Vortec 8.1 hesitating on acceleration and under load

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drisley

drisley

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Aug 11, 2013
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Currently out west from Florida, riding on the W22 with the Vortec 8.1. It recently began hesitating on inclines. And today?s even on acceleration from a stop. Didn?t notice any of this until after I had to climb a long grade on the way into Monument Valley. I downshifted it and it seemed to have a lot of power. But on another incline, the hesitation began. Almost like something happened on that long climb.

Spark plugs and wires were replaced last year. Air filter replaced. I cleaned MAF sensor. No codes (I have a Scanguage). No audible backfiring. Just a hesitation you can feel as it climbs hills. And I feel like I have to practically floor it, but it just doesn?t have more to give. No overheating. Engine sounds totally normal. Doesn?t appear to idle weird.

Any ideas? I?m currently outside Zion and got a lot of driving ahead of me before I return to Florida. Want to get my power back.
 
MY GUESS is the plug wires are arcing due to long periods of high heat. M y 454 would do the same thing. I have put on racing wires with ceramic boots and fiberglass cover and installed headers.

The reasoning is the dog house is so small that numbers 7 and 8 plug area runs to hot for the wires.
 
How could I check that? And would that make sense seeing as these wires were put in just a year ago?
 
Are you headed towards Salt Lake City? i know a good shop there. Meanwhile I'm with darsben on the wires. 

You could take the doghouse cover off at night and rev the engine to see arcing between the wires.

Who put the wires on and where did you buy the wires?

How many miles on the coach
 
Wires came from a shop in North Carolina when I asked them to do a tune up. I don?t know the brand.

Just under 50k miles on it.

Looks like your coach is quite similar to mine at the mechanical level.
 
I've never had good luck with aftermarket electrical items of any sort for my vehicles, especially plugs and wires. 

Let us know what finally cures it.
 
No engine will run correctly if it has fuel delivery problems. Electric in tank fuel pumps can go 40k or 200k. I'd check the fuel pressure and volume. Fuel pressure means nothing if it can't deliver on volume.
There should be a Schrader valve to attach a pressure gauge. If the valve core is removed and a hose is attached it should fill something like a pop bottle rather quickly, no dribbling or surging pulsing.

I agree with the statement about aftermarket wires. I always buy OEM. It's also good to not just replace the original wires as a maintenance item. If there is a problem after ohming out a wire some oem sell individual wires. I have seen GM vehicles pop, spit and sputter and barely run with aftermarket wires. Worse case I've seen a friend replace sensors and other parts all the way to replacing the intake manifold gasket. I told him you go to Chevy dealer and get cap rotor and wires. Instantly ran perfect.
 
My first thought would be a dirty fuel filter, starving the engine when the horsepower demand is high. Your rig is 16 years old and has probably used a lot of less-than-clean gas, plus sitting around a lot. A gas tank tends to accumulate moisture (condensation) when in storage and the water combines with other particles to form and gooey sludge that can clog a filter.  Besides, a filter can become clogged after just one tank full of dirty gas  and there are many fuel stations that have old and dirty storage tanks.

I'm guessing you have a Workhorse chassis with that 8.1L and they usually have the fuel filter near the front on the driver side.
 
So, had a guy come put his computer on it and the only thing that comes up is low fuel pressure. So we?re replacing the filter. He said it was old and seemed pretty clogged when he blew through it. So, as of now, that seems to be the issue. I?m gonna get 2 filters so I have one handy if it happens again. This guy saved me a lot of trial and error, but if I had known it was just the filter I could have done it myself. :) It?s all good. I paid for time and confidence.
 
BUT, you didn't have fuel running down your arm. :)

If you do wrench on vehicles a pressure gauge is handy. Get a better model. It looks like they sell some with an additional valve and hose which probably let's you dump through the hose to see volume. Mine just connects to the Schrader for pressure. How old is your pump?
 
True. :)

We?ll see what happens. The pressure still read a little low after replacing the filter, but the filter was definitely in need of replacement. Pressure did increase and it will help fuel volume. So we shall see. We didn?t road test it, but will watch when we travel down to Vegas later this week.

Edit: I?m sure the pump is original. No reason to think otherwise.
 
As a follow up, we drove to Las Vegas (where we are currently) and the engine performed fine for the first hour or two. Then it began to hesitate again and lower power when climbing hills. Apparently the fuel filter wasn?t the full solution.

Might just proactively replace some spark plug wires here.

Hard to duplicate conditions with a mechanic and the computer because it only happens when engine is warm, loaded.
 
If issue was spark plug wire, would it ONLY show up in these conditions? As I said before, the mechanic didn?t find anything on his computer indicating misfiring.
 
If you have a lot of crud in your fuel tank, the fuel filter may have clogged up again.  If you refueled at a station that had a bad underground storage tank, or one that had just been filled and stirred up all the crud at the bottom, you may have a dirty fuel tank in yur coach. It's not common, but it happens.  You might check again to see if the low fuel pressure problem has recurred.

I'm not trying to rule out plug wire problems, but they are not common in modern engines, especially when only 6 years old & 50k miles.  Nor is the 8.1L particularly prone to the cylinder 7-8 heat problem of the 454 V8.  But since the OEM plug wires were replaced (why?), it's possible the new ones are poor quality or poorly installed.  Might not hurt to get a top quality set and replace again, just to be sure.  The Delco replacements run around $50 online, and "racing" grade ceramic wires around $100-$125.
 
Any heat shields been removed and not put back?? (Original wire set changed out)
 
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