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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
(3482 views)
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94' 7.4 wont stay running
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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)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 25, 2009, 7:34 PM
Post #2 of 4
(3449 views)
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Re: 94' 7.4 wont stay running
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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
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amslawn
New User
Sep 27, 2009, 2:15 PM
Post #3 of 4
(3437 views)
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Re: 94' 7.4 wont stay running
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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
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 27, 2009, 2:38 PM
Post #4 of 4
(3434 views)
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Re: 94' 7.4 wont stay running
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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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