Firebird 3.1 1991 runs good now bad no good bad good bad

My 1991 Firebird 3.1 has driven me to hell. I am down here wondering why this car runs good for 15 to 20 minutes (1 to 2 fan cycles) then bad, idles with a vacuum that is about 10HG below normal (pressure between 11 & 13). If I was driving, it would slow down to a stop when it runs bad. When it’s bad & I open the throttle plate, it idles even worse or dies. Fuel pressure (tested at the schrader valve on fuel rail) reads 45psi in bad mode. The more I try running it in bad mode the more it stumbles. I have left it sit over night & miraculously it runs good the next day (everyday) until it reaches bad mode again. I don’t know exactly how long before this thing resets itself from bad to good though. I replaced the fuel filter (looked like 2 tablespoons of water in the excess fuel from filter while replacing), fuel pump, O2 sensor (was damaged physically anyway), ignition coil, ignition module, spark wires & distributor cap. Cleaned the platinum spark plugs, tested ECT, IAC, TPS, MAP, IAT (resistance is telling me temp is 35 to 45 when it was about 70 degrees F), tested grounds, resistance & --computer–? voltage (all checked good). I got numerous flash codes, in bad mode, all on different days in the last month some of them where MAP high, O2, fuel circuit voltage low(?) & IAC . I removed the IAC & found the pintle dirty as well as its mate surface, it was not hitting dead center, looked off by a few degrees. I cleaned it & put it back, don’t know if it is hitting dead center because it is clean.

For over a year my new KS has not been connected to the engine but is grounded. I removed the old KS & left a stud in the engine (tight fit). Never got a code for that this whole time.

A couple weeks before it was undrivable, if I would run over some bump/s or ran up the RPM’s too high, it would stumble. Once it stumbled it would stumble the rest of the day usually (but was still drivable). The next day the stumble would be gone again (car ran good / reset?).

It is at a shop and the guy told me he hooked it to a scanner and everything looks good? My folks are telling me to pull the plug and I got real sick since I have so much time invested into personally renovating this car. I am sure with my memory lapse I forgot to tell you everything. I am praying to the Click and Clack Clan (CCC) that they can figure out what 6 other mechanics can not.

If you got a spoon or two of water from the fuel filter then you really should drain the tank, replace the gasoline, and add a gas line drier.

A handful of water in the tank will wallow around in there and depending on how it sloshes around, can feed water into the pump intake at various times.

The low manifold vacuum might be normal IF this reading is when the idle is very low and the engine is stumbling.
If the reading is that low when the engine is idling smooth then you have a problem other than water in the gas.

There are a few other things it could be but the water issue is something that should be examined first.

Here is more FYI. Exhaust is normally clear and can be felt coming out the tail in good and bad mode.
The O2 sensor wiring connector was slighty melted though it attached to the new O2 sensor, I am not sure if the wire itself was in bad shape (possible). After doing some reading about vacuum I saw a comparable gauge from my college books say: either retarded valve timing or retarded ignition timing. I am doubting it is a retarded valve problem since the car runs for 15 to 20 minutes good. When I did rip out the O2 sensor I also ripped two layers of exhaust pipe and the mount for the O2 sensor of while I was trying to remove the O2 by hand. Ended up buying a larger diameter pipe, drilling a hole in it and securing a nut on one side to hold the O2 and clamping it over the hole filling the gaps with muffler cement. Figured if I get the car running right again I’ll buy the third Y pipe I hav bought for that car. Air filter is good. Exhaust does not get cherry red or red at all for that matter. I have been asked if I thought it was the catalytic converter getting clogged. I then asked others and was told that once a catalytic converter is clogged it does not unclog. Anyone with any different ideas or knowledge on anything I wrote I am more then open to criticism, sarcasm, foolishness and most of all help.

Thank you. I will keep this information in mind. I thought I already replied. This is my first posting here. So if I did not, my vacuum is normally 22 or 23 hg when the car runs good, when the car runs bad it is about 10hg lower around 12 or 13hg.

Another thought. It sounds like an intermittent vacuum leak. This could be due to a bad EGR valve not seating properly, and creating a bad vacuum leak in the intake. Or, a bad vacuum switch that is leaking when activated. I was thinking also of the brake booster having an intermittent leak. Also check the air intake hoses after the MAF sensor for breaks and leaks. These engines will stumble if air gets into the intake that doesn’t pass through the MAF sensor.

That’s a good point about an intermittent sticking open EGR valve since an EGR is a vacuum leak, although it’s supposed to be a controlled one.

You might also consider pulling that new filter off and dumping the contents into a jar for examination. If you find water in it then the tank needs to be completely drained considering this would be the second go-around.

There is no MAF. One thing you said about the brake booster has caught my attention. In the very first week this was happening while it was still drivable the brake pedal went to the floor on me. This never happened to me before and since I filled it with fluid it didn’t leak. When I did fill the master, I ran the engine and lightly pressed the brake pedal and while I did the engine started stumbling. It did that a couple more times and finally stopped. I then placed the master lid back on and the brakes were fine as well as the engine idle with or without the brake pedal depressed. My EGR is digital and I am a young buck(green) when it comes to understanding what to look for on that. Vacuum switch and EGR are a little more unlikely as the problem occurs after 2 cycles of the cooling fan or 15 to 20 minuted each time every day.

If this Digital EGR is sticking open then why would the car run great consistantly for the first 15 to 20 minutes (2 fan cycles) of running it each day? Or does it open in open or closed loop?

