Smokeysvette

This is on a 92 corvette LT1
First off the car runs great and very smooth with about 53K on the clock. But ever so often when I hit WOT (wide Open Throttle) at cruising speed she takes off at first just fine but all of a sudden she'll fall on her face at the higher RPM's but then picks up again. If I do it again for a second time and hit WOT, no problem at all as if nothing happened to begin with.
It seems it happens after driving at cruising speed and I hit it for the first time. After that it won't do it again.
Again, she runs great and runs very smooth and with no codes at all.
At first I thought fuel pump getting weak but if it was you'd think it would do it every time I hit WOT. But it only does it the one time after cruising at normal speeds and if I go to WOT after that she runs out fine.
Just wondering if anyone else experienced this before and what fixed it?
Thanks in advance for any help on this.

Cheechsmith

My 96 will do this if it's below a 1/4 tank of gas. From what I read its normal. I think it's crazy that a car would be designed this way but I just keep it above a 1/4 tank. If that's my biggest problem with this car I'll live with it.

touyech2883

I agree my 93 will do this with 1/4 or less around turns or hard accel. Fill her up and try it.

Smokeysvette

No, can't say that's it. I have a full tank almost all the time. I'm pretty **** about that and always try to keep a full tank of fuel at all times.
Please bring on any more ideas.
Like a mentioned if it did it all the time on WOT I could understand but just once and it's always the first time I hit it at WOT after just cruising.

Just for the sake of asking, what is the rev limit on these cars? Mine shifts right as it hits the yellow hash marks on the tac. I just wonder if the rev limiter could cause this?????
Thanks again in advance for all the help from all the tech gurus on here.

Cliff Harris

If your car has a problem when the gas tank is low on fuel then you most probably have a leak at the pulsator on top of the fuel pump or the connection between the fuel pump and the output pipe.

Ozzstar

When was the last time the fuel filter was replaced? Have you checked the fuel pressure with a gauge?

Paul Workman

FUEL - AIR - SPARK

1) KNOW how the system works (Got FSM?), 2) NO ASSUMPTIONS! Take NOTHING FOR GRANTED, 3) TEST & EVALUATE, & 4) DIVIDE and CONQUER in that order...

Whether anyone said it or not, the guys that responded so far are trying to follow these rules (above) for logical trouble shooting. But, right off the bat, I get the sense you'd rather dismiss the process of logical troubleshooting, replacing it with ye ol' "SHOTGUN" approach, aka "changing parts till the problem goes away".

I might agree that it is logical to ASSUME it isn't a pressure issue, but until you actually measure pressure when the problem exists, it is still an ASSUMPTION which will remain so until you VERIFY (by measuring it) that it is NOT a problem. Slap a pressure gauge on the Schrader valve and go for a drive...

Dynamic pressure testing on an LT5, for example...



This tests incorporates ALL of the preceding components, e.g., fuel strainers, plumbing, pump(s), filters, pressure regulator. What is left (far as fuel goes) is the injectors Are they pre-93? Then if so, they are suspect until verified... (Catch my drift?)

Personally, I'd like to see fuel delivery eliminated before going on to anything else - simply b/c the weight of experience skews my focus in that area first. Being able to eliminate that possibility goes frees us up to concentrate on the other remaining two possibilities - AIR & Spark.

As I said, please don't take offense. (Most of us don't know you/your level of expertise - experience.) It is just that so many requests for help fixing problems begin with incomplete information (test results) descending to a disjointed (albeit well intended) list of suggestions and wasted time and expense too, perhaps. If one works, it is in spite of systematic troubleshooting - not because of it!

Let's see what fuel pressure tests show us first, shall we?

P.

cv67

x2 on checking fuel pressure
LT1 is about done around 55-5800 somewhere in there the exact rev limit someone here will know

Had that exact same symptom on an 89 turned out the MAF was bad and would go dead lean. Not saying thats your problem though.

Know anyone that can do a live scan on your car?

Smokeysvette

Paul, no offense taken of course and yes I agree with you in the test,test test.. But,the only fuel pressure tester that I have is a short one and not long enough to run through the hood. But, I'll get one because I need one anyhow. So I'll get that and get the readings.
What should the pressure be at the point of WOT? At lets say 5000-5500? I'd test other things to but wouldn't know where to start because it doesn't shoot out any code and none stored either.

cuisinartvette, Yes the filter is pretty new, I changed it about a year ago but only about 2000 miles have been put on the car since.
Also no one out here in the country where I live. At least no one that I'd trust my car to. If it was a MAF wouldn't I get a code to work with? did your set a code when it did it? I'm not sure but I don't think the 92 LT1 has a MAF though. I could be wrong though.

