P300 - Misc. Misfire after Remanufactured 4.0 Install

[RangerTJ01]

Recently had a remanufactured 4.0 installed (shop done, not by me) on a 2001 TJ sport (32RH, fyi). Long story short, along the way the following were replaced as well: 1) radiator and hoses; 2) valve cover (previous was cracked); 3) water pump; and 4) starter.

Tj was returned to me and was running better than it ever has in the 5 years I've had it. Within 30 miles it started throwing a P300 with absolutely no signs or symptoms of it. Mechanic can see it missing on his live scanner, but agrees there are no signs of misfire other than in the data. Data shows random misfires in all cylinders, but is only throwing the P300 currently.

Running this issue down has been a bear. We are stumped everywhere we turn. Compression and fuel pressure are fine. We've been through 3 or 4 sets of plugs (including the forum recommended), Standard Motors Bluestreak coil, and replaced all injectors.

Any ideas to at least help narrow the scope of parts being thrown at it?

 

[macleanflood]

What brand of crank position sensor is on there?

How dirty is it?

Verify wiring. Check grounds. Battery connections. PCM connectors for corrosion.

-Mac

 

[Jakes-2004-TJ]

Recently had a remanufactured 4.0 installed (shop done, not by me) on a 2001 TJ sport (32RH, fyi). Long story short, along the way the following were replaced as well: 1) radiator and hoses; 2) valve cover (previous was cracked); 3) water pump; and 4) starter.

Tj was returned to me and was running better than it ever has in the 5 years I've had it. Within 30 miles it started throwing a P300 with absolutely no signs or symptoms of it. Mechanic can see it missing on his live scanner, but agrees there are no signs of misfire other than in the data. Data shows random misfires in all cylinders, but is only throwing the P300 currently.

Running this issue down has been a bear. We are stumped everywhere we turn. Compression and fuel pressure are fine. We've been through 3 or 4 sets of plugs (including the forum recommended), Standard Motors Bluestreak coil, and replaced all injectors.

Any ideas to at least help narrow the scope of parts being thrown at it?

I have a 2004 TJ with 4.0L with a manual 5 speed tranny, it has about 170k miles on it. Symptom's: initial problem was random CEL (Check Engine Light), usually steady, but later would flash at times with jerky acceleration. Code reader gave cylinder 1 misfire that later became cylinder 5 misfire. During acceleration, engine would backfire into the breather, so I thought it was a gas/air mix ratio problem. New spark plugs had no effect on fixing the problem. With the engine running, I could hear the fuel injectors clicking by placing a long screwdriver on each injector and the handle on my ear. I disconnected and did a resistance test on all of the fuel injectors, all of them read 13.7 ohms. I saw a message that the IACV (Idle Air Control Valve) can cause all these problems, especially if stuck open or stuck closed. I removed the IACV and found lots of carbon build-up. With the engine off, I pushed the throttle butterfly fully open and looked inside the intake, it was also caked with carbon. GUM-OUT cleaner was sprayed heavily throughout the intake and IACV passages, I also used a toothbrush to scrub some areas. I disconnected the battery (for about an hour) while I installed a new IACV. Once everything was back together, I started the engine and the CEL remained off, went on a test drive and the CEL remained off. As I understand it, disconnecting the battery resets the ECM (Engine Control Module) so it has to learn where to set the new IACV during start / idle / acceleration and steady driving. It appears the IACV is a jack-screw type valve, a dual direction electric motor extends or retracts the IACV plunger, which varies the gas / air mix ratio based on engine temperature, but adjusts for power demands too.

 

[hear]

Relevant thread from earlier today.

https://wranglertjforum.com/threads/the-dreaded-p300-code-and-what-worked-for-me.85864/

 

[macleanflood]

And this one...

Thread 'How to clean your IAC (Idle Air Controller) valve'

Jan 2, 2016

If you're experiencing idle issues on your Jeep Wrangler TJ the most likely culprit (and the first thing you should check) is your IAC (Idle Air Controller). Often times the IAC gets very gunked up causing the Jeep to idle improperly. A simple cleaning is usually all it takes to get it running as good as new.

If you end up needing to replace your IAC valve (they do fail on occasion), you can find the part numbers (and the links to purchase them on Amazon) below:

2005-2006 IAC Valve (Part # 4861552AC)
1997-2004 IAC Valve (Part # 4874373AB)

There is no need at all...

• Chris
• iac idle idle air controller idle valve
• Replies: 191
• Forum: TJ How-to Guides

• 

-Mac