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Ok... Diagnose me! please... :(

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Old 06-28-2002, 12:36 AM   #1
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Ok... Diagnose me! please... :(

Well, I've been slowly working on fixing all of my 'Bird problems (305 TPI, 87 Formula) and I've got one that I can't quite nail down...

Here's the deal: I had a code 15, CTS friedo. Replaced it. Code go bye bye, engine now has SOME power cold, and doesn't fight dying as hard while cold. warm/hot idle good now, more power.

Cold idle still surges and runs rough, and it wants to die instantly after a cold start. A bit of throttle keeps it going, but it don't sound quite right.

VSS needs replacing, I'm getting to that next weekend, but I know it needs doing. New oil/oil filter, air filter.

Now, the REAL problem...

I have a fuel smell, generally comes up after hard acceleration/deceleration. If it is low on gas (I just ran it dry yesterday...) the smell is barely noticable. Full tank, stinky! I'm only getting about 7-8 MPG on 91 octane (what does this one use normally, anyway? ) and there are definate problems with the cold idle. I know the VSS isn't responsible for everything, cause this happens when I start, before I move (VSS code 24 comes up after a bit of going) and the light comes on.

What would you check first? I'm thinking the VSS and the EVAP canister filter/lines. I can't find a fuel leak...


Once it warms up, it seems to run great (limited smell, too.) and idles solid at 700, without a hiccup.

Any other ideas?
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Old 06-28-2002, 01:41 AM   #2
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87 TPIs still had the cold start valve on the driver's side of the TPI I believe. I would check that. Maybe it's leaking when it's cold causing the smell and the poor gas mileage. Also if you say the engine struggles to run when cold that could also point to that cold start valve. Take a look at it...
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Old 06-28-2002, 02:29 AM   #3
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Car: 1988 Trans Am GTA
Engine: 5.7L TPI (L98)
Transmission: 700RJunk


When's the last time you've had a tuneup (02 sensor)? That definately sounds like a fuel leak to me, though. Possibly leaky injectors? Leaky fuel pressure regulator?
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Old 06-29-2002, 02:07 AM   #4
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No idea on the tune up, I bought it for 1500 a week ago (given body condition, interior condition, and solid looking engine, it would still be worth it if I have to drop a 350 in).

I'm going to replace the O2 sensor asap... What exactly does the cold start valve look like? I know where the sensor/switch is (near the CTS, I had to remove it too...). I do have a minor coolant leak, would that cause a problem with the sensor?
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Old 06-29-2002, 02:13 AM   #5
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Car: 1988 Trans Am GTA
Engine: 5.7L TPI (L98)
Transmission: 700RJunk


The coolant leak shouldn't have too much of an efect on the sensor and even then, cold start injector circuit is only hot during start-up, so thats not the problem. The injector itself is located on the driver's side of the base manifold between the pairs of runners. A fuel pressure guage might be a good investment right now to test for fuel leaks.
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Old 06-29-2002, 06:47 AM   #6
ede
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check the Fp and volumn, look at the cold start injector and look at a clogged cat
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Old 06-30-2002, 03:11 PM   #7
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Getting a fuel pressure gauge. I'll do the volume test by undoing a line and grounding the pump...

I'll check the cat... That hadn't crossed my mind.

The coolant leak is so minor (looks like a once a month, add a bit) that I don't think it is the cause of any of these problems.


Oh, and how hard is it to replace a tranny mounted VSS?
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Old 07-02-2002, 06:11 PM   #8
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Take this with a grain of salt, since I'm still relatively inexperienced:

1. I wouldn't worry about VSS; it doesn't do much as far as how your engine is running.. In the long-term it might confuse your tranny.. I don't know-- I haven't looked at the TPI ECM code...

2. Let's hope it's your O2 sensor (~$25)... could easily be the problem since the mileage is so horrible. If you're getting only 7-8 MPG you should've gotten a code... however it might happen that O2 is just returning bogus voltage...

