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| [GMCnet] Engine suddenly running rough [message #172802] |
Sun, 10 June 2012 13:32  |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Here is one of those posts looking for a miracle answer. We pulled the coach out Friday night to go to the coast and instead of letting it warm up I thought I’d baby it and let it warm up on the road. Pulling out of our neighborhood to the busy street she coughed, backfired and died. I started the engine and continued (very slowly) my left turn pulling over to the curb to let it warm up.
The engine was now running rough. Once it warmed up we drove to the coast and, though it was still misfiring it drove well. Pulling out a few hours later on the way home I heard a series of backfires as I was trying to accelerate. Still she got us home without issue. The engine is running rough, but it idles, starts and stops without dieseling. I now smell what I think is an NOX like smell from the exhaust.
I thought I’d be brilliant and change the ignition module and spark plugs. I did this and she runs just the same. Upon inspection of the spark plugs I see that #3 is slightly oily, but the rest look good. Here is a picture of the plugs - a complete tune up was performed by Tom Hampton about 15,000 miles ago and the miles driven since the back-fire incident are about 100.
<http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44496-spark-plugs.html>
<http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44497-spark-plugs.html>
I’m beginning to think that the backfire jarred the carburetor somehow. I have a Rockwell manifold, so the crossovers are not an issue and it looks like the vacuum lines are okay, but I didn’t give them a thorough inspection. The cap and rotor looked okay, and I just don’t think 15k miles is enough to kill a cap and rotor.
What could I be missing, a burned valve?
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Engine suddenly running rough [message #172805 is a reply to message #172802] |
Sun, 10 June 2012 13:44  |
mickeysss
Messages: 1476
Registered: January 2012
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My mechanic always states start with the plug wire that had the oil on the plug. If you have an old plug wire change that one with the old one.
If you have already thought of this, i am sorry to bother you with it. regards. mouse.
On Jun 10, 2012, at 11:32 AM, Larry Davick wrote:
> Here is one of those posts looking for a miracle answer. We pulled the coach out Friday night to go to the coast and instead of letting it warm up I thought I’d baby it and let it warm up on the road. Pulling out of our neighborhood to the busy street she coughed, backfired and died. I started the engine and continued (very slowly) my left turn pulling over to the curb to let it warm up.
>
> The engine was now running rough. Once it warmed up we drove to the coast and, though it was still misfiring it drove well. Pulling out a few hours later on the way home I heard a series of backfires as I was trying to accelerate. Still she got us home without issue. The engine is running rough, but it idles, starts and stops without dieseling. I now smell what I think is an NOX like smell from the exhaust.
>
> I thought I’d be brilliant and change the ignition module and spark plugs. I did this and she runs just the same. Upon inspection of the spark plugs I see that #3 is slightly oily, but the rest look good. Here is a picture of the plugs - a complete tune up was performed by Tom Hampton about 15,000 miles ago and the miles driven since the back-fire incident are about 100.
>
> <http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44496-spark-plugs.html>
> <http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44497-spark-plugs.html>
>
> I’m beginning to think that the backfire jarred the carburetor somehow. I have a Rockwell manifold, so the crossovers are not an issue and it looks like the vacuum lines are okay, but I didn’t give them a thorough inspection. The cap and rotor looked okay, and I just don’t think 15k miles is enough to kill a cap and rotor.
>
> What could I be missing, a burned valve?
>
>
> Larry Davick
> The Mystery Machine
> 1976(ish) Palm Beach
> Fremont, CA
>
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| Re: [GMCnet] Engine suddenly running rough [message #172808 is a reply to message #172802] |
Sun, 10 June 2012 13:52 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Larry,
Did you check the mechanical and vacuum distributor advances?
