Workhorse Hesitation with Load

I have a 2004 Winnebago Workhorse Vortec 8.1L Suncruiser with 40k miles.  I use the unit as my work apartment so I travel weekly from home to work from for my two day work week.  I live in rural Tennessee and travel mountainous roads to the city and started having hesitation on acceleration going up hills. 

I followed a previous post on the RV Forum but it seemed to drop without a solution.  I have taken the unit to a dealer in Kentucky who I trust and have replaced wires and sparkplugs.  They thought it was the catalytic converters but the muffler shop I took it to said they could change them but it was not my problem... WOW an honest muffler shop.. (grin) They suggested a mechanic who was "honest" who I traveled to see--yep he does not work on big rigs but suggested trying Chevron Techron fuel cleaner which seemed to help at first.  I called the dealer I use they said BRAVO... unfortunately, it was only a temporary fix.  They have suggested I run as much of the fuel out as I could possibly get out--then add the additive and fuel up with premium fuel in the process of doing today.  They seem to think I have gotten some bad fuel.  I always bring the unit home with a full tank of fuel.  I boondock at work so I run the generator for a couple of hours after work to recharge batteries and to run the microwave.  Usually I burn about 30 to 35 gals of fuel per week.

If there someone has traveled this road and has the solution I would be grateful.  Thank You.

I've been down that road with my coach. At risk of jinxing my fix I'll tell you what I found. Your mileage may vary.

My miss would occur on grades that caused a shift out of overdrive to 4th, then to 3rd. There was a slight miss pulling in 4th, but when it downshifted to 3rd the miss was very pronounced.

I did all the things you described with the same results. There was never a "Check Engine" light nor were any codes stored to give some guidance. Then one day we were pulling a grade near Monteagle, TN in the rain. This time I did get the Check Engine light. The code indicated a problem with the MAF sensor.

My son pulled the MAF sensor out (accessible from the right wheel well) and we cleaned it and reinstalled. I had done this before as part of my shotgun approach.

The next few days of driving (Georgia to Arizona) were uneventful with the engine running great. Then we hit heavy rain and the problem was back. Once we were settled in Arizona I gave close inspection to the connector on the MAF. It is where it gets wet driving in rain. I found that one of the pins had some corrosion. I thoroughly cleaned plug and socket and applied a film of De-Ox to them. I also applied a good layer of dielectric grease to the sealing surfaces of the plug and socket. Hopefully that will keep the moisture out.

The coach ran great on the return trip to Illinois. Weather was good except for a medium rain the last 150 miles. I'm not quite ready to declare a clean bill of health but I do have confidence that I found and fixed the problem.

I'm not sure if the corrosion was there when my son removed & reinstalled. I suspect it was and he missed it. Tough to see the pins.

I second checking / cleaning the MAF, also check the fuel pressure regulator, if yours has one, I think they were eliminated around 2004 or 2005.

If you haven't done it yet, change the fuel filter.  It's usually found along the frame member on the driver side, toward the front. A dirty tank of fuel is enough to partially clog it, reducing max fuel flow. And of course it gradually accumulates dirt over the 16 years it has likely been cleaning your fuel.

Check the fuel pressure.

Thank you for your suggestions as I continue to work through this process.  I did run all the fuel out of the motorhome yesterday.  When I filled up it held only 68.5 gallons of the 70 gallon tank.  I put the Chevron Techron fuel additive in first and then filled the tank with Bp Gold 93 Octane.  I can tell you I was nervous to run it that low but I was going all in for this theory.  The first 50 miles I still had some hesitation but not as bad as it had been.  I was driving in rain mixed with snow on the trip.  I stopped for about an hour started back home for the final 50 miles home.  I cannot remember when the coach has run this smoothly.  I pray my workhorse is not addicted to 93 Octane fuel @ todays prices not so bad but Fuel in my area is $1.49 for 87 octane and $2.02 for the 93 Octane or about $35 more per fill up.  I suppose at $135 per hour of mechanic time it is a bargain.

I do think it is a good idea to check the MAF sensor, check the fuel pressure, and change the fuel filter.  I do hope this is a remedy for the hesitation and rough acceleration on my workhorse.  I thank all of you who had suggestions I am encouraged by the positive support from the forum!  I will keep you posted to the progress we make.

