2002 GMC Denali "loping" at start up

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jgunn

2002 GMC Denali "loping" at start up

Unread post by jgunn » Thu Sep 02, 2010 12:18 pm

My 2002 GMC Yukon Denali "lopes" on start up only. I can start driving it immediately and it doesn't do it anymore, not does it do it after I get going. Only at start up "sometimes". Otherwise truck runs like a top. Any suggestions? Thanks,

MeccBoy

2002 GMC Denali "loping" at start up

Unread post by MeccBoy » Fri Sep 03, 2010 2:37 pm

Some common cuases for this problem are a fuel pressure regulator leaking. This causes a rich condition and will cause this problem until it gets cleared out by driving or reving it up a few times.
Also the lower intake manifold gaskets leak vacuum and will cause idle problems until the engine warms up and the gaskets seal better.

96realwe

P0303 problem after a 1000 miles of no problem after new

Unread post by 96realwe » Wed Dec 08, 2010 2:32 am

96 jimmy 4.3 4X4 144k miles, I rebuilt the upper end both heads machined a 1000 miles ago, bought ebay used injector spider was clean and listed as tested good, all new cap, rotor, wires, and plugs. Started and ran good with no codes for about a 1000 miles now throws P0303 every time you drive it a while 20 miles or so. I can't believe the compression has changed it test good after the rebuild and the electric parts are 2 months old hard to believe they are failing so it leaves the injector spider
anyone tell me how to test the injector without having to pay for dealer visit. Any help would be great!

protech

Re: P0303 problem after a 1000 miles of no problem after new hea

Unread post by protech » Wed Dec 29, 2010 9:15 pm

You should check to make to sure you have spark and compression first, since that is fairly easy to do. If that all checks ok, then you can proceed to checking fuel. The spider unit you've got was new for 1996 and changed from the 1995 and older central port injection spider. You have individually serviceable fuel injectors that are sequentially fired. If you have a proper scanner, and fuel pressure tester, you can try a fuel injector balance test to see if there is a difference on cylinder number 3 (P0303 code is a misfire on cylinder 3). If you can't do that test, you can try to ohm out each injector and see if there is a noticeable resistance difference. You probably have a bad injector, or some restriction heading into the poppet port of that cylinder. I would remove the spider and look for debris blocking the fuel path too. If the injector ends up being bad, it is fairly easy to change.

alfr
Posts: 1
Joined: Fri Nov 15, 2013 7:09 pm

GMC 301 misfire cylinder 1

Unread post by alfr » Fri Nov 15, 2013 7:16 pm

96 GMC 305 engine continues to miss on #1 cylinder. Replaced intake manifold gasket, spider, distributor cap & rotor, Plugs and wires and coil, but it still codes out to 301. I don't know what else to do! HELP!!! Any suggestions would be of great help!! Thanks.

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carriedi
Posts: 2573
Joined: Wed Apr 10, 2013 12:42 pm

Re: GMC 301 misfire cylinder 1

Unread post by carriedi » Sat Nov 16, 2013 4:17 pm

well if you did the injectors, the intake gasket, plugs, wires, cap and rotor that pretty much takes care of anything up top. hows the compression or a problem with the valve train or springs? coolant leak into the cylinder? Did you hook it up to a scanner and look at the misfire counter to see when it is missing?
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