Fastmax32168

So this morning while on a nice sunday drive in my 94 convertible I experienced an issue that caused me to have to Dolly my car back home. Everything was working fine when I pulled away from a stop sign and suddenly the car wouldn't take more than about 1/4 throttle without shutting down. I managed to drive it about 3 miles at light throttle settings and it just kept getting worse, taking less and less throttle before dying. Finally it quit and I coasted into a mini mart. Sounded like a bad fuel pump, It would start and barely run then die. Barely a dribble at the fuel rail, but I could hear the pump running If I went to the back and listened while my wife turned on the key, So I used my lifeline, phoned a friend, and he came and took me home. Came back with my Truck and Dolly, pushed the vette on, drug it home and of course it started right up and runs perfect. I put a fuel gauge on it and drove it around the block a few time, I am unable to duplicate the problem. Has 42 PSI when running. It has a Walbro 255 in it that has about 5000 miles on it. Several times before this happened this morning I ran it through the gears and it buried the tach pulling hard with no problem. I hate to start replacing Wild *** guess parts, but I am afraid to use it now. Any suggestions? Maybe I am on the wrong track thinking fuel pump? No Error codes
Thanks
Roy

aklim

Not much choice since it won't repeat itself. Get to Autozone and buy a fuel pressure gauge you can have handy for future needs. Tape it to the glass and do a WOT run to see if the pump is fueling it properly at WOT. Turn the key on without cranking. Does the pressure go up to 43 psi? Does it hold? Also, while at Autozone, rent the noid light and keep it handy. You can have it for 90 days till they charge you. When the problem occurs, check fuel pressure and use the noid light to confirm injector pulse.

Fastmax32168

I have a fuel pressure gauge on it now. You get about 47 with the key turned on, holds pressure just fine. About 42 driving normal around the neighborhood, nowhere to wind it up nearby. One thing that doesnt look right to me is if I snap the throttle open while sitting at Idle the pressure drops to around 35 before it recovers, but I cant say I ever payed that much attention to it, this car has been a sweetheart, no letdowns in a dozen years of ownership.

Fastmax32168

Does anyone think a TPS issue could cause this behavior? I ask because one thing I noticed really odd, is that when I was stuck in the parking lot in a no start condition, my snow performance alcohol injection system was activating when I turned on the key. It is TPS activated and normally doesnt come on until it sees about 80% TPS. I had to unplug the pump to stop it from running almost like it was seeing high throttle even though the throttle was in the idle position. I thought maybe the system had malfunctioned and was flooding out the car, but unplugging it made no difference in the no start condition and doesn't explain the lack of fuel pressure in the rail at the time. It also appears to be functioning normally again. Just another chess piece to add to the confusion.

aklim

If you have any doubts, scan the TPS and see what the ECM thinks.

Roger Willingham

Might invest in a new fuel filter while poking around...

h1duck

I agree on the fuel filter as it may have trash in it and intermittent blockage.

pacoW

When you did the pump did you replace the filter? You can use a voltmeter to check the TPS output by back probing the connector. Any check engine light? If so does it flash when you are getting the poor running condition?

h1duck

I did have a similar problem happen on a vette I just bought. I was test driving after I got it running and it would die down unless you gave light peddle and than died and would not start. My problem was a piece of foam on the MAF so check to see air way is clear

Fastmax32168

Thanks all. Some good feedback there. I will get on it as soon as I have some time and report back the solution.
Roy

jazfe

I would suspect something in the fuel tank is floating around and clogged your pickup screen.

aklim

Get an install kit so you have the gasket and bolts and a piece of hose of the right material to replace the pulsator if you want to do it.

Fastmax32168

I had some time to do some driveway diagnosing today and I am suspecting the FPR may be bad and here is why. It is not something I have ever replaced for one, it is original to the car. Also it is my understanding when I rev the car the fuel pressure should go up, whereas mine goes down. It idles at 42 PSI, when I hit the throttle the pressure falls to about 35 before recovering. However if I disconnect the FPR, pressure goes to 48 and stays there when I hit the throttle. I am thinking if the filter was clogged, or the pump was bad, It wouldnt be holding 48 PSI with the FPR disconnected. Thoughts?
Thanks
Roy

aklim

Sounds somewhat normal. Drop before you get a rise.

aklim

What does this do on a real WOT run?

RalfKramden

I've been watching a series on YouTube and something I saw makes me ask you this. Try pulling the pcv valve and then put your finger there. If you're feeling a vacuum, you have a bad gasket between the manifold and block but it's internal. That may be why the pressure is dropping since the FPR is vacuum controlled.

Fastmax32168

Aklim, I havent had an opportunity since the problem to try a WOT run and check fuel pressure. Honestly I dont want to drive it even around the block before trying something, because I dont feel like towing it home again. The last WOT run I did was only minutes before the problem occurred and it pulled like a beast to 6500 RPM with no issues. I am going to put a new FPR and fuel filter on it since they are not expensive and I have enough summit bucks to cover them and almost consider them both maintenance at this point. Then I will give it a run again and see how it acts.
Ralf, Thats an issue I have had on other motors with a whole different set of symptoms, I dont see that being related to what happened to me sunday, but thanks for the suggestion.
Roy

ctmccloskey

Hello Fastmax32168,

I have an older model C4 that does the exact same thing with the fuel pressure, 42 and then it dips and then back to 42.

I hate to admit it but one time I had a friend who bought an old Pickup truck that was running poorly so we tried running some fuel system cleaner through it and that killed the truck, it would not run at all after the fuel cleaner. After removing the fuel filter I saw why, all the junk in the fuel system broke loose and plugged the filter. A new Filter and the truck ran like it was new.