I may need to clarify something here. The car currently starts off running good, after it runs bad it stays running bad for hours, maybe until it cools down completely (? unsure)

Digital or vacuum actuated, the EGR is simply a valve that will open and close to allow exhaust gasses into the intake manifold. But, the system gets clogged with carbon deposits. Typically, the EGR system doesn’t start to work until the engine is warmed up. If the EGR valve doesn’t seat properly, it will behave like a vacuum leak. The only way to know is to remove the EGR valve, and check for carbon tracking on the valve. Another way is to disconnect the EGR when it is running good, and see if the problem returns while it is disconnected.

I have removed the EGR and inside it looked pretty clean. I did not look for a valve but will. I think the EGR was disconnected after the car was already running in bad mode. I had the pleasure of meeting my a neighbor who also is a mechanic (now on aircraft). I believe he disconnected or attempted disconnecting it although I remember he got there long after I had gotten the car in bad mode. I will disconnect the EGR and run the car to see if this works. The car is at a shop (not mine) so I can not fiddle with it till I give this fellow some time with it.

I recently worked on a 1990 Pontiac GP. It’s emissions and engine controls are much like the Firebird’s. It stumbled badly, at idle, anywhere. I found the digital solenoids on the EGR were energized OPEN constantly. Pulled the IGN fuse in the engine fuse box to cut the power to the EGR valve and the purge control valve. It, then, would idle. It wasn’t a bad computer…tried another…same. Don’t know what it was. Neighbor found a shop which found the cause. I haven’t gotten the feedback from the shop, yet. /// Your car’s engine has three engine computer (ECM) controlled components which can allow excess air into the engine intake: the EGR valve, the charcoal canister purge valve, and the air select valve. They are fed by the same fuse: the Gauges Fuse 10A. Pull that fuse and check the intake vacuum, again. You could, also, plug ALL the vacuum hoses … to the brake booster, the charcoal canister, the pcv valve. Check vacuum again. /// The engine management will inject additional fuel during warm up, until the ECM get the signal from the coolant temperature sensor that the engine has reached a certain temperature. This is, usually, near the point where the engine control system goes into closed loop operation.

Change the engine computer if it is the $100 one and see what happens. Try one from the junkyard. Don’t lose the PROM chip. There are instructions with the computer, but don’t listen to the ones that don’t involve changing it. The fact that there are no service engine now lights coming on is a sign that the computer may be cooked.

The computer service engine soon light does light. I apologize if I was not clear there. I wrote that I flashed codes. I didn’t write that the Service Engine Soon SES would light almost if not every time after the car ran in bad mode for a while. I am keeping the computer in mind.

Today, I learned what was done, and how it was done (which is, actually, more important), on the very rough running 1990 Pontiac GP with V6 engine (sister to your car). The three left bank fuel injectors have a single power wire and fuse. The right bank of three fuel injectors have a single power wire and fuse. The fuse was pulled on fuel injector bank one. NO change in the engine. The fuse for bank two fuel injectors was pulled. The engine ran MUCH better on the three fuel injectors of bank one(though still rough). Tests showed that one of bank two fuel injectors had shorted. Changing two of the bank two fuel injectors brought light and happiness. The patient is, now, doing fine. /// The mechanic who troubleshot, and cured, this car, looked at the problems with your car. He thinks that there is a poor ground connection which is heating, with use, and breaking the ground. Without a ground, there is no circuit. Whatever component(s) the ground serves, cease to operate, or operates poorly./ Just change the battery cables. Everywhere on the engine, transmission, fender, firewall, under the dash, wherever you can find a wire(s) or cable attached to those areas, loosen the screw, or nut a couple of turns, turn the wire terminals to and fro, a bit, and retighten the bolt, screw, or nut. This should give better electrical ground connections. If you wished, you could put new lock washers on them.

You’ve admitted you found water in the old fuel filter.
Why would you think that is all of the water in the system?

Sounds like fun. Maybe it is the O2 wire with the melted connection.

Guessing the problem is not this since it occurs after two cyles of the cooling fan be it 15 or 25 minutes. The car runs great until it changes modes. When it changes modes it does it instantly, unlike the feel of water slowly disturbing the system. When I get the car again I will pull some fuel out of the car from the lines to take a closer look.

This is a sample of the threads where the forum regulars, or, anybody else, never get the final response from the poster when a repair is completed. Those who responded would like to know what, if anything, they said helped to solve the problem… and IF possible, to learn why and how, it helped.

HOLD YOUR HORSES BUDDY!! If you look back on 11/05/07 I wrote “the car is in the shop (not my shop)” I intend to let you all know what actually happened or what is happening. The mechanic who has my car has had it for over 3 weeks and this past week he was sick, so the saga continues. I am beside myself because my other car (in another state) is a clutch away from perfect and I was not working continuosly enough to fix it or get it fixed. I know, my buddies say just do it on your chest, well I used to R&R 2 to 3 transmissions a day and would rather walk than have the weight of a transmission on my chest while I try to CORRECTLY remove, clean and replace any items I see fit.

Please remove or edit that last comment, as it is completely untrue of my nature to leave people in the dark.

I do understand what you are talking about as to how most of the postings I have ever read never give that final key piece. As God is my witness, I will try my hardest to keep my computer alive and find the time in my days in the future to make sure I give you all this key answer.

That would be great! Then, at your convenience.