Update post added at end ************

My wife's 86 4-cyl auto developed a bucking/chugging problem. It does it at certain RPM, and its sort of intermittant. It idles fine, but starts messing up around 1-2000 RPM, and at certain speeds. Sometimes it is fine on acceleration, sometimes it bogs down. It sometimes stalls when coming to a stop.

I had the following codes:
13, 22 (i disconnected the TPS to test), 35 (IAC is fairly new), 44 (a bad oxygen sensor can trip this code)

I've replaced:
TBI injector
plugs
wires
cap
rotor
coil (recently)
fuel filter
oxygen sensor

I checked:
Alternator output by disconnecting the positive battery cable. Voltage was 15.5
Fuel pressure. Steady at 13
Timing
TCC solenoid (unplugged, did a test drive)

After I replaced the oxygen sensor, all codes disappeared, then it set code 45

It seems to have good spark, fuel delivery, alternator voltage. It idles fine, but sometimes stalls after you rev. This is driving me nuts. Any suggestions?

UPDATE

Yesterday, pokeyfiero and I tinkered around with the car again. We did the following:

Checked sparkplugs visually and for spark
Tried a different coil
Cut off the cat converter to check for restrictions, put in a straight pipe. Tried it with out the pipe, which will eliminate any exhast restrictions
Checked the EGR valve
Changed the TBI unit, which includes the TPS, from a known good car
Checked the IAC
Replaced the distributor with a brand new one, which includes a new ignition module and pickup coil

Still get a chugging at certain rpm, and at higher speed has a bit of a hesitation/missing feeling.

At this point, I have to consider a wiring problem, bad ECM and/or chip, or internal engine problem. I'm at wit's end here. Suggestions?

[This message has been edited by fierobear (edited 07-10-2004).]

could it be the bearings in the dist. itself? I had a 280zx that did the same thing and then I noticed shredded bearings under the dist cap. I wound up replacing entire dist.

And I know the code is not comeing up you could check the egr valve with a vac gauge if you dont have access to one disconnect the vac hose and reach under the egr valve and GENTLY press up where the vac hose goes on the egr ,plug the valve with your finger if it holds it is good if not its bad, but never hurts to check.

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86 Fiero GT 13,000 org mi
KCFOG member

Posssibly the main plug wire that attaches to the center of the distributor cap (if you have a spare try replaceing that).Try removing the EGR and clean the carbon out of any of the ports on the bottom.Can you hear any vacume leaks?I once pulled the top off a 4 banger and directly under that thing that looks like a carberator were 2 ports that were cloged with carbon,the carbon was so compressed it almost looked like a dirty gasket.Another possibilitie could be the ignition modual and pickup.Your timeing could be off,did you mess with the distributor?

[This message has been edited by James Bond 007 (edited 04-09-2004).]

Bump for saturday

bump for updates, added to first post

Check your coil as well. It might have developed a temperature sensitivity. Mine did that a few weeks ago.

[This message has been edited by hajii (edited 06-19-2004).]

According to Ben Watson; if the O2 sensor is O.K., other things to check when you have a 45 code are fuel pressure, leaky injector, saturated evap canister or defective purge valve, MAF and TPS. If everything else tests good, replace the ECM.

edit fer spelin.

[This message has been edited by spark1 (edited 06-19-2004).]

bump

I would say it's your ignition module and pickup (there usually replaced at the same time or the ignition switch (not the key switch).Also make a better ground for the small ground wire that comes off the battery.I once pulled the throttle body off a 4 banger (the whole thing, looks sorta like a carb), to my surprise 1 port was complety closed off with carbin the oter was partually clossed.The carbin was so compressed it looked like a black gasket.

[This message has been edited by James Bond 007 (edited 06-19-2004).]

Hey bear,

There's a whole lot of bumping going on! Can't help you, but I know how you feel. My daughters 85GT keeps on stalling, had to get it towed today.
Hope you can find your problem. We will be replacing the fuel pump tomorrow, then who knows what else.

I don't see a check for solid electrical grounds among all the things done so far, but you've really covered the bases well. I'll keep kicking the issue around my single-celled brain while the calvary arrives.

Good luck!
Beno

Checked alt. output with positive cable disconnected? Never tried that. A voltage that high might shift the ECM out of closed loop, right?

Might be a stupid idea, but is there a crank sensor on these things? I haven't played with mine enough to know, yet.

Mark

quote Originally posted by Firefox: Might be a stupid idea, but is there a crank sensor on these things? I haven't played with mine enough to know, yet. Mark

86's have a distributor, so I doubt there would be a crank sensor. I don't ever remember seeing one, or any reference to one in the Helm manual.

quote Originally posted by ralpy: Checked alt. output with positive cable disconnected? Never tried that. A voltage that high might shift the ECM out of closed loop, right?

