?Backfire?

Killer Cougar

Well-Known Member
Joined
Jun 26, 2006
Location
Newport
OK, been having some problems with the ZJ. It first started about a month ago. The jeep seems to be backfiring a little bit at some but not all shift points. Seems to be at higher rpms. The only problem is that it comes and goes, but recently it has been here to stay. It kept getting worse until last week when the jeep just would not start. Had it taken home to my dad's house. He replaced the fuel *filter* on Monday and he said it fired right up and ran fine until yesterday while he was out "testing" it. It started to have little backfires again. So he got it home and found a leaky vacuum hose which he replaced and due to corrosion and just in case replaced the distributor cap and rotor button. He is thinking that maybe the cat could be clogged up. What do you guys think? Its a 93 ZJ with a 4.0 and about 185,000 miles.
 
Did you change the fuel filter screen when you replaced the pump?
 
Thats my bad. He replaced the fuel filter not the pump. I am guessing it is not the pump goes when it does start it will run for a little while. He had it out last time driving around for like 20 or 30 minutes.
 
So we pulled out the O2 sensor to open up the exhaust in case it was a clogged cat but that didn't work and we also checked the throttle positioning sensor and that checked out fine. Any other ideas?
 
My guess is fuel pump. All the Jeeps were kind of known to have problems with them. You can try hooking up a gauge to it and get a reading but it may show you have good pressure but the pump could still be bad. Do multiple tests and see what you get. It may read good the first time but check it again and you might not have any pressure. I know it doesn't make sense but I'm sure others on here know exactly what I'm talking about.
 
I agree, I would bet it is the fuel pump as well. I had one the same way, would start and run, but would backfire and spit and sputter while trying to drive.
 
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