Was just curious about the rev limiter. Because that's kinda what it feels like just when it hits the yellow hash marks. When it happens it's like you just turned the key off right when the tac hits the hash marks. Then let off a tad and she'll take of again and run out as fast as I want her to run without missing a lick. Again,when I hit it again a second, or third time at WOT runs very strong and never does it again.
Paul, again I'll try to run into town today or Monday to see if I can pick up a fuel pressure tester with a long hose so I can run it up to the windshield.
Thanks again for everyone's help

SpedRacr93

Don't worry about what the fuel pressure "should be" if it is an intermittent problem. Just watch it to see if it falls as you accelerate. You want to see what it is under a load and make sure it doesn't fall off.

Even if you have a new filter don't discount that the pump could be weak, the amperage within your wiring could be suspect or even just the sock could be having issues on the pickup. It's a 20 year old car, so just work your way down the list of possibilities. If it's intermittent like you describe, it's probably fuel.

FYI, Summit Racing has a gauge setup that has a 40" hose. It works perfect for taping it to the windshield and reading while you drive.

Paul Workman

[QUOTE=Smokeysvette;1588477561
***What should the pressure be at the point of WOT? At lets say 5000-5500? I'd test other things to but wouldn't know where to start because it doesn't shoot out any code and none stored either.***[/QUOTE]

The LT1/4s fuel pressure is held to a very narrow range across the rpm spectrum: 41#(1)

While I have the page open, here are the values for all C4s/motors (except L83):

Fuel Pressure (psi):

L98, 1985: 34-40
L98, 1986-1987: 37-42
L98, 1988-1991: 41-47

LT1/4 1995-96: 41

LT5, 1990-95: 49-55 (Note: Twin pumps. Air Tech pumps: Pressure when idling as low as 43-44 min, 45-46+ typical. At WOT, both pumps come on, and fuel pressure typically is 52-55 in my experience)

(1) I highly recommend this book: "Corvette Fuel Injection" by Charles O. Post, ISBN 0-8376-0861-9

TractionControlOff

I remember this happening to me in the late summer. The other problem is that I usually kept my tank pretty full but I don't drive it that often, so that led to its own problems. I ended up having to do the water filter and opti, and the acceleration "issues" are fixed - the car runs much smoother now too.

Bandit's C4

Its a common problem - especially due to the age of originally installed parts - eventually wear out. Found out the hard way after purchasing the '93 BAM with 55K on the clock a few years ago. The big red flag was the fuel filter - still had undercoating on the canister (OEM - gasp)... meaning there was a 20 year old fuel filter. Combined with today's gas didn't tell me good news. Also showed me the lack of maintenance by the previous owners. Wound up playing catch up with overdue maintenance in the process.

Over the next two years - had sporadic gremlins; each one having separate issues and repairs - ultimately replaced every gas/ignition/air component over time due to either part failure or preventative maintenance..

First was the fuel sending unit (failed), air, and fuel filter (overdue)- replaced and fixed the problem.
Three months later - was the IAC, ICM, MAP, and TPS (TPS failed, MAP was borderline) - each component replaced due to age.
Following spring was plugs, wires, injectors (starting to ohm out), and Fuel Pressure Regulator replaced (all OEM)- another problem with hesitation solved with preventative maintenance
Most recently was the Opti and waterpump - having a random miss and falling on its face when cold... resolved with Petri Opti plus GM waterpump).

Please note - the car did not display or register an Opti-related trouble code at this time - however there was tremendous corrosion inside the boot surfaces where the plug wires were connected with the opti. Definitely signs of random misfire.

Today the car's response has been rejuvenated and restored to a reliable status once more - necessary to extend the car's lifespan.

mazdaverx7

A lot of good information in this thread!

canuck buick

did you ever find the answer to this problem?

Smokeysvette

Sorry guy's I have been out of town and been very busy with family business. But to your answer it still has the problem. It is VERYrandom and will do it just every once in a while. I changed the fuel filter and next will be the fuel pump and sock. I did check the pressure check and it never did drop but the of course when I had the gauge set up it never would do it. It could be the car doesn't get driven much at 55K and only gets driven about 2K a year usually. I did replace the water pump as I saw a wet spot on the bottom of the pump. I always keep an eye out for a leaking pump and I just noticed it looking up at it with a mirror. It probably never leaked enough even to get to the opti as I caught it the day I drove it and it was just a very tiny mark like it was just was going to start to leak. Like I mentioned I'm always looking at it with a mirror when I drove it since it was the stock water pump. Other than the falling on it's face just ever so often it runs great with no missing or cutting out at higher RPM and runs very smooth especially at hiway speeds. I might change out the opti but hate to do the "if it ain't broke don't fix it" thing.
Thanks goes out for everybody trying to help.

antfarmer2

mine was doing that and got worse changed the o2 sensors and found new power never sent a code but they were original

antfarmer2

I also changed my knock sensors while I was under there so I could drain and flush all coolant one side was pluged up pretty good could not see putting back twenty some year old parts

canuck buick

My 89 is doing the same thing I am waiting for a fuel pressure tester to do the tape it to the windshield thing to see if the pressure has anything to do with it. If it was the o2 sensor couldn't you just unplug it and go for a test drive to see if this was the culprit?

antfarmer2

Don't know give it a try