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Old 08-08-2014, 08:20 AM
tp250 tp250 is offline
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Default 2003 Ranger 4.0L runs rough low/high idle. no codes

Hello, I'm having an issue with a 2003 ranger 4.0l with 310,000kms.
I have been working on diagnosing the problem for a number of days now and I'm looking for help or suggestions. I have another similar ranger for parts and a scanner.

The complaint is poor engine performance. It stumbles, misfires and bogs down at idle, high idle and particularly under load. There are no DTCs.

Max RPM i can get is 2500rpm, or 3000rpm with the exhaust manifold plugs removed. The condition generally gets worse as the engine warms up. When it is cold and first started at idle there are no symptoms.

Fuel pressure is 72psi with good flow, all speeds

I have replaced spark plugs and wires. The old plugs were worn normally and had a nice tan colour. I have tried swapping the coil.

Compression ranges from 190psi at best, going downhill to 125psi @ #3 cylinder (worn rings)

I have tested the injectors for continuity (~7.5ohms, except #6 i haven't tested due to being under the coil) and for pulse signal.

I cannot find any vacuum leaks, spraying fuel or soapy water all around, nor any collapsed lines or blockages.

Vacuum fluctuates rapidly between 12 - 14"Hg at idle and quickly drops to nothing as idle is increased.

I have;
cleaned the MAF sensor and the throttle body
swapped/cleaned the TPS and IAC
swapped PCV valve, ignition coil
tried running it without exhaust manifold plugs in to eliminate the cats
cleared codes and KAM

Linked is a video of it misbehaving:

The plugs on the exhaust manifold have been removed to rule out the 5 year old CATs. removing them raised the high idle about 500rpm. Tomorrow I will drive it with the plugs out to see if I have more power.

Does anyone have any suggestions on what to test or what parts to swap? What parameters to check on the scanner?

Any help or ideas are greatly appreciated, Thanks!
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Old 08-08-2014, 11:42 PM
tp250 tp250 is offline
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Join Date: Aug 2014
Posts: 2
Default Re: 2003 Ranger 4.0L runs rough low/high idle. no codes

Resolved. CATs WERE plugged. The funny thing is that the rev limiter kicks in at 3000RPM. TPS also turned out to have a code after KOEO due to an open in the 5v supply wire.
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idle problem, misfire, no codes, runs rough

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