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Old 08-09-2014, 07:32 PM   #1
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chaperon's Avatar
Newmar Owners Club
Join Date: Aug 2010
Posts: 112
460 EFI Eng Miss when Hot

Hi Everyone!

Here's one I hope I can get some opinions on.
I have a 98 Newmar with a 97 Ford Chassis, 460 Engine.
A couple of week back, we got caught in a traffic jam on a long hill and engine temp got into the top end of the operating range.
When we got to the top of the hill, I filled the fuel, but noticed a bit of a miss when pulling in and out of the service station.
We finished our weekend and went home(all down hill), but noticed a miss just before we got home.
Next trip out the engine ran fine until it got up to temperature, pulled same hill, but when we pulled off highway, there was no power - full throttle barely got us through the stop light. Turned around and went home sputtering all the way.
Have been testing and will pull under power, shifts up and down, but seems to be a timing issue - reading lots of forums, but to date no resolution.
Engine starts no problem, fuel pressure is where specified with no indication of fuel problem, fuel filter has about 300 miles on it.
Changed cap, rotor, wires and plugs last year, about 1000 mile on them.
I have changed the Ign coil and checked all the connections to sensors etc. Made sure there were no vacuum leaks. Plugged in OBD1 scanner and KOEO test got 111 code, no problems, KOER test would not complete, would not identify engine cylinder etc
Jiggle test did not find any stored codes.
My thinking is that something is effecting the timing when the engine is hot, but not sure what would do this, I'm sure it is something simple, but has so far evaded me.
Thanks in advance for your help.

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Old 08-09-2014, 09:05 PM   #2
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Posts: 601
What comes to my mind is a vapor lock. If it runs fine until it gets to operating temperature, I don't think it would be timing because timing would be consistent, cold or hot. Coils can be heat sensitive, but that is new. Interesting problem. Let us know whaat you find.

Jim and Darlene Wright
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Old 08-10-2014, 07:12 AM   #3
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Ford Super Duty Owner
Join Date: Dec 2009
Location: Easton, Ks
Posts: 2,519
First off make sure no one has replaced the ICM with a Gray one as a Gray one can cause timing problems. Your F53 takes a Black one and is not wired for a Gray one.

Other than that I would guess your fuel pump is starting to go or the FPR is sticking open.
You might want to put a fuel pressure gauge on it and drive it until this happens and see if your fuel pressure drops at WOT on a hill with a warm engine. It should hold at about 40psi.

I have heard others say a PIP sensor can do this too. The bad PIP sensors I have had dealings with either worked OK when cold and then shut the engine off when they got hot.
1995 COACHMEN Santara 350FL on a 1994 Ford F53
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Old 08-18-2014, 11:07 PM   #4
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Posts: 112
Problem fixed - It was the spark plug wire boots, I had installed heat sleeves on the wires concerned with heat around the exhaust manifolds, appears he boots basically disintegrated allowing the wires to arc through the heat sleeves when the engine got hot. I installed new wires with straight boots(old ones were 110 degree) and the old girl ran like a top...well at least as good it did before my problem started.
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