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Another GMC ignition system conundrum


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Next thing I would do is run a new, 00 or 000 ground cable from the engine to the battery Negative terminal. Basically run the entire circuit from the battery terminals.

 

I know you said you checked grounds.. but all the easy stuff is done.. time to get creative. Run from the battery (+) to the coil, and add a new, shiny, just scrubbed off with sand paper and used dialectic grease ground to the battery (-).

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I wrote too soon!

 

The 5-mile trip to the prom went fine, however on the way back it began doing the same coughing and spluttering thing. The owner pulled over and as he was trying to call me it cured itself and he drove home with no further problems. On Saturday he drove it 20-odd miles to the Capel show with no trouble. I've not yet heard whether he got back ok.

 

Someone suggested excessive alternator output as I measured 14.5V at the battery at high revs. This does seem a bit in excess of the 13.8V I've always understood to be the normal maximum. However I have no idea if or how this could be the cause of the problem.

 

I plan to fit a spark tester in line so that next time it misbehaves he can pop the bonnet to see if it is losing spark.

 

- MG

 

It seems the newer alternators do put out 14.4 volts have seen this on several cars now dont think thats a problem, one other thing are you sure the coil is not a ballasted one and is being over volted this might cause it to short out !!

But what do I know...

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Hi

 

Fuel level, maybe not be off the mark, have a friend with a CCKW, who had a strange fuel pickup problem. Pin hole in the fuel pickup tube part way up the tube. As fuel level got nearer to the hole engine would start stumble as slugs of air got sucked in, problem was compounded by unreliable gas gage.

 

Have you tried putting a fuel pressure gage in the line to see if the pressure is staying constant?

 

Please let us know what the problem or combination of problems you eventually narrow the problem down too.

 

Cheers Phil

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Hi

 

Fuel level, maybe not be off the mark, have a friend with a CCKW, who had a strange fuel pickup problem. Pin hole in the fuel pickup tube part way up the tube. As fuel level got nearer to the hole engine would start stumble as slugs of air got sucked in, problem was compounded by unreliable gas gage.

 

Have you tried putting a fuel pressure gage in the line to see if the pressure is staying constant?

 

Please let us know what the problem or combination of problems you eventually narrow the problem down too.

 

Cheers Phil

The truck is due to do around 300 miles in the next week so we'll see how it gets on.

 

The electric pump can be heard to tick at the correct speed even when the engine is stumbling, plus the first time the problem happened the fuel tank had just been filled (there are two filters in the system both of which are clean, so I don't believe it was caused by dirt being stirred up). We've also seen similar problems with pin-holes in pick-up pipes, as well as objects of various types floating around in the tank and blocking the bottoms of pipes.

 

FYI the comments about checking fuel level were a nudge towards a certain other GMC owner who recently suffered an 'embarrassment'...

 

As for my on-going problem, I'll report as and when it breaks again :undecided:

 

- MG

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  • 11 months later...

Hi Mike,

 

I'm guessing this was my truck that was causing issues?

Did you ever get to the source of the problem, as I have not yet experienced this issue?

 

Makes me a little nervous that gremlins I don't know about may be lurking!

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Hi Mike,

 

I'm guessing this was my truck that was causing issues?

Did you ever get to the source of the problem, as I have not yet experienced this issue?

 

Makes me a little nervous that gremlins I don't know about may be lurking!

Hi Paul,

 

No it was a different truck so don't worry. We established it was the distributor at fault with an unidentified earthing issue. Replaced the distributor and it was fine after that.

 

- MG

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