[lexmarks567]

Originally Posted by Stoner

Has anyone run a fuel pressure test?
You could have anything from a weak check valve to a weak fuel pump that is aggravated when warmed up.

Have you tried loosening the gas cap to see if it's venting properly? Too much of a vacuum can aggravate the before mentioned problems.

the shop did a fuel pressure test. they said it was within specs but pulsates (10LB-12LB) cylinder number 2 is misfiring and cylinder 4 is misfiring with cold so they think the coil could be failing. the gas tank is rusty and so are the lines but just cause its on the outside does not mean its on the inside.

[Drabdr]

Geeze.... where were all you guys back when I would spend all night trying to get my 1979 Chevrolet Silverado going?

Very nice and helpful posts everyone.

Aren't fuel filters directional? Just saying if they are, might want to watch the flow marks.

I have had similar instances. Honestly, it took two or three fillups of gas to get the old out. Then, it would seem to run better.

[Drabdr]

Originally Posted by lexmarks567

the shop did a fuel pressure test. they said it was within specs but pulsates (10LB-12LB) cylinder number 2 is misfiring and cylinder 4 is misfiring with cold so they think the coil could be failing. the gas tank is rusty and so are the lines but just cause its on the outside does not mean its on the inside.

If you are in the mood, it might not be a bad idea to get some of that rust off and repaint. Obviously it has nothing to do with the current issue, but may get you some more mileage out of that tank.

[aka Brett]

Originally Posted by Drabdr

Geeze.... where were all you guys back when I would spend all night trying to get my 1979 Chevrolet Silverado going?

Very nice and helpful posts everyone.

Aren't fuel filters directional? Just saying if they are, might want to watch the flow marks.

I have had similar instances. Honestly, it took two or three fillups of gas to get the old out. Then, it would seem to run better.

We were hiding and watching,,,placing bets on how long it would take you to crease the hood when you slammed it from one side

[Knotbored]

This whole thread has sure been interesting and illustrates a couple of things.
1. When a mechanic asks an exobitant amount to find a problem he anticipates more then the drivers description ("it makes a funny noise".)
2. The complicated features of a modern engine to satisfy EPA and other emisions situations are bandages making a relatively simple mechanical devise difficult for an amature to analyse.
3. When us old codgers long for "the good ole days" about cars, clothes, computers and building products go ahead and roll your eyes, but give some credit to the fact that it used to be far easier to repair and upgrade all of those.

[lexmarks567]

i've had it in the shop sense before this for other repairs and none said anything about the rusty tank. even pep boys didn't say anything when i took in to have the horn and turn signal fixed. the only other problem they could see was i needed 2 new front tires.when i took it in to have the exhaust pipes replaced he said the ball joint on the front passenger side needed fixing. he didn't say anything about the rusty tank or the fuel lines.

[Drabdr]

Hello, Lex!

How long has it been running this way? Do you still have the problem?

Have they read codes off the car, and everything is clear?

[lexmarks567]

they never told me the codes and they reset them. I took it to another shop and hes almost certian that its the ignition modular. He called the other shop sense they cleared the codes and they didn't save the codes for future use. So he has to make the car stall and keep doing it untill he can get a SES light sense the other shop reset it and hopefully get it to produce a code.its still at the shop right now.

[lexmarks567]

ok got it back from the shop. did not get it fixed yet as i do not have the money.its a bad E.C.M. the guy said do not drive it you could damage the engine.
this is the quote from the invoice

Tech pulled codes they popped up and disappeared very fast. Ran flow chart found bad E.C.M. and idle air control fault. tech needs to replace E.C.M. first and see if idle air control comes back. Check and advise electronic control module.

[JohnWill]

Sounds like they're guessing it's the ECM.

[Mumbodog]

Vapor lock is out, since fuel injected cars now have an open loop fuel delivery system, this only affected old low pressure closed loop fuel systems.

I would suspect a crank sensor also, they can be weak and cause the symptom without setting a code.


The MAT sensor may not have been bad, but it could be the wiring that connects it to the fuel computer, whenever you read data on that vintage of GM car, high resisitance wiring can cause -4 readings, the sensor is fine, the wiring is bad, no way for a scanner to diagnose this, you must check connections at the sensor for corrosion, and use a DVOM to check the wiring for high resisitance or open circuit.

Clogged fuel filter is at the top of the list. Cheap and easy to replace.

Fuel filter loacation:
Under vehicle, driver side, below seating area near fuel tank, mounted on frame.

.

[lexmarks567]

the computer is saying that the mat sensor is still reading -4 but the sensor was just replaced.

[Mumbodog]

the computer is saying that the mat sensor is still reading -4 but the sensor was just replaced.

Like I said the wiring from the sensor to the fuel computer is damaged, most likely an open circuit (broken wire or damaged terminal end)

Most mechanics these days are parts replacers, the can't "fix" anything.

Find a competent mechanic.

.

[lexmarks567]

well after talking to my mom sense she took the car in the tech said the wiring was bad around the computer.

[JohnWill]

Yes, but did fixing the wiring actually solve the problem, or is this yet another guess by yet another mechanic?