8.1 Performance Problems

[Bill Senick]

I will try and explain this the best way possible. Approximately 4K miles ago I had a complete tune-up (plugs and wires) done on my 2003 Kountry Star 3740. The coach ran perfect from Florida to Arizona and back, however about 30 minutes from my house we hit a tremendous rain storm, I started to have a slight miss but was able to come home and park the coach.

Now fast forward 10 days, left home for trip to Clemson, SC, about 20 miles from home the engine started to miss and when under load sounbded like the old days backfiring through the carb. I drove another 20 miles until I was able to purchase a new air filter from NAPA, replaced filter and still had the same problem although not as severe, found as I continued to drive the miss and backfiring got less and less and if I drove without cruise and did not floor the gas it ran perfect.

Now it only misses and backfires once or twice under full power and I do notice a loss of performance under full power conditions.Could their possibly be a problem with the MAF and would you recommend a good cleaning. I am now in SC and will be leaving for KY this Monday. Any help or Ideas will be greatly appreciated.

Thanks, Bill Senick

[Bill Senick]

I will try and explain this the best way possible. Approximately 4K miles ago I had a complete tune-up (plugs and wires) done on my 2003 Kountry Star 3740. The coach ran perfect from Florida to Arizona and back, however about 30 minutes from my house we hit a tremendous rain storm, I started to have a slight miss but was able to come home and park the coach.

Now fast forward 10 days, left home for trip to Clemson, SC, about 20 miles from home the engine started to miss and when under load sounbded like the old days backfiring through the carb. I drove another 20 miles until I was able to purchase a new air filter from NAPA, replaced filter and still had the same problem although not as severe, found as I continued to drive the miss and backfiring got less and less and if I drove without cruise and did not floor the gas it ran perfect.

Now it only misses and backfires once or twice under full power and I do notice a loss of performance under full power conditions.Could their possibly be a problem with the MAF and would you recommend a good cleaning. I am now in SC and will be leaving for KY this Monday. Any help or Ideas will be greatly appreciated.

Thanks, Bill Senick

[troth]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Could their possibly be a problem with the MAF and would you recommend a good cleaning. </div></BLOCKQUOTE>
Yes. Napa has spray MAF cleaner. Be gentle.

[JonBrazel]

Sounds as though you perhaps have a burnt spark plug wire. When the tune up was performed, what kind of plug wires did they use?

[edgray]

BILL: the symptoms you describe are classic results from excessive moisture effecting the MAF sensor to ECM signals, which results in the engine "thinking" there is not sufficent air flow, thus the ECM cuts fuel delivery and probably other "timing" issues creating the mis fires and stumbling.

In addition to replacing the paper filter and cleaning the MAF-hopefully you won't have to replace it- you need to SEAL the filter box. There is a plastic push pin holding the forward facing hose transition piece into the rounded part of the filter box housing. I bet you will find a small gap somewhere around this area where the transition piece mates up to the filter housing.

I totally removed my filter box, cleaned inside and out with alcohol wipes and then used silicon sealer inside and out all around this "snapped together" joint. I also replaced the plastic push pin with three machine screws and nuts to ensure a solid connection across this bottom flange.

Result: no more water ingestion.

IMO, this filter box assembly was not designed to withstand the environment inside a wheel well, where even damp roads will create a fine mist spray which is being sucked into it. The box would be fine in another location, but the box builders apparently do not see fit to relocate it to "dry" location, rather it remains where WCC installed it on the bare chassis. Since I don't see any changes coming from the manufacturers, a pro-active approach using silicon should prevent you having any further issue. Good Luck. ED

[Finhawk]

Is that mounting location the same in the newer coaches?

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Finhawk:
Is that mounting location the same in the newer coaches? </div></BLOCKQUOTE>The air cleaner box has been in the same location since 2001 on all W Series chassis.

[Bill Senick]

Thanks, edgray I will clean the MAF and seal the air box as soon as the rain stops, however if I need to replace the MAF is this a standard GM part, WCC part or are their aftermarket available and if you know, the approx price.

I love my coach but after all the brake related problems, four A/C compressors (and still does not work)incompetent repair facilities I am about to haqng it up and go to a diesel pusher, bath and 1/2 of course.

Thanks again for all of your help, I will let you know the outcome.

Bill Senick

[max49]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JonBrazel:
Sounds as though you perhaps have a burnt spark plug wire. </div></BLOCKQUOTE>

I think so too. IMO that's the first place to look when the 8.1 misses under load. I'd start in the back of the engine on the drivers side.

[oemtech]

Bill,

The MAF used on the 8.1L is nothing special. It is a standard 85 mm version that is used on lots of GM engines. I got one off Ebay (new) for $26 plus shipping (maybe $10). I posted this info on the following thread GM/Delphi - MAF

OBTW - I have the $26 one on my coach at this time and have been running it since Jan.

[Capt Joe]

Just had the same problems with mine and thought it would be plug wires. Scope showed #6 cylinder wasn't firing. Tests showed a bad coil on that cylinder....replaced the coil and all is fine now.
Taking a day trip to a cookout at a friends farm (100 miles round trip) with a load of 10 people tomorrow so I'll get a good test in before our next trip.
Hope yours is as easy of a fix. Let us know how yours turns out.
Good Luck!!!

[Bill Senick]

I still think I am on the right track with the MAF, I always thought that a burnt plug wire or bad plug coil wouldn affect the performance at all RPM ranges, tell me if I am wrong.

Just a side note, its 9:55pm and I just looked at the engine as it was running and had no indication of plug wire arcing. I have had plug wires go bad in the past and it was obvious throught all RPM ranges. Engine idles and revs up without a hint of miss.

Thanks for the help, hopefully in the morning I will clean the MAF, will not be able to road test until Monday, at a horse show and will leave for KY.

Bill Senick

[Full-Timers]

I have burnt 4 plug wires on my motorhome and the last one showed no signs of being bad until I put my foot into it. It seemed to run fine cruising down the highway and at idle but as soon as I tried to pass or climb a grade it would act up.

[Joe Gilbert]

It is not impossible for a MAF to fail however, it is highly unlikely. You seem to have eliminated the air filter though a wet filter will behave exactly as you describe. A bad coil, plug, or plug wire can also behave as you describe.

I'm not sure if your coach is one of the ones which are known to have air flow/plug wire problems or not but I'll bet it is a plug wire (since changing the air filter did not correct the problem).