Help with 2002 4.6is rough running

murf · #1 10-22-2014, 10:16 AM

Hi guys,
looking for some help with my rough running 4.6is.
I bought the truck with the timing guides toast so I fixed that. now the truck runs rough and I can't figure it out. Timing appears to be spot on and no codes until the engine safe mode kicks in. I occasionally get error 134 test at lower stop. I only get this when I punch the throttle and let it drop off. Might be a problem but I don’t think it has anything to do with whatever else I have going on.
I will post some screen shots and any advice I can get would be great. right now I am thinking it might be a clogged cat or a bad o2 sensor.

I am only posting the screen shots where the readings were not in the specified range.

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bcredliner · #2 10-22-2014, 11:52 AM

How was it running before you replaced the timing guides?

murf · #3 10-22-2014, 12:38 PM

Guides were toast when I bought it, so not running.

I just went out and took a bunch of screen shots from DIS/GT1 diagnostics that I will post.

bcredliner · #4 10-22-2014, 12:43 PM

Have you tried disconnecting the MAF and see if the idle improves?

murf · #5 10-22-2014, 12:48 PM

Here are some more screen shots from INPA

murf · #6 10-22-2014, 01:29 PM

Quote:

Originally Posted by bcredliner

Have you tried disconnecting the MAF and see if the idle improves?

I just went out and unplugged it. seems to run about the same with some initial change in idle speed when I first unplug it. I also swapped the MAF with my 2000 540M Sport with no real change.

romeokc10 · #7 10-22-2014, 02:33 PM

Nice screen shots, awesome looking software!

murf · #8 10-22-2014, 03:03 PM

Here are the screen shots specific to the o2 sensors.

The bank one after cat sensor looks to be very suspicous.

David.X5 · #9 10-24-2014, 08:20 PM

I would check the condition of the plugs before you go too far. New plugs (& properly tightened) solved my last stumbling at idle issue.

David.X5 · #10 10-24-2014, 08:27 PM

I've been told that post-cat O2 sensors are not part of the loop controlling engine performance, but instead are used to determine the health of the cat system. So if this theory is correct, it may throw a code, but the post-cat O2 shouldn't cause poor performance.

See for example - 12v Pages - The Engine - How it Works

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