88 fifth ave. 318 backfire

cranked up · #1 10-20-2005, 11:10 AM

my freind and i are trying to solve a big problem with his 88 fifth ave. 318. it runs fine at idle, but on a load it spits and backfires. at first it was overheating and low vacuume. i found that the exhaust was plugged and fixed that problem. but it didn't fix the backfire problem. next we went to the timming. it was a few degrees off, but not bad. we went into the timming chain. it was clearly bad (streatched) so that got changed. still didn't solve the problem. we tried 3 different spark controll computors, 1 distributor, and checked for bad sensors. the carb seems ok fuel wise, but i think i should test the fuel pump. there also is a brand new cam installed yesterday on someone elses suggestion. (this is getting expensive!) next step is compression test. i would be thankfull for any suggestions!

cranked up · #2 10-20-2005, 05:45 PM

the compression test turned out fine. we changed the cap and rotor and it seemed to help a very little bit. it still runs fine at idle but backfires at high idle.

theFREAKnasty82 · #3 10-20-2005, 09:57 PM

I'm not sure if you mentioned this, but have you checked the condition of your plugs?

cranked up · #4 10-21-2005, 08:08 AM

the plugs, wires, old cap and rotor were all under a year old (which doesn't really mean too much). everything that way apperes good. last night the local parts store sent a tech they knew over. he's stumped. he says he can hook up a scan tool to this car. i don't know were, but if its possible maybe we can find something from that. i guess there was more than one problem with this car and its time to go back to the basics.

cranked up · #5 10-22-2005, 08:24 AM

just as i thought, he couldn't hook up the tester. but he did retard the timing so far that most of it is gone, but not all. problem is still there. i went back and double, triple checked all the basics(timimg, plugs, firing order,etc.). it's all still fine. next step i think would be leak down test for cracked head or burnt, broken valve. maybe coil is weak and can't keep up with high rpm. one more thing, the backfire seems to be a little less under load. help anyone?

theFREAKnasty82 · #6 10-23-2005, 11:18 PM

it could be possible that you have a vacuum leak on your intake.

cranked up · #7 10-24-2005, 06:48 AM

with a new cam, the intake had to be removed. there are new gaskets everywhere now.

theFREAKnasty82 · #8 10-24-2005, 09:31 PM

Are there any emissions devices, such as the EGR valve? There's a very good possibility that the EGR valve is stuck open thus causing the backfire.

cranked up · #9 10-26-2005, 07:47 AM

the egr tested out fine. the intake exhaust bypass is clean. the lean burn system was checked(carb, egr, knock,temp, etc.) by 4 different people. new cap, rotor, wires, plugs. i tried a leak down, but its an old car and the rings wouldn't hold enough for a decent test. it's still backfiring. don't know what else to do besides blow it up.

cranked up · #10 10-26-2005, 07:50 AM

we also tried a new coil

theFREAKnasty82 · #11 10-26-2005, 09:58 PM

have you checked for any crossed wires, making sure the wires go to the right cylinders on the distributor cap? Also, are you positive that while the distributor was out, that the engine was never turned over? Check also your basics such as the wires going to the spark module, make sure that there are no spread or loose terminals and also that there is no corrosion or garbage in between the terminals.

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