Running Rich

[Rkelch]

So I have 88′ Chevy celebrity 2.8L V-6. Let me start off with this car sat without moving for 7 years. So needless to say it needed a “little” TLC. The radiator was shot so that was the first task. After that was completed I set in to get the car to smog (California) Pain in the ass as you can imagine. The engine runs smooth at about 800 rpm, but once she warms up she is struggling to idle after awhile she would die. So I set out to replace all the cracked vacuum lines, checked the plugs, replaced the wires as they were cracked. The symptoms are rough idle running rich. IAC was not responding so I replaced it, got a little better. STFT and LTFT were pegged at -50, so I figured there had to be a couple bad injectors (which were evident in the plugs) So I pulled them I found 3 bad injectors that would not fully close. Decided to replace all 6. New intake gaskets, She still runs rich LTFT and STFT still -50. Fuel pressure solid at 35psi at idle and about 40psi at KOEO. EGR is operating properly with nothing leaking by. O2 sensor is responding so I know its reading the the condition correctly. car runs smooth as silk in open loop but as soon as it goes closed loop it starts struggling. MAP is reading between 46-52 KpA depending on the idle stumble, atmospheric is 101 KpA, Maf is responding with an average idle reading of 6-8 g/s. TPS is responding and working with an idle voltage of .55. The ECU is trying to cut back the the injector pulse width, that leads me to believe that it doesn’t have a problem. The scan tool I have does not allow me to graph. But seems to give me all the right information. My experience has hit a wall… Any suggestions would be greatly appreciated. I am thinking that 1 or more of the new injectors are not closing I really don’t want to think that, but I can’t think of anything else it would be.

BTW Matt – your videos are awesome I appreciate the no nonsense – systematical – logical – approach to troubleshooting a problem versus trying to fix the symptoms of the problem.

[gkellerman]

Is the fuel pressure regulator vacuum operated?

Could you possibly be sucking fuel in through a bad regulator?

Is there any other patch where fuel could get into the engine besides the injectors?

Also, is the fuel pressure on the rail within spec?

[Rkelch]

FPR is good and not leaking by. fuel rail pressure is 35psi at idle. no patches anywhere, and I did confirm this weekend that the injectors are all good. nothing leaking by. I have decided to go back to the EGR and see if I missed anything there. Only so many ways a rich condition can be introduced.

[Woefman]

1. does your scan tool show closed loop capabilities
2. what does coolant sensor and iat read
3. is this a single wire o2 sensor
4. does map sensor voltage read roughly 2.2v or little less at idle
5. after finding super rich condition and replaced injectors did you change oil
6. did you pinch off canister purge , might have saturated canister….need to prove.
7. ( do at idle only) disconnect MAF sensor plug, how does it idle, remember un metered air leaks on vehicals with Maf will typically result in rough idle

8. if single wire o2 , un plug it and harness side jump it on off with test light hooked to ground, that is, using then test light tip to harness side on and off the pin quickly while monitoring scan tool.

In old days we liked to bench test 02 in a vice, using propane torch and dvom on volts or preferably with DSO…..the premise is the propane torch uses up oxygen so it reports rich
then quickly remove torch and it should very fast show lean.

p.s. reason for my questions such as coolant sensor, if single wire o2 when gets hot it starts to work this might fool you into thinking its in closed loop. On gm of that era if coolant sensor not warm it may never see closed loop. A disconnected or open in coolant sensor circuit on gm cars often reads -40 on scan tool. This is quick test of computer and wireing, diconnect it and look for -40 on scan tool. As an engine gets warm it needs less fuel at idle. If you are not really in closed loop the ecm may be giving more pulsewidth to injectors by thinking engine still cold. Thus your rough idle when warm and excessive fuel in warm engine. Bad Coolant sensor reading can fool ecm , might tell ecm the car is in alaska winter. The ecm back then are not as smart as todays cars.

[Author]

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