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TPI Issues



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Old 03-25-2006, 11:27 PM   #1
 
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TPI Issues

I have a 1988 YJ with a 92 350 TPI out of a Z28 backed up by a 700R4.

Starts fine, idles great, drives down the road. If you give it more than 1/2 throttle or so it pretty much falls on it's face.

Sounded like fuel pressure to me, I checked, 44-46 lbs at prime and idle, right where it should be. This rules out fuel delivery.

New cap, rotor and module.

So now I'm thinking TPS or MAP.

Every once in a while it will refuse to start, just turns over. Quit on my wife one hot day while driving down the highway, lifted the hood and it started just fine a few minutes later. I was thinking fuel pressure then and probably a bad fuel line route causing vapor lock... in conjuction with a lack of fuel. I don't see evidence of a bad fuel line routing and have ruled out fuel pressure.

Thoughts?

I'll probably need to take it to a Chevy dealership to get it scanned and see if there are any codes but thought I'd see if anyone has run into this before.
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Old 03-26-2006, 12:31 AM   #2
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You can pull the codes yourself. Jump the A & B terminals on the ALDL port with the key off, they are the two on the top right with the plug mounted horizontally. Turn the key to the on position, but dont start. Watch the check engine light, it will flash a code twelve (one flash, short pause, two flashes, long pause) three times. A code twelve is normal and will show up all the time, if there are any codes stored in the computer it will flash each one three times. When it is finished it will flash the code 12 three times again.

Once you have the codes you can probably look them up online or you can call Autozone and they can tell you what they mean.

This is what the ALDL looks like, but mine is mounted vertically. Stock, it is usually mounted under the steering column, but there is no telling on a retrofit.
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Old 03-26-2006, 05:29 AM   #3
 
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....IF it's hooked up to a check engine light.

Mine is mounted under the right side of the dash. It's the 12 pin OBD1. I was going to buy an Actron CP9001 $30.00 at AutoZone but it basically does the same thing you are talking about. Guess I'll just have to jumper the ALDL and see if the prior owner actually attached something to a light in the dash.

I'm willing to bet he hooked it up. I am lucky in that I received a serious stack of paperwork with this Jeep including some very detailed notes, diagrams, receipts, etc and after looking over the notes this morning I'd say there is a good chance this will work.

Oh, and if you haven't seen this before http://chevythunder.com has in depth information on TPI systems, troubleshooting, including codes, etc.

Thanks,

Last edited by American; 03-26-2006 at 06:01 AM..
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Old 03-26-2006, 08:41 AM   #4
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long shot, but how close are your gas lines front the tank going to the motor away from the exhaust? could be exhaust is heating up the fuel before it gets to the motor.
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Old 03-26-2006, 12:10 PM   #5
 
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Yeah.. vapor lock. That was one of my thoughts too. However, except for one instance where it died on my wife while driving down the highway, temperature doesn't seem to be a factor. I looked at fuel line routing when I was checking fuel pressure, routing looks ok.

I just ordered a sensor tester to check TPS, MAP..etc individually and should have it Wednesday.
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Old 08-23-2006, 07:23 AM   #6
 
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Question

Hey, American, ever find out what was wrong? I have the same thing going on, just started the other day.
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Old 08-23-2006, 08:51 AM   #7
 
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Not yet.

I replaced the TPS and MAP sensors. New distibutor cap and coil. Had a code 36 so I replaced the EGR then replaced the catalytic converter. I don't have the occasional non starting issue which was lilely EGR related.

Fuel pressure shows 44lbs at prime and idle. I can rev it and it will hold pressure good, may drop to around 36lbs.

I still think it's a fuel problem as it falls in it's face and pings when driving down the road when floored which tells me it could be a lean fuel issue. Timing looks good and it doesn't act like the timing is advancing too much under accelleration. I'm going to change the fuel filter next but my suspicion is that it's a regulator issue which require pulling the TPI plenum next...if the filter doesn't cure it.
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Old 08-23-2006, 10:08 AM   #8
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injectors... some Z28's were 305's not 350's
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Old 08-23-2006, 07:59 PM   #9
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is the cam stock, if you put in a performance shaft it will cause that problem also, eng just falls flat , feels like a carb loading up when it revs. seen 2 veh have that problem
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Old 08-23-2006, 08:19 PM   #10
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Isn`t the knock senser supposed to adjust the timing when the engine starts pinging?
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Old 08-23-2006, 08:35 PM   #11
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Originally Posted by RVREDDOG
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Old 08-25-2006, 09:39 PM   #12
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Quote:
Originally Posted by American

Fuel pressure shows 44lbs at prime and idle. I can rev it and it will hold pressure good, may drop to around 36lbs.
This is most likely the issue, it shouldn't be dropping. I would check for a restriction in the lines (flattened or kinked line), clogged filter or 'sock' in the tank, or a fuel pump that isn't up to the job. I don't think the regulator is the issue, when they fail they usually increase the pressure instead of lowering it.

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Old 08-25-2006, 09:50 PM   #13
 
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Stevo,

I agree, I'm going to pull the filter and find a new one in the morning. I already looked for kinked lines and what not.

I'm going to change the O2 sensor as well.... if I can get to it.

One thing about a SBC in a YJ.... it really needs the inner fenders removed!
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Old 09-09-2006, 04:40 PM   #14
 
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Well...finally got a chance to change the filter. No difference.

I'm stumped. I'm starting to wonder if it's not a flaky computer.
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