Thanks,

A Grateful HoboTWD 

I'm afraid that is wishful thinking.  93 octane allow for greater compression of the fuel and thus the engine can produce more horsepower.  Your engine can't run any better on 93 octane than 87 because it compresses the fuel exactly the same regardless of octane.  If your engine knocks or pings with 87 but not 93, you have an engine malfunction that needs to be fixed, e.g. MAF, O2 sensor, etc..  Besides, I'm pretty sure your 8.1L V8 has an anti-knock sensor built in and retards the spark a bit if a knock/ping occurs. You would lose a bit of horsepower but it would not appear as a momentary loss or hesitation.

When I filled up it held only 68.5 gallons of the 70 gallon tank.

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Kind of a side note, but aircraft manufacturers must rate the fuel tanks with not only total capacity but they also must list usable fuel quantity. Unfortunately ground vehicle manufacturers are not required to do this, though all tanks will have folds, creases or whatever that will make some amount of fuel unusable.

Gary, the anti-knock sensors on the 8.1L have a problem detecting high speed knock, and generally only detect knock at idle speeds, which is one of several limitations of the ECM which it inherited from its predecessor the 7.4L Vortec, another is the lack of a fuel pressure sensor, so it always assumes the pressure regulator is doing its job, and that the fuel pump is supplying enough fuel.

Good to know, Isaac.  I drove a coach with the 8.1L for 4 years, including over the Rockies using the lower 85 octane fuel commonly found at higher altitudes.  Only experienced a momentary ping a few times, at around 9000 ft. It immediately ceased so I figured the ECM anti-knock program kicked in, but maybe not. In any case, it doesn't act anything like what I would call "hesitation".

Please describe this "hesitation". In my mind it means there is a delay from the time you press the accelerator pedal down and then runs normally. If this is what you're talking about, i would suspect a timing problem.

Well--I did have wishful thinking!!! met with huge disappointment!  My problem is not fixed and could possibly be worse.  Hesitation, is rough acceleration even a loss of power.  I am pushing the gas pedal further than usual to get it to increase power.  It is almost like the engine bogs down then when it shifts to a lower gear then again rough not a smooth engine running.

This is a discouraging event today but, I will persist to find the solution.  Thank all of you for your insight and experience.

Thank you!

HoboTWD

I would suggest getting to the bottom of this sooner rather than later as you may be doing damage to the engine.

HoboTWD said:

I am pushing the gas pedal further than usual to get it to increase power.  It is almost like the engine bogs down then when it shifts to a lower gear then again rough not a smooth engine running.
HoboTWD

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We have the Vortec 8.1 in our 2005 Pace Arrow.  Don't recall a rough engine but there are times on a grade when it will not downshift until I take my foot off the pedal and hit it again.  But I've had the same issue with every vehicle I've owned.  Not every time but enough to remember.  In spite of that issue, if it even is an issue, it runs like a champ the rest of the time.   

As promised I want to follow up with my workhorse Hesitation with Load and if it was fixed or not.  The best news is yes Larry at Larry's Auto Clinic diagnosed and repaired the issue.  WOW and it only took about five hours.  Larry is a gift! 

The issue was the coils.  The coils on my Workhorse were producing 9 to 10KV and were after market coils replaced prior to my purchase.  The Workhorse requires 11.7 to 13.2KV to operate properly.  Larry and is mechanic Justin replaced all coils with AC Delco # 12558693 and the motorhome has never ran this good.  It is an unbelievable difference and something that should have been easily tested by the numerous repair shops we tried before Larry's Auto Clinic in Myrtle Beach SC. 

My biggest lesion of this challenge is to use ONLY original replacement parts no substitutions.  I will only purchase the original equipment from here on out.  When I dealer says "oh its the same thing just cheaper..." always say no I want the original replacement parts.  This was a simple repair for a shop that knows their trade!!  I have returned two other times to have Larry make other repairs and I am completely satisfied.  Thanks Mike for the referral and Thanks to Larry what a blessing!

Larry is a warrior--he has devoted his life, knowledge, skill, and love to help others.  I am honored and privileged to know Larry  and had the opportunity to work with him. 

Good to know and glad you solved that problem.  Maybe Larry can recommend a Workhorse expert in the So Cal area.

As I was reading this thread through I was confident the answer was going to MAF or coils. With low mileage, it's crazy that either would be an issue but it was definitely gonna be one or the other.

So many shops put crap aftermarket coils on cars it's criminal. OE coils are always the right answer... especially when it comes to GM, as their factory coils are remarkably high quality. People use GM coils in upgrades & projects because they're that good.

It's not a bad idea to keep the crap aftermarket coils in storage somewhere in case of emergency, though... it's nice to have a fall back option even if it's not perfect.