8.1 Reduced Engine Power

[AFLA]

My '08 Winnebago 35J on a WH Chassis had trouble starting and charging. When I checked all the battery cables I discovered that a Knife Switch disconnect was my culprit. I eliminated the switch and connected strait to battery. This solved that problem for me.
My rig is now in need of a resurrection after sitting idle way to long so I am very interested in all you have to say about 8.1 V8's.

[brunson67]

What is the knife switch disconnect?

[Unplanned Tourist]

Originally Posted by brunson67

What is the knife switch disconnect?

A manual cut-off for the battery like this one..........

https://www.globalindustrial.ca/p/ba...y+%7C+In-Stock

[TandW]

So that's quite a load. A misfire under heavy load will slowly load up one of the cats, causing backpressure and then compounding the problem. Then you shut it down and while cooling down the cat continues to burn off the obstruction. Off you go again later, with a misfire that happens under heavy load and it happens all over again.
When you open the throttle, cylinder pressures go up, and this is when some misfires tend to occur as it is harder to propagate a spark under higher pressures. The result is that the spark begins taking the easier route through failing insulation. The 8.1 wires have been a PITA for many of us. Cooling the engine bay starts with having an air tight forward bulkhead where the radiator sits. This eliminates recycling engine heat forward, especially when sitting at idle. Next, you need two 20 inch cooling fans mounted atop the frame rails and blowing directly against the plugs. Premium wires and plugs all around of course. Good luck!

[vagaron]

Originally Posted by Unplanned Tourist

A manual cut-off for the battery like this one..........



https://www.globalindustrial.ca/p/ba...y+%7C+In-Stock

I recently bought a knife blade type battery disconnect. Is the price for it on the link you supplied a joke? $794 ?!?! I bought mine on eBay for $15.

[vagaron]

Oh, I see. That was for a set of 12. But STILL... $66 each??

[vagaron]

I bought my UltraRV parts from Brazel’s RV, incl the computer upgrades for engine and transmission. They sent me a small recording module I can plug into the OBD port. I then upload the resulting file to Jon @ Brazel’s and he's always been able to diagnose my problems.

[Unplanned Tourist]

Originally Posted by vagaron

I recently bought a knife blade type battery disconnect. Is the price for it on the link you supplied a joke? $794 ?!?! I bought mine on eBay for $15.

Just some I found with a quick search. I don't really like them because there's another connection that can go bad.

If I have to access my battery to flip that switch, I may as well just disconnect the battery. That way you can clean the terminals when it goes back together.

[Full.Monte]

If you are running out of ideas, you might want to read my post from a couple years ago on this forum:

Workhorse 8.1 and Stalling...dealing with a real problem

It sounds like you are considering electrical problem and a couple others. Yet a solution is evading you. I am not claiming my solution is THE one you seek, but you might check. I can tell you that I fixed my problem. Once fixed, it has not happened again in thousands of miles. Mine turned out to be vapor lock. Yours doesn't appear to shut your engine down like mine did, but it could be a minor vapor lock problem that causes the slow engine performance without completely shutting it down. Here is my thinking. You are always towing a heavy trailer. The load produces engine heat....a lot of it. The gas system is designed to return unused gas to the tank, more specifically to the gas pump reservoir inside the gas tank. The hotter the day is, or the heavier the load, or the steeper the up-hill grade, the hotter that unused fuel is when it gets back to the fuel pump reservoir. On mine, it got so hot that it formed a gas bubble when the fuel pump tried to pump it back to the engine. I decided to take the return line and re-route it to the gas tank in a different place than the fuel pump cannister. This allowed the gas in the tank to cool down the gas coming from the return line, before it got pumped back to the engine. The solution worked. Good luck with your 8.1!

[brunson67]

Hi Full.Monte - At this point I/We have done just about everything we can to see if the problem is fixed, although I wont know for sure until we head out for our annual New Years trip to Ocotillo. We will be leaving Wednesday, December 29th. SO far here is what has been done - MAF cleaned, Throttle body cleaned (was really dirty with carbon build up), new air filter, new fuel filter, new plugs & plug wires, checked fuel pressure and it appears to be good, checked all engine grounds and cleaned, removed my "knife" battery disconnect, installed the CRecorder and drove it around town and on freeway and sent the data to Jon Brazel at Ultra RV he reported everything looks as it should. My local shop ran a diagnostic and found nothing, no codes, no miss fires, fuel trims look good. I like your suggestion, I also ran into this with my generator fuel pump, being right above the exhaust, and getting to hot during summer and creating a vapor lock, had to relocate the fuel pump. I'll definitely keep this in mind.

[ralphl]

I know this is late and you probably solved the problem by now, but just to add my experience with a bad MAF sensor on an 8.1. Coach missed when i put the gas pedal to floor going up hill. I cleaned MAF, but it didn't help. Bought a new one (a cheap after market one), installed it and everything was fixed. I have had problems with just cleaning MAFs before and had the fault remain. Apparently MAF failures are caused by more than just dirt. Just to let you know, when I put in the new MAF, I was very careful to not scar it so I couldn't take it back, which I would have done if it hadn't fixed the problem. I have had 3 MAF failures on various cars and the motorhome, so MAFs aren't the most reliable thing in the world.
One other thing. 8.1s are well know for having intake manifold gasket failures--sometimes venting to the outside and sometimes venting to the engine interior sucking in oil. A friend of mine had missing going uphill and finally traced it to a leaking intake manifold gasket. There are at least 2 GM bulletins on leaky intake manifold gaskets

[Arch Hoagland]

brunson67 ......... Any update available?

ralphl ........ I agree with your MAF and manifold statements. I've had problems with those items too on my 8.1.