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Old 10-04-2008, 06:29 PM
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Stumped! Need help with stumbling TPI motor

I have a 1987 Corvette with 150k miles on it. In the last 500 miles I've replaced the in tank pump, fuel filter, spark plugs, wires, rotor, dist cap, and coil. My problem... I'll crank the car and it runs fine at idle for about 2-3 minutes. Then the rpms slowly sputter down until it dies. I can rev the engine with no problem. I checked my fuel pressure and found that when I first crank the car it holds at about 25 psi, then starts to drop after a couple of minutes until it hits 0 and the car dies. Let the car sit for a few minutes and it repeats itself. I tried running the vacuum line from the regulator straight to the plenum, to hold it open, and got no change. I do notice this weird hissing noise coming from the air pump shortly before it dies. I'm stumped. Been trying to figure it out for 2 days, please help. thanks, Brian

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Old 10-04-2008, 07:33 PM
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The fuel pressure is 25 psi?

Should be ~43. Check the diaphram in the fuel pressure regulator. If you have a hand vacuum pump pull some vacuum on it and see if it will hold it or if it leaks down. If no vac pump you can suck on it and you can tell if there is a big leak but hard to detect a small one this way.
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Old 10-04-2008, 07:37 PM
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Do you know if the pump is still running when the engine dies? Try restricting the fuel return line.

I have never heard of this.

If no one know here,try over at thirdgen.org under the TPI message board.
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Old 10-05-2008, 12:12 PM
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Did a little experimenting and sprayed some throttle body cleaner into a vacuum port on the plenum and I can keep it alive as long as i want. So its definately a fuel delivery problem. The pump is working fine. So its gotta be my regulator. Gonna slap one on today and boost it back up to 43 psi and see what happens.
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Old 10-06-2008, 02:02 AM
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Ok, I sorta fixed it. I put a new regulator diaphram and spring in this afternoon ($41 at the zone, seemed a little steep to me), which required removal of the upper plenum and a special theft deterrent torx bit (T10 if anyone cares) . Got everything back together, connected my fuel pressure gauge, and fired it up. Fuel pressure gauge reads 35#s at idle which is still to low. However, its not bleeding down and the car seems to drive 100x better. But why am I still only at 35#s and not 43? I wanted to put an adjustable regulator on but couldnt find one that I could buy today and I had to fix it since my daily driver is $600 away from being back on the road. Anyway I have no clue why I've still got low pressure, any ideas or suggs would be greatly appreciated. Thanks, Brian
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Old 10-06-2008, 04:11 PM
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well dang it, I thought it was fixed until I tried to drive home from work today. Started out fine, get about half way home, and the same problem started again. It got progressively worse to the point it wouldnt go more than about a quarter mile before it would die and I'd have to let it sit for a couple of minutes before I could crank it again to go another quarter mile. I noticed my voltage was dropping and was down to about 13.2 volts by the time I got home. ***, Ive replaced all these parts and its a bad alternator? I don't get it. Any ideas?
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Old 10-06-2008, 04:48 PM
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Do you have a TPI (tuned port injection), or PFI (port fuel injection) system?

35 PSI sounds right at idle. Key on engine off should be around 43-45 PSI.

The ECM commands the fuel pump relay on, using a signal from the ignition control module.

So you could have a ignition control module, or pick-up getting hot, and shutting down.

The fuel pump relay shutting down, or it's connector could be corroded, or burnt. This can cause a lack of voltage going to the fuel pump.
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Old 10-06-2008, 04:50 PM
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Try removing the fuel cap and see if it does the same thing. I think either you are not getting air into the system or you have a line somewhere that is twisted or collapsing. I have seen a blocked vent cause this type of issue as well as a steel line that was twisted due to a fliter change

Chet
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Old 10-06-2008, 06:21 PM
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Quote:
Originally Posted by DaSouthWon
well dang it, I thought it was fixed until I tried to drive home from work today. Started out fine, get about half way home, and the same problem started again. It got progressively worse to the point it wouldnt go more than about a quarter mile before it would die and I'd have to let it sit for a couple of minutes before I could crank it again to go another quarter mile. I noticed my voltage was dropping and was down to about 13.2 volts by the time I got home. ***, Ive replaced all these parts and its a bad alternator? I don't get it. Any ideas?
Among all the other things it could be, system voltage is also an issue. Many of what appear to be injector problems are cured with a new battery and or alternator. However it is more common for low system voltage to create start but not run problems.

