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02-25-2023, 09:05 AM
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#15
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Member
Join Date: Dec 2017
Posts: 56
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Trims
My mass air flow sensor was replaced last spring. So I don’t think that is the explanation for my high trims. After talking to a couple mechanics all agreed that I don’t have much risk taking a four hundred mile trip next week even if they are high. I have an appointment when I get back to have a smoke test done to check for leaks. One of the mechanics said the long term trims are averages. When I started up the coach yesterday to turn off the monitors on the ScanGauge3 to eliminate the annoying alarms I already saw the trims slowly coming down at idle and when I ran the rpms up and held them for a minute or so the LT trims continued to slowly move down.
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Doug P
2004 Holiday Rambler
P32 Workhorse Chassis
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02-25-2023, 10:20 AM
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#16
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Senior Member
Join Date: May 2017
Posts: 1,299
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Quote:
Originally Posted by DougASE
Any ideas as to whether at idle seeing numbers this high is normal?
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Double digit long term fuel trims is never "normal" !
Personally, I would want to test drive under typical conditions, before I would be too concerned. Many, MANY, things affect fuel trims. Shotgunning parts is expensive and you may never find the answer.
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Retired. 31 year of automotive engineering for one of the Detroit 3, specializing in Powertrain Control Systems.
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02-25-2023, 10:22 AM
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#17
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Senior Member
Join Date: May 2017
Posts: 1,299
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Quote:
Originally Posted by DougASE
My mass air flow sensor was replaced last spring.
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Non-OEM MAFs can not be trusted ! Oil impregnated air filters (K&N) are know to cause erroneous readings.
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Retired. 31 year of automotive engineering for one of the Detroit 3, specializing in Powertrain Control Systems.
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02-26-2023, 01:39 PM
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#18
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Senior Member
Join Date: May 2005
Location: Illinois
Posts: 128
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fuel trim
where can I watch Kevin Caudil's videos?
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02-26-2023, 07:13 PM
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#19
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Senior Member
Workhorse Chassis Owner Rexhall Owners Group
Join Date: Feb 2003
Location: Everywhere,USA
Posts: 1,518
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Quote:
Originally Posted by hoggem
where can i watch kevin caudil's videos?
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youtube
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Full-Timers
in a
2003 Rexhall Aerbus 3550BSL
W22 Workhorse
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03-05-2023, 09:36 AM
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#20
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Senior Member
National RV Owners Club
Join Date: Sep 2018
Posts: 248
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One thing to remember about our 8.1 vortex in our M.H. is that Workhorse deleted a lot of the check engine codes so we will never see a check engine light for those conditions . I do belief that high fuel trim is one such condition we will never get a check engine light for. One of Kevin Caudill's videos shows a list of the inactive codes. I think is on the Scan gauge 3 video .
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Ray & Melinda
2005 National Dolphin 5355 (MEPAW) , Koni FDS shocks, Safe-T-Plus , Front & Rear track bar , Sumo springs . She tows a 2006 Tacoma 4X4
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03-06-2023, 09:46 AM
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#21
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Member
Join Date: Dec 2017
Posts: 56
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Fuel Trims ScanGaugeIII
I’m the original poster on this thread. I took my 400 mile trip after getting multiple mechanics to opine that my LT trims at idle running at or near 25 but coming down at higher RPMs wouldn’t damage the engine. The motor ran great all during the trip. I had some short steep grades. Temps were normal as were all the other conditions in my new SGIII system. It’s pretty cool. The LT trims ran 4-9 most of the trip at highway speeds and as soon as I would pull away from a stop. Mostly 6-9. There was about a 1.5 difference with bank 2 running a little higher. The rig went in the shop today for a smoke test to see if we have a vacuum leak somewhere which I have been advised by Ultra RV products and others is the most likely source of the high trim at idle.
