Jeep 4.0 ping solved with colder plug

[dnastrau]

Greetings:

Background: I have a '96 Grand Cherokee 4.0 that is in great shape now with 170K miles. I bought it 1.5 years ago with 133K on the clock. I had a frustrating problem with spark knock under load on hills and highway grades when I used the owner's manual recommended 87 octane fuel. This engine does not have a knock sensor. It does not burn oil and I always try to use top-tier fuels. Driving mix is 70/30 highway/city so carbon buildup is unlikely. A piston soak with Mopar combustion chamber cleaner didn't help. Using 89 octane eliminated most of the pinging but I wanted to solve it since this engine is supposed to run on 87. This is mostly on principal - running 89 or 93 won't break me.

I tried a new cap/rotor/wires (Blue Streak Standard Ignition brand) and a set of OEM type Champion RC12LYC plugs as it was time for a tune-up anyhow. I also tried a set of Bosch Copper Plus plugs. None of this helped. No OBDII codes set and the exhaust after the manifold and O2 sensors are recent. No vacuum leaks were found either.

After reading on the 'net that some Dodge 5.2/5.9 truck owners solved pinging problems by running a colder plug (Champion RC9YC) and that the late '80's-early '90's Jeep 4.0 used that plug, I thought that might work. A lot of the Jeep 4.6 stroker motors are using this plug too. I popped in a set of the RC9YC Champions and my pinging is gone and the Jeep still runs great otherwise. After 200 miles I pulled one plug to make sure it wasn't too cold of a heat range and it looked great - no fouling and a nice color.

In closing I think the problem is a combination of the stock heat range being too high and the original RC12LYC plug design has an extremely long nose that probably exacerbates the problem. If your 4.0 pings I'd give this a try as it is a cheap experiment even if it does not solve your problem.

Andrew S.

 

[Chris142]

I think that the colder plug is just a bandaid for another problem. The 4.0L has used that plug forever and I've never heard of any issues with them on the Jeep boards.

 

[KW]

I had the same problem with my '98 4.0 and I had to run 89 octane fuel for years. Believe it or not after a couple tanks of about 30% E85 and regular gas the problem is gone. Now I use E10 after every few tanks of gas. Every once and a while it will give a cackle while pulling a trailer but nothing like before.

 

[dnastrau]

Originally Posted By: Chris142
I think that the colder plug is just a bandaid for another problem. The 4.0L has used that plug forever and I've never heard of any issues with them on the Jeep boards.



My father-in-law had a '96 4.0 Grand Cherokee nearly identical to mine and it did the same thing. He ran 89 octane to keep it from pinging. His 2004 4.0 runs fine on 87 however.

Band-aid it may be, but nothing else at this point is the obvious cause. Since the earlier Jeep 4.0 years (pre '92 I think) used the colder plug I am pretty comfortable using it. If any problems arise I will switch back to the original plug and use higher octane fuel.

 

[dnastrau]

Originally Posted By: KW
I had the same problem with my '98 4.0 and I had to run 89 octane fuel for years. Believe it or not after a couple tanks of about 30% E85 and regular gas the problem is gone. Now I use E10 after every few tanks of gas. Every once and a while it will give a cackle while pulling a trailer but nothing like before.


Wow - it is very strange that using some E85 fixed it. For what it is worth, all of the gas around here is E10 and I have never seen E85.

 

[KW]

Shoot I might try the RC9YC plug in my Jeep. That ping is not right at all.

 

[tig1]

Originally Posted By: Chris142
I think that the colder plug is just a bandaid for another problem. The 4.0L has used that plug forever and I've never heard of any issues with them on the Jeep boards.



I agree. Have you cleaned the MAF sensor? If this gets dirty it can cause pinging. If you decide to clean the MAF be sure to clean it correctly.

 

[crazyoildude]

could be carbon build up maybe the first owner used super instead of regular like that engine calls for..

 

[GOPHER FREAK]

I run autolite 3923 in my 1995 Ram with a 318. Same thing as you described, light annoying ping. The 3923 is one heat range cooler than the Champion RC12YC or autolite 3924 that is specified. Solved it right away with no issues.

