racsan2448

Hey guys

I have a junk yard 2000 5.3 that was just freshened up internally and put into a 54 Chevy truck. It had 160k km on it. At times it will start and run perfect. Other times it will turn over, but backfire through the exhaust and intake and won't start. If I cycle the key on and off a few times trying to start, it will eventually start and run perfect. When it does start, it starts within two cranks of the engine. Every time I turn the key on the fuel pump pressures up. I did not change the crank sensor, but put a new cam sensor in.

Thanks for any help
Jeff

G Atsma

I would thoroughly check ALL connections for a possible intermittent loose or bad connection. Sounds like a hit and miss situation.

racsan2448

I've been through all connections a couple of times. I'm leaning towards the crank sensor or cam sensor as the engine seems to be firing on the wrong cylinder, but don't know enough about what each sensor controls. I can start it hot or cold multiple times running perfect every time. Then when I try to stat it will backfire and no start. This can happen one to three times, then it will start up immediately and run perfect again.

Thanks
Jeff

NHRATA01

iTrader: (10)

My memory isn't perfect (sorry hate to tell you to go search because you probably already have) but I swear I've run across several posts over the years basically stating that cranking 2-3 separate times before firing is a hallmark of a crank sensor issue - supposedly the pcm will then use the cam position sensor as a backup for the ignition trigger once the crank is deemed no good. Sorry I can't be of better help.

racsan2448

Thanks for your reply. Yes I have done a search (at least I think I did it right) and did come across similar issues, but not exactly the same. I agree with you and I'm leaning to the crank sensor.

Thanks again
Jeff

G Atsma

It's actually the other way around. When a CAM sensor is bad, it will crank longer until the ECM figures out where the rotation is. If the crank sensor is bad it will not start or run.

racsan2448

Update: I changed out the cam sensor and the engine fires up perfect every time.

Thanks for the guidance. Very much appreciated
Jeff

NHRATA01

iTrader: (10)

Thank you for updating as I'm sure someone will find this useful in the future - and apologies for being 180 degree opposite with the cam/crank sensor as G Atsma was nice enough to correct. Dang memory...