Hello I recently bought myself an 88 C4 with 79,000 miles I was driving it for a couple days then one afternoon when I was leaving the BMV it lost fuel pressure and sputtered out, since then we have replaced the pump filter and regulator but nothing has changed does anyone know any other problem areas or solutions?

 

You changed the pump but maybe you lost fuel pressure for another reason? The next logical question would be to test if the fuel pump primes when you turn the key to acc. If you do not hear it prime, then the fuel pump relay is not energizing and points to an electrical problem.

 

What do you mean by pump filter??

Did you change the fuel pump in the tank? If not start with that, then your fuel filter.......

 

^^^^^ No! What he needs to "start with" is diagnosing the problem and replace THAT part. To the OP - If you don't have the Factory Service Manual, then you need to purchase one. It has charts and such for finding problems. Trust me, if you are going to own one of these cars, then you need to be able to do your own repairs or go bankrupt.

 

Uh, no. The fuel pump only primes when the key is turned to RUN. Never in "acc."

I think there is a missing comma. "we have replaced the pump, [fuel] filter and regulator."

To the OP: Your description of the original symptoms indicate loss of power to the fuel pump. In a 1988 you can power the pump by introducing 12V into cavity G of the diagnostic connector under the dash. The pump should run and build pressure. If it does not run, check for 12V at the connector at the tank connector. One possibility that can be overlooked during a pump renewal is the pass-through connector at the top of the tank where the internal harness connects. Occasionally the gray wire (pump power) terminals become cooked and resistive.

Arbee is right. Diagnosis before guessing saves time, money, and frustration. Cheers.

F-E-D-C-B-A
G-H-J-K-L-M

 

Your post says you lost pressure. Unless you actually had a gauge attached how would you know. Use a gauge check for proper pressure at prime and while cranking to see if you are getting fuel. As arbee said you need to diagnose problem before throwing parts at it.

 

so far what I have diagnosed, was originally when I started it that morning, the fuel pump began stuttering as it was primed, then later failed completely about 40 seconds later, we originally believed that that was the only problem and got a new pump, after installing the new pump we checked, the pump was now building pressure yet the pressure was not traveling to the rails. we decided to change the fuel filter and fuel pressure regulator as when we checked the regulator while diagnosing as we noticed the diaphragm was leaking, we replaced both, we attached a fuel pressure gauge to the Schrader valve, primed it, (the fuel pump did turn on) cranked it a few times, then it fired up, it built fuel pressure then after we turned it off and tried to crank again after that it failed and now just cranks but doesn't turn over. so the pump is priming but we are still not getting pressure to the rails. after I get off work today I will also be going over all my previous work to see if I may have made a mistake in installation.

 

Hi, just wanted to confirm a few things...

1 - So, you've changed the fuel pump, fuel filter, and the fuel pressure regulator... correct?
2 - What fuel pressure did your gauge read at the Schrader valve? If I'm not mistaken (I have an 84, so mine is different), you should be getting like 42 PSI at the Shrader valve. Can you verify that you are getting that?
3 - Are you getting a check engine light? ... and if yes, did you check the codes?

 

> Is there gas in the tank?
> Could the jumper hose between the pump and metal line have blown off or split? You can check by listening at the fuel filler with the cap removed, have someone cycle the key. You shouldn't hear anything other than the hum of the pump. If you hear liquid splashing or sloshing, something is wrong.
> I've also seen new pumps have a leak at the pressure relief valve on the top of the pump. This squirts fuel everywhere, and results in a loss of performance. You should be able to see/hear this too.

 

no check engine lights

this is my first project Car I have had I’ve mainly just been doing general maintenance on my last two so I’m not crazy knowledgeable about a lot of stuff.

 

I am guessing that no gas is running out on the ground. If pump is running you should have pressure unless there is a leak or blockage. This may call for a little old school end to end flow checking to find where it stops. Also I have seen brand new fuel pumps run but not pump.

 

Ok, let me just summarize everything here:

1988 C4 Corvette - L98 Engine (Tuned Port Injection... e.g., MPFI for those of us who are less automotively affluent)

- Fuel Pump Replaced
- Fuel Filter Replaced
- Fuel Pressure Regulator Replaced
- Getting 43 PSI at the Schrader Valve


Ok, so from my standpoint... you've confirmed the pump is good, the filter and regulator are now replaced, and you confirm 43 PSI on the Schrader valve... which is actually ON the fuel rails. So there's a discrepancy here, because I'm not really sure you would be able to tell that there's no fuel going to the rails because if you see 43 PSI on the Schrader valve... the rails HAVE 43 PSI going to the injectors.

I think you now have a secondary problem (this DOES happen). Remember that fuel, air, and spark (and timing + compression) are required for an engine to move. You have air, and you are trying to determine whether or not you have fuel or spark.

First thing I would do, is get a can of "starting fluid." I would crack the throttle body on the TPI (remove the air cleaner assembly) and I would spray some starting fluid into it... a healthy amount. I would then get someone to crank the car while you begin spraying starting fluid into the intake. If the car runs (albeit bad), then you DO in fact have a fuel issue. But if the car doesn't run at all, like... doesn't even TRY to start... just cranks without any sign of combustion, then you have a SPARK problem.

