by decipha » Thu Dec 04, 2014 9:42 pm
alright this is an easy one
said vehicle is a 96 crown vic 4.6L w/ 4r70w trans, completely bone stock
vehicle runs fine but has a random misfire at idle and very low loads, its a random misfire but occurs on both banks of the engine and at random times while idling and cruising. Has no rhythm to it and sometimes you can go days without a single hiccup.
The owner of the vehicle says it's not really an issue just a nuisance and the vehicles runs fine otherwise. WOT is nice and strong and the engine feels very responsive. The engine is completely bone stock with 140k miles on the clock but a complete full tune up was done less than 15k miles ago. The problem has persisted since 90k miles and nothing has seemed to helped it. When it first occurred he brought the vehicle to the dealership (car has always been a dealer only vehicle for maintenance) and they replaced the following. Note that since the issue arouse 50k miles ago the following has been changed to no avail
ECU is throwing no codes
timing chain and tensioners
plugs
wires
coil packs
cam and crank sensors
pcv valve
fuel filter
fuel pump (went bad at 130k)
air filter
maf sensor (mechanic changed originally thinking it was the problem)
EGR valve and flow sensor
The vehicle has been to 3 different ford dealerships and 6 different independent highly regarded repair shops that specialize in fords. The issue was never resolved. I was contacted by a friend of mine that owns a local repair shop to come check it out, he had the car for 2 weeks and was completely baffled but was determined to get it fixed.
I come over and first thing I do is plug in to see whats going on in the ecu, everything looks perfectly nomal but when the engine misfires i can see that hego go lean and the lambse richen up to compensate then come back to normal. I see its occurring on both banks of the engines and there's no repeatability to it, it's a completely random misfire and when you rev the engine up it doesn't do it.
So I get to snooping under the hood and voila!!! The problem is staring me right in the face.
anyone want to take a stab at it?