97 4.0 misfire issues

[mdsilva75]

Hi everyone,

I have been chasing a misfire issue on my 97 TJ 4.0 with just shy of 150,000 miles. I am getting codes p0300, p0303, p0304. It idles rough and has a hard time accelerating especially with any kind of uphill grade.

Things I have already done is new spark plugs. Autolite coppers. New spark plug wires, new distributor cap and rotor. New ignition coil. New O2 sensor. Had to go with Denso since the NGK seems to be discontinued. Checked wiring and grounds as much as I could see. Checked ignition coils and pressure but not changed.

Any help to look next would be appreciated. Previous owner was a hack.

Thanks again. You guys are always a great help!

 

[macleanflood]

Crank position sensor fixed mine. No Mopar available so I used a Napa Echlin.

Did everything you did and more... that's what fixed it.

-Mac

 

[mdsilva75]

Thanks Mac. I'll give it a shot.

 

[Jerry Bransford]

There was a TSB issued for multiple misfires on some 97/98 TJs. The problem was found to have been caused by a bad/weak batch of valve springs. Replacing them fixed my 97's multiple misfires. However by now weak valve springs could have damaged the valves and/or valve seats so you may also need a valve job. The same valve spring part numbers are still valid for replacements, they pulled all the bad springs out of the system.

 

[mdsilva75]

Thanks Jerry. Hope it is not that but I will check it out.

 

[hear]

There was a TSB issued for multiple misfires on some 97/98 TJs. The problem was found to have been caused by a bad/weak batch of valve springs. Replacing them fixed my 97's multiple misfires. However by now weak valve springs could have damaged the valves and/or valve seats so you may also need a valve job. The same valve spring part numbers are still valid for replacements, they pulled all the bad springs out of the system.

So what all is involved for a valve job on our engines? is it just a matter of replacing parts and checking clearances, or does it involve machine work? Totally clueless on this.

 

[Jerry Bransford]

Thanks Jerry. Hope it is not that but I will check it out.

You have already replaced the easy most likely parts, that's why I suggested it's very likely going to be fixed by the new valve springs or perhaps the valve job too. It happened to me too.

 

[Jerry Bransford]

So what all is involved for a valve job on our engines? is it just a matter of replacing parts and checking clearances, or does it involve machine work? Totally clueless on this.

A machine shop typically performs a valve job. Lots of info on this at https://www.google.com/search?q=wha...S4xOC4ymAEAoAEBsAEP&sclient=mobile-gws-wiz-hp

 

[mdsilva75]

Haven't been able to check anything out yet but it smells really strong of exhaust. So strong that I only take it to work and back right now. The check engine light will blink when accelerating to get on the highway and then stop blinking. Driving me nuts. Any thoughts?

 

[macleanflood]

Any thoughts?

Cracked exhaust header...my 97 came out in three pieces...

-Mac

 

[Tj02Wrangler2.5L]

Thanks Mac. I'll give it a shot.

Did you make sure the gap on spark plug is at spec? Clean throttle body too. It won’t hurt.

 

[Tj02Wrangler2.5L]

Cracked exhaust header...my 97 came out in three pieces...

-Mac

All these models exhaust manifolds crack. You will hear it pretty strong on cold starts.

 

[mdsilva75]

Craziness ensues. Looked for exhaust leaks and had a few small ones. Found a small one on the exhaust manifold and changed it out with the Dorman. When checking the exhaust I noticed that the cat is completely bare. Nothing inside but my light. Didn't have the money to replace that so I buttoned it up and ran on the new manifold. Quieter but ran way worse. Backfiring, stuttering, stalled out several times once it was warm and ran for a while. 20 minutes or so.

Had to make it to work with it today so I grabbed a Masterpro crankshaft position sensor. I know, figured if that was it I would get the OEM. No dice. Running slightly better and not stalling but still the same codes of P0300, P0303 & P0304. Uggh! I noticed that she is idling very low at stops and letting off the gas. Still vibrating and low power.

Going to clean the throttle body which actually looks pretty clean as it is next. Going to pull the valve cover off this weekend and look at that. Any other ideas? This is driving me insane.Missing out on the summer.

Thanks again to everyone! Appreciate all your advice.

 

[tworley]

Are you getting 5v to the cam sensor (also known as ignition pickup coil) at the distributor?

 

[mdsilva75]

Finally got the chance to get back to it today. Checked and getting 5v to the cam sensor. Cleaned the throttle body thoroughly. Still the same. Maybe even a little worse. Going to take off the valve cover tomorrow and check grounds.

If anybody has any other ideas, please let me know. Thanks again.

 

[catbones2010]

Finally got the chance to get back to it today. Checked and getting 5v to the cam sensor. Cleaned the throttle body thoroughly. Still the same. Maybe even a little worse. Going to take off the valve cover tomorrow and check grounds.

If anybody has any other ideas, please let me know. Thanks again.

Any updates on this? having same issue but only during first acceleration after sitting overnight, then its fine, idles fine, etc..

 

[Jerry Bransford]

Finally got the chance to get back to it today. Checked and getting 5v to the cam sensor. Cleaned the throttle body thoroughly. Still the same. Maybe even a little worse. Going to take off the valve cover tomorrow and check grounds.

If anybody has any other ideas, please let me know. Thanks again.

Besides the fix for it mentioned above in post #4 that is for 97 to early 98 models? Just because a fix isn't easy doesn't mean it's not the right fix.

@catbones2010 which of your TJs is having that issue?

 

[tworley]

Any updates on this? having same issue but only during first acceleration after sitting overnight, then its fine, idles fine, etc..

Misfiring (Code 43 on the early models)

From the 97 FSM:
43* P0351 Ignition Coil #1 Peak primary circuit current not achieved with Primary Circuit maximum dwell time.
43** P0300 Multiple Cylinder Misfire detected in multiple cylinders Misfire.

My suggestion, check to see if you are getting 5V to the CAM (ignition pickup coil), CPS (crankshaft) sensor and ignition coil. All determine the firing order so if one is out of whack, then all three will struggle.


According to the FSM--the primary resistance at the coil should be 0.95-1.20 Ohms. Secondary 11,300-15300Ohms.

 

[Jerry Bransford]

Misfiring (Code 43 on the early models)

From the 97 FSM:
43* P0351 Ignition Coil #1 Peak primary circuit current not achieved with Primary Circuit maximum dwell time.
43** P0300 Multiple Cylinder Misfire detected in multiple cylinders Misfire.

There was a TSB issued for the 43 codes, they are fixed by replacing the valve springs. The factory's first batch of the TJ's valve springs was bad, they were a little too weak. I had the same problem in my previous '97 TJ and replacing the springs completely fixed all the 43 codes, misfires, etc.

 

[catbones2010]

Besides the fix for it mentioned above in post #4 that is for 97 to early 98 models? Just because a fix isn't easy doesn't mean it's not the right fix.

@catbones2010 which of your TJs is having that issue?

My 97... drove it till about 149k and daughter took over it for school. She's having misfires when she starts driving it in the morning for about a mile, then it goes away and doesn't happen till it sits overnight again.

Looking at Rockauto, they only got 4 of the Mopar springs. How much would you see free height are the Mopar springs to match the other ones available?