Dennis
| ljdavick wrote on Sun, 10 June 2012 13:32 |
Here is one of those posts looking for a miracle answer. We pulled the coach out Friday night to go to the coast and instead of letting it warm up I thought I’d baby it and let it warm up on the road. Pulling out of our neighborhood to the busy street she coughed, backfired and died. I started the engine and continued (very slowly) my left turn pulling over to the curb to let it warm up.
The engine was now running rough. Once it warmed up we drove to the coast and, though it was still misfiring it drove well. Pulling out a few hours later on the way home I heard a series of backfires as I was trying to accelerate. Still she got us home without issue. The engine is running rough, but it idles, starts and stops without dieseling. I now smell what I think is an NOX like smell from the exhaust.
I thought I’d be brilliant and change the ignition module and spark plugs. I did this and she runs just the same. Upon inspection of the spark plugs I see that #3 is slightly oily, but the rest look good. Here is a picture of the plugs - a complete tune up was performed by Tom Hampton about 15,000 miles ago and the miles driven since the back-fire incident are about 100.
<http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44496-spark-plugs.html>
<http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44497-spark-plugs.html>
I’m beginning to think that the backfire jarred the carburetor somehow. I have a Rockwell manifold, so the crossovers are not an issue and it looks like the vacuum lines are okay, but I didn’t give them a thorough inspection. The cap and rotor looked okay, and I just don’t think 15k miles is enough to kill a cap and rotor.
What could I be missing, a burned valve?
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
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Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: [GMCnet] Engine suddenly running rough [message #172809 is a reply to message #172805] |
Sun, 10 June 2012 13:52 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Larry,
Take a squirt bottle with water in it and while it is running squirt water at each exhaust port. The one that is not firing the water will not boil off instantly as compared to the others. If that is okay check your timing to make sure it is correct. If you have a vacuum gauge check your vacuum. Should be between 18 and 20 inches.
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: [GMCnet] Engine suddenly running rough [message #172813 is a reply to message #172802] |
Sun, 10 June 2012 14:15 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| ljdavick wrote on Sun, 10 June 2012 14:32 |
Here is one of those posts looking for a miracle answer. We pulled the coach out Friday night to go to the coast and instead of letting it warm up I thought I’d baby it and let it warm up on the road. Pulling out of our neighborhood to the busy street she coughed, backfired and died. I started the engine and continued (very slowly) my left turn pulling over to the curb to let it warm up.
The engine was now running rough. Once it warmed up we drove to the coast and, though it was still misfiring it drove well. Pulling out a few hours later on the way home I heard a series of backfires as I was trying to accelerate. Still she got us home without issue. The engine is running rough, but it idles, starts and stops without dieseling. I now smell what I think is an NOX like smell from the exhaust.
I thought I’d be brilliant and change the ignition module and spark plugs. I did this and she runs just the same. Upon inspection of the spark plugs I see that #3 is slightly oily, but the rest look good. Here is a picture of the plugs - a complete tune up was performed by Tom Hampton about 15,000 miles ago and the miles driven since the back-fire incident are about 100.
<http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44496-spark-plugs.html>
<http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44497-spark-plugs.html>
I’m beginning to think that the backfire jarred the carburetor somehow. I have a Rockwell manifold, so the crossovers are not an issue and it looks like the vacuum lines are okay, but I didn’t give them a thorough inspection. The cap and rotor looked okay, and I just don’t think 15k miles is enough to kill a cap and rotor.
What could I be missing, a burned valve?
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
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Larry,
If you have or can borrow a gage, compression checks are cheap. Do that first.
If that is in the ball park, then check out the wires and cap.
If the carb is leaking fuel in, then I would expect 4 to look like 3 as they are on the same runner.
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] Engine suddenly running rough [message #172829 is a reply to message #172802] |
Sun, 10 June 2012 18:27 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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The good news is that I checked the compression and it’s about the same as it was when Tom Hampton checked it three years ago. When I pulled the spark plugs #3 already looked a little oily so I replaced that wire, but it still runs rough. I suppose I should check the cap, as the oily spark plug has me wondering. The odd thing is that the coach has run very well since Jim’s boys installed the Rockwell manifold. It’s always grumpy ‘till the choke comes off and when she back-fired while cold I think that’s when the engine started running rough. No proof, just a suspicion.