You need to keep a look at fuel pressure, a TPI should be at and hold about 45 psi give or take a few. Besides a bad or poorly performing fuel pump, can be issues with:

- plugged filters

- failure on the pressure regulator

- failure in the pump relay circuit

- failure of the oil pressure sender (safety measure this and a right side up sensor buried somewhere in the circuit are there to shut off the fuel pump if the car is upset or the engine fails to maintain oil pressure which is an assumption the car is no longer on its wheels)

- failure or miss adjustment of the throttle position sensor

- failure of the tank vapor purge system preventing proper venting

- failure of engine temp sensor

- failure of either the manifold pressure sensor or the mass air flow sensor I don't remember which your's has

- my favorite, bad wiring or connector somewhere in all those wire bundles

Last question, is it showing codes for anything?

Happy hunting
Bogie
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Old 10-06-2008, 07:18 PM
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Fuel pressure is 34-45, and the pump should maintain 60-90 dead head pressure.

It does have a MAP sensor, which is used to increase fuel pressure to the injectors during low manifold vacuum situations.

If the fuel pump relay quits, the oil pressure switch is supposed to close maintaining fuel pump operation.
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Old 10-06-2008, 09:06 PM
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Hmmmm

This is almost exactly what happened to my truck when the fuel filter became plugged. I had a mechanic pal unbolt the motor side of the filter & then screw in a fuel pressure gauge.... I only had 6 lbs of pressure.

A new easy to change filter & I was off to the races again!
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Old 10-06-2008, 09:19 PM
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OK, did some poking around and here is what I found. Pulled alternator off and took it to autozone, checked ok per their wiz bang computer.

At idle, my fuel pressure was back around 20#'s and doesn't rise much with reving of the engine.

Hooked up fuel press gauge and listened to the fuel pump, found something wierd. As the fuel pressure drops the pump sounds like its increasing in RPM speed, making a higher and higher pitch sound until I can't hear it anymore. Kinda like its NOT SUCKING FUEL THROUGH THE SOCK.

I know its not a vacuum in the tank, it does it regardless of whether or not the fuel cap is in place.

Thought maybe it was a bad ground, so I traced the cable and made sure it was securly bolted to the block.

Made sure all vacuum lines and fittings were good.

I guess tomorrow I'll pull the tank sending unit to check the sock and replace the fuel filter just to be sure. Ran out of sunlight...
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Old 10-06-2008, 09:29 PM
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Oldred had a post about a Kia fuel pump.

It turned out to be the length of rubber hose in the tank, that goes between the pump, and the pipe.

If you could be so lucky.

Last edited by carsavvycook; 10-06-2008 at 09:30 PM. Reason: forgot to spell check
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Old 10-07-2008, 02:39 PM
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I gotta give it to ya carsaavycook, you hung in there with oldred for a good long while. One other thing I forgot to mention, I have replaced the pump relay, and the car seems to run fine when its cold. It doesn't develop the problem initially until after its been running a while. It's raining today so I can't do to much. I waste money on the internet on days like today. I just ordered a new set of bilsteins for the front and now I'm looking for some new rims and tires. Wifey gonna be madddddddddddd!!!!!!!lol
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Old 10-07-2008, 02:46 PM
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Oldred had a different thread about the fuel pump, hose? I think.

I do know he has one very happy young neighbor girl, that can drive it to school.
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