Hi all,

Hoping to get some help/advice on a problem I am having on my 1988 GTA daily driver.

I have been having some bad idle issues and it has gotten a little worse (stalled on the road once at a stop sign). Car would turn on right after. Whenever had bad idle issues, the check engine light would always be on. It was always intermittent, and sometimes when the light came on, I would just turn the car off and restart, and the check engine light would turn off and car would run great (I did never really have any issues w/ running/driving though...would always get me from point A to point B).

Something that does happen though is when I try to turn the car on/over sometimes, rather then firing up the car just 'shuts off'.....and I have to turn key again to get to turn on.

My mechanic had told me a while back that I needed a new fuel pump and/or MAF sensor. I never thought to get the Codes from him at the time, and it was odd as the previous owner told me he put a new fuel pump in it recently (probably 2 years ago).

Fast forward to now. Last weekend I had another mechanic friend take my car to his shop while I was out of town to weld in a set of subframe connectors I had.

He noticed the car running terribly, missing, etc and did a tune up and put new plugs, wires, cap and rotor in. He also said timing was way off and adjusted that.

He also pulled codes on the check engine light and said he got code 54, but isnt versed in Chevy FI so didnt do anything w/ it. (Based on research I have done today on this, I think I need to start w/ getting a new Fuel Pump Relay)

Now I get the car back last night and I have a terrible backfire through the exhaust. I was trying to car drive back home last night and was hearing it at low RPMs and at idle. On Freeway it was fine. When this happened, the check engine light wasn't even coming on. The car is running really rich and smells like gas on the backfires.

Also, had massive pressure in the tank when I parked car in my garage. Unscrewed the cap and heard pressure release for a good amount of time (Note, I am in Las Vegas and it was probably 100 degrees out last night)

Any ideas on where I should start to troubleshoot/correct this problem?

Thank you in advance for your assistance!!

 

Yes, code 54 is a fuel pump circuit problem. Need to check both the relay on the firewall and the oil pressure switch near the oil filter. I too have a lot of pressure build up in my tank when I drive it on hot days( it was 103* today in Austin). Seem to be a very common thing. I've read every post about the problem, seems to be a number of possible causes and fixes. I have tried a few of the fixes related to the vapor canister solenoid and relay, blowing out the vapor and fuel lines, didn't help a bit in my case. Based on my research, I think my problem may be the in tank pressure regulator valve. It appears to be part of the fuel sender/pump holder assembly with the 4 hard tubes that go into the tank. I'm going to replace the fuel pump because as far as I can tell I have still have the original one, still working but can go any day. I'm going to replace the whole assembly then, if it solves the pressure build-up problem, I'm be sure to write a post about it.

 

I have owned several f-bodies and have yet to have one that didn't hiss when you opened the gas tank. I attribute it to "an F-Body thing".

My car was running terrible a few days ago. Here are a couple things to check. TPS Voltage (should be 0.54 +- 0.07 v), check CCV and PCV valve (mine had 2 PCV valves).

Just maybe a couple things to look at.

 

Yeah, I agree. Most cars that I have owned build up some pressure in the tank, but my Firebird seems excessive. It gets high enough that it vents vapor through the gas cap, and yes it's new AC Delco cap. Not having owned a 3rd gen when it was new, I don't know if this is "normal". I would think this would have been an emissions issue even back in the '80s. The whole idea of the charcoal canister and all it's plumbing is to keep gas vapor from escaping into the atmosphere, mine's not doing a very good job of it at the moment.

 

Our cars fuel system is designed to hold pressure. The regulator valve you speak of is a one way valve only to let air into the tank so not to cause a vacuum. Not to let vapor out. One of the emission test that used to be done on our cars was a pressure test on the fuel system to make sure it held pressure , The car would fail if it leaked down at all.
Now a problem could be to much pressure if your purge valve on the charcoal canister is bad.
If you think your fuel pump may be going bad jut do a pressure test on the fuel line at idle the fuel pressure should be 40 to 43 psi. Shut the engine off and the pressure should hold there, if not then its your fuel bump.
If the fuel pump is good then I would check the relay to it.

