Help! Rough Start When Hot

[John Robinson]

Friday I ran the car 600 miles and when I stopped to eat the car would only fire for a couple of seconds and then die. After I tried several time to keep it running I went into the restaurant and got a pitcher of ice water and poored it on the pressure regulater and the fuel rails. This allowed the engine to run long enough to clear out and run. On Saturday I started it cold and it ran but with a flat spot until about 2500 RPM almost like it was starving for fuel. I drove it a couple of miles and shut it off and when I restarted it it backfired and was down on power and I had to run it in low and second for a mile or so and it cleared out. Before it cleard out it backfired ran rough but there was no black smoke from the exhaust which I think means it is lean. Suddenly it cleared up and the performance was the best it has ever been. When I got it home I checked the resistance readings on the injectors and they all were dead on 13 Ohm's.

What I have not been able to find information on is how to check the fuel pump preassure and the preassure from the pressure regulator along with getting the lines apart. I am thinking that the vapor lock at restart is from low pump preassure not being able to purge the fuel rail.

 

[G Winter]

Black smoke is usually rich indication.My first guess would be your fuel pressure regulator. there is a shrader valve on the fuel rail. A pressure gauge is attached at the point. You may be able to obtain the use of a gauge at an Autozone .

Glenn

 

[LT4man]

John, you attach the fuel pressure gauge like you would screw an air pump onto a bicycle tire.

Look for the fitting at the rear of the engine. Start the engine & correct fuel pump pressure would be between 41-47psi. at idle.

When you have the engine turned off, remove the vacuum hose which is attached to the fuel pressure regulator. The regulator is the 2in. long silver dashpost attached to the fuel rail. There should be NO gas in the vacuum hose. If there is, you need to replace the fuel pressure regulator. But, only after bleeding the pressure from the fuel rail. Wrap a rag around the fuel connector & push in on the needle valve to relieve the pressure. Another good idea is to remove your gas cap. But, remember to put it back on when you are done!

You do not need to take apart any of the fuel lines.

SAVE THE

 

[John Robinson]

I will try to read the preassure I have a vacuum preassure gauge but do not know if it will read high enough for the fuel preassure.


Found the connector but my preassure gauge only goes to 10 lbs. There is a round vacuum pot ( it looks like a smaller version of the vacuum advance that was on distributors) I ran the car and pulled the vacuum hose off there was no fuel in it or at the connection to the manifold just below the check valve connection. Looks like I will try to have to find someone with a gauge I can borrow or maybe if its the pump it will quit and then I will know for sure what is wrong.

I should also say that when I bought gas in KY it was at a non name brand gas station and perhaps I just got some gas that was not 93 octane. I can only hope that is the answear I will fill up with shell or some other name brand and see what happens.

 

[LT4man]

John, you will have to find a fuel pressure gauge. You are right in assuming a vacuum gauge will not work for that application.

You did find the fuel pressure regulator. If you found no fuel in the vacuum hose you are good to go with that part.

As you said, you might have received a tainted tank of fuel. Does not happen that often anymore but you might have been the unlucky recipient of one.

Putting a container of Techron fuel additive would certainly help in the meantime.

SAVE THE

 

[John Robinson]

John, you will have to find a fuel pressure gauge. You are right in assuming a vacuum gauge will not work for that application.

You did find the fuel pressure regulator. If you found no fuel in the vacuum hose you are good to go with that part.

As you said, you might have received a tainted tank of fuel. Does not happen that often anymore but you might have been the unlucky recipient of one.

Putting a container of Techron fuel additive would certainly help in the meantime.

SAVE THE

I had a pressure check of the fuel pumo done. The pressure without engine running was 26lbs and went to 41lbs with engine running. When I shut the engine off the pressure dropped to zero. I am guessing the check valve inside the pump is leaking so I will have to replace the pump.:ugh

PS my computer is in for repairs so I will not be able to respond to messages for a few days

 

[John Robinson]

Problem Solved

Just an update on my thread. I replaced the pump and the car runs like a scalded cat. (Cat lovers forgive me for using that analogy)

 

[LT4man]

John,

Congratulations on your repair!

Do you consider the job an easy one? On a scale of 1 to 5 with 5 being the most difficult, what would you rate a fuel pump replacement?

How many miles on your Vette?

SAVE THE

 

[John Robinson]

John,

Congratulations on your repair!

Do you consider the job an easy one? On a scale of 1 to 5 with 5 being the most difficult, what would you rate a fuel pump replacement? 2.5

How many miles on your Vette? 97K

SAVE THE

This probable is the easiest fix you can do on a C4