Car backfires on acceleration
11-08-2010, 05:24 PM
#1
Staging Lane
Thread Starter
iTrader: (1)
Join Date: Apr 2010
Location: va
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
Car backfires on acceleration The car is a 94 z. Every now and then my car will backfire and sounds like its coming from the intake. If im crusing at say 25 and hit the throttle half way or so it will backfire and take off, and when I hit the throttle for it to downshift. Other than that it runs fine and like I said it only does it every now and then. My buddy said its doing it because its running really lean. Car has stock ported aluminum head and intake along with comp 306, with ful bolt ons and tuned by madz28. I checked my fuel pressure and it was fine.Pulled the plugs and they looked to be running lean. Does this sound like im not getting enough fuel to the motor? I would think it is since the motor is just h/c/i and bolt ons. And I can take it into high rpm's without it running bad. I havent beed able to see what the duty cylce is at WOT but im working on it.
11-08-2010, 08:13 PM
#2
Don't think you're in a lean condition. Sounds like you're not completely lighting the mixture in the cylinders when you hit the throttle. Extra fuel lights off in the exhaust and you get a backfire. What was the gap on the plugs when you pulled them? Have you checked and set the TPS position for correct voltage at idle > WOT?
11-08-2010, 08:48 PM
#3
Staging Lane
Thread Starter
iTrader: (1)
Join Date: Apr 2010
Location: va
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
Ill have to recheck the plugs again which I might just replace. Its been a few months since I had pulled them and they were gapped fine. And I did check the TPS and that was reading fine. I did put roller rockers in about a year ago i guess it was and I want to say it started doing this after I installed them and I have adjusted them plenty on times and it didnt change so they should be adjusted right. Would a coil or opti cause this? They do have 100k miles on them.
11-08-2010, 09:31 PM
#4
Ahhh... in that case you may still be a little too tight on your lifter preload. An excerpt that originated I believe on Crane's site in the past:
"...with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine."
What lifters do you have and how much preload in 'turns' did you set them at? Did you measure & maybe replace the pushrods after the head work? Might have needed a slightly shorter PR if the heads were milled.
"...with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine."
What lifters do you have and how much preload in 'turns' did you set them at? Did you measure & maybe replace the pushrods after the head work? Might have needed a slightly shorter PR if the heads were milled.
11-09-2010, 07:06 AM
#6
Staging Lane
Thread Starter
iTrader: (1)
Join Date: Apr 2010
Location: va
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
It has the stock lifters in it for now. I set them and half a turn if i remember right its been a while. Only thing is I adjusted them plenty of times and turned them different after it still backfired (1/2 turn, 1/4 turn, full turn) They are new PRs but there same length as stock just hardened PRs.
