'97 Cherokee 4.0L 4WD 80,000 miles

I've been experiencing this for more than a year so I can describe it pretty accurately.

When CEL is ON. Car starts and runs fine. Code is evap system leak. About 18 mpg. Have done the gas cap etc, but no longer need emissions test so no worries.

When CEL is OFF. Car starts but bucks, hesitates and even backfires. This lasts for 60 seconds or so or about 1/4 mile. Then clears up and runs fine. About 15 mpg. This occurs approximately 3/4 of the time and includes any start condition - hot or cold. When the CEL comes back on, the problem goes away. This cycle can take weeks or hundreds of miles. Or it can cycle from day to day.

I have changed fuel pump, wires/plugs/cap, injectors, TPS, Idle air, MAF, MAT, coolant sensor. Fuel pressure is a solid 40. No leakage.

I know it sounds crazy, but can anyone offer an explanation? I have not changed the crank sensor or the CAT. The CAT is original, I think.

Thanks

 

What code is it throwing?

 

You might try taking the battery cables off and touching them together and re installing. That will clear the ECU

 

There is a solenoid in the evaporative control system, and it can become defective, causing strange engine running symptoms

Check the codes

Apparently it can give off a buzzing sound

Maybe a vacuum leak ?

Details in the FSM, but its obscure!

a member chased this issue for ages before he found the problem (replaced the solenoid)

 

I agree with the recommendation of removing both battery cables, touch them together for 30 seconds, then reconnect. Sometimes there are electrical gremlins and just like your computer or phone needing to cycle power, a reset can help.

Also, I'm not saying this is your problem but the fuel pressure spec for your 97 4.0 XJ is 49.2 plus or minus 5 psi. If you are truly at 40 psi (I'd verify with 2 different gauges), then you are definitely out of spec.

Good luck and keep us updated!

 

Evap system leak.

 

Thanks for this idea. I'm gonna disconnect that solenoid and drive it awhile.

 

Thanks for this. Will try it.

 

time to check the vacuum lines to the canister.