I'm just about at my witts end trying to get my 88 2.5 5-spd running correctly. Between yesterday and today I've sunk about $400 into it and it runs worse than ever!

BEFORE:

- Initial start up would take a few cranks, but it would fire up and idle normally.
- Car would then drive fairly well except for some stumbling on take off and an occational exhaust backfire (fairly normal for non-cat exhaust?).
- After engine was hot the car would often bogg and stall out when coming to idle.
- Hot engine would just crank and not start, or after starting would bogg and chugg badly.
- Car would bogg and almost stall when ever headlightswere turned on , HVAC blower was turned to full (i.e. increased load on engine).
- Issues became increasingly worse.

R & R 'd

- New fuel filter
- New MAP sensor
- New MAT sensor
- New EGR valve
- New IAC
- New TPS
- New CPS (old one was cracked) , Coils, & Module
- New plugs & wires
- Fuel injector removed and examined. Both O-rings present and appear normal.

AFTER:

- Car needs multiple cranks to start and then has very rough and iradic idle.
- Engine stumbles severely and usually stalls at the slightest touch of the accelerator pedal.
- Still boggs/stalls when headlights or HVAC turned on.
- Several intake backfires
- Smells like it's running very rich.
- Car undrivable!


OBSERVATIONS:

After watching the engine trying to run it appears to me that the fuel injector seems to be dumping an awful lot of fuel into the TB. While cranking and idle there is a pretty good amount of spray going on. As the throttle is opened up (and the engine is bogging) the fuel is just pouring into the TB. Its spraying like a shower head! Would a bad fuel pressure regulator cause too much fuel to dump and flood the engine?

A very interest thing happened as I was trying figure out why it was now running so badly. I decided to start UNPLUGGING things to see what happened:

EGR vacume hose = no significant changes. Reinstalled.
MAP electrical connector = idle improved a little (after system went into closed loop), but still stumbled and bogged when throttled. Reinstalled.............

MAP vacuum hose = WTF? Idle improved 100% ! No bogging or stumbling! Electrical loads (headlights/HVAC) had no affect on engine. Basically the car ran great. But the exhaust now had whitish smoke coming out and smelled bad. Drove the car around and it ran GREAT except at full throttle it still had some stumbling and power loss occuring.

MY THEORY:

I may be all wet on this but here is my theory of whats happeneing. The engine is getting too much fuel and the ECM/engine sensors can not compensate for it or don't recognize that it's happening. Thus the air-to-fuel ratio is messed up. Things are only made worse when a load (electrical, mechanical ) to the engine is introduced because the ECM thinks it needs to increase the RPMs. Thus it dumps more gas into the TB/intake and the air-to-fuel ratio gets even more out of wack. But when the MAP vacuum line is disconnected the TB/intake is suddenly getting more air. Enough to counter the abundance of fuel and therefore brings the air-to-fuel ratio close enough for the engine to run fairly normal.

NEXT MOVE:

If the engine is indeed getting too much fuel, I need to get that under control. Either the fuel pressure regulator needs R&R or the fuel injector itself might be bad. Or both. Or maybe neither one is the problem! Perhaps the ECM is freaking out? I don't know. And that is the problem, I don't have a scan tool and for some reason the cars "check engine" light doesn't work. So I have no way to see any codes thrown. And I'm not very well practiced at using a volt meter or understanding electronics. I pretty much winging it here. So any ideas would be greatly appreciated.

Looks like you have answered your own question. Seems to be "Bad injector parts" month on this board...

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carpe diem

Disconnecting the vac line to the MAP sensor will increase fueling and use the 100kpa fuel values. This should have flooded the engine and made it run worse, not make it run better.

I suspect your fuel pump or fuel pressure regulator is going bad and your engine is running lean due to insufficient fuel pressure. Removing the vac line to the MAP sensor keeps the injectors open longer and could compensate for low fuel pressure - but at WOT the issue would return.

My guess it the MAP is NFG

Double-check that your MAP sensor is plugged into the appropriate port on the TB. If the vacuum line is either not plugged in or plugged into the wrong place, the car could actually run better with it unplugged.... You are getting the check engine light both with it plugged in and unplugged, right? What are the codes?

