Home » Public Forums » GMCnet » GMC MOTORHOME POWER LOSS PROBLEM (STRICKEN FOR YEARS WITH POWER LOSS-ASKING FOR HELP)
GMC MOTORHOME POWER LOSS PROBLEM [message #292162] |
Tue, 15 December 2015 10:35 |
Gatsbys' Cruiser
Messages: 91 Registered: August 2014 Location: Illinois
Karma: 0
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*** First, let me apologize for bringing this to the table. I do not like to bring my problems out to anyone else, preferring to find a solution myself. I do not like to bother anyone else. However, this problem has lasted almost if not 10 years, has restricted any kind of travel and is becoming a money pit. If any of you could come up with a solution I would owe you so much, I can never repay you. So, here is my delema ***
Hello folks. I have a bad problem that has plaqued the GMC for years now and my mechanic and I are running out of ideas. Here is the history...
*** When I bought the GMC, I headed home and experienced a power loss. This occurred miles down the road and started at 65 but as the miles added up, the top speed slowly began to go down. After having the distributor replaced by a GMC dealer ( I did not know at the time but it was NOT the Motorhome type, but it turned out it didn't matter because there was NO VACUUM lines working thanks to the PO cutting them off. Only the brakes had vaccuum. I was able to drive with no problems other than a gas leak at fill up. It was the fuel lines.
***After having the fuel tanks inspected and fuel lines replaced, it experienced a power loss. At first could'nt get above 35mph. It was determined that the carborator had a problem but the 3 rebuilt carbs that were put on, didn't make any improvement. The distributor was changed out with a used one from a GMC motorhome and the used Carb from a GMC motorhome and it seemed to run ok.
On the way home everything seemed ok until I refueled. Upon setting off from the gas station the power loss occurred at 55. We pulled over and tried to figure out what was going on but couldn't find anything. We sat about 30 minutes, then started back on the road. The power loss problem did not come back until we refueled again. After stopping for 30 minutes, we headed home and no problem again????? This would happen all the way home.
***I took it to the mechanic and he made some adjustments to the carborator and the problem seemed to be gone. He had found that the vacuum lines were not connected so he put vacuum back to the distributor.
***Went on a 6 hour trip to some friends place where I stayed a week. I did not, that I can determine, experience any problem on the way to thier cabin. After being there a week, Time came to go home and she started up ok, stopped at a gas station to fill up and as we started down the road, the power loss was back at 55 mph. The problem would be there all the way home but this time my top speed would decrease until I was trying to get as fast as i could go to be able to "coast" over the hills and bridges. I was able to limp home.
***It was determined that the carborator needed to be over hauled so that was replaced with rebuilt one and the fuel pump was replaced and a in line fuel filter was added. The problem seemed to be gone. I did take a couple of trips that seemed to be without a problem but the problem returned on a return trip.
***It was taken back for carborator adjustments again, inspection never turned anything up unusual visually. Timing was checked, plugs, wires, coil.
***Winter was here and the GMC was stored. I tried to start the GMC occasionally since she did IDLE very nicely. Come Spring, the GMC was to be at the mechanics to try to find the problem again. Over the coarse of Winter, The GMC was now becoming hard to start, I suspected The fuel was draining back to the tank and the fuel pump struggled to bring fuel back up to the carborator. It became harder to start until she wouldn't start at all. The problem was fuel and I tried different ways to get fuel to the carborator, nothing worked. I ended up using an external gas can and electric fuel pump to get her to start. With this crazy configuration I drove it to the mechanic again.
***This was going to be the final repair. Everything was checked, wires, distributor, timing. We found cracks in the manifold so that was replaced and the cross overs blocked. Replaced the fuel solenoids and added an electric fuel pump to purge after sitting a long while. The fuel filters were replaced, But the carborator was not responding to any adjustments. There was no warrentee being honored on the carb so I told the mechanic to open it up and inspect it.
What he found would be shocking. The carborator was full of RUST. The rust had infiltrated everything and was determined to be unrepairable. The filter at the carborator was plugged solid with rust. We cut open the fuel filter back by the fuel solenoids and it was CLEAN. So where was the rust coming from? We cut open the fuel pump and it was destroyed by rust. The interior was rusted out.
The fuel pump was replaced, the fuel lines forward the fuel pump replaced and I found a GMC motorhome carb that was rebuilt, had been used and stored on a shelf for a year. I purchased the carborator and it was installed.
We started the GMC up, she idles like a new car. No vibration, smooth as silk. We took it for a test run, got it up to 65 mph but had a hesitation. We found that the right front brake was stuck braking and thought that might be the problem. In the Spring, The brakes were gone through and we ran her for a test again. This time top speed was 45 mph.
We've tried to get the adjustments on the carb but the power loss occurrs at different speeds from 35mph to 45mph. Cant get her above 45mph.
