an intake manifold leak can cause a lean problem. To check, spray starter
fluid around the intake manifold gasket. An increase in engine speed
signifies a leak. A dealer did this to my '89, and found the intake
manifold gasket was leaking. He simply adjusted the carb idle jets to
compensate....an easy and cheap fix... But maybe this is not your
problem..??
"Carl Saiyed" <carlsaiyed@REMOVEhotmail.com> wrote in message
news:42fecfb6$1_5@newsfeed.slurp.net...
> The 2.5L in my 89 YJ has been backfiring for a while. When cold, it idles
> smooth and runs fine. When hot the idle can drop as low as about
5-600rpms,
> but sometimes is smooth. Sometimes it will backfire on deceleration. This
is
> only usually if you downshift to slow down. The backfiring is pretty bad,
> sounds like a gunshot. There is a hesitation off idle. Typically, the rpms
> will drop before rising when I press the gas pedal. This is all pretty
much
> when the engine is warm. It's not over heating. I used to smell gas fumes
> when it was cold. Lastly, the tail pipe is pretty black on the inside.
>
> Where do I even start?
>
> Carl
>
>

 

Rusted wrote:
> Sounds like it is runninig too rich. You are gettiing too much fuel, not
> enough air. Turn in the adjustment screws 1/4 - 1/2 a turn and see if it
> runs better. Is the air filter in good shape?

Change the timing chain lately? My Chevy was 3 teeth off when I
finally changed it at 160K. You can't compensate for that with timing.

 

Rusted wrote:
> Sounds like it is runninig too rich. You are gettiing too much fuel, not
> enough air. Turn in the adjustment screws 1/4 - 1/2 a turn and see if it
> runs better. Is the air filter in good shape?

Change the timing chain lately? My Chevy was 3 teeth off when I
finally changed it at 160K. You can't compensate for that with timing.

 

Rusted wrote:
> Sounds like it is runninig too rich. You are gettiing too much fuel, not
> enough air. Turn in the adjustment screws 1/4 - 1/2 a turn and see if it
> runs better. Is the air filter in good shape?

Change the timing chain lately? My Chevy was 3 teeth off when I
finally changed it at 160K. You can't compensate for that with timing.

 

Rusted wrote:
> Sounds like it is runninig too rich. You are gettiing too much fuel, not
> enough air. Turn in the adjustment screws 1/4 - 1/2 a turn and see if it
> runs better. Is the air filter in good shape?

Change the timing chain lately? My Chevy was 3 teeth off when I
finally changed it at 160K. You can't compensate for that with timing.

 

If the EGR valve is getting sticky with carbon, it will cause that.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Carl Saiyed wrote:
>
> The 2.5L in my 89 YJ has been backfiring for a while. When cold, it idles
> smooth and runs fine. When hot the idle can drop as low as about 5-600rpms,
> but sometimes is smooth. Sometimes it will backfire on deceleration. This is
> only usually if you downshift to slow down. The backfiring is pretty bad,
> sounds like a gunshot. There is a hesitation off idle. Typically, the rpms
> will drop before rising when I press the gas pedal. This is all pretty much
> when the engine is warm. It's not over heating. I used to smell gas fumes
> when it was cold. Lastly, the tail pipe is pretty black on the inside.
>
> Where do I even start?
>
> Carl

 

If the EGR valve is getting sticky with carbon, it will cause that.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Carl Saiyed wrote:
>
> The 2.5L in my 89 YJ has been backfiring for a while. When cold, it idles
> smooth and runs fine. When hot the idle can drop as low as about 5-600rpms,
> but sometimes is smooth. Sometimes it will backfire on deceleration. This is
> only usually if you downshift to slow down. The backfiring is pretty bad,
> sounds like a gunshot. There is a hesitation off idle. Typically, the rpms
> will drop before rising when I press the gas pedal. This is all pretty much
> when the engine is warm. It's not over heating. I used to smell gas fumes
> when it was cold. Lastly, the tail pipe is pretty black on the inside.
>
> Where do I even start?
>
> Carl

 

If the EGR valve is getting sticky with carbon, it will cause that.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Carl Saiyed wrote:
>
> The 2.5L in my 89 YJ has been backfiring for a while. When cold, it idles
> smooth and runs fine. When hot the idle can drop as low as about 5-600rpms,
> but sometimes is smooth. Sometimes it will backfire on deceleration. This is
> only usually if you downshift to slow down. The backfiring is pretty bad,
> sounds like a gunshot. There is a hesitation off idle. Typically, the rpms
> will drop before rising when I press the gas pedal. This is all pretty much
> when the engine is warm. It's not over heating. I used to smell gas fumes
> when it was cold. Lastly, the tail pipe is pretty black on the inside.
>
> Where do I even start?
>
> Carl

 

If the EGR valve is getting sticky with carbon, it will cause that.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Carl Saiyed wrote:
>
> The 2.5L in my 89 YJ has been backfiring for a while. When cold, it idles
> smooth and runs fine. When hot the idle can drop as low as about 5-600rpms,
> but sometimes is smooth. Sometimes it will backfire on deceleration. This is
> only usually if you downshift to slow down. The backfiring is pretty bad,
> sounds like a gunshot. There is a hesitation off idle. Typically, the rpms
> will drop before rising when I press the gas pedal. This is all pretty much
> when the engine is warm. It's not over heating. I used to smell gas fumes
> when it was cold. Lastly, the tail pipe is pretty black on the inside.
>
> Where do I even start?
>
> Carl