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Author Topic: Please help, I don't ask often, but..  (Read 1232 times)

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ab8127542

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Please help, I don't ask often, but..
« on: April 28, 2015, 05:36:52 AM »

SEVERE misfire on my tgp. Especially at idle, but it comes and goes. And is worse at when the engines in low rpms and has a load on it (going up hill, etc). I'm a pretty good mechanic, but this ones got even me stumped. You can't give it any boost, period, or it runs like hell. No knocking, pinging, and when it runs good, it runs good. Usually at a higher speed and it takes a while to get there.

Initially thought I had it diagnosed, but I was wrong. Multiple times.

That's what got me here. I've replaced the following trying to chase down
This specific problem, and in acending order;

Fuel pump.
Fuel filter.
Fuel regulator, all injector o rings as well.
Ran some injector cleaner ofcourse.
Plugs and wires, twice, just to make sure.
Ignition module and coils. Twice.
Tps, map, iac, and crank sensors.
All fluids changed regularly,
Complete vacuum line replacement, and
They are all routed correctly. I took pictures.
Intake manifold gaskets, pcv valve.

And it goes on. Completely stumped and discouraged.
Any suggestions?
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89 TGP
90 Beretta

flybynite

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Re: Please help, I don't ask often, but..
« Reply #1 on: April 30, 2015, 03:24:43 PM »

Any codes present in the pcm? If the injectors are original to the car I would start there...
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1989 TGP Pace Car
1990 TGP Red/Tan Leather

ab8127542

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Re: Please help, I don't ask often, but..
« Reply #2 on: May 02, 2015, 05:51:11 AM »

The only code being thrown is 31, which is cam sensor, which I don't have, and/or the boost solenoid, but i get a fuel cut at high boost and then get a check engine light for a few seconds, then when the computer restores fuel it goes off. I dismissed code 31 as being left over from one off those instances, since it doesn't throw the light, but is present when you pull the codes.

Anyway I've got some yellow tops and they've been flow matched to 3%. I'm going to put them in this weekend, hopefully it's a problem solver. The fuel cut could be related to bad injectors? Maybe? I know the pcm is cutting the fuel, but possibly due to excess resistance from and injector?
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89 TGP
90 Beretta

jimmy

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Re: Please help, I don't ask often, but..
« Reply #3 on: May 02, 2015, 08:36:37 PM »

My car when it was together would do the same but not as frequent. It would be months before acting up. So  let me know if it fixes.

ab8127542

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Re: Please help, I don't ask often, but..
« Reply #4 on: May 03, 2015, 07:27:37 PM »

Got the injectors in, didn't really fix anything. But did narrow things down a little, I think. It's draining fuel back into the tank just minutes after shutting it down, leading me to also assume the hard first starts are for directly related. New injectors eliminated the risk of injector leakage, though there is a also a new pressure regulator.

We're thinkin the lack of power and misfire is due to some fuel going right back down to the tank, the psi is only around 30. Question is, where is the anti drain back located on a TGP? In the pump, in the regulator? If so, they've both been changed.


Couldn't help but notice a round aluminum drum coming straight off what I believe to be my return line, just off the fuel rail. Any idea what this is because I can't find anything on it, and I'm wondering if that's playing part. But you can hear fuel returning to the tank.
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90 Beretta

GPChief

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Re: Please help, I don't ask often, but..
« Reply #5 on: May 15, 2015, 08:22:21 PM »

Call me crazy but how is your catalytic converter?
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2004 GTP -  3.8 Blown - Only modding for MPG.
1997 GTP  - 3.8 Blown - Too many mods to list.
1996 GTP - 3.4 DOHC - Twin to my 1997.
1995 SE - soon to be a 3.8 turbo car.
1990 TSTE x 2 white cloth
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1990 TGP - 5 speed.

meltboy11

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Re: Please help, I don't ask often, but..
« Reply #6 on: May 16, 2015, 06:31:34 AM »

Call me crazy but how is your catalytic converter?


