Need ideas on 8.1 reduced power and MPG drop

Alfred622 · 08-19-2021, 02:46 PM

Driving a 2005 Winnebago Sightseer with Workhorse 8.1 engine. Almost always average between 8 and 8.6 mpg on the long straightaways.

Motorhome was stored for 2 years and not driven. Coming out of storage this year, it didn't feel that it had the normal engine power. I thought it might be the old gas. Has RV professionally serviced (oil, filter, lube, check all fluids, etc). Back now from a 1,000 mile trip (and several fuel-ups with fresh gas) I'm noticing:

1) MPG has dropped from about 8.6 down to 5.3 or so

2) Takes longer to accelerate from 0 to 60 that it used to.

3) At about 2100 rpm a significant vibration starts, in a few seconds the engine rpm jumps to 3000 (gearing down I assume) and the vibration ends. This is new behavior. Happens consistently at this 2100 rpm mark.

When cruising along at 60mph, the engine sounds normal.

Can anyone suggest what should be checked? Could I have bad spark plug wires (wasn't there a harness issue years ago with spark plug wires?), fouled spark plugs, maybe a gas filter clogging with old gas, or some other item to check?

I'd sure value any expertise you might have to offer!

Alfred

**Eagle5** · 08-19-2021, 03:40 PM

Hi Alfred,
The first thing to do is to get a code reading on your computer. Something certainly is wrong, and with the vibration, it would indicate the loss of a cylinder. If the engine cranks smoothly on start-up, it probably is an ignition issue. If the engine has an irregular crank, it is loss of compression. The codes will tell the story.
Eagle5

Alfred622 · 08-20-2021, 02:51 PM

Thanks Eagle5! Since the engine cranks smoothly on startup, I may have an ignition issue. I'll call the repair shop I use and see if they can work me in yet this year (groan).

I tried using an ODBC II reader that I have for my Honda CRV. I don't think it was able to connect to the ECU in the Workhorse. It is just an eBay cheepie ODBC reader, I may need to get a more sophisticated unit for the Workhorse. Nothing in the Workhorse manual about ODBC however.

Time to let the repair shop earn their big bucks!

Thanks very much!

catmandoo62 · 08-20-2021, 06:41 PM

setting a couple years i would check the plug wires,mice love plug wires,

Sparky19053 · 08-20-2021, 06:46 PM

Plug line or vacuum hoses. Also a stuffed air clean Mice love to build nest in air filters.

bigb · 08-20-2021, 07:08 PM

Yes like the other said first inspect all vacuum lines and wires, air cleaner. Starting the engine in the dark can sometimes expose bad wires but it's possible they might not leak at idle.
I remember one time my stepdad's Buick was doing a similar thing but it kept getting worse till finally it would barely run. I popped the air cleaner open and didn't see anything till I looked down the snorkel and there was his oil checking rag sucked in there.

DavidM · 08-20-2021, 08:41 PM

It could be that ethanol laced gasoline has turned to varnish and fouled the carb, assuming it is a carbureted engine. Remove it, partially disassemble and soak overnight in carb cleaner.

David

**Eagle5** · 08-20-2021, 09:53 PM

You know, it seems to me that if a hamster caused this loss of power, then perhaps that same hamster could be put to work replacing that power? Just a thought.

hamster power

bigb · 08-21-2021, 07:53 AM

Quote:

Originally Posted by DavidM

It could be that ethanol laced gasoline has turned to varnish and fouled the carb, assuming it is a carbureted engine. Remove it, partially disassemble and soak overnight in carb cleaner.

David

There is no way a 2005 model is carbureted. General motors was pretty much done with carburetors by the early 1990's.

wwr · 08-21-2021, 07:03 PM

i have a 05 with 8.1 my mileage went from 8.2 to 4.9 code 131 and 141 o2 sensor low voltage changed both o2 senors plugs wires coils fuel filter worked great for 70 to eighty miles now light back on and mileage back in 4s don't know yet working on it

Chitter · 08-25-2021, 04:25 PM

I have a 2005 Adventurer with the Workhorse 8.1. I ran into the same problem with loss of power. The previous owner warned me that when that happens it is most likely the air filter. Even though it might look fine he suggested I change it anyway. Well sure as poop it happened to me a few times. I replaced what looked like a perfectly good air filter and power was back to normal. I now carry several air filters with me.
I hope that helps. For me it turned out to be a cheap easy fix.

Bmoredad · 08-25-2021, 04:31 PM

Weird Mines a 2004 chev 8.1 WH winni siteseer 30b . I'm having about the same worse after heats up . A few weeks ago I couldn't even back into the campsite . Once I entered another that I had to get a running backward start .the auto park brake failed . Nice had just fixed it before I left .brown rotten switch. At the edge of the street we set camp around 930pm ugh. I was thinking the pumps whining its the relay .put it in fixed .yet loss of power and the rumbling I had just had tires put on the front. I figured they weren't balanced properly. Dam what's going on cause I had already replaced fuel filter air filter. Oh and I assume they have a throttle body looks just like a carb but for the computer generation.

mariner949 · 08-25-2021, 04:53 PM

Quote:

Originally Posted by Alfred622

Driving a 2005 Winnebago Sightseer with Workhorse 8.1 engine. Almost always average between 8 and 8.6 mpg on the long straightaways.

