Back Fire Through Intake
 

I just put new heads on a 2.8L '86 Camaro. It seems to run Ok, but I get a backfire at WOL sometimes. I think I'm either off by a tooth or my valves are too tight. I'm checking this tomorrow. My compression is 125,130,130,135,135,140, does this sound like tight valve? I'm hoping it's my timing.

Is it a Carb or Fuel Injected?

If it's a carb, the mixture is too lean.

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Chevy 2.8L 60° V6
Mods:
?K&N Filter Lid
?87 Formula Hood
?Bosch Platinum +4
?Hi-Flo CatCo CAT
?Flowmaster 80 Series Muffler
?83 Trans Am 15x7 Turbo Fin Wheels
?B.F.Goodrich Radial T/A 225/60-15
?Chevy 2.8L Heddman Headers (Going on soon)

Aol instant messenger: FIREAM

http://www.geocities.com/fiream/RobsCarArtPa.html?994187591828

MPFI - No Mods have been done.

Check, Dist cap and rotor, check for broken spark plugs, and check valve clearance.

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Chevy 2.8L 60° V6
Mods:
?K&N Filter Lid
?87 Formula Hood
?Bosch Platinum +4
?Hi-Flo CatCo CAT
?Flowmaster 80 Series Muffler
?83 Trans Am 15x7 Turbo Fin Wheels
?B.F.Goodrich Radial T/A 225/60-15
?Chevy 2.8L Heddman Headers (Going on soon)

Aol instant messenger: FIREAM

http://www.geocities.com/fiream/RobsCarArtPa.html?994187591828

(Fiream, all 85-up 2.8's are injected; carb'd stopped in '84.)

What is WOL? Wide open Lean? The compression sounds a bit low; how'd you adjust the lifters? (edit: Well, the numbers are low, unless the piston rings are worn out!) I'd suggest ignition timing (not cam timing) before digging deeper.


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-Tom P (Hot rodded 1986 Firebird 2.8l)

[This message has been edited by TomP (edited October 04, 2001).]

Sorry, I meant WOT, what should normal compression be? I adjusted them by moving the pushrod up & down & did not turn nut after the play was gone..

You -didn't- turn the nut after the play was gone? Uh oh...

You set the valves to zero lash; but you need some pre-load in the lifters. Basically what you're doing with the hydraulic lifters is pushing the pushrod into 'em. That's how the lifters are self-adjusting. If the valvetrain loosens up, the lifter "pushes" the push rod out a bit more (all due to oil pressure), and takes up any slack in the valvetrain.

By pre-loading the rocker arms, you give the hydraulic lifters their adjustability. After zero lash, you're supposed to turn the rocker arm nut an extra 90 degrees. This puts the pushrod in the "middle" of the lifter.

If you don't, the pushrod's at the "top" of the lifter, and the lifters can't adjust themselves. It'd be like you were running solid lifters.

On my engine, back at, oh, hell, I guess around 160,000 miles or so, I checked compression. 5 out of 6 cylinders checked between 140-160 PSI. The remaining cylinder, cylinder #1 (front PASS side), was a dog at 125ish PSI... but I had already figured that. (Detonation blew a spark plug to pieces in that cylinder, it probably injured the rings.)


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-Tom P (Hot rodded 1986 Firebird 2.8l)

TomP thanks...I'm going to check compression again this Friday. I did Not tighten down the nut after zero lash. I'm going to post a topic on what others say the compression should be. Sounds like your right. I wish I could pull off the covers without taking off the plenum. Also after it warms up the temp light comes on, could it related to compression, I don't see how. More stuff to check out.