Engine back firing at 4000rpm

[Jeff Strube]

I have a 87 GN that is backfiring at 4000rpm. Changed coil and module wires spark control meter computer and chip doesnt go away. Not shure what to look at. Mybe grounds on the block.


Thanks Jeff

 

[ttypewhite]

I bet you its your mass air. Tap it with your knuckle when the car is running. If its bad it will stumble at bit when idling.

 

[onefastgn]

Or your 02 sensor might be getting bad do you have a scan tool?

 

[Jeff Strube]

NEW O2 changed Mass air no differents

 

[Fuelie600]

Jeff, How many miles on the motor? Are you still using the original timing chain? Are you still using the original valve springs? Brian

 

[Jeff Strube]

There is 40,000 mile on rebuilt engine double roller can 40,000 mile vavle springs

 

[83ttypecooled]

Hi,
I had a lot of misfire problems that I had initially attributed to ignition which ended up being fuel starvation. It was obvious when I took a ride with scanner connected, O2 voltage was in the cellar at .1 v while I was on it. A Walbro 340 fixed all that. If you don't use a scanner, please start. While this may not be your trouble, you need additional information, which a scanner will very often provide. Good luck, keep up the posts!

 

[bogie1]

My backfire turned out to be fuel related also. The top hose clamp had come loose on my XP pump and only acted up under boost. I had replaced everything electrical and regounded everything trouble shooting the backfire. Car runs great now.