Motorhome was stored for 2 years and not driven. Coming out of storage this year, it didn't feel that it had the normal engine power. I thought it might be the old gas. Has RV professionally serviced (oil, filter, lube, check all fluids, etc). Back now from a 1,000 mile trip (and several fuel-ups with fresh gas) I'm noticing:

1) MPG has dropped from about 8.6 down to 5.3 or so

2) Takes longer to accelerate from 0 to 60 that it used to.

3) At about 2100 rpm a significant vibration starts, in a few seconds the engine rpm jumps to 3000 (gearing down I assume) and the vibration ends. This is new behavior. Happens consistently at this 2100 rpm mark.

When cruising along at 60mph, the engine sounds normal.

Can anyone suggest what should be checked? Could I have bad spark plug wires (wasn't there a harness issue years ago with spark plug wires?), fouled spark plugs, maybe a gas filter clogging with old gas, or some other item to check?

I'd sure value any expertise you might have to offer!

Alfred

Given 2 years in storage and what sounds like a plug wire issue, suggest check for rodents chomping on your plug wires.
If wires are intact check that the plug wires are secure on all 8 spark plug tips.
I have an '04 Sightseer 35N with Workhorse 8.1. Slightly different cause but the symptoms are the same as you're reporting.
I had the shop replace the plug wires as routine maintenance. When I picked up my rig it had reduced power, the idle was rough, gas mileage was lousy.
Took it back to the shop and they found they hadn't set the plug wires perfectly on 1 plug. They snapped it in place and she purred like a happy kitty.
I'd be interested to learn what your resolution is so please post when you can.

Bmoredad · 08-25-2021, 06:56 PM

Thanks I think myself I will be getting wires and plugs . How does everyone get parts at a regular store napa fishers advanced? In my experience with two other rvs they can't look up winnebago. Unless someone has part numbers Mines the same basically. 2004 winnebago siteseer 30b chevrolet workhorse 8.1
Thanks to all
Be safe

mikemakay · 08-25-2021, 07:15 PM

I had the same thing happen to my 02 8.1 engine in my brave. Turns out it was my spark plugs and wires. Had them changed out to new and all was good.

HappiHenri · 08-26-2021, 08:26 AM

As many others have suggested - get an OBD reader and see what faults it shows. Very useful tool to have anyway.

Is your check engine light on? If engine is mis-firing it should be.

On our 2005 Adventurer with the same engine here is what I found:

Replaced all speak plugs, and spark plug wire set after noticing mis-firing and roughness. Also installed new air filter as good air flow is critical.

Still had problem so finally replaced the 2 harnesses which run across the top of the engine and connect the individual spark coils. That fixed the problem. Turns out they are very small wires which had lost connnections over time due to drying out grease on them and from vibration.

Got all parts from Amazon. Found the AC Delco plug wires to be better quality than most aftermarket, very expensive, plug wire sets.

For your case - again - get an OBD reader. One of the issues with this engine is that if it detects an engine fault it goes into "limp" mode, meaning that to protect itself it cuts back all engine management settings - giving you reduced power and poor fuel economy. But clearing codes with your OBD reader will restore it to proper running settings - as long as you have fixed the problem(s) which caused the Check engine light to go on in the 1st place.

barneybak · 08-26-2021, 02:52 PM

I have the 8.1, 2006. I did the following: Changed sparkplugs ( AC 41-101 ) .045 gap. UltraPower plug wires ( SPW8100 ) make sure the metal heat shields are installed. Clean the MAF sensor. Change frame mounted fuel filter ( p/n; WHG481FK ). All info was sourced from the Workhorse chassis link. Good Luck.

Alfred622 · 09-02-2021, 10:19 PM

Just to let everyone know... my issue was Spark Plug Wires. The misfire started getting worse after 8 hours into a 9 hour trip. The next day when I took it to the repair shop it was behaving. The shop diagnosed the degraded wires and replaced them with new. A ninety-mile road test later and I do believe the problem was solved!

**Eagle5** · 09-02-2021, 10:40 PM

Hi Alfred,
That makes sense. A bad plug is a consistent problem, and the plug wires tend to be an intermittent problem. Glad you have it fixed!
Eagle5

SmilingSimon · 09-07-2021, 02:31 AM

Personally I would think you were LUCKY to EVER get 8mpg unless very lightly loaded !!! As generally for 'real' roads it is 5-7mpg if loaded at all for 50+ mile averaging.

If possible, switch to your 'instantaneous mpg via trip mode' I have seen 1.5 to 20 mpg !!! A shocker and relief !!

GL !