need help

[cobrasbutterfly]

I was wondering if anyone would know why my jeep backfires when cold, after if warms up it does not do it bad just minimal. We have replaced the o2 sensors, distributor cap, spark plugs and wires. I was running great for about a month then went back to doing to same thing PLEASE HELP

[Roger]

How old is your timing belt? They stretch over time and need to be replaced. Also, have you checked your timing?

Oh, and welcome to MJR! There's some really smart guys on here and may have better advice. You might try posting in the appropriate technical section. I hope you resolve this issue quickly.

[Materdaddy]

Kent, WA? I have relatives there and used to visit as a young child. Sorry I can't help with your backfiring.

[Russ Chung]

You didn't specify what year or engine you have but it appears to be a temperature related mixture problem. Since you said that you changed the distributor and O2 sensors, I'm guessing that you have a YJ with an HO engine. I would focus on the sensors that provide temperature feedback to the computer such as the engine temperature sensor, the outside air temp sensor and the intake air temp sensor. My guess is that when the engine is cold, the computer thinks it is warm so it makes the mixture too lean.
The ODBII data from my TJ shows the engine, OAT and IAT readings but I don't know if a pre-1996 engine provides that data.

[Lumpy Grits]

I was wondering if anyone would know why my jeep backfires when cold, after if warms up it does not do it bad just minimal. We have replaced the o2 sensors, distributor cap, spark plugs and wires. I was running great for about a month then went back to doing to same thing PLEASE HELP

Need info on your Jeep. Is it carb'd or FI?
What work have you done to the engine.
One thing you can do is to be sure ALL of the manifold bolts are tight.
Also-check your vacuum lines.
LG

[cobrasbutterfly]

oh sorry it it is a TJ 1997 Wrangler. Straight six. It has been a couple days it has been running better but still back firing. I will have the timing checked and let you know.

[Lumpy Grits]

CK the trouble codes.
Other than the back-fire on deceleration. Does it accelerate OK?
Have you ck'd the vacuum hoses? Manifold bolts?
The 'puter pretty much controls timing.
LG

[SKIDOG74]

Help? Need opinion/expertise and/or pointed in right direction. I have a 95 jeep wrangler yj 4.0 l in-line 6cyl. I rebuilt upper and lower with pistons, main, rod bearings, honed cylinder walls. When i took off original timing chain. Marks were off one to two teeth. When put back together ran weak! I mean weak. 1it ran, but 1st through 5th were weak power. Could hardly make up a hill.

When i put back together, i aligned timing chain marks, distributor bug facing #1 spark plug while piston #1 was at tdc. Ran like shit. So i advanced a tooth or two or three and even retarded it one, two, three teeth. No start. Then i went 180 out, started but ran worse???

Replaces crank also. That only goes in one way right? I cant mess that up??? Please help me get my baby running????

[Lumpy Grits]

Help? Need opinion/expertise and/or pointed in right direction. I have a 95 jeep wrangler yj 4.0 l in-line 6cyl. I rebuilt upper and lower with pistons, main, rod bearings, honed cylinder walls. When i took off original timing chain. Marks were off one to two teeth. When put back together ran weak! I mean weak. 1it ran, but 1st through 5th were weak power. Could hardly make up a hill.

When i put back together, i aligned timing chain marks, distributor bug facing #1 spark plug while piston #1 was at tdc. Ran like shit. So i advanced a tooth or two or three and even retarded it one, two, three teeth. No start. Then i went 180 out, started but ran worse???

Replaces crank also. That only goes in one way right? I cant mess that up??? Please help me get my baby running????

Maybe, you should start your own thread....:wink:
LG

[4xfiend]

Tj's have a timing chain. They don't wear out like belts.

Backfire issues while cold are usually a CPS issue.

[RAT]

Have you read the trouble codes yet? Best way to trouble shoot. Do this first. If there are none it is probably not a sensor. Could be a vacuum leak. You say you changed the plugs. What did they look like? Any of them way dirtier than the others? But really. Get a code reader. Post up any trouble codes.