 

I have an 87gta edition firebird my tps is only reading .02 volts on a to b with a new sensor a to c is 4.92v. Any ideas?

 

If your tps is .02 v from the blue wire to black ground koeo and the ecm is supplying the 5.v ref on c try to adjust the tpi to .54 and wot will be 4.75-5v on the blue wire. If this cannot be abtained the tps is bad. You can use a ohm meter on the tps only to do a slow sweep preferably a analog meter.

 

That's impossible at this point. From a to b is .02v ... from a to c is 4.92v. There is absolutely no variation on volts when the throttle is open or closed or anywhere in the transition. Why am I getting low voltage on the b wire? Tps is new.

 

You need to adjust the TPS, to do that all you need to do is loosen up the two screws that hold it on then move it up or down until the tps is at .54v. then tighten it up being careful to keep the tps @ .54v as it can move when you tighten the screws.

 

That's what I'm telling you it won't adjust everything is loose. The highest I've seen come out of it was. 20v and that was going b to c the adjust ment is a to b I understand the voltage is supposed to be at. 54 that's the problem no matter what you do no matter what way you have it its staying in one spot .20 and the tps is new I have the computer out from under the dash as we speak trying to see if there is a loose wire or bad connection

 

Well then the problem is that you have a bad tps, I understand it is new, but if you can not set it @ .54v and tighten it down there, then it is bad.
Does your tps have oval slots not round holes where the screws go threw to tighten it down, If it does not then they sold you the wrong one.

 

Mechanics words mean ZERO. Tell him you're from Missouri - the Show Me state. Show me why you think the fuel pump is bad. Show me a static fuel pressure test, showing no static fuel pressure.

And Show Me why a new MAF. Like 5V voltage TO the sensor with a multimeter, and a good MAF ground, on a MM, so we know for sure a new MAF is needed.

Previous owner's words mean the same thing - ZERO. Show me.

'Another' mechanic changed the wires? How come? Too much impedance on the multimeter, on all 8 wires? Show me.

Fuel pump relay test bad on the multimeter? 12 volts to input, ground output, and see no continuity on the other 2 leads with a multimeter? (12V makes the other connection in the relay close).

Buy a multimeter first - save ton$ of ca$h YuP!

Static fuel pressure test FIRST.

Clear codes after static FP test, then pull codes in Closed Loop - warmed up.

 

You must be from Missouri with saying show me.
I hope you are reading everything before you reply to thee post. The OP has a multimeter as noted on some test done. And if you are reading than you can tell that the TPS is bad. And maybe the timing is off if the mechanic did not know to unplug the ecs, tan and black wire before setting the timing, With the wire connected the timing seams way off. I don't think it is a fuel pump or FPR problem based as it started off as an idle issue, Not a upper rpm range problem where a bad fuel pump would start being seen. I believe the mechanics may have made thing worse by not knowing.
With the TPS showing .20v instead of .54v like it should be and the OP saying it wont adjust to .54v then I'm sure the tps is bad even if its a new one. Just because it is new doesn't mean it's good.

To: miamivice,
Before you do anything else get a new TPS and set it to .54v then check the timing to make sure it is at 6* with the ecs wire unplugged, Its the tan and black wire in the main wiring harness above the heater/ ac box on the firewall on the passenger side of the car. And let us know how it turns out.

 

I am out of town right now, but as soon as I get back, will do this and report back!

 

Have you tried Intake Air Leak test?

With the engine running spray some carb cleaner arownd the Vacum hoses and arownd all the Gasket in te plenum and the tube aroun the intake if the car RPM Jumps you have a Leak.

 

NEW TPS?

Why not test the one in there now?

TEACHER IN (again)


After Off-Vehicle tests, do a backprobe with TPS in place, and check reference FEED voltage, and reference RETURN voltage, as TPS is worked through ROM range of motion. [/quote]Snappics forthcoming

 

TPS Backprobe (Instead of buying a new one blindly ), for ROM Range Of Motion check, of 5V Reference Voltage

(good stuff, and we're lucky to have some others on the boards yUp!!! )



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