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Old 07-06-2022, 04:33 PM   #1
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8.1 Workhorse running rough backfire

We last used the motorhome in Sept. it is a 2003 Winnibago Adventurer v33 with 8.1 workhorse ran great last fall. Took it out on pulled out of the garage on Thursday OK Leaving on Saturday didn't know if we were going to go or not ran so rough too much throttle and misfire backfire changed the air filter and cleaned the MAS not change ran about 60 much more than that and it fought it. Back home now suggestions?? What plugs should I purchase and change, I know that is almost like asking ford or chevy everyone has favorites I have not have the cover off the engine yet to see what it is like. Also any recommendations for a OBD scan tool?? I can hear a definete miss on the right bank in the exhaust and smell very lean. Probably would not hurt to run a couple of bottles of injector cleaner in the fuel tank now that it is down to half a tank.
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Old 07-06-2022, 04:54 PM   #2
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Would be nice to get a look at the top of the engine, looking for nests and gnarled wires.
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Old 07-06-2022, 06:35 PM   #3
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Do you mean you cleaned the MAF?

Have the plugs and wires ever been changed?
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Old 07-06-2022, 07:09 PM   #4
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We had a similar issue. In our case the fuel (even with Stabil) gasoline additive, in the tank over the winter caused our RV backfire under load. We ran the tank down to a 1/8 tank, then added 20 gallons. Repeated this until we got about 100 gallons through the system. We also replaced the fuel filter for good measure.
It took a bit, but she now runs happy, even under load climbing a hill.
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Old 07-06-2022, 09:26 PM   #5
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That engine was notorious for burning plug wires. However, they usually don't go bad overnight and manifest as a misfire while climbing (under load).
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Old 07-07-2022, 01:38 PM   #6
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I'd first eyeball things to see if there was anything obvious such as chewed wiring or dry rotted tubing. The next thing would be, and I have a feeling this might fix the problem, is to replace plugs and plug wires.

General consensus is that the AC Delco Iridium 41-101 plugs are the way to go. The wires I went with when I had to problem were the Ultra RV Magnums.
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Old 07-07-2022, 03:21 PM   #7
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Try to run it with dog house removed & dark to see if plug wires are shorting / arcing... a lot more visible in dark than day light. Check distributor cap for any moisture.
New plugs,bwires & cap never hurt anything if it has been awhile since last change. If you change wires get the best racing wires you can with heat shields.
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Old 07-07-2022, 03:33 PM   #8
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Quote:
Originally Posted by Dutch Star Don View Post
That engine was notorious for burning plug wires. However, they usually don't go bad overnight and manifest as a misfire while climbing (under load).
x2
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Old 07-07-2022, 06:01 PM   #9
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I have also found these engines (the ECU actually) is VERY sensitive to low battery voltage. If you unit was sitting any length of time without a battery tender, try giving the battery a good over night charge and run it again.
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Old 07-08-2022, 09:32 AM   #10
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Check your fuel pressure.
If you did get a good backfire, look closely at all manifold vacuum connections. I've seen them get blown off from backfire ,then will continue to run like crap with large vacuum leak..
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Old 07-08-2022, 09:45 AM   #11
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X2 on the Ultra RV plugs and wires.............
X2 on checking fuel rail pressure.

Mike in Colorado
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Old 07-11-2022, 07:05 AM   #12
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BackFire

Quote:
Originally Posted by WhidbeyBruce View Post
We last used the motorhome in Sept. it is a 2003 Winnibago Adventurer v33 with 8.1 workhorse ran great last fall. Took it out on pulled out of the garage on Thursday OK Leaving on Saturday didn't know if we were going to go or not ran so rough too much throttle and misfire backfire changed the air filter and cleaned the MAS not change ran about 60 much more than that and it fought it. Back home now suggestions?? What plugs should I purchase and change, I know that is almost like asking ford or chevy everyone has favorites I have not have the cover off the engine yet to see what it is like. Also any recommendations for a OBD scan tool?? I can hear a definete miss on the right bank in the exhaust and smell very lean. Probably would not hurt to run a couple of bottles of injector cleaner in the fuel tank now that it is down to half a tank.
After sitting for so long, the first thing I would do is replace the fuel filter.
The replace it again after about 4 tanks of fuel.

Backfiring is often caused by a lean condition, like a blocked fuel filter.
Water condensation is a large issue, we assume you have new fuel in your tank?

Go through and do a complete service of the RV, replace antifreeze, transmission fluid, .....

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