Help!! Car running rich/misfire/starting problem. It's a mystery

[Znick742]

Updated post

[Znick742]

Without the afm, the DME uses the default value for Fuel/air ratio.

Yeah I kind of thought it would do that but I wasnt sure if a system this old would. Hmm, I guess I have a leak somewhere cause it won't stay running with it unhooked.

[dnguyen1963]

Without the afm, the DME uses the default value for Fuel/air ratio.

[Znick742]

That is practically a diagnostic for intake leaks. Have a shop run a smoke test to find them.

If it starts then dies, it means there's a vacuum leak? How would it run without a afm?

[jlevie]

I unplugged the afm and it would start then die right away

That is practically a diagnostic for intake leaks. Have a shop run a smoke test to find them.

[Znick742]

Okay... There are two possibilities here. One is that the misfires and starting problem are the result of excessive fuel delivery and the other is that the apparent rich condition and starting problems is the result of misfires. If the rail fuel pressure is correct and a noid light shows normal injector firing, the latter case becomes the more likely case.

A smoke test would be the first thing on my list of diagnostics.

Yeah the first thing I did was rule out vacuum leaks, there's no leaks at all. Then I checked fuel and it was good. I even pulled the injectors out of the head and cranked it to see the stream the injectors were spraying. All injectors were spraying the same and a consistent stream. I put another fpr on it and it did the same thing. I unplugged the afm and it would start then die right away

[jlevie]

Cold start valve was eliminated after all this started and it continued to do It

Okay... There are two possibilities here. One is that the misfires and starting problem are the result of excessive fuel delivery and the other is that the apparent rich condition and starting problems is the result of misfires. If the rail fuel pressure is correct and a noid light shows normal injector firing, the latter case becomes the more likely case.

A smoke test would be the first thing on my list of diagnostics.

[Znick742]

Check the cold start valve. It could be leaking or stuck on.

Cold start valve was eliminated after all this started and it continued to do It

[Znick742]

Sounds good.

Id perform a smoke test, generally bad/no idle issues are caused by vac leaks. Also could be a faulty icv (remove it, clean with carb cleaner...should hum/vibrate when key in in ON position)

Also did you make sure tps is adjusted correctly? Switch should close when the throttle is stop is 0.020-0.060" off the idle stop screw.

Could also be a faulty ICM

An intake leak will cause the DME to run a richer mixture...id honestly start there. Check intake boot for cracks and double check hoses. You could try disconnecting the AFM, possible an engine with an intake leak with the AFM disconnected will cause it to run better/run.

Yeah tps is right I adjusted it multiple times

Ill check for vacuum leaks again today and try unplugging the afm.

[jlevie]

Check the cold start valve. It could be leaking or stuck on.

[FLG]

Sounds good.

Id perform a smoke test, generally bad/no idle issues are caused by vac leaks. Also could be a faulty icv (remove it, clean with carb cleaner...should hum/vibrate when key in in ON position)

Also did you make sure tps is adjusted correctly? Switch should close when the throttle is stop is 0.020-0.060" off the idle stop screw.

Could also be a faulty ICM

An intake leak will cause the DME to run a richer mixture...id honestly start there. Check intake boot for cracks and double check hoses. You could try disconnecting the AFM, possible an engine with an intake leak with the AFM disconnected will cause it to run better/run.

[Znick742]

Did you confirm you are getting good solid spark? Also what was your fuel pressure?

I was thinking maybe the coil isn't giving out enough spark causing it to run really rich

[Znick742]

Did you confirm you are getting good solid spark? Also what was your fuel pressure?

Yeah I pulled the plug wires off the spark seemed strong, I'm not sure how else to check it. It was 34psi

[FLG]

Did you confirm you are getting good solid spark? Also what was your fuel pressure?

[Znick742]

Yes, it is possible. If the sensor is telling the ecu the engine is hot when its actually cold it wont be giving enough fuel...and vise versa. You could try unplugging it first and trying to start it and see what happens.

Yeah I unplugged it, it didn't change anything