Pimpinpinguino

My 1990 GXL has been acting up lately. Sometimes (keyword "some") she misfires while I'm driving whether it be while shifting, accelerating at a light or just driving in a straight line. It usually takes a while for symptoms to appear (i.e. when engine heats up) so the car usually drives great right after cranking for about 5 minutes.

Some days the misfires never happen, other days its so bad that when I stop at a light, it just starts farting and weakly revs up to about 4k until I pump the pedal to let it all out...

And also, it has lost a lot of power and only pulls (weakly) up to 4k rpms in first and any gear above 2nd pulls exponentially weaker and has no discernable powerband...feels like the clutch is slipping where rpms go up but nothing happens

WHATS ALREADY BEEN FIXED:
I installed new fuel injectors (primary and secondaries)
New spark plugs
Replaced all the vacuum hoses
New alternator
New tps
New bypass air control valve
Clutch is new too so I doubt its actually slipping
Checked compression (its good)
Didnt replace fuel pump but tested it and its good too

MAF - my old one broke and car wouldnt start so I took it to a rotary mechanic who screwed me over and charged me $660 to "start the car" where all he did was replace my MAF with an old one he had that "used to be broken" but he fixed it...supposedly.
The reason I havent replaced this is because apart from it being expensive, I've never actually known what this thing does or what problems it could cause

My best guess is that its something air related because its the only loose end and I've noticed that in cold (miami) weather, it actually drives a lot better than in the usual hot muggy weather we have

So could the MAF be causing all this or am I missing something? Any input is appreciated (even if its just to remind me that I paid $660 for a MAF)

satch

iTrader: (1)

A used AFM found in the parts for sale would go for $50 to $100 in case you need a replacement. Have you pulled error codes? You can use info in the FSM to check the AFM. You might also want to check the water thermosensor as well.

lduley

iTrader: (1)

I can't believe satch didn't say it

Did you adjust the TPS after replacing it?

Pimpinpinguino

Actually....I did not
guess I'll try that
Thanks

satch

iTrader: (1)

The Green/Red wire should measure 1 volt w/key to on after the car has been sufficiently warmed up (20 minute drive will do).

Pimpinpinguino

So I checked the error codes and got error code 17 which I believe is the 02 sensor. If it is the O2 sensor, do you think it could cause that many problems by itself? I havent checked the TPS yet because I dont have a multimeter yet (and its finals week)...
After next week I'll check it.

So O2 sensor. Could that explain misfiring? It might explain the terrible fuel economy I'm getting and strong gasoline smell exhaust right?

lduley

iTrader: (1)

Strong gas smell and bad economy yes, bucking not likely, OBD1 doesn't rely on o2 sensors as hardcore as OBD2. i bet its your tps, mine would buck all the time when i had it adjusted wrong

Pimpinpinguino

Got a multimeter today but I'm not quite sure I know what I'm doing with it... I got the engine hot, turned it off and turned the ignition to on.
I then popped the hood and connected the (+) to the red/green cable of the TPS and the (-) to the throttle body. This gave me a reading of 1.56v.
I tried looking online for how to do this but everywhere I look its different.... Do I need to disconnect the TPS sensor to test it? What other cable do I need to check?
And more importantly, what am I looking for?

lduley

iTrader: (1)

You were on the right track! Go take another joy ride, get her warmed back up and put your leads in the same place you had them before, WHILE KEEPING THEM THERE, reach up to your throttle body and turn the screw with the spring until your voltmeter reads 1.00V, after that, unhook your leads, close your hood, take a drive, go back home, grab a cold beverage, and pat yourself on the back, NOT to hard though, don't want to break your arm lol

Pimpinpinguino

Ok so I got it down to 1.00 V and it drives a LOT better now! It pulls a lot harder and misfires and hesitates a lot less than before.

