wicked backfire on deceleration

[CardinalFJ60]

I'm still working my way through the new 40 and futsin' around with random stuff. I got the idle down, passed emissions, and lots of other little things.

Next is dealing with the, as they say back East, wicked backfiyah. the Engine compartment looks alot different than my 60 and I'm not sure what the PO did to emissions, etc. OH...backfires through exhaust, not carb - and only on Decel. I can drive it carefully enough (usually) to not backfire.

When I decel 'quickly' I can get it to really backfire, especially between 3rd and 4th if I'm "gettin' on it". (Ask Subzali if his hearing is back after showing him the BF).

I've done the carb cleaner trick around the manifold...no change in rpms.

I fixed the idle, and it passed emissions with flying colors.

The smog pump is hooked up, but there are other things disconnected/plugged - not sure how they all work together. But other than the backfire it runs really strong. I kinda think that's part of the culprit...maybe it's pushing air and it shouldn't??

I'll take some pics this weekend showing what's hookedup and what's plugged. Since I don't know much about this stuff, I'm hesitant to just pull the smog pump and 'see what happens'. Like, should other things be plugged up or plugged inwith the pump off? Or will it negatively effect things.

Help...I'm babbling - don't know what to do, what to check, etc.

 

[gahi]

A backfiring in the exhaust is usually air getting in to the exhaust somewhere. But a Wicked Back Fiyah, sounds worse than the standard popping.

 

[treerootCO]

your anti backfire valve is not working and no I am not joking

 

[treerootCO]

part #5. Follow the big hose from the smog pump to the air rails. In the middle is the abv. It has one hose that hooks up to the carb. This shuts off the smog pump under deceleration. On the 79 40's the valve is controlled by another on the driver's side fender.

 

[60wag]

Does the 40 have the fuel cut solenoid on the carb? Some people modify it to be on whenever the engine is running rather than running the ground through the emissions computer. The computer actually shuts off the solenoid when decelerating - part of the "slow fuel cut" system.

 

[CardinalFJ60]

excellent!

Once again, thanks for the advice!

Can you remind me of the method to check the fuel cut solenoid? It does have the wire all hooked up...I feel like there's a "click" involved.

Also, is there a way to test the air bypass valve? Or not worth the effort?

thanks!

-s

 

[CardinalFJ60]

Anti-backfire Valve

Just thought I'd post this up...did some more digging after TR's post.

http://forum.ih8mud.com/showthread.php?t=35728&highlight=air+by-pass

 

[subzali]

when you turn the key on you should hear a click at the solenoid on the carb. I don't think it's that though...if that's not working you can also get a "dieseling" effect when you turn the key off...

 

[CardinalFJ60]

ABV going in tonight...

Just an update...I'm puttin' in the new (used) anti-backfire valve tonight...

Fingers are crossed.

 

[trucruiser]

If that dont work , keep looking for an exhaust leak, Thats usually what it is on most autos.

 

[CardinalFJ60]

will do!

cool...I'll be sure keep on lookin'! I'm hoping this does it. But I'm still just feeling my way through the dark.

 

[Uncle Ben]

Possible and a common problem is a cracked exhaust manifold. Pull the heat sheilds and see if you see the tell tale black line.

 

[CardinalFJ60]

manifold...

so...exhaust manifold...not intake.

I assume the carb cleaner spray check wouldn't work with the exhaust side, right? when the intake manny is faulty the rpms rise...but not on the exhaust?

 

[Uncle Ben]

so...exhaust manifold...not intake.

I assume the carb cleaner spray check wouldn't work with the exhaust side, right? when the intake manny is faulty the rpms rise...but not on the exhaust?

Correct. You can do the poor mans stethascope thing and take a two footish length of heater hose put one end to your good ear and move the open end around the area you want to hear. If there is an exhaust leak you will definately hear it!

 

[CardinalFJ60]

perfect.

I picked up an auto stethoscope on sale on a whim like 2yrs ago. I'll finally get to use it!

thanks!

If the valve swap and exhaust manny don't pan out, I'll just get on it hard in my neighborhood between 3rd and 4th, you'll hear the BF at your house. that'll be my signal I'm coming over. (JK)

 

[IanB]

you'll hear the BF at your house. that'll be my signal I'm coming over. (JK)

Lock the doors and hide the beer UB