[tony673]

Please Help!

My 91 YJ seems to be giving me some trouble. It is a 4.0L, auto.

Occasionally on starting (I would say 40% of the time) the Jeep will start, but then die right away. If I immediatly try to restart it, it will just crank and crank with no fire. If I return the key to the off position, then turn to the on position, wait a few seconds, then attempt to restart, it will ususally start right up. I have tried pressing the gas pedal a little upon starting once I hear the firing, but it is to no avail and makes no difference. This problem may or not be related to the next one:

While driving sometimes, the vehicle will feel like it has completly lost power. The vehicle does not stall or backfire, it just feels like the car won't "go". It will happen during any driving conditions (acceleration, cruising, and slowing down) and only lasts one or two seconds. Other than those issues, it runs perfectly.

I have recently replaced the catalytic convertor, muffler, fuel filter, spark plugs, wire, distributor cap, rotor, oil. I made sure that both the cat and the fuel filter are flowing in the correct direction, and the fuel pump does turn on when the key is put in the on position (I hear the click and a quick hum). These symptoms existed before I changed the above parts too. Also, I've ran SeaFoam through the TB and the fuel tank less than 400 miles ago.

Anyone have any ideas?? I have to drive this rig through a pretty bad part of town to get to work every day and I REALLY don't want to get stranded. Any help would be greatly appreciated!

[JGBrown]

No help but just a comment, I've got a 2.5TBI thats doing the same damn thing, its driving me up the wall.

[rustywrangler]

CPS/ crank position sensor asuming your air filter isnt all clogged up.

[tony673]

Oh, yeah, the air filter's new too.

I was thinking along the lines of the CPS, but wasn't sure if my symptoms matched everyone else's that have replaced their CPS. I have no CEL codes except for a O2 sensor code, but I don't think that the O2 sensor would prevent starting.

[rustywrangler]

Originally Posted by tony673

Oh, yeah, the air filter's new too.

I was thinking along the lines of the CPS, but wasn't sure if my symptoms matched everyone else's that have replaced their CPS. I have no CEL codes except for a O2 sensor code, but I don't think that the O2 sensor would prevent starting.

YES YES YES, the o2 sensor can do alot. If you have a code for it you should get that replaced before doing any other stuff. I am betting that your CPS is bad as well but you may as well do the o2 first.

[tony673]

Well thanks for the tip, but I think I'm going to try the Crank Position Sensor first. It's a little cheaper and the symptoms seem to match a little better.

[rustywrangler]

Originally Posted by tony673

Well thanks for the tip, but I think I'm going to try the Crank Position Sensor first. It's a little cheaper and the symptoms seem to match a little better.

But if your O2 sensor is off, you can be having these problems as well.

[tony673]

As far as I know, though, the engine doesn't run off of O2 sensors at startup. It runs "open loop" until the motor is running for a few seconds, then goes "closed loop" once the engine is started. So an O2 sensor probably wouldn't be the problem with the no start.

The more I research this, the more my symptoms match a faulty CPS (or CKS). Since that sensor is cheaper and I'm really broke cause I own a Jeep, I'll start with that. The rig has 128,000 miles on it, so the CPS could probably use a replacement anyway. I WILL fix the O2 sensor very soon though, as it may be responsible for the other symptoms.

[rustywrangler]

That sounds like a plan. Just so you know though, a faulty o2 sensor can change how the computer manages the engine and can cause you to kill a cat converter and muffler again.

[alc60560]

Mine had a similar problem. After changing the cps, o2 sensor, I changed the coolant temp sensor. You know the one in the thermostat housing. It runs great now