We are fast losing faith and the mechanic is scratching his head. Nothing seems to be helping. Do note that when she idles she runs like a fine tuned machine.
***We have tested for fuel volume and seems to be ok. Our next step will be to run it off of an external tank to see if the problem clears up. But being we were up to 60 before the problem occurred last year, this seems to be over kill. But we have replaced everything I can think of and the problem persists.
We are actually talking about having the carborator rebuilt professionally in the Spring, I don't know if there are any other options.
I am very near taking her to a GMC dealer next year and see if they can figure it out. As Winter is upon us I can only try a couple of simple things before putting her in storge over Winter.
If anyone can shed any, and I mean ANY idea on what is going on???? I would be very grateful.
I appreciate any time or help you can shed on this problem. I am at wits end after all these years.
Thank you for reading
slc
slawrence111 (at) yahoo (dot) com
847 (dash) 662 (dash) 6707
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Re: GMC MOTORHOME POWER LOSS PROBLEM [message #292164 is a reply to message #292162] |
Tue, 15 December 2015 10:55 |
Anonymous
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hi Gatsbys' Cruiser,
I think that the rust is coming from the fuel tank(s).
you can try using a clear glass fuel filter that can be disassembled and cleaned and every time is gets clogged, clean it out and go until it clogs again then repeat. this usually works but in some cases the rust is so bad that its not worth the hassle to keep doing this over and over. if it doesnt clear out after 5 tries on cars, I drop the tanks.
so probably best to just drop the tanks and inspect then and if salvageable, clean or have them cleaned.
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Re: [GMCnet] GMC MOTORHOME POWER LOSS PROBLEM [message #292188 is a reply to message #292162] |
Tue, 15 December 2015 12:38 |
Ken Henderson
Messages: 8726 Registered: March 2004 Location: Americus, GA
Karma: 9
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Stan,
I long ago did what I now recommend to you: Install two electric fuel
pumps (I like Carter 4070's) back near the fuel tanks. Toss the solenoid
selector valve and connect the tanks, through in-line filters, individually
to the two pumps. Wire them so that the dash tank selector actually
selects one of the pumps.
Connect each of the pumps' output to a check valve (McMaster-Carr has good
ones cheap) with those feeding into a tee. Connect the output of the tee
to hard line all the way to the front crossmember where the rubber line is
now. Use R-14 fuel hose only as necessary to connect hard lines and
isolate vibrations; everything else should be good quality coated steel (I
prefer PolyArmour, available from most of the chain parts stores). Remove
the mechanical pump, bypassing its location with steel line, or aircraft
quality SS clad tubing.
You now have complete fuel system redundancy from the gas station to the
carburetor. Merely flipping the dash "tank" selector should enable you to
determine where the problem is if you ever have another one.
Oh yeah, while you're installing the two electric pumps, remove the gas cap
and blow the "socks" off of the fuel pickups in each tank with high volume
compressed air. I repeat, FIRST REMOVE THE GAS CAP.
Good luck. Let us know about next summer's trouble-free trips. :-)
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Tue, Dec 15, 2015 at 11:35 AM, StanC wrote:
> *** First, let me apologize for bringing this to the table. I do not
> like to bring my problems out to anyone else, preferring to find a solution
> myself. I do not like to bother anyone else. However, this problem has
> lasted almost if not 10 years, has restricted any kind of travel and is
> becoming a money pit. If any of you could come up with a solution I
> would owe you so much, I can never repay you. So, here is my delema ***
> ...
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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Re: GMC MOTORHOME POWER LOSS PROBLEM [message #292190 is a reply to message #292182] |
Tue, 15 December 2015 13:14 |
roy1
Messages: 2126 Registered: July 2004 Location: Minden nevada
Karma: 6
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Senior Member |
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Man you have a weird problem. First off do you have a fuel filter in the carb inlet? If it is there you should not have gotten rust in the carburetor if it could have even gotten past the needle valve. You should make sure the float valve is set properly when you look in the carburetor again. You should install another new fuel filter at the carburetor and a fuel pressure gage at the carburetor inlet that you can observe when the problem occurs that way you will be able to tell if you have a fuel delivery problem or not. The pressure should be around 5 to 7 pounds when you are under power at all times.I presume you know you have good fresh gas in the tanks. Have you made sure the advance weights are not sticking in your replacement distributor?
Roy Keen
Minden,NV
76 X Glenbrook
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Re: [GMCnet] GMC MOTORHOME POWER LOSS PROBLEM [message #292195 is a reply to message #292182] |
Tue, 15 December 2015 14:02 |
James Hupy
Messages: 6806 Registered: May 2010
Karma: -62
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Senior Member |
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Have you checked to see if your intake manifold is cracked? Very common
occurance. Symptoms are exactly as you describe yours are. Worth a quick
look down the inlet tract.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Dec 15, 2015 10:25 AM, "StanC" wrote:
> Have your frame/body pads collapsed, pinching the fuel line(s)?