Your TPI engine is basically a Multi-Port Fuel Injection system. Aside from some fancy runners, it's basically the exact same fuel system that all performance-minded GM cars had in the mid-80s. There are TWO banks of injectors, meaning they fire in batch. The left side fires, then the right side fires... and as the valves open, it allows the puddled fuel to kind of get sucked in. Each side has a separate fuse (you'll have to check the manual), but for the injectors to not fire (while confirming that the fuel pump IS good), you'd need one of three things: either both injector fuses to be bad, or the computer's ECM to be bad or not getting power.

My suspicion is that you actually have an ignition problem. You can test this by removing a spark plug, and grounding it out somewhere while it's plugged into a spark plug wire... and then have someone crank it and see if you see any spark (don't hold it... just have it clamped to something grounded on the car). If you are not seeing a spark, then you're not getting spark.

A very common problem with mid-80s GM ignitions stems from what's called the "Ignition Control Module." These can and do just fail all of a sudden... and I have literally had one fail within days after replacing a fuel pump in a Fiero. It's unrelated of course, but it happens. This ICM is not to be confused with the Electronic Spark Control Module (which is totally different). The ICM sits INSIDE the distributor. You remove the distributor cap, and under the rotor you'll see a black module with two plugs (externally to the distributor) plugged into it. It looks like this: 1988 Chevrolet Corvette Ignition Module, 8 Cyl 5.7L 19179581 by AC Delco®

If it's bad, you would need to replace it with a new one, but I recommend going with an actual GM one because the aftermarket ones fail easily. You would use THERMAL PASTE on it, between the ICM's metal bottom and the distributor's body. That helps transfer the heat. It's the same stuff computer nerds use between a heatsink and a processor when they assemble computers from parts they buy online.

Another possible failure, though less common, is the ignition coil... but my bet is on the Ignition control module...

Go ahead and do the starting fluid test first... and let me know what you see... if you get no hint of starting... like it just cranks and that's it... then you're not getting spark and it's not a fuel problem.

 

I should clarify as I did not fully explain my findings in the earlier post which is my bad, after replacing the pump, regulator, and filter, we put the fuel pressure gauge into the schrader valve, and cranked the engine, it fired up after a few cranks, and was idling clean and the gauge read 43 PSI, afterward, we tried to crank again and the engine stuttered out and fuel pressure dropped down and wouldn't turn over again, today after I get off work I'm running through the fuel lines and filter checking for blockages as we did test with starter fluid last night and it turned over.

 

Ok, so, next... I would check the fuse for the fuel pump, and you can run a positive wire to the fuel pump's ALDL connector, which should manually set the fuel pump to run (regardless of the relay or any of that other stuff).

Here is the ALDL connector:




This is actually for a Pontiac Fiero, but it's the exact same thing in your Corvette... just verify that it's not upside down or something... you'll be able to tell since it should have the same leads. The single lead up there in the right (or by itself in whatever orientation your ALDL connector is), is directly for the fuel pump. You can run a positive battery cable to it (NOT THE GROUND) and it will automatically run the fuel pump regardless of anything else going on with your car. So you should get full fuel pressure, and it will tell you if your fuel pump is OK. If it runs fine with this... then your relay or something else is bad.

 

alright I've gotten to the point where I have tried everything y'all have said in the forum as well as replace almost everything just hoping for success, some issues I have seen so far have been a mad pump, a completely clogged fuel filter and a pressure regulator that almost disintegrated on contact, I have replaced, the fuel filter, relay, pressure regulator, fuel pump, and the sock that attaches to it, I've checked all the wiring and double checked my work, I'm just not sure what it could be.

 

You'll need to work from back to front. Can you confirm that you have a good pump in the tank? Did you try jumpering the fuel pump lead on the ALDL? You didn't state if you'd tried that, and whether or not it did anything..

It's kind of hard to follow... we don't really know what you're checking unless you're very specific when you tell us. When you had the fuel pump out, did you test it to see if it works by directly connecting it to 12 volts and seeing if it jumps off the table? (Be careful with this, because if it still has fuel in it, it could cause a small fire).

Basically... you'll need to work from back to front, to try to determine where your problem is. There's also a relay for the fuel pump, a fuse, etc... but you said you checked all those. So at this point... hook up leads directly to the fuel pump and see if it works. You can do this directly from the pigtail under the fuel filler. If you don't hear it run, then the fuel pump is either bad, or the pump isn't hooked up right inside the tank. If the fuel pump is good then move forward... but you haven't told us if the fuel pump is good, for example... or what the result of the ALDL lead test was...

 

alright so after taking it to a local shop to check it out, as everything in the fuel system seemed to be operating fine, the checked it out and noticed that timing was way off and the tensioner was ready to go apparently the last owner did the belt which was why it looked new and never actually changed the tensioner, stupid thing I didn't look at lol.