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94' 7.4 wont stay running


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amslawn
New User

Sep 22, 2009, 3:52 PM

Post #1 of 4 (2488 views)
94' 7.4 wont stay running Sign In

Hi, I have a 1994 gmc 3500 7.4 w/2 bbl throttle body injection, it is shutting down right after it starts, gets fuel and starts but wont stay running , its stalled a couple of times during this week usually at low rpm or on deceleration then it just died(would not stay running) all together, the fuel pump is working, i didnt test gpm but it seems to be working very well, all vac lines/wires look good and im not getting a check engine light .

When this happens it sounds exactly like when you turn off the key no sputtering no misfires , even when i give it gas it does the same thing, the plugs are new in may , cap is old but ok condition and the ignition module pass test at advanced auto. this is usually a sound running truck ,the only time the check engine light does come on is when i have it in (drive)(i usualy am towing a trailer) not over drive and i go over 50 mph if i shift into od at 50 mph the light dosnt come on that is the only other issue i've had with this truck since i bought it and have used it daily since may 1 2009
Optional Information:
http://i790.photobucket.com/...amslawn/102_4932.jpg
http://i790.photobucket.com/...amslawn/102_4933.jpg
Year: 1994
Make : GMC
Model: 3500
Engine: 7.4
miles: 280000
Already Tried:
tested fuel pump , checked vac hoses and elec. connections, ignition module, fuel does spray when cranked


(This post was edited by amslawn on Sep 22, 2009, 4:05 PM)


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 25, 2009, 7:34 PM

Post #2 of 4 (2455 views)
Re: 94' 7.4 wont stay running Sign In

If you've verified fuel is NOT the issue and this has if I read right 280,000 miles it near can't have a dependable timing chain if known original. That's almost enough miles to require a second but replacements do much better that OE ones usually. Just a guess.

If needed I can explain a way to know how much slack it may have. T chains can be intermittent with issues and still show fuel and spark. Just an idea??

T



amslawn
New User

Sep 27, 2009, 2:15 PM

Post #3 of 4 (2443 views)
Re: 94' 7.4 wont stay running Sign In

Thank you for the reply Tom, but after a week of trying to figure this out I finaly towed it to a mechanic , turns out, and he found this out kinda by accident while he had another guy under the hood with a meter , and he noticed the dash lights go out when they weren't supposed to when they were testing , it was a bad ignition switch.. I never would of found that , but at least I did know that it sounded exactly like an intentional shut off , I should've started at my biggest clue!
btw the same mechanic did the timing chain on my 82' 454 , he said it was 25 degrees off when I DROVE it in , it did miss terrible over 2.2k rpm but under it was ok, them 454s are hard to kill


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 27, 2009, 2:38 PM

Post #4 of 4 (2440 views)
Re: 94' 7.4 wont stay running Sign In

Thanks for the followup of the fix. Crazy things can happen and if we can archive the fixes they can be found.

Off this exact topic and a rare thing to me was I think an 88 Chev Van and electrical stuff would go intermittent?? It was a road call a long time ago now and luck of all luck after finding no power to interior fuse items (not all) just by chance stumbled on a lousy connection between a rubber block on firewall underhood the essentially empowers everything to the interior including ign stuff. Could have spent days but it was the first thing I checked! Go figure!

I'm betting that vehicle is gone now but I did just what I suggested and gave a slight twist (wasn't the case with yours) to what seemed like a zillion spade connections behind that block, it worked right away and was never a problem again.

Just a story for follow up. BTW - I did that in the guy's driveway with my usual abundant tools I keep with me...........

Be well and thanks for posting your fix,


T







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