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Doug P
2004 Holiday Rambler
P32 Workhorse Chassis
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03-13-2023, 10:56 PM
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#22
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Member
Join Date: Dec 2017
Posts: 56
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Took my 400 mile round trip. Engine ran great. Fuel trims under load were good always under 10 and usually above 1500 rpm's and say 35 mph and at highway speeds LT trims were running 6-8. Bank 2 was usually about 1.5 higher than Bank 1. At idle trims were still 20- 25, mostly 25. When I got back per advice here and from UltraRV had the vacuum hoses smoke tested. No vacuum leaks! The mechanic found a faulty fuel regulator which he replaced today. He called and said the LT trims at idle now were about 14. Better but still high. UltraRV said next check for exhaust leaks and that the O2 sensors were oscillating properly, talked again to the mechanic he said he saw no exhaust leaks and the o2's were good. Ultra also said check injectors and coils, mechanic said that was all good. On the back of the intake manifold is a vacuum hose that runs to a big black ball under the hood high up that has to do with the heating system vent duck controls. They said plug that exit from the intake manifold and see if the trims come down indicating a leak somewhere in that heating system duck work or the hose running forward. Talked again to the mechanic he said that was part of the smoke test but he said he would check that again. So I am still almost nowhere finding the cause of the high LT trims at idle. Any other ideas?
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Doug P
2004 Holiday Rambler
P32 Workhorse Chassis
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03-14-2023, 10:07 AM
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#23
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Senior Member
Join Date: Jun 2000
Location: Martinez, CA. USA
Posts: 354
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You mentioned that the mechanic didn’t “SEE” any exhaust leaks.
On my 2001 P32, I had major exhaust leaks on both manifolds and collection point donuts. None of which produced any visible signs. Only burning up spark plug wires.
I finally found the leaks by pressurizing with a shop vac in blow mode each exhaust bank and feeling for leaks which I quickly found.
I never compared before and after fuel trims so can’t give any input there.
Good luck
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03-14-2023, 10:40 PM
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#24
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Member
Join Date: Dec 2017
Posts: 56
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Talked to the mechanic late this afternoon. He found an exhaust leak on one side. In the morning he will get a closer look at it. Disappointing as I spent big bucks summer before last replacing exhaust manifold gaskets on both sides to correct exhaust leaks. Seems like that fix should last a little longer. Fixing the new leak from what I have learned should bring the LT trims at idle back in spec.
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Doug P
2004 Holiday Rambler
P32 Workhorse Chassis
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03-15-2023, 09:44 AM
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#25
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Senior Member
Join Date: Jun 2000
Location: Martinez, CA. USA
Posts: 354
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When I fixed my exhaust manifold leaks, I had the manifolds machined (ground) back to flat again. One of them was warped pretty bad. I inquired as to what type of gasket I should use and the shop recommended the OEM metal gasket. He advised that the thicker, header style gasket doesn’t work well with the OEM manifolds. I did what they recommended and 7500 miles later, still no leaks. I also installed all new studs and nuts. There is a very specific torque sequence for the OEM manifolds that should be followed also.
Hopefully, your shop did something similar and didn’t just replace the gaskets.
I have added air collection points at my grill that takes air while under way and directs it into the engine bay to assist with cooling of the manifolds.
Have also installed two, eight inch motorcycle radiator fans, in the engine bay that directs air over the manifolds and out past the transmission.
If nothing else, all of this air flow has helped a lot with heat intrusion into the passenger compartment.
Good luck and keep us posted.
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04-26-2023, 09:56 AM
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#26
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Junior Member
Join Date: Jul 2021
Posts: 15
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Doug, did you ever find the reason for your fuel trim issue? I have similar problem but only on the left bank, and constantly failed O2 sensor on left bank. Beginning to think I may have a plugged cat on the left side.
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04-26-2023, 10:50 PM
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#27
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Member
Join Date: Dec 2017
Posts: 56
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So there are two issues likely causing the final LT fuel trim issues. First, I had a plugged cat replaced on passenger side last fall by my usual shop. They didn’t get the weld all the way around on top so there is a leak there. The shop doing this work also found a very small crack on the back end of the passenger side exhaust manifold. Both manifolds were off and gaskets replaced about a year and a half ago. A new manifold is $700 plus installation. Work not done yet so I don’t have a final outcome. These two leaks are likely the cause.
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Doug P
2004 Holiday Rambler
P32 Workhorse Chassis
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04-27-2023, 09:03 PM
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#28
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Junior Member
Join Date: Jul 2021
Posts: 15
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Doug, have you considered deleting both cats? I have read where the cats may not be necessary for the operation of the 8.1 vortec (but I do not know this for a fact) Someone like Kevin Caudill or Ultra Performance would be qualified to answer. I figured if I had my cats were stolen, I would research this in greater depth.
Do you know what or why you ended up with a plugged cat?
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