There is still some misfiring though but it feels "weaker" than before. I think this might be because its running rich. The error code I got was for the O2 sensor so I bought a new one but after a few google searches I found that black smoke from exhaust and bad fuel economy could mean the water temperature sensor.
BUT if mine was messed up the ECU would give me a code right?
The misfiring happens most when the engine idles for a while like at a light or something. Before taking off I have to sort of pump the pedal to clear all the gunk out and let it fart out black smoke all over the cars behind me.
(I'm no expert but that sounds like its running rich to me)

So I'm just going to wait until my O2 sensor arrives and see if that fixes the running rich problem and if not, more diagnostics..

an thanks for the help!

lduley

iTrader: (1)

The ECU won't know if the thermo sensor is working right or not, all the does is read a resistance reading from it, if it wasn't working right the ECU wouldn't know better, its just calibrating for what the sensor is telling it resistance wise

When you do ypur O2 sensor is wouldn't hurt to replace the thermo sensor also, not the easiest, but still fairly simple to replace, cheap insurence also

Another thing, in all this stuff you have done, have you checked the timing at all? If not i would recommend it

Pimpinpinguino

I did check the timing before after replacing all the parts I mentioned.
Guess I'll check it again after putting in the new O2 sensor

satch

iTrader: (1)

If the oxygen sensor was not connected the ECU would rely on a default setting, but this doesn't always work, so the lack of this sensor could cause some driveability issues. It's a case by case situation.

Pimpinpinguino

Ok update. I dont know if its supposed to do this because this car has never had a history of doing what its supposed to do...

While driving home, I decided to see what the tps adjustment did in terms of performance so I started revving like crazy and then out of nowhere it backfired like never before. It was so loud that the car behind me slammed its brakes and then changed lanes. I was in so much disbelief that I pulled over to make sure the sound wasnt a tire popping or something!

After that surprise I started noticing that whenever I let go of the gas pedal, the rpms would jump immedietly after letting go and then would sort of hover around halfway down for a split second before going all the way down to idle. Is this some sort of idle system im unaware of?
Apart from the initial blood-curdling backfire, it doesnt negativly affect performance at all and as a matter of fact the drive home felt better than ever.

lduley

iTrader: (1)

You've already said that your car smells like it is running extreamly rich, and that you needed to replace the O2 sensor, don't worry about the backfire until you figure out your richness

lduley

iTrader: (1)

Also, out've curiosity, you said your compression was "good"

Whats "good"? We like #'s when it comes to compression, not werds

Pimpinpinguino

I didnt put the numbers because i didnt remember exactly but It was somewhere in the high 90s psi

lduley

iTrader: (1)

Both rotors? Your marginal, shes starting to get tired

Was that also all 6 faces or cumulative compression?

If thats 90 all 6 faces your still ok being a n/a, mine only has 70psi on the front rotor, but mine still runs smooth as silk, so don't let that scare you.

Get your O2 changed and hooked up and see how that affects it, than go from there

Pimpinpinguino

Ok so after FINALLY getting my order from partsgeek, I installed the O2 sensor.
Right off the bat I can tell its better than before. It doesnt backfire at high RPMs and it smells a lot less like gas.
BUT theres a new problem. When I'm on idle and I depress the gas pedal quickly, it starts backfiring and then the engine stalls. It only happens when I put the "pedal to the metal" from idle so if I accelerate slowly to get the RPMs past around 1500, then I can put the pedal to the metal all I want.

This is actually a pretty big problem because yesterday when making a left turn, my engine stalled which could have been pretty bad in a different situation...

I checked the timing, its fine
Checked tps again, fine
Even Installed a new K&N filter.

One thing i noticed though is that I might have overfilled the oil because the dipstick reading goes over the F a little. I assume this cant be much of a problem since these things burn oil like crazy.

CrimsonPride

iTrader: (11)

I'm not about to say I have the answer after all of the above but there are a few things I would check:

TB linkages and throttle plates - Since it runs fine during warmup and surges when letting off the gas, I would check the linkages. During warmup the double throttle system operates which changes the primary/secondary throttle opening so it could run better during warmup if the problem was in this area.

Spark plug wires-I don't think it is this but at this point I would be compelled to check if it was my car. Run your car at night and pull over some where dark pop the hood and see if you see any errant sparks near the coils, spark plugs, or wires. Would be great if you look for this while the car is idling poorly.

If the car idles too high I would do a check for vacuum leaks. I'm just saying these last 2 items because at this point I would want to make sure I had made all the basic checks.

MidnightEmpire

How about fuel mixture.. I don't know if anyone recommended it but why don't you try making it run a little more lean maybe?