I'll tell ya guys i've been having some really great luck with my cars here for the last couple weeks. I had to put a belt tensioner and water pump on the wifes grand prix and then 1 1/2 days later my jimmy takes a crap. Lol. So, anyway heres the story.

I was helping a friend move last night, had the car trailer loaded on the back. I was kinda smelling gas around the back when it was sitting there for a while not running. I thought maybe the canister purge solenoid went bad (even though i replaced it about 6 months ago). So i wasn't really to worried about it at the time yesterday. We left and i got out on the highway and made it about 4 miles down the road then it started spittin and spudderin and a strong gas smell then it died and it backfired through the exhaust right after it died, so i pulled over to the side of the road and tried to starter it back up and as i tried to crank it over it turned over and felt off balance went it was cranking over and it back fired though the intake. I havent had a chance to check for codes yet. It seems like maybe the timing chain jumped a tooth or the crank sensor went out. The funny thing is that it super quiet up front it didn't sound like the timing chain had any slop in it. I will check for codes and post them up if there are any.

Edit: There are no codes and the fuel pressure is 60psi then drops to 57psi after the pump kicks off. I really feel that the timing chain jumped a tooth but just would like some extra input or see if any one else has had this happen.

Update: I lined the marks on the harmonic balancer to the timing cover and everything was normal. i even took the distributor out and looked at it and everything appears normal so i guess a compression check is in the plans for tommorow. hope it didnt drop a valve.


Any help will be greatly appreciated and thank you all in advance.

 

Well i changed the timing chain on the jimmy b/c it was stretched. The valve timing is correct and it still turned over off balance but not as bad as before. i changed the CKP sensor because it still was backfiring through the intake with everything set right.

I checked the compression to find that the #6 cylinder had low compression. 90psi compared to the rest which were better than 120psi. i loosened the rocker arms completely on the #6 cylinder then pressurized it with air to find that it was leaking through the intake manifold. So, i removed the heads to find a blown head gasket on bank #2.

i had the heads rebuilt and put it all back together and now it turns over balanced like it should, but it is still backfiring through the intake and wont run. So now im wondering if the new CKP sensor is bad or maybe the ignition pick up coil?


Here is a list of everything i have replaced.

Heads rebuilt and all necessary gaskets
timing set
CKP sensor
plugs
wires
cap and rotor
fuel injector/ mfi conversion (i thought it was a good idea since i had it apart anyways)


I have double checked the distributor a bunch of times and even with another bravada and i know for sure that the distributor is in right.



Any help would be greatly appreciated. Thanks.

 

So, with the balancer lined up with both of the marks on the front of the motor, the rotor in the distributor is pointing at the 6, correct?

 

yes. on the compression stroke. i checked the CKP sensor and it was 810 ohms. how do i check the pickup coil for resistance? which terminals? i believe i read 500-1500 ohms.


thanks for the help. i really need to get my jimmy running again.

 

Well i put a new ignition pick up coil in the distributor and no luck still. Everything is set the way its supposed to be and it still backfires through the intake. I dont know why this thing wont run and im out of ideas. Bout ready to just take it to the shop.

 

i think the new timing cover from autozone may be made incorrectly. i think the spot for the sensor may be wrong causing the CKP sensor to set too closely to the reluctor on the crank hence making the timing off and causing the backfire through the intake.

i guess ill see if my conclusion is correct. The bad thing is that gm wants 120 for the timing cover(at the stealer). I really hope i got it figured out.

 

well after taking a break from the jimmy i figured its about time to get back with the program. i tried pulling out the CKP sensor a little bit to see if it made a difference at all, and of course it didnt help me one bit. i measured the old timing cover to see how far it was from the edge of the hole to the machined surface where the CKP sensor sits and it was .627". so i'll have to take the new timing cover off and check it also. does anyone know what the tolerance is on this? Also has anyone else ever heard of anything like this happening before? i've searched all over but found nothing. So if anyone has any ideas they are appreciated.


thanks, Dustin

 

did you ever figure your problem out. I have same issue except mine back fires out exhaust

 

no im still messing around with it. i took a break on it for a few months b/c i got tired of messing around with it and ive been busy with other vehicles. i done about everything i can think of except removing the timing cover and examining it to make sure its correct and changing the computer. No one else on here seems to have ever had the same problem or knows anything about it and if they do their not talking. ive seen alot of stuff but never anything like this. have you checked your timing chain?

 

Hurbert; What state are you in?