Don't EVER try it. It is lucky that the computer wasn't fried instantly. There is a huge voltage surge that will hit everything electrical on the car and the voltage is regulated off the battery, should have gone full out on the voltage.

quote Originally posted by Electrathon: Don't EVER try it. It is lucky that the computer wasn't fried instantly. There is a huge voltage surge that will hit everything electrical on the car and the voltage is regulated off the battery, should have gone full out on the voltage.

Nothing in the car changed after that. Same symptoms before and after.

This is almost always caused by a lean mixture condition. Valuable clues can be obtained by carefully noting when it happens: certain RPMs, certain speeds, engine lightly or heavily loaded, warmed up or running cold, etc.

Start by forcing the ECM to relearn the operating conditions - disconnect the connector in the orange wire at the battery junction box; that's the ECM "keep alive" feed. Leave it disconnected for about 5 minutes, reconnect, idle for 5 minutes then go for a nice long drive. This may be all that you needed to do to correct the problem .

If not, then it gets a bit tricky. Collect clues as outlined above, if a scan tool is available then it can offer some valuable help too.

Possible problems: EGR valve (can check good and still be bad), bad evap cannister, leak in vacuum lines, vacuum can, brake booster, etc, loose throttle body or intake mainfold bolts / bad gaskets, etc.

Wait until it is very dark out, run the engine and check visually to see if the spark plug wires are arcing to ground. Study the wires very carefully as arcing may not always be very obvious. Remember, DON'T touch the wires with the engine running, if you do you will get a shock!
I see that you put in new wires but there is a lot of junk out there, sometimes even the big names. This may seem very basic or odd but performing this night time check has gotten me out of trouble many times when other things fail to show a problem.
Glenn

somebody already asked but did you check to ignition module and the plug going into may have a short. I had the same problem with my 4 banger fiero the plug was the problem. I think I got a new pigtail for the module at www.fierostore.com

Plug wires: yes, they are new, but I've had Delco wires fail right out of the box. That was a problem on my yellow Formula, and also my 3.4. Good idea, I'll check it at night.

Ignition module: The new distributor came with one installed. I'm not sure how to check the pigtail's function. Any suggestions?

Thanks to all for the input.

Pokeyfiero and I did some more work on the car yesterday. We did a compression and leakdown check on the cylinders and valves. Here's the cylinder compression:

1 - 130 (the high reading could have been an anomaly)
2 - 120
3 - 120
4 - 120

Ok, so the rings don't look bad. Now comes the bad news - the #2 cylinder is leaking on the exhaust side BADLY. We are speculating that this is causing the chugging and loss of power. Would that be enough of a problem, or might there be other possible factors? Opinions?

By leaking on the exhaust side, do you mean you can hear air hissing out the through the exhaust? Or that the exhaust gasket is leaking? If the exhaust valve has problems that would allow unburned fuel and air to enter the exhaust and the O2 sensor would pick that up as a lean condition and drive the mixture rich trying to compensate.

JazzMan

it's leaking on the exhaust side, i believe. speculation is that it is fowling the other cylinders, in addition to not producing power on that cylinder.

120 on all four is good compression for an older Duke; the exhaust leakage you note is probably insignificant. If you had a leaking valve / head gasket / etc. you'd have low compression on one or two cylinders.

Rather than continue beating yourself up, how about coming to visit one evening and we'll take my ECM scanner for a ride. In 10 minutes we'll find out what's ailing it - no guesswork required.

You've ridden in my Fiero; Mary's should run every bit as good if not better - it just needs to have the problem(s) identified and corrected...

Edit: Beware the rich mixture symptom. If the mixture is too lean to ignite, the unburned charge goes out the exhaust and you might see black smoke or smell unburned fuel...

[This message has been edited by Whuffo (edited 07-11-2004).]

By chance, did you try driving with the EGR hose plugged?
Some times they stick open and cause your condition...
You can replace the EGR, or keep it plugged...

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crash... The Fierowrecker

Check the TPS with an ohm meter and have the ignition module tested.

EGR - no, we didn't drive with it unplugged (or disabled), but we did activate it by hand while idling. It caused the engine to stumble, so it appears to be working.

TPS - swapped the throttle body with a known good one, including the TPS attached. We even disconnected it, and there was no change. I put in a BRAND NEW distributor, which comes with an ignition module.

Back to the #2 cylinder exhaust valve. It is *seriously* leaking exhaust, and I assume that it is allowing exhaust gas back up the intake and it could be affecting the other cylinders. Does this sound right?

It's unlikely I will want to drive it down to San Jose. It's at pokeyfiero's ranch now, and I'd have to go out there, bring it to San Jose, then drive it back, then get myself back home. I should just buy my own scanner. Thanks for the offer, Whuffo.

[This message has been edited by fierobear (edited 07-11-2004).]

OK, since you haven't tried it yet the FIRST thing to do is to disconnect the vacuum line from the EGR valve and plug the line. Then try driving it - I'm sure that this will greatly reduce or eliminate the symptoms. If it does, this doesn't necessarily indicate a problem with the EGR system; while that can cause this problem the more likely source is an extra-lean mixture due to a vacuum leak.

