Chevy will not start (sometimes)

chevrolet

#1

Help. 1988 chevy pick up, 5.7 (350) V-8. If you let it cool down it starts and then stops after anywhere from 2 seconds to 10 minutes. Put gas in the throttle body and it runs a few seconds. So far replaced fuel pump, fuel filter, cap, rotor, fuel pump relay.

What would be the logical choices next? Please help before I clear the parts store of inventory and my wallet of $$$$.


#2

Do you hear the 2 second hum from the fuel tank when you turn the key to ON (don’t crank). That noise means the pump is working and you have narrowed the problem.


#3

Attach a fuel pressure gauge to the system and see if the fuel pressure drops off when the engine dies. If the fuel pressure holds, listen to the injectors with a mechanic’s stethescope to see if you hear them clicking when you try to start.

Get back to us with the results and we can go from there.


#4

Will try pressure check. But… did replace pump, filter, relay. Even if pressure is good it will go to 0 when it shuts down (like if there is an electrical problem). I will check the pressure. Also, it’s throttle body so it make it easy to see and test the two injectors that are in plain sight. Have a noid light that I can check pulses with. Thanks. Keep the ideas coming.


#5

There are two parts to the pump pressure test; dead head and regulated. Even if the pump runs, it’s no guarantee that the correct pressure is being made unless you measure it. Some of these TBI units had sintered pre-filters in the body as an extra measure of protection. If you have pressure and noid light indicates injector pulse, it may be stopped up there. If it runs for a minute or so, you should be able to view the injector spray pattern. Look for poor atomization or dribbling.

Those ignition modules were known for temp issues as they aged. The thermal grease dries up and they fry.


#6

You know TwinTurbo, that was my thought today… ingition module. I’ll be working on it again tomorrow. Here are some more items just to make this more confusing. My buddy cranked while I checked spark. No spark !! OK, ready for this…Sprayed starting fluid in the throttle body and it started and ran for about 1 minute. During this time I had plug wire #1 hooked up to a test spark plug and it had spark but a real weak and unstable one. Then a friend of mine stops by with his tow truck and says he knows just what’s wrong as he had this happen before. He said just disconnect the coolant sensor and it will start. IT DID NOT. He is going to stop by tomorrow with his scan tool and see if anything shows. This is OBD 1 so I’m not to optomistic. I’m leading toward the ignition module. I had that go on a 80 Citation and a 81 Chevy pick up and it acted the same way. And as said by TwinTurbo the thermal grease is key. Back them I remember it came with a capsul of the grease. Keep the ideas coming. When I get this thing running I’ll let all know what it was. OH… When it ran the fuel out the injectors looked great. A real nice spray pattern.


#7

Check the distributor cap and rotor. It sounds like if it is not a fuel problem, it is a spark problem. Sometimes the cap and/or rotor might get a slight crack in it and when it heats up and expands it will cause a bad connection shutting the truck off or making it run roughly. That would be where I start from here.


#8

I had an '88 1500 where the CTS took a dirt nap right before I got rid of it. In my experience, they usually fail in the “always cold” mode and the ECM dumps in tons of fuel even when it’s warm. Glowing cat and rough running when warmed up but starts and runs pretty good when cold. Not saying that it can’t fail the other way but I haven’t seen one do that yet.

Starting fluid burns much more readily than atomized gasoline. It’s way more volatile. It would run on that with a weak spark but maybe not so well on gasoline. The fact it ran on the spray but you could not see the spark seems to indicate a really weak spark. That’s where I would be looking…


#9

THANKS TO ALL FOR THE HELP.
The truck is up and running. Problem…Ignition module !! Temp swithch was also bad so replaced that to. But no start was the module.


#10

That’s great news!
Thanks for taking the time to post back on the outcome, it’s very much appreciated. Many people do not and we’re left wondering…