97 Silverado 5.7

robinap · January 4, 2011

In July 2010 my friend and I were driving down the highway 55 mph and the check engine lamp came on, the truck still runs and drives 100% ok now i pull out the superchips programer from console and pass to the driver who plugs it in for me. to check the mil, well i pushed the wrong button and started a tune and coruppted the flash in the pcm, Instantly the truck dies. I knew we needed a tow. We hadiy towed the our shop and i put on the snap on scanner i forget what i saw. I booked it in to the nearest gm dealer to flash the pcm. I borrow a neigbors pcm to get driving to the dealer. Well the truck ran but not well with the borrowed pcm. It missed badly and runs the best past 2500rpm and up but not right. I thought well this ecm maybe a differnt year and tune . Finally got it to dealer installed dead ecm had it flashed to correct # and truck still runs the same as with borrowed computer, it miss fires terbible just shakes bad only codes are for missfire on 4 and 7 the truck barely starts and doesnt idle. Ive swaped out some stuff like mass air and ign mod. and inpect cap rotor and plug wires, coil wire, spray with water and no change ive . I run it for a hour like this still no change what gives , It has spark on 4 and 7 also and has new plugs . Ive sprayed gas through intake to see if injector poppets clogged and no change. not sure where to head next. Ive double check its flash file . No noticeable vacuum leaks too.

SouthCo · January 4, 2011

Welcome. I have no idea but good luck and here's a bump.

rodram · January 4, 2011

Hi... if you have spark on all cylinders, then the issue is likely related either to fuel or timing ...

.. these 96-99 5.7L Vortecs can develop issues with the clogged injector poppets ... so I would get some good injector cleaner run through the system ... some people swear by Seafoam in the fuel tank for this purpose... or find some other good quality product ... you could also remove and inspect them individually and clean (or replace) as necessary ...

.. I would also check other issues with fuel delivery ... check the fuel pressure .. on your engine the fuel pressure should be 61 to 66 psi to maintain proper operation of the injector poppets ... low fuel pressure usually indicates the need for a new fuel pump

.. also, if you can't remember when or if the fuel filter has ever been changed, then get a new one and install it (... along the fuel line attached to the frame driver's side just behind the cab...)

I hope this helps move your diagnostics along ...

robinap · January 5, 2011

I testesd fuel pressure was right on spec . I forgot to mention that in earlier post. Also the time the truck was running fine on the road to killing the computer to intalling a used pcm was only 2 hrs I dont get it it seems related to pcm or something got screwed up from pcm failing.