New spark plugs make a big difference!

[chrisjohns38]

So just to add to the "my jeep runs much better after changing my spark plugs" controversy:
After and during a trip up to the top of Maunea Kea (13,800') from the beach, two weird things happened. The first was intermittent rough rumbly running engine, the second was sticking brakes.
The brakes cleared up by the time I burned them down a bit and work perfectly once again.
The rough running seemed to happen pretty often after that trip. Sometimes it would hardly run at startup. No new codes (always have P0442).
So, after looking around, I decided to pull a plug.

None of them looked too bad, but there was some weird deposits. They looked pretty new. I've only had the vehicle for about 5 months, and it had been running well enough that I hadn't thought about the plugs.
Denso qj16hr-u, a copper core grooved plug.
I changed them out with the ones Coach recommended, the Autolite APP985 gapped at .035, and boy, what a difference. Fires up more smoothly and really revs up smoother. Better pickup for sure.
Now, I'm not really a believer in plugs making a huge difference, but, in this case...big difference. No drugs or DIY delusional enthusiasm required to note the change.
Not sure what to say, except those skimming this thread who just bought a new old jeep (mine is 2001 Sport 4.0, 136K), change your friggin plugs and put in the ones Coach is recommending. I mean, wtf, must be the coil system makes it finicky like Coach said? I've owned many Vanagons, which were very persnickety about using only the specific Bosch plug and NEVER Autolite, which will put the old vanagon right into safety mode, but this seems to be a pretty extreme predisposition.
Now, what about my brakes. I used 4wd Low so as to not overheat the brakes on the steep descent. Did not lean on the brakes much at all. But it seemed like the rotors warped. Except they then straightened out by the time I was back on the highway for a half hour. Maybe the ABS was firing as I was skittering down the gravel? I thought its off in 4L?
Hmmmmm.

 

[C.J. Roberts]

The rough running seemed to happen pretty often after that trip. Sometimes it would hardly run at startup. No new codes (always have P0442).

Did it clear the code?

 

[freedom_in_4low]

So just to add to the "my jeep runs much better after changing my spark plugs" controversy:
After and during a trip up to the top of Maunea Kea (13,800') from the beach, two weird things happened. The first was intermittent rough rumbly running engine, the second was sticking brakes.
The brakes cleared up by the time I burned them down a bit and work perfectly once again.
The rough running seemed to happen pretty often after that trip. Sometimes it would hardly run at startup. No new codes (always have P0442).
So, after looking around, I decided to pull a plug.
View attachment 230770
None of them looked too bad, but there was some weird deposits. They looked pretty new. I've only had the vehicle for about 5 months, and it had been running well enough that I hadn't thought about the plugs.
Denso qj16hr-u, a copper core grooved plug.
I changed them out with the ones Coach recommended, the Autolite APP985 gapped at .035, and boy, what a difference. Fires up more smoothly and really revs up smoother. Better pickup for sure.
Now, I'm not really a believer in plugs making a huge difference, but, in this case...big difference. No drugs or DIY delusional enthusiasm required to note the change.
Not sure what to say, except those skimming this thread who just bought a new old jeep (mine is 2001 Sport 4.0, 136K), change your friggin plugs and put in the ones Coach is recommending. I mean, wtf, must be the coil system makes it finicky like Coach said? I've owned many Vanagons, which were very persnickety about using only the specific Bosch plug and NEVER Autolite, which will put the old vanagon right into safety mode, but this seems to be a pretty extreme predisposition.
Now, what about my brakes. I used 4wd Low so as to not overheat the brakes on the steep descent. Did not lean on the brakes much at all. But it seemed like the rotors warped. Except they then straightened out by the time I was back on the highway for a half hour. Maybe the ABS was firing as I was skittering down the gravel? I thought its off in 4L?
Hmmmmm.

the PCM makes a lot of calculations using barometric pressure. The trick is, it doesn't have a barometric pressure sensor. It takes a reading from the MAP sensor as soon as the key turns on before you start cranking, and then it uses that as the baro reading for the rest of the drive. Which means if you start up at sea level and drive all the way up to nearly 14k without turning the engine off at some point, your PCM is still using sea level 14.7psi as the atmospheric pressure even though it's closer to 9 psi up there. I can't give you an exhaustive list of what all that might cause, but running like crap and putting deposits on the plugs is definitely not outside the realm of possibility.

 

[chrisjohns38]

Did it clear the code?

