1998 Jeep Wrangler Backfiring

Tiny
19327
  • MEMBER
  • 1998 JEEP WRANGLER
  • 4.0L
  • 6 CYL
  • 4WD
  • MANUAL
I just put a new crate motor in and it started up but when I give it gas it starts to backfire through Exaust the it starts to backfire through throttle body but at idle it runs great
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Sunday, May 25th, 2014 AT 7:47 PM

6 Replies

Tiny
HMAC300
  • EXPERT
Was it a complete engine? If not check to see if pushrods are alin place and opening valves.
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Monday, May 26th, 2014 AT 7:10 AM
Tiny
19327
  • MEMBER
The was complete with all the tins on it. I just had to replace water pump and install intakes ans start it.
At 1200 rpm it backfires through exaust.
At 1600 rpm it starts to backfire through intake.
Then a little higher it does both at same time.
I have checked timing 5 or 6 times to make sure it is dead on because to distrubitor does not move on this thing.
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Monday, May 26th, 2014 AT 8:47 AM
Tiny
HMAC300
  • EXPERT
Take the valve cover off and look for valves not opening also make sure spark plugs are good as well as plug wires, and dist cap
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Monday, May 26th, 2014 AT 9:36 AM
Tiny
19327
  • MEMBER
Everything is new plugs wires cap rotor all new took the valve cover off and it all is fine. It still starts right up and idles great until I give it a little throttle and it turns to crap. My son said that it could be the flywheel but that is new as well and it only goes on one way. Still banging my head on the wall never had this happen in any of the other motors I have installed as crates of my own rebuilds.
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Monday, May 26th, 2014 AT 10:57 AM
Tiny
HMAC300
  • EXPERT
Check fuel pressure andfor vacuumleaks, check firing order. See pic
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Monday, May 26th, 2014 AT 12:02 PM
Tiny
19327
  • MEMBER
I figured it out I was 1 tooth off on the distributor. I found a listing telling me to put the rotor at 4 o'clock and turn the oil pump 30 degrees and the rotor should be just past number 1 when it drops in. I had it right on number 1. Like I do on small blocks and all the normal motors I build.
Thank you for all the ideas to check.
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Wednesday, May 28th, 2014 AT 12:28 AM

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