Late model 4.0 missfire issues discussion

Meatlord

Meatlord

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Sep 12, 2020
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Location
Lake Elsinore CA
Back story,

I bought an 06 Rubicon 6spd from a local with a misfire issue for a reasonable price. I'm no stranger to jeeps or the 4.0 engine either. 200k miles, look to be all road miles, PO was surprised on the test drive when I got the diff lock lights to come on...

This condition exists weather the engine is cold, and at operating temp.

Let's list the codes...

P0172
System too rich Bank 1

P0300
Random/multiple cylinder misfire detected

P0302
Cylinder 2 misfire detected

OPDA was pulled and inspected, was a cheap replacement, dated to 2014 with zero very little wear. It was replaced with a crown unit regardless, the CPS is also crown, as I could not source the mopar version.

The fuel injectors are all new flow matched set, I placed a fuel pressure gage in line with the fuel rail holding steady at 59 to 60 psi while running, maybe a 15 min leak down or so, not exact.

New coil rail mfg by Delphi, changed all the sparkplug to the iridium recommended on the forums here. (It did this with the copper plugs as well)

Intake cleaner, removed the TB and thoroughly cleaned,
replaced both PCV valves,
crank position sensor,
Air charge? (One on the intake tube)

PO also changed all the 02 sensors, and looks to be waterpump, idler pulley,and radiator.

At this point I am suspecting the injection wiring to cyl 2
Valvetrain issue on cyl 2
Possible cat problems
Or the notorious pcm failure.

Let's hear what the community has for me, testing procedures, thoughts, solutions.
 
I'm a brand new member and a brand new blogger, so hopefully this goes alright.
I recently bought a 1998 TJ 4.0 with 117K miles. Was supposed to have a blown engine, but thats a long story. Got to where the jeep was running great other than leaking some coolant from freeze plug at back of engine. I wanted to drive it around for a while to see if there were any other problems and it seemed fine other than the check engine light coming on. I was getting the same codes. Random misfire, misfire cyl 5, cyl 6.... I'd reset it and it would come back on within a few miles.
After reading through some posts, I decided to try changing the plugs to NGK ZFR5N. It had Autolites in it from previous owner.
Right now, I've gone over 200 miles without the check engine light coming back on, and there is a noticeable increase in power.
Definitely worth a try if you haven't already.
 
Unfortunately those were the plugs I removed initially.
I could go back to a new set to rule them out, but I think my problem is more wiring.

Thanx for the help, it has been really quiet in here. Previous forums I have used were very helpful in the past.

Here they are 1 thru 6, front to back.

1618273807908369595609511357038.jpg
 
Have you done a leak down test to confirm you don’t have a cracked head or anything?
 
Chris said:
Have you done a leak down test to confirm you don’t have a cracked head or anything?
Click to expand...
That will be next, along with renting noid light and checking wiring to inj 2.

A cracked head would show itself in other ways correct?

My oil is fine, my water stays put, no smoke from the pipe, or smell.

What about a bad valve on #2?
 
I did read one post where the guy put dielectric grease on all of the fuel injector wiring connections and it solved the same problem. I did that while I was changing the plugs, but I'm pretty sure my problem was the plugs. One of the old plugs looked like it got dropped on the floor. It had almost no gap.
Good luck. I hope you figure it out
 
Meatlord said:
That will be next, along with renting noid light and checking wiring to inj 2.

A cracked head would show itself in other ways correct?

My oil is fine, my water stays put, no smoke from the pipe, or smell.

What about a bad valve on #2?
Click to expand...

A cracked head may show itself in other ways, but not always.

I can't tell you how many times I've seen people with your same issue go through all of the diagnostics just to figure out it was the last thing they thought of...a cracked head.

Do this and report back.

If it's not the head, my second guess is you have a wire somewhere that has a break in it and is giving you issues. Problem is, those are tough to track down.

Don't rule these things out, trust me.
 
Any idea what brand of O2 sensors were installed? These rigs seem very picky about what brand they like. NTK is the factory and preferred replacement brand. But the noid light is a good idea as well.
 
Does it have an audible miss? Ive had an intermittent lifter that would cause an audible miss but not throw a code
 
I will randomly get a cyl 1 misfire on my '06. Seems to occur more when the engine has been idled extensively, such as sitting in line for 20 mins to get on base every morning and no hwy driving.

The cure for me has been to run some Techron through it and give it the Italian tune up. It will be good for several months after this, with no misfires. 223K mi on the engine.

My assumption is valve deposits.

4.0 valves are supposed to rotate if the engine if run above 3200 RPM as per this TSB:

0900303 - 4.0L MULTIPLE CYLINDER MISFIRE
Date: 08/01/03
Model Year(s): 1999-2004

Description: NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0L ENGINE. This bulletin involves inspection of all engine exhaust valves and a decarbonizing procedure if necessary.

Details: The customer may experience an incident of engine misfire during certain vehicle operating conditions. The misfire may occur when the vehicle is operated between 50 - 70 MPH and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditions are less than 0 C (32 F).

If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 - Multiple Cylinder Misfire. Various single cylinder misfire DTC’s may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in “Limp-In” mode.

The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.

This condition may occur when the engine is not allowed to run at engine RPM’s that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits. Low engine RPM’s and high carbon deposits are associated with short trip driving where the vehicle engine is not allowed to fully warm to normal engine operating temperatures. Cold ambient temperatures will increase engine warm-up time and add to the opportunity of carbon deposit build-up on the stem of the engine exhaust valve.
 
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