| Re: [GMCnet] Vent holes [message #93837 is a reply to message #93831 ] |
Thu, 29 July 2010 13:05   |
 Richard Denney
Messages: 47
Registered: April 2010 |
Member |
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On Thu, Jul 29, 2010 at 1:42 PM, Jim Moore <j.moore.jr@mindspring.com>wrote:
> Rick,
> Why would engine not start? Did you check for spark? The engine not
> restarting for 30 minutes sounds like you could have a bad ignition module.
>
No, I'm reasonably sure it wasn't a spark problem. I did think about that,
but didn't test it. I've just had no other indication of any ignition
problems. My testing was limited at the time--I didn't want to open the
hatch while the engine was fully hot, and I needed to do my shopping anyway,
so there was time to let it cool a bit.
If it happens again, I'll test it. But I'm not a believer in coincidence,
and this was just a few minutes after the more typical stumbling problem
after a traffic stop following a high-speed run.
I suppose I could take my #2 inductive timing light and wire it in for
testing so that if it happens again, I'll be able to check it without
opening the hatch.
Rick "who carries a timing light in the on-coach tool box" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Vent holes [message #93841 is a reply to message #93831 ] |
Thu, 29 July 2010 13:20 |
Bob de Kruyff
Messages: 1386
Registered: January 2004
Location: Chandler, AZ |
Senior Member |
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""Rick,
Why would engine not start? Did you check for spark? The engine not restarting for 30 minutes sounds like you could have a bad ignition module. They often fail when hot and work OK when cool. Could also be something else in the ignition system. Buy one of the cheap ignition testers that go between the spark plug wire and the spark plug and you will immediately know if you have ignition problems. Recently had a problem with the Blazer not starting and then starting several hours later. I found a broken wire in the pickup coil that would make and break the circuit when the vacuum advance moved. Blazer is a 78 and HEI pickup coil was original (32 yrs old) and had just rotted out. Same coil used in GMC's. Also had problems with the Blazer acting like it had a fuel or ignition problem. It would run fine and then cut off going down the road and immediately restart. Turned out to be a defective ignition switch with bad contacts. Found it by jiggling the switch. Same swi
tch is used on GMC's and mounts on steering column.
""
Jim, I've never had a module fail yet, but while I was chasing my fuel problem, I talked to my engine buddy at GM about that very issue. I always felt I'd be able to distinguish between fuel and ignition problems just by feel. He mentioned that even he had suspected fuel starvation when in the end it was a module starting to go--he feels the characteristics are almost identical, until it finally craps out.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Vent holes [message #93854 is a reply to message #93684 ] |
Thu, 29 July 2010 15:10 |
James Moore
Messages: 89
Registered: January 2004 |
Member |
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Bob,
You are right about the modules being very dependable. I have only had two fail.
The first one was in the 78 Blazer. It started as an intermittent failure. Going down the road, loud backfire and engine stopped. Wait awhile and engine would restart and run normally. Checked the HEI several times using a HEI tester and found nothing wrong. Finally wouldn't start and then module checked bad. Failure was caused by alternator voltage regulator failing and increasing system voltage to over 16 volts (pegged voltage gauge in dash). I use the Blazer as an example because it is the same vintage as the GMC, has the same carb and ignition system and often sits for extended periods like the GMC so most of its problems are similar to the GMC. It even lost its rear brakes last year due to a plugged hose.
Other failure was GMC. It showed up as hard starting and ran fine after it started which made me chase the problem in the fuel system. Again I didn't solve the problem until it failed completely.
In Rick's reply, he assumed the problem is in the fuel system and didn't check anything when it stopped. I am a steam turbine controls engineer and nothing is harder to solve than intermittent problems. Monday I flew from Atlanta to Oakland, CA because a Customer's turbine had tripped and would not reset. Before I arrived, he found a loose wire and was able to restart after tightening the loose connection. I spent Tuesday testing his control system to see if that was the problem. Still don't know if it was since the Customer would not shut the unit down to see if we could duplicate the problem. Flew back to Atlanta yesterday. The new control systems have excellent high speed trending capability which makes my life a lot easier. Recently a Customer had a similar problem on a unit with a new control system. He thought the unit was tripping due to low hydraulic pressure but it turned out to be caused by a speed sensor failing for 5 seconds, tripping the unit, and resett
ing without bringing in an alarm. A cardinal rule in my business is find what is causing the problem. Then fix the problem. In the case of the second Customer, he was getting mechanics setup to change the hydraulic filters and check the accumulator pressure, instrument techs setup to recalibrate the hydraulic pressure switches, and checking to see if he had a spare pump. The actual problem was fixed by changing a constant in the control logic and downloading it to the processor. Took less than 5 minutes to fix. So until someone determines what is causing the so called vapor lock problem, it will continue to get a lot fixes applied that may or may not solve the problem.
