Home » Public Forums » GMCnet » [GMCnet] Intermittent Problems
| [GMCnet] Intermittent Problems [message #211007] |
Thu, 13 June 2013 18:04  |
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fitzmorrispr
Messages: 137
Registered: February 2013
Location: Los Angeles
Karma: 0
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Senior Member |
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So, i have intermittent loss of power under moderate to heavy
acceleration. The engine basically stalls, until i get most of the way
off the gas again, but it doesn't do it every time, and even when it's
doing it I can usually get on the gas for several seconds before the
'power goes out'
I'm pretty sure it only happens when the secondaries begin to open,
and once I thought I heard a tailpipe detonation. So, maybe mixture?
What do? (could it be a vacuum leak? an issue with the timing?)
Problem #2 is that the air compressor only functions intermittently.
It seems that the compressor itself is fine, and that the problem is
the pressure switch on the tank. It seems that it works most often in
cool/damp weather. Probably I can solve this problem with a
multimeter.
Halp?
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The Greatfruit: 1973, 26', Canyon Lands or Painted Desert, in Pineapple Yellow
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| Re: [GMCnet] Intermittent Problems [message #211029 is a reply to message #211007] |
Thu, 13 June 2013 21:47  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| fitzmorrispr wrote on Thu, 13 June 2013 19:04 |
So, i have intermittent loss of power under moderate to heavy acceleration. The engine basically stalls, until i get most of the way off the gas again, but it doesn't do it every time, and even when it's doing it I can usually get on the gas for several seconds before the 'power goes out'
I'm pretty sure it only happens when the secondaries begin to open, and once I thought I heard a tailpipe detonation. So, maybe mixture?
What do? (could it be a vacuum leak? an issue with the timing?)
Problem #2 is that the air compressor only functions intermittently.
It seems that the compressor itself is fine, and that the problem is the pressure switch on the tank. It seems that it works most often in cool/damp weather. Probably I can solve this problem with a multimeter.
Halp?
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Patrick,
Re: Problem #1
At a recent GMCMI, Dick Paterson said (paraphrase) - Most Carburetor problems are caused by ignition problems.
Indeed, when I have had such problems, they turned out to ignition issues. What you describing can easily be caused by a secondary ignition break-down. Start by inspecting the wires and cap.
Re: Problem #2
I have no idea what the stock compressor switch looks like, mine is a SquareD compressor switch available just about anywhere for about 30$us.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Intermittent Problems [message #211030 is a reply to message #211007] |
Thu, 13 June 2013 21:56 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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You should say if you have a stock points distributor or an HEI distributor if it is an HEI it is not uncommon to have a shorting wire in the pickup when the advance plate retards with low vacuum that would cause a possible backfire and sudden loss of power.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Intermittent Problems [message #211040 is a reply to message #211030] |
Fri, 14 June 2013 00:04 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Air compressor switch is available from McMaster or Jim K. Order it from Jim K. If you do not know exactly which switch you want, order it form Jim K. You will get the correct part the first time from him.
They are easy to change.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Mon, 17 June 2013 14:17] Report message to a moderator |
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| Re: [GMCnet] Intermittent Problems [message #211087 is a reply to message #211007] |
Fri, 14 June 2013 20:59 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Check the compressor wiring for crimps that may he bad. Sometimes they crimp on the insulation or oxidation sets in. Firm tug test is a good one or back probe with a meter to troubleshoot.
Flat throttle response is often fuel but fact that if you Push past it the power comes back is a bit confusing. To me ignition is more like missing, popping and if not fuel starvation but intermittent ignition will load the mufflers and then bang when ignition comes back. That said, i always remember the Dick P /Smokey Yunik quote Matt brought up about carb problems being ignition.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Intermittent Problems [message #211383 is a reply to message #211007] |
Mon, 17 June 2013 13:53 |
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fitzmorrispr
Messages: 137
Registered: February 2013
Location: Los Angeles
Karma: 0
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Senior Member |
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I really should have specified, shouldn't I?