>
> THANK YOU FOR THE REPLY
> OTHER THAN ABOVE THE TANKS, THE LINES HAVE BEEN FOLLOWED UP TO THE FRONT
> OF THE GMC.
> A SECOND CONSIDERATION IS.... THE POWER LOSS VARIES... IT WILL HAPPEN AT
> 35 MPH. TRY TO ADUST, THEN MAY SEE THE POWER LOSS AT 45MPH. ANOTHER WRENCH
> IN THE WORKS IS IF I PUNCH THE GAS, SHE WILL REV UP NORMALLY TILL IT GET
> TO ABOUT 30-35MPH, THEN THE POWER LOSS OCCURS. --BUT-- IF I PRESS THE GAS
> GENTLY AND SLOWLY INCREASE SPEED, I MAY GET TO 40-45 MPH BEFORE THE POWER
> LOSS HAPPENS.
> THE VARIANCE IN SPEED POINTS KIND OF ELIMINATES PINCHED FUEL LINES THOUGH
> WE ARE CONSIDERING TESTING WITH AN EXTERNAL FUEL TANK.
> THANKYOU
> SLC
>
>
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Re: GMC MOTORHOME POWER LOSS PROBLEM [message #292197 is a reply to message #292162] |
Tue, 15 December 2015 14:33 |
lqqkatjon
Messages: 2324 Registered: October 2010 Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I think you all ready have your plan. As much of a pain as it is, get that boat gas tank, and hook it up to your new mechanical fuel pump.
That will cut your hunting down the problem by 50%.
that should very quickly after 50 miles of driving, tell you if your problem is fuel delivery, before or after the pump. If it runs great, at speed, Then your next task is dropping tanks, new fuel lines all around, and go from there. If it still cuts out, then you need to revisit the carb/intake, distributor, ect...
I would wonder though if your mechanic is scratching his head on that carb. the $250 Jim Bounds charges to make sure your carb is 100%, without scratching your head, might be a good investment. I do not work on my own carbs, but i always have success with someone that is confident in their ability to work on carbs and "have done it many times, and it worked great!"
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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Re: GMC MOTORHOME POWER LOSS PROBLEM [message #292201 is a reply to message #292197] |
Tue, 15 December 2015 14:56 |
Gatsbys' Cruiser
Messages: 91 Registered: August 2014 Location: Illinois
Karma: 0
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THANKYOU FOR YOUR RESPONSE.
tell you if your problem is fuel delivery, before or after the pump. If it runs great, at speed
THE TANKS WERE DROPPED AND FUEL LINES CHANGED BEFORE THIS ALL HAPPENED. WE HAVE DONE TESTS TO TRY TO PROVE A LINE IS PINCHED BUT DONT SEEM TO HAVE ANY EVIDENCE TO THAT FACT.
WHEN WE ARE TESTING WITH THE MAIN TANK, WE HAVE CHANGED TO THE RESERVE, WHICH ALSO TURNS ON THE ELECTRIC FUEL PUMP. THERE IS NO CHANGE IN THE POWER LOSS. SO THIS SHOULD INDICATE THAT EITHER BOTH LINES ARE PINCHED, IF THAT CAN BE SO, OR THE PROBLEM IS ELSE WHERE. WE ARE TALKING ABOUT USING A EXTERNAL GAS TANK AND ELECTRIC FUEL PUMP TO RETEST THE gmc LINES ARE CLEAR.
I AM KEEPING DROPPING THE TANKS AS A LAST RESORT BUT IT IS IN THE PLAN.
make sure your carb is 100%, without scratching your head, might be a good investment.
THE CARB BEFORE THIS ONE AND THIS CARB WERE SUPPOSEDLY REBUILT, AND I AM TOLD BY THE SAME OUTFIT. THEY ARE SUPPOSED TO DO VERY GOOD WORK. I AM CONSIDERING HAVING A PROFESSIONAL UP HERE REBUILD THE CARB, THEY GUARANTEE TO TEST AND BRING IT UP TO STANDARDS. BUT THIS WON'T HAPPEN UNTIL SPRING. IT WILL BE ABOUT 2 WEEKS TO DO THIS REBUILD. MY MECHANIC DOES CARB REBUILDS ROUTINELY, THOUGH HE WON'T BE DOING THIS ONE. HE IS A COMPETENT AND VERY BUSY MECHANIC. BUT HE IS NOT THE ONLY ONE THAT IS SCRATCHING HIS HEAD OVER THIS ONE. REMEMBER, WE'VE BEEN TRYING TO FIGURE THIS OUT FOR A FEW YEARS NOW AND HAVE BEEN THROUGH SEVERAL CARBORATORS, ONE BAD BECAUSE THE MECH FUEL PUMP RUSTED INTERNALLY.
THANKYOU
SLC
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