No. To clear the old code not related to misfires, I think I need to do a little dance with the headlights and battery cable...or go to a parts store to reset it. Still just the one code, not an issue.

the PCM makes a lot of calculations using barometric pressure. The trick is, it doesn't have a barometric pressure sensor. It takes a reading from the MAP sensor as soon as the key turns on before you start cranking, and then it uses that as the baro reading for the rest of the drive. Which means if you start up at sea level and drive all the way up to nearly 14k without turning the engine off at some point, your PCM is still using sea level 14.7psi as the atmospheric pressure even though it's closer to 9 psi up there. I can't give you an exhaustive list of what all that might cause, but running like crap and putting deposits on the plugs is definitely not outside the realm of possibility.

Interesting. There was a distinct increase in instances of very poor starting and generally reduced performance AFTER summiting. We stopped for 30 minutes at the visitor center (9200') on the way up to 13800'.

On the way down, no stopping from 13800' to 0'. So with that low initial reading at 13800', you'd think I'd have been running rich by the time I got down to sea level, if I did my thermodynamics P1V1=P2V2 assessment properly.

I think it is strange that the deposits are not on the anode/cathode, but the base of the plug.

While the reduced performance was especially notable after this trip, compared to how smooth the motor is running now, its safe to say those Denso plugs are NOT good for this 2001 4.0 engine, even when properly installed and new and not subject to the huge pressure difference.
Another before and after change that is very clear, is the idle rpm. Before (the trip and changing plugs) it would hover at 1000 often, and rarely drop to the 700-800 and 500 rpm range. Now it drops right down to the second tic ~670 rpm consistently when cold, and lowers down when warm, but in no way does it idle roughly.
I'd thought about addressing the idle, but, it wasn't a pressing issue. Now had I done what I always used to do with used cars and changed the plugs when I got it....
I checked for new codes, still nothing new through all of that. Weird. How it didn't throw a misfire code with how roughly it started, barley running, I'll never know. Puter must know not to bother us with a transient issue .

 

[freedom_in_4low]

Interesting. There was a distinct increase in instances of very poor starting and generally reduced performance AFTER summiting. We stopped for 30 minutes at the visitor center (9200') on the way up to 13800'.

On the way down, no stopping from 13800' to 0'. So with that low initial reading at 13800', you'd think I'd have been running rich by the time I got down to sea level, if I did my thermodynamics P1V1=P2V2 assessment properly.

I don't have the answer off the top of my head so I'm gonna think it through as I type this post.

The presence of Baro in the denominator of the Load equation creates an inverse relationship between Baro and injector pulsewidth. (Baro low->pulse width long, Baro high -> Pulse width short). Since your PCM on the way down would have been using a Baro of ~9psi instead of 14psi, the base injector pulse width would have been inappropriately long for the conditions, seeming to agree with your running rich assessment.

That said, I'm not sure why the STFT wouldn't have been able to adjust for it, and if for whatever reason it couldn't, I would have expected an oxygen sensor or fuel mixture code. Maybe it was just low enough or just short enough duration to fly under the CEL radar.

 

[chrisjohns38]

I think the bottom line remains "new spark plugs matter"
so strange how much it matters to this old 4.0. so smooth now.

 

[never monday]

On the way down, no stopping from 13800' to 0'. So with that low initial reading at 13800', you'd think I'd have been running rich by the time I got down to sea level, if I did my thermodynamics P1V1=P2V2 assessment properly.

Because the ecu is using the baro at start up (13.8) to avarage with the live MAP value. It moves the mean load value lower than a SL start up. So at the bottom of the decent you would be in a mild lean condition.
The plugs show a rich condition, probably from the trip up the mountain.
The carbon is left on the rim of the threads because that area is cooler and out of direct contact with the burn.

 

[chuck47]

Hijacking this spark plug convo because it got me thinking about mine...

I've never replaced plugs before, does anyone have a recommendation for a good youtube video on how to do it on a 2.5L?

 

[C.J. Roberts]

No.

I didn't figure it would, but it was worth asking. My wife's Durango has the same code, and two different mechanics haven't been able to fix it.

 

[Breto31]

I just changed my plugs to the Autolite Iridium XP985's today (the old ones were REAL bad - probably originals). If anything, it feels more sluggish than it did before IMO. It's not missing, just feels a bit more sluggish than usual getting up to speed. Best way to describe it is 2nd-4th gear seem go up in RPM's, but once I get to about 2200 it seems like it doesn't pick up any more speed as the RPM's get higher. 5th gear is pretty solid still, and now 6th is pretty much nothing. It was next-to-nothing before, but now it feels non-existent. It was never a workhorse in 6th gear, but I could run 75 on the highway, and only lose a bit of speed on long hills. Now it just feels like I'm losing power in 6th on the flat backroads.