What happens is that the ECM can compensate for the extra air due to the leak, or it can compensate for the EGR - but not both at the same time.

The proof is to run with the EGR disabled - if this produces normal operation you'll know that the ignition system, fuel injection, etc. are working fine and that the problem is mixture related.

quote Originally posted by fierobear: Back to the #2 cylinder exhaust valve. It is *seriously* leaking exhaust, and I assume that it is allowing exhaust gas back up the intake and it could be affecting the other cylinders. Does this sound right?

If the #2 exhaust valve is leaking that badly, when the piston comes up on the compression stroke it is pushing unburned fuel and air out past that valve. The O2 sensor will see that oxygen because that's what O2 sensors do, and the ECM, having no idea where the O2 came from will simply assume the mixture is too lean, and add extra fuel to compensate. This very rich mixture will cause poor driveability and gas mileage, and will eventually destroy the catalytic converter. Even if every other part on that engine was brand new and in perfect operating condition you would still get this rich problem from the false oxygen.

JazzMan

quote Originally posted by JazzMan: If the #2 exhaust valve is leaking that badly, when the piston comes up on the compression stroke it is pushing unburned fuel and air out past that valve. The O2 sensor will see that oxygen because that's what O2 sensors do, and the ECM, having no idea where the O2 came from will simply assume the mixture is too lean, and add extra fuel to compensate. This very rich mixture will cause poor driveability and gas mileage, and will eventually destroy the catalytic converter. Even if every other part on that engine was brand new and in perfect operating condition you would still get this rich problem from the false oxygen. JazzMan

If the #2 exhaust valve was leaking THAT badly, he wouldn't have gotten the compression test results he did. It's not expected that the valves in a 120,000 mile engine will seal perfectly...

I think what the car has is "Dukeitis". The backpressure EGR system on these engines is notorious; subtle malfunctions will cause gross drivability problems. Usual symptoms: good idle, pulls well at full throttle, misfires badly at part throttle. The speed-density ECM on these cars leans out the mixture at part throttle to compensate for the exhaust gases being injected; less oxygen, so less fuel. However, the EGR system is not controlled by the ECM - it works on the pressure differential between ported manifold vacuum and exhaust backpressure. A small vacuum leak or a little excess (or not enough) backpressure in the exhaust will cause the EGR to open / close at the wrong time.

Usual failure is due to low backpressure due to blown-out catalyst or a vacuum leak; either one of these will cause the EGR to open late if at all. But the ECM still reduces the fuel at mid-throttle so you end up with a seriously lean mixture and extreme drivability problems.

Best way that I know to get a handle on this is to disable the EGR valve by disconnecting and plugging the vacuum tube. Once that feedback loop is broken the ECM can learn the proper trim and (maybe) run normally. At this point, it's usually straightforward to find and fix the problem.

Otherwise you get into traps like: partially plugged muffler causes EGR to open too early, engine runs crappy. A cursory check reveals worn plugs and a dirty air filter. Replacing the parts allows the engine to run stronger which builds up even more backpressure in the exhaust, causing the EGR to open even earlier - and the engine runs even worse than it did before. It's easy to imagine that one of the new parts you put in was bad or connected wrong; you can go around the block for days and never find the real problem.

I had the same symptoms you are having on an 84. It turned out that the problem was originally the EGR. Static testing, that is, applying vacuum or depressing diaphragm, indicated correct function. The internal valve in the plunger was clogged with carbon. That caused irregular/incorrect function. The real kicker was that during the time it took to determine the EGR was bad, an exhaust valve spring broke. Fiero's can throw some real curve balls!
If it is the EGR get an OEM replacement. The aftermarket units may or may not have the internal back-pressure valve in them.

Hey Fierobear,

sorry to hear you are having such problems. This is just a guess from an amateur, but I had the solenoid that runs through the EGR go bad when I first got my Fiero, and it seems like this tripped the code 44 with the check engine light. I did not have the same mechanical symptoms as you, but when I replaced the EGR solenoid with another one, my car did run better. Maybe you can swap the solenoid off of your other cars to check it?

Also, we are still investigating setting up some sort of get together in COLO. and we found a multi-use track in Colorado Springs. This could make for a cool trip, because it is close to the mountains and everything else. We'll keep you updated.

-Kevin

quote Originally posted by 88Kevin: sorry to hear you are having such problems. This is just a guess from an amateur, but I had the solenoid that runs through the EGR go bad when I first got my Fiero, and it seems like this tripped the code 44 with the check engine light. I did not have the same mechanical symptoms as you, but when I replaced the EGR solenoid with another one, my car did run better. Maybe you can swap the solenoid off of your other cars to check it?

Hey, Kevin, nice to hear from you.

4-cylinder Fieros don't have an EGR solenoid like V6s do.

quote Also, we are still investigating setting up some sort of get together in COLO. and we found a multi-use track in Colorado Springs. This could make for a cool trip, because it is close to the mountains and everything else. We'll keep you updated.

Sounds like fun. Keep me up to date.