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Engine misses under load - 4.0 L

3K views 2 replies 2 participants last post by  Pumpman 
#1 ·
We converted my wife's 86 CJ7 to a '92 model 4.0 L fuel injected engine about two years ago. Recently, it has developed an under load miss like when climbing a hill or cruising at higher speeds like 60 mph plus. Lower loads like accelerating away from a stop on level ground - no problem even under moderately hard acceleration. I have two inline fuel filters - one between the gas tank and the external fuel pump, and another between the fuel pump and the injectors. I have changed the one before the fuel pump, but noticed no difference in performance. I have also been putting Lucas fuel injector cleaner in the tank regularly. It starts and runs fine other than this miss - any ideas?
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#2 ·
Sounds like lack of fuel volume to me. I have experienced this before. Your fuel pump can show pressure within spec, but still not provide enough volume. If you can jump the pump and pump it in to a container you should produce at least a quart of fuel per minute. If you do not you have found the problem. When I had this proble it was the sock on the bottom of the pump. It was all clogged with crap. Hope this helps.
 
#3 ·
Thanks - that was my thinking also, but I will continue to follow the fuel theme by changing the other fuel filter and following the rest of the flow.
 
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