Corvette C4 Forum 1984 through 1996

1991 C4 Fuel Pressure Problem

Old 05-10-2015, 10:55 AM
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Default 1991 C4 Fuel Pressure Problem

Hello All,

I'm trying to assist a neighbor with his C4 TPI Automatic Corvette, which will not start. The car sits idle for weeks to months at a time, but generally has had no starting problems in the past. He did relay that in the past, he's had a hot (normal temps) engine cutoff while driving.

He's been trying to start the car for the last several days, and I offered to help (11 yrs as a mechanic), but not too familiar with Corvettes (some older Corvette experience C2). At any rate, I've been trying to isolate the problem. I originally though the problem might be related to old gas (10% Ethanol - you guys know that drill), so I put in 5 gallons of fresh fuel - No joy.

He had been trying to jumpstart (battery) to another vehicle (car has a new battery but was discharged), so I used my battery charger to bring the battery up to full charge (successful). I recall that some of the newer electronics don't deal well with low battery voltage. Still no joy.

I started checking to see if the car had fuel pressure but turning the key to the run position, and briefly, there's a shot of fuel delivered to the fuel rails, but it appeared that the fuel pump stopped pressurizing after about 3-4 seconds. I tested the FP1 fuse (OK - in fact all of the main panel fuses tested OK). And I noted that the power to the FP1 fuse turned off after about 3-4 seconds, accompanied by what appeared to be a relay (perhaps normal) noise at what seems to be in the area of the dashboard. As I have no FSM, I looked at his owners manual, and speculated that if there was an FP1 Fuse, that there might be an FP2 fuse (and there is, although harder to get to under the glove compartment area, as per the owner's manual). That fuse test OK (not blown) but it never seems to be powered, regardless of any delay exercise in turning off the ignition switch and turning it on after a few seconds. Note that the FP1 Fuse DOES power on using that technique, but then turns off (again, I suspect that's normal).

There are no abnormal noises from the fuel pump (just the normal, if brief whirring sound during initial ignition run switch).

A note here, some months ago, the car was parked and rear-ended (not severely, but enough to require replacement of the rear bumper cover). I initially thought that perhaps the inertial safety switch (location not known) might have tripped as in an accident, all of the FI systems that I've seen in modern cars have a safety shutoff which must be reset. But the neighbor indicated that he'd driven the car successfully after that incident, so that seems unlikely to be the problem.

My feeling is that the clues are there, but as I have no FSM, or other diagnostic decision tree, I though perhaps one of you might have a fairly quick answer for the problem. Note that when I drizzle gas lightly into the TPI inlet, the car will start (no missing, but of course not normal - but smooth - no missing or odd noises). So clearly it's a fuel supply issue (I cannot say that the injectors are OK, but I would expect to hear missing due to poor distribution in the intake when actually running, which I don't see).

Any thoughts/suggestions are welcomed. It does seem as though the problem is due to the FP2 circuit/fuse not powereing up.

Any thoughts/suggestions are appreciated.

Old 05-25-2015, 12:13 PM
73shark's Avatar
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Join Date: Apr 2006
Location: KC, MO area
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Welcome to the forum. The first thing I would do is put a fuel pressure gauge on the rail. There should be about 50 psi after you turn the key on before you start.
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