What I really need is to break the piggy bank and buy the TBI, Electronic distributor, EBL, speed sensor, and aluminized single muffler exhaust. Well, it’s on the map...
Some of you might be interested in the results from my compression check -
1 = 140
2 = 140
3 = 140
4 = 140
5 = 135
6 = 130 (+ a little)
7 = 135
8 = 135
Not too bad. I believe this is an original motor and my beloved PO said that he replaced the timing chain at 75,000 miles. She now has about 145,000 miles.
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Engine suddenly running rough [message #172830 is a reply to message #172829] |
Sun, 10 June 2012 18:30 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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I guess you check the timing
and
any chance your backfire plugged a muffler?
( i only have one .:)
gene
On Sun, Jun 10, 2012 at 4:27 PM, Larry Davick <ljdavick@comcast.net> wrote:
> The good news is that I checked the compression and it’s about the same as
> it was when Tom Hampton checked it three years ago. When I pulled the
> spark plugs #3 already looked a little oily so I replaced that wire, but it
> still runs rough. I suppose I should check the cap, as the oily spark plug
> has me wondering. The odd thing is that the coach has run very well since
> Jim’s boys installed the Rockwell manifold. It’s always grumpy ‘till the
> choke comes off and when she back-fired while cold I think that’s when the
> engine started running rough. No proof, just a suspicion.
>
> What I really need is to break the piggy bank and buy the TBI, Electronic
> distributor, EBL, speed sensor, and aluminized single muffler exhaust.
> Well, it’s on the map...
>
> Some of you might be interested in the results from my compression check -
>
> 1 = 140
> 2 = 140
> 3 = 140
> 4 = 140
> 5 = 135
> 6 = 130 (+ a little)
> 7 = 135
> 8 = 135
>
> Not too bad. I believe this is an original motor and my beloved PO said
> that he replaced the timing chain at 75,000 miles. She now has about
> 145,000 miles.
>
> Larry Davick
> The Mystery Machine
> 1976(ish) Palm Beach
> Fremont, CA
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] Engine suddenly running rough [message #172834 is a reply to message #172830] |
Sun, 10 June 2012 18:43 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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Gene,
I have not checked the timing yet and I suppose it’s possible that a muffler plugged. The mufflers are only 3 years old, though I will replace them with the single rear soon.
Would any of this make it run rough at idle?
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
On Jun 10, 2012, at 4:30 PM, gene Fisher wrote:
> I guess you check the timing
>
> and
> any chance your backfire plugged a muffler?
> ( i only have one .:)
> gene
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
_______________________________________________
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Engine suddenly running rough [message #172841 is a reply to message #172802] |
Sun, 10 June 2012 19:21 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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You should have also have changed out the rotor, cap and spark plug wires.
Also check the timing and check all vacuum lines especially where they attach.
Once you have done that let us know how it's running.
If its till running bad check the fuel filter.
If you've had bad plugs and/or wires it can kill a cap and rotor in a short time.
Get back to us and we'll tell you more things to do.
Emery Stora
On Jun 10, 2012, at 12:32 PM, Larry Davick <ljdavick@comcast.net> wrote:
> Here is one of those posts looking for a miracle answer. We pulled the coach out Friday night to go to the coast and instead of letting it warm up I thought I’d baby it and let it warm up on the road. Pulling out of our neighborhood to the busy street she coughed, backfired and died. I started the engine and continued (very slowly) my left turn pulling over to the curb to let it warm up.
>
> The engine was now running rough. Once it warmed up we drove to the coast and, though it was still misfiring it drove well. Pulling out a few hours later on the way home I heard a series of backfires as I was trying to accelerate. Still she got us home without issue. The engine is running rough, but it idles, starts and stops without dieseling. I now smell what I think is an NOX like smell from the exhaust.
