cujiman

Hi everyone.Hope you can help me with this one need my van for work.1999 safari 4.3litre.in the morning specially when its cooler or wetter out.it wont start or sometimes starts after crankin it a long time.it has backfired real bad now a lot of times when im tryin to start it.it peeleed at least 3 mufflers like a banana peel on me .verry frustrating.i put a code readre on it showed p018 which said coolent temperture cuircuit low end.i changed coolent temperture sensor but still doin it.when i turn key on the fuel pump runs for about a good 15 seconds.Is that too long?.is it flooding thats why the backfire?please help im pullin my hair out.

old_master

When the ignition is initially turned to the RUN position, (engine off) the fuel pump should run for approximately 2 seconds and then shut off. If it stays on longer, the fuel pump relay might be sticking. If the pump continues to run for longer than 5 seconds after the engine has been running, it's probably the oil pressure sending unit sticking. You might want to check fuel pressure and leakdown rate also. Ignition in RUN position, engine off, fuel pump running, pressure must be 60psi to 66psi. Pressure must remain above 55psi for 3 to5 minutes after the fuel pump shuts off. Post your results.

cujiman

Thanks old master.I know the fuel pump runs way too long on run position.I think also after engines runnin it does too but been so long since i had it runnin not sure on that one.SO the bad backfire im getting which blew up 3 mufflers so far what causes that ,too much fuel its floooding?the fuel pump relay do i just buy a new one or can it be bypassed.?ill check fuel pressure now and let you know Thanks again.

old_master

Don't start throwing parts at it. Eventually you're bound to replace the bad part, but unless you have a reliable crystal ball, it can get real expensive real fast. Proper diagnosis is always cheaper in the long run.

Several things can cause a backfire, but to rip up a muffler, there must be a substantial amount of unburned fuel in the exhaust system. From your description of the symptoms, checking fuel pressure and especially the leakdown rate, should be top on the list of things to check. The test is inexpensive, easy, and will tell you immediately if there is a problem, (or not) with fuel delivery.

The most common reasons backfireing occurs is due to faulty ignition parts and/or ignition timing issues, and problems with fuel delivery. Fuel delivery problems will not set a DTC, and typically a problem with secondary ignition will set a DTC in the P0300 series. Start by checking fuel pressure and leakdown rate, then post your results.

cujiman

ok i did the fuel pressure test and heres what i got=when key first turnd on it went to 64 then i let sit for about 4 minutes and it dropped to 46 psi.so i guess thats a problem.ok im gettin somewhere now.Please tell me what to do next.Thanks.

old_master

The only way to determine if the leak is under the plenum or in the tank, is to isolate the fuel pump from the system immediately after it pressurizes the system. If pressure holds, the pump is leaking. If pressure still drops, the leak is in the plenum. Check your private message inbox for details.

Blue Bowtie

I've had the same symptoms on several GM CPFI systems. As long as the system produces the requisite 61 PSIG while cranking, it should be adequate. The leak might be through the FPR or back through the pump checks. Neither of those conditions would cause a problem. Either or both of those conditions would neither prevent starting nor cause flooding.

I believe the Master is right on the mark, and solving the long pump run cycles might solve the problem.

Incidentally, fuel ignition in the intake tract is "backfire" and fuel ignition in the exhaust is "afterfire" for future reference.

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diggin

I kinda had the same problem but mine was a bad ignition coil that was leaking out the side , every time I have had a backfire or afterfire it has usually been an ignition problem. If you get it running drive it with the doghouse off and look or listen for spark jumping around,that's how I found my problem.