How could that affect it? Being clogged and too much back pressure?
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90 TGP ~70k miles 5/15
04 Wrangler 4.0 5 spd
Litchfield, NY

mfewtrail

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Re: Please help, I don't ask often, but..
« Reply #7 on: May 17, 2015, 01:41:00 AM »

Got the injectors in, didn't really fix anything. But did narrow things down a little, I think. It's draining fuel back into the tank just minutes after shutting it down, leading me to also assume the hard first starts are for directly related. New injectors eliminated the risk of injector leakage, though there is a also a new pressure regulator.

We're thinkin the lack of power and misfire is due to some fuel going right back down to the tank, the psi is only around 30. Question is, where is the anti drain back located on a TGP? In the pump, in the regulator? If so, they've both been changed.


Couldn't help but notice a round aluminum drum coming straight off what I believe to be my return line, just off the fuel rail. Any idea what this is because I can't find anything on it, and I'm wondering if that's playing part. But you can hear fuel returning to the tank.


The fuel pump contains the check valve or anti drain as you've called it. Did you replace the fuel pump recently or prior to this issue? If the injectors are not leaking and the FPR isn't, then your pump has to be the source of the pressure bleed-off. What pump did you replace it with? It wouldn't too much of a stretch to have a bad pump right out of the box if it was a cheaper quality unit.  Did you replace the pulsator when you did the pump or did you re-use it...or did you throw it away and use a piece of fuel grade hose in its place? That pulsator or fuel hose from the pump to the fuel supply line on the sending unit is another source of a possible leak. If you reused the pulsator, I think it's safe to say it is leaking and your fuel pump(s) were probably fine. To check the pulsator, they tell you to "shake" it and if you hear fuel sloshing inside of it, it is bad.

That little cylindrical aluminum piece on the rail is a dampener, similar in function to the pulsator in the tank. It's there to cut down on noise and smooth out fuel delivery. If it's not leaking externally which would be very obvious, there's no real issue it can cause.
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ab8127542

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Re: Please help, I don't ask often, but..
« Reply #8 on: May 19, 2015, 05:10:08 AM »

I cut the cat off early on. It seemed to breath better, but didn't fix this issue. Had a local muffler shop weld in some pipe.

The first time I replaced the pump I reused the pulsator and did use a standard pump. Second time I tossed it and put some injector hose in its place. Also put a walbro in and that fixed the drain back issue. But it hasn't fixed my misfire. At this point it's had everything swapped out twice. I mean, could this be an ecm issue? The long starts, misfires, it smells like it gets way to much fuel. You can smell it at the tailpipe something awful. Can't handle high rpms without bogging down. It's still a stock ecm. I'm just shooting it the dark here guys.

Plus it will cut fuel with minimal boost. If you do happen to catch it running okay, as soon as you give it gas and, according to the stock gauge, 4-5 psi, it cuts fuel. You get the check engine light for like 15 seconds and then it's restored.

Gotta be a short somewhere?
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90 Beretta

meltboy11

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Re: Please help, I don't ask often, but..
« Reply #9 on: May 19, 2015, 05:56:10 AM »

Could his problem be vacuum related? I re-read the whole topic and didn't see that mentioned.
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90 TGP ~70k miles 5/15
04 Wrangler 4.0 5 spd
Litchfield, NY

ab8127542

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Re: Please help, I don't ask often, but..
« Reply #10 on: May 22, 2015, 05:45:19 AM »

Put a new ecm in it. The car is a different animal. I pulled it out and swapped the memcal, it runs great. Not sure why it failed but at least that's over with.

Thanks for the input, guys.
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meltboy11

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Re: Please help, I don't ask often, but..
« Reply #11 on: May 22, 2015, 06:09:29 AM »

ah yea. I just replied to your PM btw. I had a chip go bad on me before and it caused all sorts of issues. It may not have been the whole ECM, but just the chip. Either way, glad your car is working again! Wish mine was.  :icon_frown:
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90 TGP ~70k miles 5/15
04 Wrangler 4.0 5 spd
Litchfield, NY
 

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