I gapped them between .030-.035 as suggested. .030 fit within the electrodes easily, but .035 didn't fit. I've got 33's and 3.73 gears, so I don't expect a sportscar feel. It will still get up to 65 (top on, windows down), but I haven't had it on the highway yet, just backroads - and that's pedal on the floor... It's never been a powerhouse, but I feel like it ran harder before I changed them. That said, the engine does feel more smooth than it did with the old ones.

EDIT: I also could have been expecting some crazy result, and in reality, it's just still running the way it's supposed to

 

[WallyWest]

EDIT: I also could have been expecting some crazy result, and in reality, it's just still running the way it's supposed to

Possible. I've also read that you shouldn't gap Iridiums. They come set from the factory and you can damage the electrode trying to change the gap.

I've never used them, that's just what I read somewhere, so take it with a grain of salt.

 

[Breto31]

Possible. I've also read that you shouldn't gap Iridiums. They come set from the factory and you can damage the electrode trying to change the gap.

I've never used them, that's just what I read somewhere, so take it with a grain of salt.

Mostly they were. I was just checking to be certain. Only 1 of the 6 needed to be adjusted - it was too small - less than .030. The others were good as-is. I made sure to NOT use the wedge-style gapper, and I used the gauge instead.

 

[Jerry Bransford]

Possible. I've also read that you shouldn't gap Iridiums. They come set from the factory and you can damage the electrode trying to change the gap.

I've never used them, that's just what I read somewhere, so take it with a grain of salt.

Generally that's true so long as the spark plug wasn't dropped so its electrode got bent.

They can be gapped so long as you use the right type of gapping tool like shown here. You use one of the to notches cut into it to bend the electrode to the right gap near where it attaches to the threaded base, making sure to keep the notched opening away from the iridium or platinum coating.

Use the notch located at the far left in the below photo to bend the electrode so it has the right gap if it didn't come properly gapped or it was bent somehow.

 

[Lectrichog]

Recommendations for newer TJ 4.0L engines like yours are the Autolite APP-985, Champion 7412, or Autolite XP-985. I recommend against Autolite's AP-985 (one 'P') which only has the platinum coating on one side of the gap which causes rough idles/misfires on the newer waste-spark ignition system used on 2001 and newer 4.0L engines. The APP-985, 7412, (both platinum) and XP-985 (iridium) plugs have their coatings on both sides of the gap which is what a waste-spark ignition system needs.

Waste-spark means the spark plug is fired twice as often, the "wasted" spark being on the exhaust stroke. That newer 4.0 ignition systems fire the spark plugs twice as often as is required means the spark plugs last half as long. That's why the recommendation for platinum or iridium tipped spark plugs and not plain

copper plugs on newer waste spark 4.0L engines. The waste spark is there to help reduced emissions by firing during the exhaust stroke to insure no remaining raw gasoline fumes will get out the exhaust.

Jerry I have a 2006 with a 2.4. Do you know if it is a waste- spark ignition and does the same advise apply?

 

[Jerry Bransford]

Jerry I have a 2006 with a 2.4. Do you know if it is a waste- spark ignition and does the same advise apply?

Yes the 2.4L has a waste spark design ignition system too. It does not however take the same model spark plugs the 2.5 and 4.0 engines do.

For iridium I'd go with Autolite's AI5263 and for a double-tipped platinum Autolite's APP5263. The iridium would be good for probably no less than 200k miles and the platinum about 100k miles. Both would perform the same during their lifespans.

 

[Zorba]

Speaking of sparkplugs, anybody remember "SplitFires"?

 

[Jerry Bransford]

Speaking of sparkplugs, anybody remember "SplitFires"?

I do. Like E3 spark plugs, they are just one of many snake oil products.

 

[Zorba]

I do. Like E3 spark plugs, they are just one of many snake oil products.

Yep. The arc is going to jump to one electrode or the other, not the advertised both. I ran a set back in the day - they worked no better but no worse than anything else. They kind of looked cheaply made.

Not familiar with E3 though.

 

[never monday]

Yuck!

 

[williambmac]

I didn't figure it would, but it was worth asking. My wife's Durango has the same code, and two different mechanics haven't been able to fix it.

If you have had it to two different mechanics and they have been unable to diagnose the concern by smoke testing the vehicle, I would replace the purge solenoid then the leak detection pump.
Both of these components a prone to failure .
P0442 which is a small evap leak can be difficult to diagnose.
P0442 usually sets when the ECM performs a self test during shutdown after a drive cycle when certain conditions/parameters have been met.
If your mechanic has performed a smoke test and has been unable to find a leak at any of the lines in the evap system, I would consider replacing the purge solenoid first, then the leak detection pump if the concern re-appears.