I have a 1996 Chevy k1500 fleet side with the 5.7L vortec V8. The truck use to start up and run fine for a few minutes, then it would start backfiring and run terrible until it would shut off. I threw every part I could at it but nothing fixed I it until finally I swapped the fuel injection manifold for a duel plane with a Holley and a HEI distributor! That fixed the problem, but with things the way they are now a days I can't afford 6 to 7 mpg so I decided to swap it back to fuel injected recently. When everything was put back together and all new sensors again installed the truck had no fuel pressure. fuel gauge was pegging out so I added 5 gallons and got 60 psi! I tried it again and still nothing so I did a spark test and no spark. I tested the coil with a multimeter and it wasn't getting a signal from the icm so I tested the icm and it wasn't getting a signal from the vcm. So finally I checked the new crank sensor and discovered that the vcm supplied ground on the b terminal middle wire was getting a good ground but with the key turned off but with the key in the on position it would drop from 12 volts to 10 and with the key turned to the run/start position it would drop down to like 2 or 3 volts meaning that the ground was being compromised when the ignition was activated. So I did a regular voltage (black to black) and with the key on I was reading 8 volts! 8 volts coming from a ground circuit isn't good so just to be sure I checked the wiring closest to the vcm and with the connector unplugged the voltage went away so I'm pretty sure the fuel injection computer is toast. But if anyone has any ideas please let me know, thanks.

 

Why did you think a carb would be better then fuel injection? My 98' K-1500 with the original Chevrolet F-I system works fine. I am glad carburetors are gone. They were a pain in the ****. They leaked; they didn't get great fuel mileage, and crossing the Rocky's. they would flood out with too much fuel.I spent too much time overhauling other peoples' carburetors, and needing re-jetting too.

Never again !

 

I carb swapped it because I couldn't get it to run any other way. I suspected the fuel injection computer may have the issue for a while and eliminating the vcm from the equation the engine runs fine carbureted.

 

Holley makes some great, highly modified carburetors these days, the only carburetor I would ever run. If I was a person with a carburetorated motor, I'd use one of those. That said I will NEVER go back to a carburetor engine. In my lifetime I overhauled many types of carburetorated motors, but since 1986, when I owned a fuel injected non-Chevy car, which ran great, until the ignition system had a defect, and the driver's seat almost fell apart (I am not 300 lbs) I sold that car, and it's right been back to Chevrolet's' ever since. At my age, I doubt I will buy another vehicle, but IF I do/did it will be a Chevrolet, no doubt at all .I love all my Chevy's that I've had, and none have had *any* major issues that needed to be addressed at all, even at 350,000 miles.

 

My 99 express 4.3 just died today I just check the signals from the ckp & cmp spark and fuel pressure all are ok seems like ECM fail because the injectors pulse are not synchronizing, any idea here ?




192.168.100.1 192.168.1.1

 

What do you mean it died, do you get any ignition at all when you turn the engine over? Check your injector plug and make sure all the pink wires are getting 12 volts with the key on, the pink and black are signal grounds from the vcm that control the injectors. Have you done a compression test on all of your cylinders? If you have spark, compression and fuel then you should be getting something like a backfire at least. Before I decide it was the vcm I would also check your timing chain for stretch or if it jumped a tooth and check your distributor's rotor orientation and reference marks at TDC#1 to make sure it was installed correctly. If you engine is out of time that can certainly cause a no start condition with an irregular fuel injection pulse. Hope that helps.​​​​​​