On my C4 I have replaced the Fuel Pump Relay as mine was old and it was not consistently working any more. It seems that everybody blamed fuel issues on the poor relay and the wiring had been cut and crimped connectors attached. I replaced the relay and wire connectors with good solid connections and the relay lives on to this day. On my car the FP relay is the same as several other relays on the car so I have a spare in my rear compartment for that once in a blue moon times. The spare is vacuum sealed in a bag I made for it so I don't have to worry about it's condition.

Loose wires, dirty connections, low voltage and heat will all help a relay die faster. With the amount of heat near the firewall the FP relay gets exposed to a lot of abuse. Try the relay but check your voltage at the fuel pressure relay output and be sure it is getting the proper voltage to the fuel pump. Mine is very close to the battery voltage which is what you want.

I am sorry I can't be that much help as I am not intimately familiar with the LT1 engine you have. Out of curiosity, How do you like the Snow Performance Water/Methanol Injection system? What made you choose to use the Snow system on your car? The reason I ask is I too have a Snow Performance injection system on my 1968 C3 Convertible with it's 427 running high compression (12.25-1) I use a solenoid to hold back any pressure when the engine is not actively running. My system is from the early 2000's and only used a 150 p.s.i. pump in my rear compartment behind the passenger. I need it for the compression (only on the worst hot days) and mine uses vacuum to activate as I still have a carburetor for now. I am in the process of switching my lines over to -4 AN SS braided lines from the pump to the carburetor so I can feel better about 150 psi of alcohol and water shooting everywhere not happening!

Good Luck!

Fastmax32168

CTM, I know it isnt a relay issue, I could hear the pump running and I still had no fuel pressure. I put the snow system on because when I put the motor together things were a little tighter than I anticipated and I was having to use either octane booster or mix in a little race gas to stave off detonation and spark retard. To get it to run properly I had to pull so much timing it made a big difference in how the car ran, turning it from beast to blah. With the Snow system it runs great on pump premium. I dont know how it will hold up long term, but at this point it performs as intended. It was not easy getting everything to fit in the C4, there aint much room left here GM didnt use!
Roy

ctmccloskey

Hello again Fastmax32168,

Intermittent relay issues are not uncommon when they start to fail however this might not be your problem. On my 1988 I let the car sit for a couple years and it had corrosion forming inside the fuel supply line that runs up the right frame rails. When I started the car it would not get enough gas through the fuel line to allow it to even rev very much above idle. It was a tough one to find until I measured the fuel coming out of the fuel pump directly and compared it to what was coming out of my fuel filter inlet. I had to replace my entire fuel supply line to fix the problem.

The Snow injection system is a nice kit. My car really likes that 116 octane fuel it consumes when the injection system is operating. That point about your injection system running when the car was off is really weird. That should never happen and doesn't on my car. I am always concerned with flooding the engine with windshield washer fluid as my Compression would break or bend something. With my car needing something above 105 octane I use 87 octane to fill the tank and then I use the Boost Juice and have never had any problems. The Snow system should not affect your engine that much. I used one on my 1994 Cadillac STS which got 12 mpg and required premium. With the Snow system it was using regular and happy with it. Saved me a lot of money over the years of ownership.

Just for your knowledge I have found a company who makes a product that would probably help you make even more horsepower. Check out the "J&S Safeguard", this little baby will guarantee that you make more power on a performance engine. I have been talking with the owner/developer for about 20 plus years now. Their universal system is going to be installed on my 1968 C3 in the spring. I have MSD everything on my ignition system and it looks like it will work with all the other goodies on my engine. I can't wait to test it on my car.

One last thing, how do you determine if what you did makes more power or costs you power? I use a GTECH Pro and it will show even small improvements, after replacing the exhaust I saw a 14 hp increase in my engine. I used it to help set up my carburetor and see if it helped at all. This is a very handy tool to own as you can use it in any vehicle as long as you know the actual vehicle's weight. I have been using one since for over 20 years. To get the weight I went to our county's "landfill" and they weighed the car for me. So now when I test anything it is easy to find out if I helped the car or not.

If the pump is running but making no pressure I would pull it out and check the pulsator or hose that is between the pump and the fuel lines. Some people have used hose not designed for submersion in gasoline and that does not last very long. Also use the fuel injection band style hose clamps. I measured the flow at the pump and then again near the fuel filter to be sure the line is clear. Also make sure that somebody did not accidentally crush your fuel line with a lift or jack, it happens too often. I even blew air through the lines and quickly found my blockage inside the fuel supply line as it was seriously plugged and had to be replaced.

One last thing, what is the voltage going to the pump from the fuel pump relay? I would measure at the relay and then again at the pump itself. Also check your fuel tank to be sure it is grounded properly as that can lead to problems with the pump and the sending unit. One of the three wires going to the fuel pump is a ground, check to be sure it is a good ground.

I had a VW that had a electric fuel pump and one day the car would start for about three-to five minutes before shutting down. I spent a week trying to figure out what was happening. It turned out the Fuel pump could not draw enough current through the wires. The power wire (12Vdc) to the pump had a scrape on it that allowed water and other contaminants into the wire. The wire corroded and as the power was flowing through the wire it would make a higher resistance and the pump was then unable to run after that. Once it cooled down for several hours it would do the same thing, I replaced the wire and the car ran fine. Just another wacky scenario to consider....

I hope that you find the problem with your Corvette without too much more trouble!

Chris