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Backfires!


 
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johnnykomac
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Joined: 28 Feb 2008
Location: Oahu, Hawaii

PostPosted: Sat May 10, 2008 8:13 pm    Post subject: Backfires! Reply with quote

The damn thing back fires and has no power down low.

I took my wife out 4wheeling and told her to drive 'over' the big rock but she chickened out. She ended up straddling it and busted 3 huge holes in the down pipe.

So, naturally when it was backfiring and running like crap I assumed it was due to the 3 huge holes in the down pipe (time to get some armor).

But, with the down pipe all welded up the thing still backfires and runs like crap down low.

I looked it up in the manuel and it said that it could be an EGR valve however, it seems really odd to me that it would just decide to go bad during a 4wheel session. I was thinking it would be something impact related.

Another friend says it could have jumped time... god I hope not!

Any thoughts.

Thanks in advace!
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IBTJn
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Joined: 31 Dec 2004
Location: Just Outside of Portland, OR

PostPosted: Mon May 12, 2008 5:54 am    Post subject: Reply with quote

(Moved to General Tech from "Drive Train")

Not knowing what you own, I'd only be guessing this is an XJ? And I'd also guess the "down tube" is the exhaust system? ???

If so, usually an exhaust leak won't usually cause backfires. But vacuum leaks, jumped time, bad gas, plugged fuel line, and a few other things can. Check the easy (and cheap stuff) first. If it were me I'd focus on the vacuum lines first. Pull each one off and look closely at them. Cracked, brittle or broken vacuum lines should be replaced. When was the last time the air filter was replaced?

I can think of a couple of other things to check as well...but I like starting with easy stuff first.

Wink
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johnnykomac
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Joined: 28 Feb 2008
Location: Oahu, Hawaii

PostPosted: Thu May 15, 2008 8:55 pm    Post subject: Reply with quote

Ok... i guess i forgot i wasnt posting in the XJ section anymore. And I did mean exahust system.

The air filter looks good. Im really hoping it hasnt jumped time or bent a valve or anything. I would hate to overlook something as stupid as a clogged vacum line.

Im deploying in only a few weeks and not having the car running means ill basically have to sell it for half of what its worth.

a few vacum lines have been fixed since the last post, along with a million other things.

The whole time ive been thinking its probably electrical. Ive replaced the plugs, wires, cap, and rotor.

its not the egr valve like i thought. I replaced the fuel filter and the fuel pump seems to be working fine.

How do I test for a clogged fuel line?

Any other thoughts what it could be?
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Orangeamc13
Got Rev Limiter?
Got Rev Limiter?


Joined: 20 Feb 2006
Location: East Springfield, Massachusetts - U.S.A.

PostPosted: Fri May 16, 2008 9:24 am    Post subject: Reply with quote

What year and motor? Did the problem start immediately after the rock encounter?
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ThePhantum
Pissed-Off Admin
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Fri May 16, 2008 12:50 pm    Post subject: Reply with quote

Also, how many miles?

Assuming that it's an 87 or newer XJ, it's a fuel injected motor...so it could be the Camshaft Position Sensor or the Crankshaft Position Sensor...
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johnnykomac
Member


Joined: 28 Feb 2008
Location: Oahu, Hawaii

PostPosted: Fri May 16, 2008 6:51 pm    Post subject: Reply with quote

its an 89 XJ with the 4.0L inline six with 176,000 miles. I was reading some other posts of similiar problems and now im leaning towards Crankshaft Position Sensor, O2 Sensor or MAP sensor.

Because i was wheeling at very low speeds i didnt notice the problem until we were all done but yes, it did happen right after the 4wheeling and the rock incident was at the end of that.

PHANTUM, wheres the camshaft position sensor?

thanks guys.
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Fri May 16, 2008 7:23 pm    Post subject: Reply with quote

It's in the distributor. Once you remove the cap and rotor there are two screws that hold the sensor to the distributor assembly.
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