98 5.7 runs ruff.

[trapperman83]

OK got a 98 5.7 with 195k on it. We replaced lower intake last year with plugs wires and cap an rotor and new dist. Gear. Well bout 2 weeks ago it just started running really bad at idle it shakes the truck but get going 30-40 it seems to be fairly OK. CEL will flash when u get above 30mph. I scanned it and it showed Bank 1 sensor 1 Bank 2 sensor 2 shows multi cyl misfire and #4 misfire. So I replaced the bank 1 sensor and it also showed an EGR code so I replaced that as well. And it made no difference. So I figured i d replace the upper plennium gasket and when I removed it I noticed it was wet with fuel back by the 5&7 injectors it was all dry around the rest of the injectors but back there it had the carbon washed off. So I replaced gasket and it still runs ruff it starts a little easier now. But it still ruff. Did a leak down test on fuel system pump is running 56-58psi.. Gonna replace the plugs next cuz there coal black. But I'm wander a out those injectors? Are the cats plugged? Thanks for the help.

[operator556]

Your fuel pressure seems to be low. Anything below 60lbs of pressure and you'll start to have misfire problems. Could be time for a new pump

[2018GMC]

56 - 58 psi is normal at idle. The only official spec is 60psi key on engine off.

 

http://www.gm-trucks.com/forums/topic/173183-96-98-fuel-pressure-spec-57-vortec/

 

Replace both O2 sensors closest to engine. Or better yet replace all 4. They are cheap at rock auto.

 

Did you inspect and clean the poppet injectors when you did intake gasket?

[dcheeseman]

If its wet when you removed the intake.....sounds like some leaky injectors. I'd consider replacing the whole spider injector assembly

 

Daniel