Yes, it is a points distributor. I've been thinking that an HEI dizzy would be a good upgrade, but haven't gotten to it yet, and, well, I wouldn't want to spend money on that until I had first determined the cause of this issue.
It doesn't come back if I 'push past it'. If I keep my foot down after the 'power goes out', it will sometimes lunge repeatedly, making less power on average than it would if I backed off enough for it to stabilize. Other times, keeping my foot down means it just stalls (the difference between the two failure modes seems to be road speed. Down around 20, i'm more likely to stall, up above 30, more likely to lunge). If I let off the gas enough for it to stabilize, I can usually get a few more seconds of healthy throttle response by waiting a moment and then reapplying the throttle.
Maybe it is the fuel filter. there's an inline one which was there when I bought the coach in February, and then there's a new one I installed in the carburetor inlet's filter housing (which had been lacking a filter before) The problem seems to have started when my fuel level got low-ish (~5 gallons left in each tank)
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I have no idea if the compressor switch is stock or not, and i hadn't thought to check the crimps. Would they really cause intermittent run like I described? i would have thought that they were an all-or-nothing type of deal.
The Greatfruit: 1973, 26', Canyon Lands or Painted Desert, in Pineapple Yellow
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| Re: [GMCnet] Intermittent Problems [message #211388 is a reply to message #211383] |
Mon, 17 June 2013 14:21 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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The compressor switch has a set of contacts that over time can pit and burn. Sometime they make contact and sometimes not. Take a good look at the contacts. Clean and file them smooth if you do not want to replace the switch.
If you do replace the switch, get one with an unloader they are 2 or 3 dollars more and we will explain how to use the unloader later.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Intermittent Problems [message #211392 is a reply to message #211383] |
Mon, 17 June 2013 14:30 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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| fitzmorrispr wrote on Mon, 17 June 2013 11:53 |
I really should have specified, shouldn't I?
Yes, it is a points distributor. I've been thinking that an HEI dizzy would be a good upgrade, but haven't gotten to it yet, and, well, I wouldn't want to spend money on that until I had first determined the cause of this issue.
It doesn't come back if I 'push past it'. If I keep my foot down after the 'power goes out', it will sometimes lunge repeatedly, making less power on average than it would if I backed off enough for it to stabilize. Other times, keeping my foot down means it just stalls (the difference between the two failure modes seems to be road speed. Down around 20, i'm more likely to stall, up above 30, more likely to lunge). If I let off the gas enough for it to stabilize, I can usually get a few more seconds of healthy throttle response by waiting a moment and then reapplying the throttle.
Maybe it is the fuel filter. there's an inline one which was there when I bought the coach in February, and then there's a new one I installed in the carburetor inlet's filter housing (which had been lacking a filter before) The problem seems to have started when my fuel level got low-ish (~5 gallons left in each tank)
Sounds like you figured it out changing the inline filter would be at the top of my list
----
I have no idea if the compressor switch is stock or not, and i hadn't thought to check the crimps. Would they really cause intermittent run like I described? i would have thought that they were an all-or-nothing type of deal.
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Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Intermittent Problems [message #211401 is a reply to message #211007] |
Mon, 17 June 2013 15:23 |
An87ttype
Messages: 157
Registered: September 2012
Karma: 0
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Senior Member |
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If its not backfiring I would check the filter. Ignition problems could cause the intermittent problem that was originally described, but yours does not really sound intermittent. Did the problem start after you got gas? Maybe a bad batch of crapohal?
1975 Eleganza II
Hudson Valley NY
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| Re: [GMCnet] Intermittent Problems [message #211417 is a reply to message #211383] |
Mon, 17 June 2013 16:38 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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It sounds like a case of fuel starvation to me. Change ALL your filters. While you're at it, remove the gas cap and blow ait into the lines back to the fuel tanks to blow any crud out of the intake socks. If you do this in front of the fuel selector valve, do one, switch the valve, and do the other.
I installed a pressure switch on my air tank very similar to this one that I bought from Jim Bounds at the Co-op:
http://www.ebay.com/itm/321082661150?item=321082661150&viewitem=&vxp=mtr
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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