3. If it's the cat, you'll know, because your car won't push much after certain RPM.. A clogged up cat = rev limiter?

4. Otherwise... textbooks say -- compression loss... trouble, trouble... Least troublesome: messed-up valvetrain.. could explain low-mileage, fuel smell... More troublesome: cracked ring.. worse: cracked piston ring, worse: cracked block.. (you have to really molest the engine to do this to a chevy block)

5. Slight coolant leak might be slightly leaky heads... Check your oil after driving it a little more... if it's milky you need a new head gasket and/or new heads... No, it shouldn't cause these problems...

6. You say you ran the car dry. Maybe you messed the fuel pump up and now your injectors spray crappily (sp?), because of low pressure in the fuel lines...

I'd do a compression test, just in case... Shouldn't cost you more than $30 if you don't want to do it yourself/don't have the tools...

See, I wonder why there is so much fuel needed to keep the car idling...Can you smell the fuel when it idles?

Idle @ 700 RPM when warm... if it's in neutral, it's OK. if it's in drive, it means the ECM is running open-loop - something's wrong with the sensors...

Oh, yes, I HOPE you changed the sparks (I know, it's a pain)... how do they look like?
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Old 07-03-2002, 10:55 AM   #9
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Just for arguments' sake, clean the IAC. You might also want to check the TPS voltage and continuity (for "dead" spots), but that might not affect the idle if the dead spot is at part-throttle.

Do the fuel pressure and injector leakage test, and also look at the FPR for fuel leakage out the vacuum fitting (ruptured diaphragm).
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Old 07-08-2002, 05:59 PM   #10
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All right. We got the speed sensor replaced, and it did help with the running of the engine after warm-up...

Then the radiator blew.

So, we replace the radiator and the plugs this weekend, maybe the O2 sensor.

How would one check the cat?
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Old 07-09-2002, 09:01 AM   #11
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It helped? Wow... didn't expect that to do anything..

I wonder how your sparks will look like... I strongly suggest replacing the O2 sensor...

The easiest way to check the cat is to unbolt it (if it's a bolt-on one) and see if the car runs different. If it runs better, the cat was most likely a part of the problem. Otherwise, see if the car won't go past certain revs before the redline or whether it advances too slow.. If that's the case, it's very likely that the cat is clogged up.

Obviously, your car runs rich (the fuel smell, low mileage, etc.), and it could be that even if the cat were OK before, it's fried now -- when gasoline enters the exhaust, it increases the temp. in the cat by several times, and eventually the catalytic compounds can't take it anymore and decompose, potentially blocking up the exhaust and creating a huge backpressure.

BTW, how's your timing, what procedure did you use to set it?

Last edited by Marin; 07-09-2002 at 09:04 AM.
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Old 07-09-2002, 09:20 PM   #12
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Quote:
Originally posted by Marin
It helped? Wow... didn't expect that to do anything..

I wonder how your sparks will look like... I strongly suggest replacing the O2 sensor...

The easiest way to check the cat is to unbolt it (if it's a bolt-on one) and see if the car runs different. If it runs better, the cat was most likely a part of the problem. Otherwise, see if the car won't go past certain revs before the redline or whether it advances too slow.. If that's the case, it's very likely that the cat is clogged up.

Obviously, your car runs rich (the fuel smell, low mileage, etc.), and it could be that even if the cat were OK before, it's fried now -- when gasoline enters the exhaust, it increases the temp. in the cat by several times, and eventually the catalytic compounds can't take it anymore and decompose, potentially blocking up the exhaust and creating a huge backpressure.

BTW, how's your timing, what procedure did you use to set it?
Never set the timing, I don't have the equipment.

It is no longer running noticably rich. No fuel smell after warm up, but the exhaust smell is a bit strong. Smoother run/idle too.

I'll take the cat off. Around here, we also think that running it rich for a month probably fouled the plugs, O2 sensor, and might have plugged the Cat. Those plugs are going to be a bitch...

What's the easiest way to get to the plugs?
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