Car is running LEAN! Good fuel pressure (Page 1/4)
gmctyphoon1992 OCT 12, 02:50 PM
1998 pontiac fiero gt. The car is just running lean somehow now after fixing the EGR system. All the rear side plugs are white. The car runs sluggish as well, hesitates a little, rough cold start and rough cold idle. The car runs alittle better warm. The car runs with a BLM of 135 and a INT of like 140 to 160 at idle but drops to 128 as soon as you give it throttle. the BLM how ever stays at 135 ish. THE IAC value is around 70 which I assume is somewhat high? (20 to 50 range is normal)

Fuel pressure is 44psi key on ignition off. maintains around 42 ish psi with the engine running. It will jump to 45 psi or so when you blip the throttle and will come back down and hold at around 40 to 42ish psi when holding at a constant rpm above idle (i think like 1500 rpms or so). Fuel pressure holds at 40 psi with key on ignition off after fuel pump stops and drops very slowly to just hair and holds around 38psi. I only checked for like 5 mins or so with no movement but maybe go back and check longer?

New AC Delco EGR Valve, New rodney dickman EGR Tube, all the ignition components are fairly new. I checked the Timing is close to around 11 or maybe 12 degrees before top dead center no codes thrown, no map sensor leaks as map sensor puts out the right voltage on the scanner 1.2 volts at idle. 4.5v at key on ignition off.

The fuel filter has not been changed in a long time atleast 60k miles so I bought a new one from K&N still waiting for delivery but ill install just because.

IAT sensor records normalish temp reading like 100F to 105F? (I live in South Florida) Coolant sensor reads 220F at idle engine warm to 227F engine warm fan turned on. Although my water temp gauge in the car is off by 30F on the low side and jumps around like an idiot?

O2 sensor is fairly new but its a Bosch product, It does trip over and under 0.450 volts constantly which assumes its working ok? I can always get a AC Delco one for cheap if I have to.

When in the WinALDL program though the car is saying at idle under ADVANCE to be at 15 Degrees and jumps to like 20 or 30 degrees with throttle idk if thats right or not maybe the harmonic balancer has slipped and read the timing on the car wrong? I didnt adjust the timing and from the looks of the harmonic balancer It doesnt show very much wear maybe just moderate.
Any one having ideas? Could it be vacuum leak elsewhere I would assume the car would want to run rich if I had a vacuum leak.

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1988 Pontiac Fiero Gt (fully optioned, factory leather, 5-speed, CJB T-Tops: Black w/ gray interior and blk wheels)
1992 GMC Typhoon #0203
1971Chevorlet Corvette 454cu/ LS5/ 4-speed/ convertible
1993 BMW 850 Ci 6-speed V-12

[This message has been edited by gmctyphoon1992 (edited 10-12-2016).]

Patrick OCT 12, 02:59 PM

quote
Originally posted by gmctyphoon1992:

All the rear side plugs are white.



It might be best to clarify that. Do the front plugs look normal... or was it only the rear plugs you looked at?
gmctyphoon1992 OCT 12, 03:07 PM

quote
Originally posted by Patrick:

It might be best to clarify that. Do the front plugs look normal... or was it only the rear plugs you looked at?



Yes sorry, for clarification I only checked the rear plugs facing the back of the car because they were easiest to get to I have not checked the front plugs. All back three were white so I was more assuming that the problem is more consistent throughout than a possible bad or clogged injector on an individual cylinder. I can however if necessary try to get to the front plugs when I have a chance.
Patrick OCT 12, 03:31 PM

quote
Originally posted by gmctyphoon1992:

I only checked the rear plugs facing the back of the car because they were easiest to get to...



I figured that was the case.

It would be rather surprising if the front plugs looked much different than the back ones... but I just wanted to make sure that this wasn't what you might've been implying.

[This message has been edited by Patrick (edited 10-12-2016).]

Gall757 OCT 12, 03:33 PM
If all 6 plugs look the same, I would change the O2 sensor.
gmctyphoon1992 OCT 12, 03:41 PM

quote
Originally posted by Gall757:

If all 6 plugs look the same, I would change the O2 sensor.



Okay ill check and I might just go ahead and get an AC Delco one since its cheap and see if there is a difference. I did however notice that I didn't re-tighten the clamps on my intake snorkel on both sides If that matters at all.
Patrick OCT 12, 03:53 PM

quote
Originally posted by gmctyphoon1992:

Okay ill check and I might just go ahead and get an AC Delco one since its cheap and see if there is a difference.



I do recall reading some criticism here of the Bosch O2 sensor not working as well as the AC Delco units with the 2.8 (and possibly 2.5).

[This message has been edited by Patrick (edited 10-13-2016).]

edfiero OCT 12, 04:09 PM
I don't have an answer, but I'm not sure its the O2 sensor.
If you are getting fast response on either side of .45v as you've indicated, its responding appropriately.
Also, a BLM of 135 (as I understand it) says based on the 02 feedback the ECU needs to add more fuel over what is called for by the fuel table. ECU added more fuel to get the A/F to aprox 14.7. The point being is that it was able to add the fuel to get you where you need to be. If you were maxed out at 160, that would mean that it wasnt able to add enough fuel to get you to 14.7.

Are TPS and MAP values what you would expect them to be?
cebix OCT 12, 07:41 PM
Are injectors clean and good? If you spray gas in the intake does it smooth out?

[This message has been edited by cebix (edited 10-12-2016).]

gmctyphoon1992 OCT 12, 11:16 PM

quote
Originally posted by edfiero:

I don't have an answer, but I'm not sure its the O2 sensor.
If you are getting fast response on either side of .45v as you've indicated, its responding appropriately.
Also, a BLM of 135 (as I understand it) says based on the 02 feedback the ECU needs to add more fuel over what is called for by the fuel table. ECU added more fuel to get the A/F to aprox 14.7. The point being is that it was able to add the fuel to get you where you need to be. If you were maxed out at 160, that would mean that it wasnt able to add enough fuel to get you to 14.7.

Are TPS and MAP values what you would expect them to be?



The TPS sensor is reading appropriately with no dropouts into the throttle. Map sensor voltage goes from 1.4 to 4v into throttle and and drops below 1v out of throttle but comes back to 1.4v when at idle.
The car doesn't get passed 160 for the BLM or the INT. I drove the car around today with the laptop hooked up and the INT is now 127 to 130 at idle but the more important BLM is 140 at idle.

As far as the fuel injectors I haven't checked I would have to assume they are all dirty than to be causing the lean problem in all cylinders