2004 Jeep LJ 6 cylinder auto

Last week, my check engine light came on. Just in time for my now overdue state inspection. Just got paid on Friday, so I went to auto place to get needed parts and to read the OBD2 codes. Looks like the dreaded combo of camshaft synchronizer and crankshaft position sensor are wonky.

I watched a you tube video of how to replace these items as well as a video for the TIPM fuel relay issue.

This morning, I had plans to go somewhere, so I took the parts and some tools with me in case of emergency.
Well, at one stop, it cranked several times without starting. Very unusual up to this point. Very strong battery, so no actual traditional jump was needed.

One comment in the video mentioned that if ECM doesn't get both signals, it won't start the fuel pump.

So, very MacGyver like, I took a spring from a ball point pen stretching it out as somewhat straight wire.
My kid cranked the engine, I jumped power from an accessory position to the fuel fuse. Started right up.

Ran fine, but not restarting, still cranks like crazy with starting occasionally. Got to replace those sensors now.

Thought I'd share a success story as I'm usually a reader verses a contributor here. Might help get someone home if stuck somewhere.

This message has been edited. Last edited by: TRIO,

Cool.

A good working knowledge of your ride is always a plus.

When I bought my Suburban as a repo from the bank, it wouldn't run. They sent an on site mechanic to try to fix it before selling it.

I had placed the highest bod at $503.

New starter, alternator, injectors, all kinds of stuff. I turned the key. Nothing. Again... Nothing.

Checked the fuses. Pulled the fuse for the dome light and put it in the empty slot for the fuel pump.

Cranked right up and idled smooth as can be. When I drove off, the guy at the bank had eyes about the size of dinner plates.

While watching You Tube videos, I fell asleep. When I woke up, this video was playing. I know nothing of the video creator, but his comment saved me towing expense.

https://youtu.be/9lrnFpEI5WU

This message has been edited. Last edited by: TRIO,

Cool story about your good fortune at the auction!

It is funny how easy people throw stuff on the car without knowing how to fix properly.

Another example is the "death wobble" 4x4 are known to get. Often mechanics replace ball joints and hub bearings only to find out that it is often just bushings on the control arms. I have that wobble now, and my lower arm bushings are deteriorated. More to replace for it to pass inspection.

Sounds like either a Relay or PCM is going bad.

quote:

Originally posted by .38supersig:


Checked the fuses. Pulled the fuse for the dome light and put it in the empty slot for the fuel pump.

Cranked right up and idled smooth as can be. When I drove off, the guy at the bank had eyes about the size of dinner plates.

Sounds like the previous owner pulled the fuse as a makeshift kill switch.

quote:

Originally posted by Jelly:
Sounds like either a Relay or PCM is going bad.

I would have thought the same about the relay, but the codes reflect issues with the other sensors. I don't know much about the electronics in a car. So, I'm open to suggestions to look into getting it fixed.

My mechanic did swap out the item that contains the fuses and relays from another Jeep a while ago for the fuel pump relay issue. He said that the relay is soldered in place. What are the odds that it is that same issue again?


If the ECM or PCM or whatever it is called, is bad, what OBD2 code would that be?

quote:

Originally posted by TRIO:

If the ECM or PCM or whatever it is called, is bad, what OBD2 code would that be?

All of them....or none of them. I know little of jeeps, but in an 04, you're probably only looking at 1 computer for engine related issues, maybe another for transmission.

If the computer is bad, it can look like a bad sensor - or 2 as in your case. or it can just take a shit & not run at all.
You're probably not going to diagnose that over the internet or youtube. Without swapping parts until you find the bad one, you need an experienced tech & a good scan tool (not an autozone one).

All that said, I wouldn't jump to the ECU based on what you've said so far - I think you're on the right track. On some older cars, the 'won't start fuel pump' could be bypassed as the fuel pressure sender would take over control of the relay once it detected adequate fuel pressure - sounds like yours is one. Probably once started, the crank position sensor was giving enough of a signal for the ECU to not throw a fit.

quote:

Originally posted by TRIO:
It is funny how easy people throw stuff on the car without knowing how to fix properly.