Good Luck!
Kurt

If youre using platnium spark plugs change them to reg and see what that does. Even prefect looking or new platniums can cause all sorts of problems. I know some will say no-way, but I've seen it and know a great shop that wont put them in anything.

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[IMG]



Trueleo.com/fiero.htm
RSpiderII@aol.com

The MAP is used for fuel control and power enrichment. When the vacuum goes low as in acceleration the MAP voltage goes high (up to 5V) . If you remove the MAP hose there is no vacuum and the MAP goes to 5V which in turn requests that the ECM adjust for more fuel. If you car runs better with the MAP hose disconnected it must be runing lean.

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87GT 3.4 Turbo- 0-60 5.2 seconds
2006 3800SC Series III swap in progress
Engine Controls, PCM goodies,
re-programming & odd electronics stuff
" I'M ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by KurtAKX: Double-check that your MAP sensor is plugged into the appropriate port on the TB. If the vacuum line is either not plugged in or plugged into the wrong place, the car could actually run better with it unplugged.... You are getting the check engine light both with it plugged in and unplugged, right? What are the codes? Good Luck! Kurt

Kurt,

The MAP vacuum was definetly plugged in, but I will double check the location. As far as codes and check engine light, for some reson the check engine light is not functioning and I have no code reader. So I have no idea what codes it may be throwing.

quote Originally posted by Dennis LaGrua: The MAP is used for fuel control and power enrichment. When the vacuum goes low as in acceleration the MAP voltage goes high (up to 5V) . If you remove the MAP hose there is no vacuum and the MAP goes to 5V which in turn requests that the ECM adjust for more fuel. If you car runs better with the MAP hose disconnected it must be runing lean.

Dennis,

What would cause it to run lean? Temp sensor? 02 sensor? Just watching the fuel injector while it is running it sure looks like it's getting lots of fuel. So I'm confused as to how it could be lean with that much fuel being dumped into the TB.

Fuel pressure regulator is easy to check on 88 just use care remove.. just back off screws ,sort of equally then use finger to press pot cover as final removal of screws .. I have had trouble with aftermarket .delco if available make sure install is proper this part failed on me in 6 months the rubber looks rugged but it is easy to dammage if another pair of hands available have finger press inward while you set screws,, this is a part that needs to be pushed in straight the first time,you can reuse if no damaged rubber.. allways check spark when car does not run well make sure both coils put out equal a 87 88 duke will run on 2 cy;linders and can be driven a bear to start tho

quote Originally posted by turbotoad: Kurt, The MAP vacuum was definetly plugged in, but I will double check the location. As far as codes and check engine light, for some reson the check engine light is not functioning and I have no code reader. So I have no idea what codes it may be throwing.

If you don't have a working SES light (with the key on, engine off), thats the FIRST thing you need to fix. Helm has a pretty good troubleshooter in the Fiero FSM IIRC. The bulb may be out, but alternatively you might have a burnt ECM, or the connectors might be backed out. Fix that first, then go for running/driveability issues.
A computer-world analogy is this: Don't try and waste time figuring out why iTunes isn't working right on your computer if it won't even boot it up.

Dennis,

What would cause it to run lean? Temp sensor? 02 sensor? Just watching the fuel injector while it is running it sure looks like it's getting lots of fuel. So I'm confused as to how it could be lean with that much fuel being dumped into the TB.


Some of the items are already pointed out here but lets summarize.
Lean mixtures can be caused by:

A vacuum leak such as a broken diaphragm in the vacuum reservoir in the power brake system, a leaky hose, leaky TB or manifold gasket etc. .
Clogged or defective fuel injectors.
Low fuel pressure caused by a bad FP regulator, worn fuel pump or clogged fuel filter
A malfunctioning O2 sensor- use only AC Delco or Denso.
A defective or leaking EGR valve or removing the EGR valve washer restriction.
TPS output voltage not increasing with throttle position.
A small amount of water in the gas- add dry gas!

There are more resons for a lean runing engine so back yard mechanic please chime in.

------------------
87GT 3.4 Turbo- 0-60 5.2 seconds
2006 3800SC Series III swap in progress
Engine Controls, PCM goodies,
re-programming & odd electronics stuff
" I'M ON THE LOOSE WITHOUT THE JUICE "

"As far as codes and check engine light, for some reason the check engine light is not functioning and I have no code reader. So I have no idea what codes it may be throwing."

