Misfire at idle only.... - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 11-24-2009
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Misfire at idle only....

Alright, folks. I'm new to this Ranger (it's my Dad's)....I had one a few years back that was bagged and body dropped. Loved it, but had to sell before the Navy transferred me from Washington to Connecticut. Anyways, on to my issue.....

2001 Ranger 4x4 with 4.0L, almost 120K miles. Truck has been great for my Dad, and being in CT, it is used heavily in the snow. He has done all of the maintenance as required, and oil changed every 3000 miles. For some reason, his truck is misfiring at idle, but only at idle. When he first mentioned the CEL, I took my code reader over.
P0300 - Multiple Misfire
P0171 - Bank 1 Lean
P0174 - Bank 2 Lean

So I decided to start with plugs and wires. Misfire is still present. Changed both downstream O2 sensors, the coil, throttle position sensor, crank shaft sensor, cleaned the throttle-body, K&N, IAC. Still rough at idle. Friend works at Advanced Auto Parts. He let me plug in a new MAF, but didn't change anything. New IAC, nothing changed.

I've been into cars for a long time, and know enough to hold my own, but I am honestly out of ideas for this thing. IAC was my first thought, because it happens at idle only, but thinking about it, the IAC doesn't really do anything once the engine is warmed up, and the misfire gets way worse once warmed. My next thought is that it's something fuel related?? Pressure regulator, or dirty fuel filter (was changed about 25K miles ago as well)....maybe an ECM issue?? I don't know...
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Old 11-25-2009
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It sounds like vacuum leak to me. One of the first places I would look is the PCV elbow under the top radiator hose. It is part of the PCV line the comes from the back of the engine, where the PCV valve is located, to the intake/throttle body. This rubber elbow deteriorates and cracks resulting in a vacuum leak.

If that is OK look for other sources of a potential vacuum leak.
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Old 11-25-2009
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Dan, 4.0's are notorious for bad upper and lower intake gaskets (seals).

Replace those, it'll get rid of the lean condition and I bet the misfire disappears too.

The vacuum leak on my 99 Ex's 4.0 (SOHC) was so bad (I could hear it hissing) that I could put my body weight on the (plastic) intake and rock it side to side and hear the hissing change.

How to replace upper intake manifold gaskets - Ford Explorer Ranger Enthusiasts "Serious Explorations" is a pretty good how-to.
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Old 11-25-2009
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I knew the 4.0 OHV engine was notorious for intake manifold leaks but I was not aware the SOHC engine also experienced that problem. So far so good with my 02 SOHC but I will keep an eye on it.
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Old 11-25-2009
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Quote:
Originally Posted by Earl43P View Post
Dan, 4.0's are notorious for bad upper and lower intake gaskets (seals).

Replace those, it'll get rid of the lean condition and I bet the misfire disappears too.

The vacuum leak on my 99 Ex's 4.0 (SOHC) was so bad (I could hear it hissing) that I could put my body weight on the (plastic) intake and rock it side to side and hear the hissing change.

How to replace upper intake manifold gaskets - Ford Explorer Ranger Enthusiasts "Serious Explorations" is a pretty good how-to.
yea not so much, it'll be that rubber elbow that causing him issues.
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Old 01-18-2011
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Posible bad ecm???

I have had the same problem and have done the same fixes without fixing anything.
My truck is a 04 with a 4,0 2wd auto and I dont have any vacume leaks, Im at my wits end on this one and also had an injecotor changed on the problem #4. Nothing left to do but set it on fire.
HELP PLEASE!!!!!
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