside it. You can disconnect the EST (black and tan) timing wire. That will bypass the ICM and the computer controls for timing. See how it runs then. Take a flashlight and shine it down the throttle body and look at the injectors' spray pattern, s/b an even cone with no dripping.

 

[opus]

I dont recall what dist I have but tried 2 and I borrowed an OEM one. Replaced ICM as well. Maybe I will disconnect the timing wire and start it cold.

Spray pattern is good.

Timing should be 0 right? Its at about 8 now. It ran flat at 0.

 

[PlayingWithTBI]

It should be TDC but for this test just leave it at 8* BTDC. It's sounding like you need a tune if you have to set initial timing at +8, a lot of times 3 - 6 helps but when you go to 8 the PCM doesn't know where it's at, it'll keep adjusting based on zero initial timing.

 

[opus]

Tune as in a fuel table tune or tune up? Doesnt need a tune up. 20k on new engine, new ignition parts from stem to stern.

 

[PlayingWithTBI]

Tune the PCM's VE and SA tables. If you get a 3 or 4 wire (heated) O2 you can get more accurate on your "choke" routines, otherwise you can play with them and "see" what you get.