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Old 04-24-2012, 09:56 PM
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Engine Trouble (Sorry for the Generic Title)

Okay, so I fairly recently bought a '97 ZJ 4.0, and I've been having a ton of engine troubles I get the feeling are all stemming from one source problem.

Usually it starts fine, but sometimes, it won't start unless I open the throttle, then it starts right up. It dies sometimes, while driving, usually while coasting, and the throttle gets peaky sometimes. It's backfired like a rifle a couple times, and the issue, combined with a poor installation (I plan on yapping the shop's ears out), has caused my muffler to literally explode. It's running pretty rich, I can smell, but nothing worse than my old GMC has been for years.

I'm thinking it's a fuel pressure regulator or O2 sensor causing a rich condition (I hear these engines are supposed to run pretty lean, for that matter), but I haven't checked yet, and I'd like to hear some of your insights.

As a by-the-by, it's got 245,000 miles on the original engine and transmission, and it's running fantastic when it's not trying to die on me in a way that doesn't seem like internal engine trouble. I was thoroughly impressed. My next-highest-mileage car I've owned was a '90 Pathfinder with 210k when I sold it.
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Old 04-24-2012, 10:43 PM
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Re: Engine Trouble (Sorry for the Generic Title)

I'd replace the O2 sensors and the crank sensor.
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Old 04-25-2012, 03:10 PM
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Re: Engine Trouble (Sorry for the Generic Title)

I'll check those out, but I forgot to mention, it doesn't like to work at all until it's hot, then it doesn't screw around much. I'm gonna pull my plugs and see if they're sparking properly. The coil's definitely giving enough spark to register on the tach, but I think it's probably time to give it a full tune up and oil change.

And, of course, with an oil change, comes Seafoam.

EDIT: Plugs were all fine, but the wires were disintegrating in my hands. Gotta change those, and do a cap and rotor, then I'll get back to you guys.
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Old 04-26-2012, 08:50 PM
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Re: Engine Trouble (Sorry for the Generic Title)

Double post because I'm pissed off.

I did a full tune up this morning, and it ran fine. So I decided, I have the day off, I'm gonna go yell at the guys who installed the muffler wrong and have them fix it. So I got the muffler replaced, and it was running fine until I got home. Everything was running smooth, until I got grandma in the car to take her to the grocery store. Then it started stumbling, died a couple times, and backfired harder than I've ever seen anything backfire. (and I've worked on carbed rotaries) The new muffler exploded.

But it's not running rich, it's got proper fuel flow, injectors are all good, it's not throwing any codes from OBD, except one regarding my brakes, its ignition components are all new, and it has good compression across the board. I'm really at a loss here. I can't think of any reason it should be stumbling and backfiring. All I can really come up with is the new muffler put backpressure on the exhaust, but it shouldn't have been enough to blow anything up.

Does anybody have any insight into this? Inevitably, I'm going to have to spend the money on a new muffler, but why bother if that one's gonna explode?
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Old 04-26-2012, 10:01 PM
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Re: Engine Trouble (Sorry for the Generic Title)

So your new muffler that they just put on exploded?
You went in and yelled at the guys and told them to fix it?

Did they stuff a rag in it?

Please post some pics and don't go back to that shop again.
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Old 04-26-2012, 10:21 PM
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Re: Engine Trouble (Sorry for the Generic Title)

I'll get pics in the morning (should have taken pics of the last muffler, but this is exploded worse). I really have no idea what could be causing this. I've got good fuel flow and my injectors are all good, so what could be sending so much fuel and air that far back? I mean, it's gotta be stoichiometric to explode that hard, and it's gotta be a lot of fuel.

EDIT:

My muffler as of right now


And for the hell of it, '97 ZJ:
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