Jim Moore
-----Original Message-----
>From: Bob de Kruyff <NEXT2POOL@AOL.COM>
>Sent: Jul 29, 2010 2:20 PM
>To: gmclist@temp.gmcnet.org
>Subject: Re: [GMCnet] Vent holes
>
>
>
>""Rick,
>Why would engine not start? Did you check for spark? The engine not restarting for 30 minutes sounds like you could have a bad ignition module. They often fail when hot and work OK when cool. Could also be something else in the ignition system. Buy one of the cheap ignition testers that go between the spark plug wire and the spark plug and you will immediately know if you have ignition problems. Recently had a problem with the Blazer not starting and then starting several hours later. I found a broken wire in the pickup coil that would make and break the circuit when the vacuum advance moved. Blazer is a 78 and HEI pickup coil was original (32 yrs old) and had just rotted out. Same coil used in GMC's. Also had problems with the Blazer acting like it had a fuel or ignition problem. It would run fine and then cut off going down the road and immediately restart. Turned out to be a defective ignition switch with bad contacts. Found it by jiggling the switch. Same swi
>tch is used on GMC's and mounts on steering column.
>""
>
>Jim, I've never had a module fail yet, but while I was chasing my fuel problem, I talked to my engine buddy at GM about that very issue. I always felt I'd be able to distinguish between fuel and ignition problems just by feel. He mentioned that even he had suspected fuel starvation when in the end it was a module starting to go--he feels the characteristics are almost identical, until it finally craps out.
>--
>Bob de Kruyff
>78 Eleganza
>Chandler, AZ
>_______________________________________________
>GMCnet mailing list
>List Information and Subscription Options:
>http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Vent holes [message #93864 is a reply to message #93854 ] |
Thu, 29 July 2010 16:32 |
Richard Denney
Messages: 47
Registered: April 2010 |
Member |
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On Thu, Jul 29, 2010 at 4:10 PM, Jim Moore <j.moore.jr@mindspring.com>wrote:
> So until someone determines what is causing the so called vapor lock
> problem, it will continue to get a lot fixes applied that may or may not
> solve the problem.
>
>
Agreed. Those pesky occasional problems, however, don't always happen at a
time when one can pull all the tools out and go to work on it. I was already
late getting up onto the mountain, and driving on that road after dark is
not to be considered. So, I went with my gut, figuring if the problem
persisted after my shopping, I could deal with it them. I wasn't being paid
to troubleshoot a problem at that moment, heh.
Rick "who does carry the old distributor, just in case" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Vent holes [message #93923 is a reply to message #93684 ] |
Thu, 29 July 2010 21:50 |
voodoolng
Messages: 30
Registered: February 2004
Location: Colo |
Member |
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Hi Tim here in the process to stop vapor lock. I installed a shield in front of the gas tanks. I finally took some fair picture to show the shield I put in to prevent the hot air from going thrugh the gas tanks. Using heavy alum sheeting some 1 ich angle iron. Shaping the iron and drilling and tapping to hold the angle to the two cross frames and screwing the alum to the angle iron. I posted the pictures on the gmc photo under modifications section.
I also move the filter and pump to the outside of the frame rails. I have cross finger so far towing and trips no vapor locking. It use to bring me to a stop on trips.
73 Glacier Voodoo lounge
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| Re: [GMCnet] Vent holes [message #94006 is a reply to message #93684 ] |
Fri, 30 July 2010 13:06 |
Steve Stolley
Messages: 79
Registered: April 2008
Location: Washington, Utah |
Member |
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There is another problem that could cause symptoms similar to vapor lock. How about a stuck vent in the gas cap? Given the water and ethanol vapor floating around that area it's easy to see how it could get mucked up. It's hard for any fuel pump to suck gas out of a closed system.
Steve Stolley
76 Glenbrook
Washington, Utah
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| Re: [GMCnet] Vent holes [message #94198 is a reply to message #93684 ] |
Sun, 01 August 2010 14:58 |
voodoolng
Messages: 30
Registered: February 2004
Location: Colo |
Member |
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Just posted some pictures of a durable plastic scoop to mount in the front like Emerys. Used a 3 inch Y pipe and modified it into a scoop that should last for a while feels very ready to standup to conditions.More cooling, it vents on top of the motor and cools electronics and TBI while driving. Its under modifacations or voodoolng photos
73 Glacier Voodoo lounge
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