hey everyone. long time reader, finally cannot get help through search so im posting hoping someone has the answer. 2000 gmc jimmy 4x4, vin w, 251k kms. driving to work last week truck was running smoother than normal, enough to take notice of. pulled of the road into the coffee shop, took my foot off the brake and gave just a slight bit of throttle to make it across the parking lot. as soon as my foot hit the gas it died with a pretty good bang.got it towed to my shop and waited a week until i could get a fuel pump. i have been worried about pump for a while, gauge issues, low pressure. so i got a brand new delco pump and put it in last night. still no start. have 61 psi and turns over nicely. have spark. when i pour a little fuel in the intake it backfires from the intake with a good bit of smoke. im thinking timing chain? i was thinking injectors but the backfire leads me towards timing. hurtin without my truck (forced to borrow a dodge lol) any help is greatly apprectiated.

 

I take the bang was in the front of the engine?its rare that these chains and gears jump time but with high milege it can happen.

 

did you check to see if the distributor has loosened up and moved? i had a 95 with over 300k on it and the timing chain was original and the timing was dead-on. although back in 95 they werent balance shaft motors either.

i would check the distributor just to make sure. did you change the fuel filter as well? if the fuel pump blew up, it probably filled the filter with all kinds of junk.

just my

 

not clear on the bang. i more felt it than heard it. had the music on and wasnt paying much attention. i pulled my dist cap and the rotor was moving with the motor, so i am back to thinking fuel injectors. did a leak down test and im losing pressure at a pretty good rate. i have a known good spider assembly from my old truck that im going to pop in and try. dist cap was all fine when i took it apart and ive got a new filter on it.

 

I dunno...running smoother than normal....stopped running....backfire...makes me think timing. Maybe something moved and the smoother feeling was because it either retarded or advanced somewhat? The bang could have been a detonation...when a piston was on the way up spark plug fired, trying to force it back down...not a good thing.

Maybe do a compression check on each cylinder? Check the distributor for movement? Put the #1 cylinder at TDC on the compression stroke, take the distributor cap off and see if where the rotor is pointing. Just throwing things out there. But I'm definitely no expert.

 

well just got back from my shop. not alot of progress. swapped the spider and regulator, still no go. just the odd cough from the intake. not exactly a backfire more of a hiccup. put the motor to tdc and took the cap off and rotor was perfect. i was too tired to bother to pull the plug to make sure it was compression stoke. what are the odds it could have jumped a perfect 180*?im really stumped now and really need my truck back. all i can think of now is to put the test light to all the fuses. i have visually checked but ill test to be sure. i should mention that for the past few months the truck would ocasionally have a stumble while accelerating from a stop and way worse if i was trying to take off left.

 

I personally couldn't see it jumping 180 degrees. Do you have a manual transmission? If so, the stumble you had would sound to me like an engine mount. I'm not sure if it is the same type of feeling with an automatic transmission.

 

nope shes automatic. stumble is more of a misfire stumble, although i do need to do mounts eventually. prob going to throw a new cap and rotor at it. hopefully ill get more of a blue snappy aprk out of it. im clutching at straws at this point. thanks for all the help so far everyone.

 

If per say there is wear on time chain and gears it could have jump a tooth or two that would make sort of bang and if bad enough your engine would just pop or backfire.Worst case could have bent some valves also!I would dismantle the front of the engine remove the timing chain cover and see what you got going on inside there.

 

im pretty confident that im in the clear as far as timing. like i said at tdc the rotor was perfectly lined up to the mark and the rotor rotates perfectly with the engine. thats alot of work to get it all apart to check. really baffled here. have proper fuel, have air, have spark and 99% sure im in time. the only thing i can think of is weak spark. i put a spare coil i had around on to try, wasnt it.

anyone ever have a cap or rotor just crap out all of a sudden like that? for me its always been a slow noticable thing. ill admit they are not delco, but have ran for 8 months or so.