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Old 05-10-2024, 05:59 PM   #1
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2002 8.1L fuel trim issue solved

I have been dealing with fuel trim issues on my 2002 P32 coach with 8.1L for some time, the the last couple of years my main issue has been fuel trim going high at idle.


First I cleaned the MAF and it helped some, one bank was higher than the other so I concentrated on the things that would effect one side more than the other, I replaced the O2 sensors and the coil packs (the steel laminations in the old coil packs were rusting and swelling), this got LF1 and LF2 closer to each other, but still going high at idle. I then found I had an exhaust leak at the exhaust donuts, I changed them out, and finally LF1 and LF2 tracked each other closely, but were still going up to around 12-14 at idle.


So I finally invested in a $75 smoke tester machine off amazon https://www.amazon.com/gp/product/B0BGB41DLK/ (requires an air compressor for an air source), there are cheaper ones down to about $55, but this one has a flow indicator, and inflatable blocking adapter. At which point I discovered I had a leak between the EGR Regulator (the thing the EGR valve bolts onto) and the intake manifold. Upon removing the EGR regulator I discovered the I assume factory gasket was crumbling away to nothing, I would show you a photo, but it literally disintegrated at the touch of my finger. I replaced it then I found the factory bolts had stretched and would not go back in tight enough to seal the new gasket, after replacing the EGR regulator to intake gasket, as well as the EGR tube and EGR valve gasket for good measure while I was in there, my fuel trims are finally good, I am now getting LF1 and LF2 of around -7 at idle with engine up to operating temperature, with numbers dropping closer to 0 if I give it some gas.


Ike


p.s. Note only the 01-03 8.1L have an EGR valve, later models did away with it. Here are a couple of photos of the EGR Regulator, and the point on the intake where the bad gasket was.
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Old 05-10-2024, 06:25 PM   #2
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Thanks for posting. The more information we have, the better our ownership will be.
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Old 05-10-2024, 07:55 PM   #3
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Thanks for the update. Good info.
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Old 01-14-2025, 10:39 AM   #4
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Is the simplest thing to do is get an EGR Block off plate? If you were to simply block off the EGR with a block off plate, what else would you have to do?
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Old 01-14-2025, 10:56 AM   #5
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Great wright up Ike.
Glad to see someone post a solution instead of a problem.
While you are in there, you should replace that little rubber cap on the vacuum line just above the EGR. The rubber cap in the bottom picture looks like it's bad shape (about to leak). A couple of cracks are visible in the picture.
OR, just replace it with a brass fitting just for the hose.

Mike in Colorado
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Old 01-14-2025, 01:00 PM   #6
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Quote:
Originally Posted by Flyer15015 View Post
you should replace that little rubber cap on the vacuum line just above the EGR. ... OR, just replace it with a brass fitting just for the hose.
Anything as old as the P32's are getting should be considered failed. My rubber cap and hose looked OK but I was getting high LTFT's on both banks. I used carb cleaner spray and the thing lit up when I sprayed near the manifold vacuum fitting. The culprit was the hose, it had relaxed on the barbed fitting and air was getting in around it. I cut a couple inches off, stuck it back on and LTFT's are normal. Don't have to smack me between the eyes a second time, new hose and cap installed. My 2005 does not have EGR so one less thing to fail. The only thing I ponder is the CPS but ain't fixin' what ain't broke yet.

Mark B.
Albuquerque, NM
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Old 01-17-2025, 09:34 AM   #7
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Excellent information, thanks. I will examine my 2005 8.1 for the similar condition.

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Anything as old as the P32's are getting should be considered failed. My rubber cap and hose looked OK but I was getting high LTFT's on both banks. I used carb cleaner spray and the thing lit up when I sprayed near the manifold vacuum fitting. The culprit was the hose, it had relaxed on the barbed fitting and air was getting in around it. I cut a couple inches off, stuck it back on and LTFT's are normal. Don't have to smack me between the eyes a second time, new hose and cap installed. My 2005 does not have EGR so one less thing to fail. The only thing I ponder is the CPS but ain't fixin' what ain't broke yet.

Mark B.
Albuquerque, NM
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Old 01-17-2025, 11:30 AM   #8
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George they did away with the EGR on the 8.1L after 2003
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Old 01-17-2025, 05:38 PM   #9
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Well, you said so in your first post. Wonder what happened to my memory?

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George they did away with the EGR on the 8.1L after 2003
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Old 01-17-2025, 06:04 PM   #10
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Block Off Plate

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Is the simplest thing to do is get an EGR Block off plate? If you were to simply block off the EGR with a block off plate, what else would you have to do?
Disabling or removing a federally mandated emissions device IS a federal crime punishable by fine and/or jail time
Be Careful
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Old 01-17-2025, 07:10 PM   #11
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Bob, I don’t live in Colorado. We have no inspections of any type, much less emissions testing. I think the feds will concentrate on the rolling coal diesel pick up trucks before they look at me and my 22 year old motorhome that gets driven a few thousand miles a year.
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Old 01-17-2025, 07:56 PM   #12
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Maybe, but you never know when they will change the law and start requiring emission testing. We don't have it here where I live in western Louisiana, but it is required in the southeast part of the state.
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Old 01-17-2025, 10:08 PM   #13
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Thanks for your diligence, for not only finding the problem, but for letting the rest of us know the fix!
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Old 01-17-2025, 11:56 PM   #14
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Inspections

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Bob, I don’t live in Colorado. We have no inspections of any type, much less emissions testing. I think the feds will concentrate on the rolling coal diesel pick up trucks before they look at me and my 22 year old motorhome that gets driven a few thousand miles a year.
They now have rolling inspection stations
Just mentioned that because they are in use in Denver. They don’t care if you live in the state and have Colorado tags or not, if you pass one of these stations on the road and their sniffer goes off they Will stop you regardless of how your tagged. They inspect the vehicle at that point and things then get interesting.
Just want to put that out there.
Happened to an out of state person I knew at one point
It’s funny because when I moved out here in 1992 my parents told me they did away with safety inspections. As my dad said “ They don’t care if you’re brakes fail coming down the mountain but don’t pollute or air”
Never did figure that reasoning out
Bobby in Colorado
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