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Hesitation after sitting idle


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I need some help from the MJ gurus. So far this problem had only plagued me on the trails but it happened to me the other day in traffic. Maybe heat related? I'm not sure. Anyway here's what it does....

 

After riding around a while, I get on the trails or in traffic (low speed or mostly stopped while idling) everything is fine unless I stop the engine for a couple minutes. When it cranks back up it doesn't want to idle smooth and will hesitate if I give it gas then it'll start suttering. The idle surges sometimes and it'll kill if I don't hit the gas to keep it alive. It will continue to do this unless I either 1) Turn it off and let it cool for 15-20mins or 2) Get up to highway speeds for a few minutes.

 

Other notes on this...

-The temp gauge says the engine isn't getting too hot when this happens. The aux fan doesn't even come on so I know its not getting too hot.

-The voltage gauge reads low (right around 12) constantly when lights and AC and Aux fan are on. I've measured with a multimeter at the battery cables and its getting high 13's with all of the accessories on.

-All sensors, fuel pump, fuel tank, fuel filter, fuel pressure regulator and fuel injectors are less than a year old

-All aluminum 3 core radiator, and higher rpm fan clutch

-This problems happened before I replaced everything too. Its gotten a little better, but its still a problem.

 

Any advice would be much appreciated!

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Some, not many of those apply to us H.O guys. Check fuel pressure at rail while this is happening, to be sure your able to do this go to the DIY forum and look up Hornbrods permanent fuel pressure gauge. Honestly one of the best mods I've done. Then diagnose from there, but that is good starting point. Let us know how it goes

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Some, not many of those apply to us H.O guys. Check fuel pressure at rail while this is happening, to be sure your able to do this go to the DIY forum and look up Hornbrods permanent fuel pressure gauge. Honestly one of the best mods I've done. Then diagnose from there, but that is good starting point. Let us know how it goes

Nice. I'll try that too. I wanted to do that anyway, thanks for pointing me in the direction of a good writeup.

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I had that same problem on my 91 especially on hot summer days when stopping and shutting down for a few minutes. When starting back up I'd get long cranks before it fired up, then rough idling for a bit. Sometimes it wouldn't fire at all so like you I'd let it sit for 15 minutes then it started right up. I figured IAT sensor heat might be the cause.

 

What I did was pickup a new IAT sensor, drilled and tapped a new hole (1/8 NPT) and mounted for it in the cold air intake. I left the original IAT in it's stock location on the intake manifold. So in the summer I plug into the CAI tube; in winter it goes back to the stock manifold location. It required extending the IAT harness a few inches to reach the new location. It cured the long crank times and rough idling for me.

 

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