Sadly, many (but not all) folks working in car repair garages, especially dealerships, are “parts changers”, not “mechanics”. A mechanic works to understand what is going on and adjust, repair, or replace whatever is not working correctly. A mechanic will read codes, but runs what the computer says through his filter of common sense. A parts charger reads the codes, changes whatever parts the computer says to change. If that doesn’t fix it, he’ll read the codes again and change whatever else the computer says to change without understanding why, applying logic, or common sense. Sigh…

TRIO, have you pulled the codes yourself?

I can't think of any reason that the relay would have been soldered in place from the factory. The power distribution module should have them all slide in and out (maybe I am thinking of the wrong year?).

Most of the Diamler-Chrysler vehicles of that time frame will have a powertrain control module located on the passenger side firewall. There may also be a multiplexer that controls everything else (AC, radio, etc...) located in the instrument cluster assembly.

quote:

Originally posted by Nismo:
Sounds like the previous owner pulled the fuse as a makeshift kill switch.

Yup.

OK, here is an update...

The codes were: P0340, P0351, P0352, P0353, and P1391.

I had misplaced confidence in using a wire to jump my Jeep. Got stranded at a shopping center, tried the wire again and nothing. So I turned key forward and heard the fuel pump prime. Oh boy, humble pie time. Must have been a fluke the first time with using that wire.
It just cranked and cranked without firing.

Since it was so late and no tools on hand, had to get it towed home. This morning, I start with the camshaft synchronizer sensor. Noticed something odd: the magnet was stuck onto the rotating metal shutter that causes the sensor to know the timing. I know that isn't how it is supposed to work. My plan was to superglue old magnet back into it's proper place. Then figured if the silver solder broke loose, the glue won't hold.

So I replaced the sensor instead. Jeep fired up on 1st try. Drove it around for some errands, with tools this time. Check engine finally goes away. Starts and runs great now.

The two hardest parts of this ordeal was convincing AAA that it wasn't a battery or starter issue and a tow was valid. Second, getting that damn clip off the sensor!

Thank you all for the suggestions and discussion.

Fantastic!

I have a 2004 Grand Cherokee with the inline 6. I know you can turn the key on and off twice then leave it on the third time and it will display any existing codes on your odometer. Just turn the key far enough to turn on the dash lights. Write down the codes and look them up on the internet, Like "Jeep 0340'. You can remove the negative battery cable for 30 minutes to clear the codes.

Texas Bob, thanks, that's a good tidbit to know. I had forgotten how to do that.

Many times you'll get multiple codes which only show as a result of the initial code, once you fix the sensor the others may go away, since they happen because the first fault causes other issues.

Best you replaced it vs using Gorilla glue and finding yourself stranded with a non running Jeep....

quote:

Originally posted by HRK:
Many times you'll get multiple codes which only show as a result of the initial code, once you fix the sensor the others may go away, since they happen because the first fault causes other issues.

Correct! Once the sensor was replaced, all of the codes cleared up.

quote:

Originally posted by HRK:Best you replaced it vs using Gorilla glue and finding yourself stranded with a non running Jeep....

Yep, good call!

quote:

Originally posted by TRIO:So I replaced the sensor instead.

quote:

Originally posted by Texas Bob C.:
...I know you can turn the key on and off twice then leave it on the third time and it will display any existing codes on your odometer. Just turn the key far enough to turn on the dash lights.....

Did this today to see if the last known codes were still there. Even though "check engine" light was off, the codes were still stored.
Including a code from a previous separate incident from about two weeks ago. Very handy tip!

I envy your knowledge and resourcefulness. My vehicles have two conditions, runs great and shits broke. When shits broke I step away until runs great has been restored.

My very smart industrial engineer friend explained that the sensor uses the "Hall Effect" to know the signal. Instead of a moving magnet, this one uses a stationary magnet with a moving "vane interruptor". My issue was that the magnet being stuck on the vane, that I previously called a shutter, is that the sensor was getting two signals at 180 degrees apart. Creating two weak signals. One signal was correct, the other was not. No wonder the car was so wonky!

TXJim...I know my limits, especially with electronics. If a simple replacement doesn't fix it, the vehicles goes to my more experienced mechanic.

Basically, I'm a cheap bastard as I can't always afford the repair bills. Between being under-employed and kid in college, very little cash. So I do as much as I can.

Many years ago, I witnessed a decent mechanic tune a car withut a timing light. Car was stuck far away from tools, so he replaced the cap and rotor, then tuned it by ear. At the time, I was young and dumb and very impressed.