>
> I thought I’d be brilliant and change the ignition module and spark plugs. I did this and she runs just the same. Upon inspection of the spark plugs I see that #3 is slightly oily, but the rest look good. Here is a picture of the plugs - a complete tune up was performed by Tom Hampton about 15,000 miles ago and the miles driven since the back-fire incident are about 100.
>
> <http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44496-spark-plugs.html>
> <http://www.gmcmhphotos.com/photos/miscellaneous-stuff/p44497-spark-plugs.html>
>
> I’m beginning to think that the backfire jarred the carburetor somehow. I have a Rockwell manifold, so the crossovers are not an issue and it looks like the vacuum lines are okay, but I didn’t give them a thorough inspection. The cap and rotor looked okay, and I just don’t think 15k miles is enough to kill a cap and rotor.
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| Re: [GMCnet] Engine suddenly running rough [message #172842 is a reply to message #172834] |
Sun, 10 June 2012 19:24 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Sometimes a backfire will destroy a muffler
FREE WIFI @ Mickey D
On Jun 10, 2012, at 4:43 PM, Larry Davick <ljdavick@comcast.net> wrote:
> Gene,
>
> I have not checked the timing yet and I suppose it’s possible that a muffler plugged. The mufflers are only 3 years old, though I will replace them with the single rear soon.
>
> Would any of this make it run rough at idle?
>
> Larry Davick
> The Mystery Machine
> 1976(ish) Palm Beach
> Fremont, CA
>
> On Jun 10, 2012, at 4:30 PM, gene Fisher wrote:
>
>> I guess you check the timing
>>
>> and
>> any chance your backfire plugged a muffler?
>> ( i only have one .:)
>> gene
>> --
>> Gene Fisher -- 74-23,77PB/ore/ca
>> “Give a man a fish; you have fed him for today --- give him a URL and
>> -------
>> http://gmcmotorhome.info/
>> Alternator Protection Cable
>> http://gmcmotorhome.info/APC.html
>> _______________________________________________
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Engine suddenly running rough [message #172937 is a reply to message #172802] |
Mon, 11 June 2012 11:35 |
enate98690
Messages: 23
Registered: January 2012
Karma: 0
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Junior Member |
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Hey George,
The rough running happened to me also and it was nothing more than spark plug wires running parallel on the passenger side (i.e., so the spark jumped from one wire to the next). Once I separated the wires and made sure they crossed (rather than ran parallel) the engine smoothed out. I think this issue is more prone to happen in hot weather but I don't know why (perhaps because the wires expand and lose some of their insulation ability).
Personally, I find "rough running" is usually one or more cylinders "missing" firing and is usually due to ignition rather than gas/carburation.
I hope this helps!
Keith Lee
-----Original Message-----
>From: George Beckman <gbeckman@pggp.com>
>Sent: Jun 10, 2012 10:02 PM
>To: gmclist@temp.gmcnet.org
>Subject: Re: [GMCnet] Engine suddenly running rough
>
>
>
> :blush: ljdavick wrote on Sun, 10 June 2012 21:44
>> The more I think of it the more I think it could be a vacuum line that blew off from the backfire. That could effect the timing causing that NOX smell and would explain rough running at idle and at speed.
>>
>> The muffler, though plausible, probably would not effect the idle.
>>
>> This has to wait ‘till next weekend. Weekend shadetree mechanic.
>>
>> Larry Davick
>> The Mystery Machine
>> 1976(ish) Palm Beach
>> Fremont, CA
>
>What color is the exhaust at idle? May need your wife to give it a bit of gas. Backfire and popping through the carb can happen when it is lean.
>--
>'74 Eleganza, SE, Howell + EBL
>Best Wishes,
>George
>_______________________________________________
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