2008 C4500 8.1L odd issue

[Consolenut]

 

Hi everyone long time since i posted here. Heres the deal maybe someone can help. I have an 08 topkick 8.1L 6sp allison. First of all no check engine light.

 

Under load meaning my heavy heavy 5th wheel rv in tow only. Tow haul button no overdrive button pressed. Keep in mind i tow peak torque 3k. Flat ground its fine. But any incline or climb it starts popping and breaking up. Back off the throttle a tiny bit it clears up. It acts maybe like a coil getting weak. Fuel filter replaced 5k miles go. Only feed it premium fuel. new plugs and wires same time as plug wires. New O2 sensors and i got AC delcos. Hauled a second time. everything id done till then hadnt helped still popping. New MAF sensor and air filter a week before i hauled my 5ver for the 3rd time. Same result. It has a 195 thermostat in it. Forgot to include that info as well.

 

I did the usual suspects when it started popping and breaking up the first time about 4 months ago. which is all the parts listed above in varying levels.. No check engine light makes it hard to diagnose. No GM dealer near by will diagnose the 4500.

 

Perhaps there is someone with EFI Live or HP tuners near Memphis TN. that could look at it in real time towing that could tell me where the issue is.

 

Not that it makes a diff but i run 5w30 mobil 1 synthetic. Around town on its own its fine. You can go WOT throttle until it pegs the speedo but it never acts up.

 

Any ideas, tuners, or someone that can monitor in real time in my area. Greatly needed.

 

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[davester]

Just because the CEL is off, doesn't mean there are no engine and/or transmission codes.  Perhaps just start with reading codes.

 

If this is a vehicle you plan on keeping for some time, I would suggest:

-getting a good code reader, that can access all the computers in your truck, such as a tech ii (or even a clone), or something like Autogenuity w GM Enhancement

-getting a subscription to the full-service manual for your truck, at a site like alldatadiy.com

[Consolenut]

my obd2 code reader says no codes it will need a tech2 or efi live to see deeper into the issue. Seeing whats going on in real time will be best. throwing parts at it isnt my plan.

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[C/K Man]

I would want to see fuel pressure under load.  Might be dropping off on you.  Check fuel trim with a scanner, see if it's running lean.

[Consolenut]

Ive ordered a fuel pressure test kit. So i can attempt to look at the pressure under load. Thw current plugs have 13k miles on them i just looked at my records I pulled a few plugs and 3 cylinders are clean. #8 is fouling. So i put in a new plug in #8 and new plug wire. Ill drive it a few days and pull #8 plug again. Ive also ordered an ac delco coil for it as well. Pulling #7 plug wire the boot ripped. So its got a new plug and wire in it as well.

So 1,2,6,7 are clean are a nice tan color at the base of the electrode. Maybe a tiny bit lean but not much. #8 was fouled quite bad. Upon installing the new plugs in 7, 8 i narrowed the plug gap to 0.45 as ive seen many references to it. If there still clean in a few days ill take the truck and rv for a ride to see if ive cured any thing. ill wait and see what happens with the plugs in the mean time. before i put in the coil that is suppose to arrive monday. Ill try and look at the other plugs tomorrow if not raining. To see if #8 is the only one showing any sort of fouling issue.

On a side note the idle has come up a tad on the tach just putting a fresh plugs on the two cylinders mentioned. in the pic below #8 is on the left. #7 on the right.

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