My son has a 97 Jeep Wrangler with a 2.5 L 4 cyl. The jeep ran just perfect until one day it the engine would crank but not start. I proceeded to start changing what I thought would be the problem. First the ignition coil then the crank shaft position sensor, camshaft position sensor and the upstream oxygen sensor. Now this is where it gets confusing.
After changing those items the Jeep would start but it would backfire and sputter as if the timing was way off. After about 10 minutes of running like complete crap, it would level out and run great. My son would drive it the rest of the day and it would be fine. But the following morning it would do the same thing. I assumed the timing was off so replaced the timing chain, spark pugs, spark plug wires, distributor cap and rotor. That did not help.
So, the Jeep will start in the morning but runs like crap for about 10 minutes then runs fine. After that it will stop and start just fine for the rest of the day. Seems to be only a morning thing. Anyone recognize this behavior?
Ok if it ran fine one day but not the next...
Did you have a CEL? Maybe it was just the battery? Or some bad gas?
Throwing a ton of parts at a unknown problem isn't going to fix said unknown problem.
You've replaced so much stuff now I'm having a hard time following what has been done?
That sounds very much like the fuel pump is going out. Try this experiment tomorrow morning before trying to start it... turn the ignition switch on-off-on 8-10 times in a row to give the fuel pump multiple on-off-cycles to get it to deliver more fuel to the engine before you first turn the ignition switch to the Start position. And the engine will sputter & misfire too if the fuel pump isn't able to continue delivering enough fuel on a continuous basis.
If the engine starts right up after doing that, replacing the fuel pump will fix it. It's important not to install a cheap store-brand fuel pump like from Autozone or an Airtex or Spectra from online sources. Go for a Bosch fuel pump, that's the only brand currently known to hold up. I have replaced TJ fuel pumps multiple times over the past 20 years and only the Bosch brand has proven itself to me as one that holds up. My TJ is no longer a daily driver and even if it sits a month without driving it, it starts instantly every time with my replacement Bosch fuel pump.
@ the first reply....why respond to my post if you have nothing to offer.
@the second reply....thanks for the tip. Unfortunately I tried turning the ignition on and off about 10 times. I could hear what I'm guessing was the fuel pump humming for a second or two then it goes silent but no luck. It took me several tries with a lot of sputtering and backfiring but eventually got it going. My son took it to school and brought it home at the end of the day with no problem.
The on-off-on was to see if part of the problem could be from a leaky check valve just outside of the fuel pump itself. But even a bad check valve won't cause it to sputter or not start afterward doing that on-off-on sequence. But a bad fuel pump can, I'm still leaning towards the fuel pump being bad.
My son has a 97 Jeep Wrangler with a 2.5 L 4 cyl. The jeep ran just perfect until one day it the engine would crank but not start. I proceeded to start changing what I thought would be the problem. First the ignition coil then the crank shaft position sensor, camshaft position sensor and the upstream oxygen sensor. Now this is where it gets confusing.
Were these items replaced one at a time, with a check to see if the problem was corrected before the next part was changed? Were the replacement sensors Mopar or aftermarket/store brand? If aftermarket, do you still have the original crank and cam position sensors? Last question, have you checked to see if the Jeep is throwing any codes?
I mentioned before that it would only turn-over due to no spark. I changed the ignition coil and then the crankshaft position sensor and no change. When I changed the camshaft position sensor it would start consistently but die and sputter and backfire until it seemed to "wake-up" and run normal.
It seems that if the fuel pump was bad it would continue to run badly.
These are the codes it gives:
12-11-11-55
Do you have answers for the other two questions:
- Were the replacement sensors Mopar or aftermarket/store brand?
- If aftermarket, do you still have the original crank and cam position sensors?
The reason for asking is it has been noted by numerous people that aftermarket non-Mopar crank and cam sensors tend to be of dubious quality, often delivering substandard performance or failing rather quickly. If you have the previous sensors still, I'd recommend reinstalling the old crank sensor to see if that makes a difference.
Code 11 can mean a few things. It would help point in the right direction if you could get the codes read and find out what the OBDII P codes are that are causing the code 11s. Reading what's been done already would seem to point to the cam sensor but the P codes would confirm it.