And you've spent $400.00 replacing parts??????? Take the car to a local Autozone, O"Reilly's or other parts place and have them check out the codes! Sheeeesh!

quote Originally posted by JohnF: "As far as codes and check engine light, for some reason the check engine light is not functioning and I have no code reader. So I have no idea what codes it may be throwing." And you've spent $400.00 replacing parts??????? Take the car to a local Autozone, O"Reilly's or other parts place and have them check out the codes! Sheeeesh!

This is not going to work for him. Autozone will do one of two things, either scan your car if it is OBD II (which this isn't) or paperclip it if it is OBD I, and since his check engine/SES light isn't working, this won't provide meaningful data.

UPDATE:

Well I finally got around to buying a fuel pressure gauge and just got done testing. Vertict = 5 - 7 lbs before the filter! So it would appear that the fuel pressure is low. Looks like I will be dropping the tank

more to follow ...

UPDATE 2: FIXED.........................................................almost.

This past Saturday my son and I dropped the tank and removed the old fuel pump. Amazingly everything looked in excellent condition. even the infamous "rotting hose" was in great shape. A brand new pump and screen was installed and then the tank was re-installed into the vehicle. We were holding our breath as the key was turned and the engine cranked over....VRRROOOOOOOMM!!!

Yes! The engine fired right up and immediately settled into a nice even idle. I then walked over to the other side of the car to look at the fuel pressure gauge and it read a perfect 14lbs. (ahead of the filter). A quick test drive (after removing the pressure gauge) was then taken and the car ran great! The best since we bought it a few years ago.

But the excitement was somewhat diminshed as the idle slowly began to degrade as the car was driven around more. When the car is sitting at idle the RPMs fluctuate up and down between 700-1000. If you then goose the throttle up to about 3500 RPM the engine will idle back down to only 300-400 RPM and buck a little before it "corrects" itself and reutrns to the slightly fluctuating RPM.

Other than the slight "idle" issue the car is back on the road and runs pretty good.

I think I might check/replace the Fuel Pressure Regulator. Perhaps this could be causing the fluctuation at idle and the near stalling drop in RPM after gunning the engine in nuetral.

[This message has been edited by turbotoad (edited 10-02-2007).]

IAC motor might be more the problem on the idle and recovery. When the rpm drops from tapping the throttle the iac has to respond fairly quickly to keep the idle from going to low. Might try cleaning it and see if it help.

quote Originally posted by Dodgerunner: IAC motor might be more the problem on the idle and recovery. When the rpm drops from tapping the throttle the iac has to respond fairly quickly to keep the idle from going to low. Might try cleaning it and see if it help.

The IAC was just replaced. I suppose the IAC passage of the TB could be dirty and cause the IAC to bind or not react fast enough.

Yeah, check the IAC passage and see how it looks. I have not played with the 88 intakes, so I am unsure if the 88s had the same issues with carbon buildup by the EGR and TBI that the pre-87-88 2.5s did.

If so, you may want to pull the entire TB, replace the gaskets and clean all of the carbon out.

I had the identical problem with my 88. Tried everything to get a smooth idle with no luck. Then I remembered the old “quicky” emissions fix-it station trick. Sprayed water mist into the idle air port at the top of the TBI with the engine idling. It was like a miracle cure!

quote Originally posted by Francis T: If youre using platnium spark plugs change them to reg and see what that does. Even prefect looking or new platniums can cause all sorts of problems. I know some will say no-way, but I've seen it and know a great shop that wont put them in anything.

+1 - Cheap ACDelco's are usually the best plugs for our cars.

I do not think the fuel pressure regulator is bad. you thought it may be bad so I gave my centavos worth..I have some experience with these and they seem to like larger problem than you have now, the fuel regulator is a rubber diaphram mounted on a round steel washer like doofoley,with a spring..easy to damage only mess with if positive it is problem,HOWEVER fiero guru was 100% correct on this diagnose from the get go

[This message has been edited by uhlanstan (edited 10-06-2007).]

You keep saying that you checked the pressure BEFORE the filter. Have you REPLACED the filter?

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carpe diem

You didn't mention replacing the CTS (coolant temp sensor). It is about an 8 dollar part. I've seen them go bad more than once with the symptoms you have described.