Yeah all the replacement parts I used are from AutoZone. I believe I still have the crank and camshaft position sensors. I'll install these and see what happens.
A couple of questions....
Can AutoZone check for P-codes or would I need to take the Jeep to a qualified mechanic?
And do the crank and camshaft position sensors differ for a manual and automatic transmission?
You don't need anyone to check your codes, your '97 can display them on its own. They won't be in P-code format which came along later, they'll be in a two digit format like is explained at
You only need to turn your ignition switch on-off-on three times within five seconds and then leave it on. Wait, any codes stored will start showing up in the odometer in 3-5 seconds. If you did it right, you will always at least get a '55' code which just means no more codes follow.
Only the crankshaft position sensor is different for automatic vs. manual transmissions.
Someone mentioned checking P-codes so I assumed (not knowing a whole lot about Jeeps) that maybe there was more info to the codes displayed on the odometer....(in my previous post I mentioned the codes displayed on my Jeep are...12-11-11-55). If not then can anyone tell me what the double 11's mean?
And say maybe the guy at AutoZone gave me a crankshaft position sensor for a manual transmission instead of an automatic you think maybe it would act up like it is?
The OBDI code 11 can mean a few things and refer to either cam or crank sensors. The corresponding P codes would be more definitive and give a better idea of where the problem lies.
I appreciate all the input. Saturday morning I'm going to try reinstalling the old crankshaft and camshaft sensors to see if that makes a difference. Then I'll get it to Autozone to see if they can read the codes. I'll post results.
Thanks again.
Your Profile is still empty of any information describing your Jeep. And please at least fill out your state too since that matters in some situations. Like California no longer allows stores like Autozone to read diagnostic codes.
I'm not sure how to update my profile but I'm in Texas, the jeep is a 1997 Wrangler, w/ 2.5 liter 4 cyl and is automatic trans.
It has a 3.5" lift and sits on 33x12.5x15.
I'm about to start work on the jeep so I'll post results later today.
Click on My Account as shown in the top-right corner of the below image. Then you'll see two 'Click here to edit' links for your Jeep information and your Profile.
If you have the more modern interface that doesn't exactly look like that, you can still find your links in a similar manner.
Well I worked on the Jeep and here is what I did:
With all the cranking and cranking I must have damaged the starter cause it was spinning but not engaging the flywheel. So I changed out the starter and the Jeep started up on the first try and is running great.
So I did not even get to switch out the crankshaft or camshaft position sensors.
So I'm on my way to AutoZone to see what codes they pickup.
I'll update soon.
Was the jeep sitting for any period of time? I had a very similar issue with my 97 2.5. It was just bad gas and probably some condensation that got in there. I got a Lucas fuel system treatment product. Sorry I don't remember which one and topped off the tank with fresh gas and that cured my problem. Not sure if that will help you or not.
No it's my sons daily driver. And we've cycled through several tanks of gas since its been giving us problems.
Today made it to AutoZone and they use a small hand-held device to check codes. Well it would not even turn on when they plugged it in the Jeep. So they said it could be a blown fuse or loose wires somewhere.
Checked all the fuses and wired and everything appears normal.
Still no answers!!
You all that have been following my post know the weird symptoms of my sons 97 Jeep Wrangler.
So yesterday I replaced the starter (damaged the starter due to the Jeep problem) and the Jeep started on the first try, my son drove it the rest of the day with no issues.
This morning I tried to start it and again with the sputtering, backfiring and dying out.
I reinstalled the old crankshaft position sensor and the jeep started right up. So I guess it could be a bad part. I hope that's it.....
Thanks all for the advice.
Despite all of the wild goose chases described above, I'm still convinced your problem is caused by a bad fuel pump. And if you replace it, make sure NOT to use a store brand like from Autozone or online brands like Airtex or Spectre. Go only with Bosch unless you have masochistic leanings and like to have to drop the gas tank to replace fuel pumps that go bad prematurely.
So far so good! I'm about 99% convinced my Jeep wasn't delivering a spark because of a bad camshaft position sensor. I believe the other weirdness was caused by a defective crankshaft position sensor from AutoZone that I bought to replace the original CPS. Once I reinstalled the original Crankshaft Position Sensor the jeep started up and has been starting in the morning and running great!
So I guess watch out for defective parts!!
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