On thing I noticed right away in my truck, is that the autolites idle much smoother than any champion I've ever used. I always used Champions and had recently swapped them before I decided to try the autolites. I will not be going back to Champions at least in that truck. Your plug choices are pretty limited in the old Magnum blocks. They really don't tolerate the new fancy plugs well, many issues with Bosch and other platinum plugs over on Dodgetalk. They seem to like a cheap standard plug and most people who try autolites have noticed the same idle differences and stick with them.

 

[GOPHER FREAK]

Originally Posted By: Chris142
I think that the colder plug is just a bandaid for another problem. The 4.0L has used that plug forever and I've never heard of any issues with them on the Jeep boards.



No actually Chrysler pretty much had the wrong plug on 4.0s 318s and 360s from the start. Pinging of the real light variety is something that is common in these trucks and there really only two ways to deal with it assuming the Belly pan gasket isn't blown and the motor is clean. One is the "death flash" a PCM program that retards timing a zaps quite a bit of power and kills your mileage or simply swap to a cooler plug. Mine pinged from day one on 87. Took it to the dealer and they tried everything imaginable to fix. 7 trips to different dealers. Finally I had it death flashed which was a bandaid. Lost 3-4 highway MPG and the truck had no power whatsoever. bought a new PCM (without the flash) as once you get it you can't go back and installed the cooler plugs and have since logged about 200,000 miles with out pinging or any fouled plug issue to date. Had Chrysler simply swapped plugs as the 3923s are cooler and about 1/2mm shorter they would have saved their customers the death flash, pinging, poor idle, and MPG. Another benefit of the 3923's is about a 1MPG gain for whatever reason. I assume the RN9YC solves most of these problems except for the idle quality.

 

[Gary Allan]

From new our 99 4.0 would ping at shifting points a bit. More in summer. If it got excessive a can of Seafoam reduced it.

Oddly, since E10 ..and that I do a Amsoil PI tank every 6 months, we don't have a peep out of it.

It's apparently not an issue with the 4.0, but in the 2.5 injector imbalance can cause some issues. I'm sure they both experience the same imbalance, it's just that the 2.5 appears to show the damage in terms of high speed detonation. Enough to burn holes through pistons. We only get the average 02 content so it's one pulse width fits all.

 

[Eddie]

I think a light pinging is OK but, knocking is bad. I suspect that carbon buildup may be the cause and the colder plug is a bandade as some have said.

 

[dnastrau]

Originally Posted By: tig1
Originally Posted By: Chris142
I think that the colder plug is just a bandaid for another problem. The 4.0L has used that plug forever and I've never heard of any issues with them on the Jeep boards.



I agree. Have you cleaned the MAF sensor? If this gets dirty it can cause pinging. If you decide to clean the MAF be sure to clean it correctly.


No MAF on this Jeep, It is a speed density FI system.

 

[dnastrau]

Originally Posted By: Eddie
I think a light pinging is OK but, knocking is bad. I suspect that carbon buildup may be the cause and the colder plug is a bandade as some have said.


I tried a piston soak with Mopar Combustion Chamber Cleaner and it showed no improvement. This truck also sees lots of 70 MPH highway driving so I don't think carbon is the problem.

 

[Chris142]

Odd and as I said this is the first time I have heard of the issue. My 4.0 wont ping even on Californias waterered down 87 octain gas while running 230F uphill with the AC on in Death Valley.

 

[CourierDriver]

I have enjoyed this read, my Dodge Ram Van even after tuneups has had this anoying mis and if the autolites solve that and the lite pinging, I will try them this weekend for sure. My mileage avgs 16mpg now, so if it goes up 1 mpg, its good for me.

 

[mechtech2]

In this case, the factory plugs may have been too hot.
In this case, they may have been all that was wrong.
But this is not the usual situation.

We want spark plugs with a cold of a heat range as possible, without fouling. That is the ideal/goal.

 

[dishdude]

My mother had a '97 GC (back in 97-00) that would ping slightly going up hills. I never really looked into it too deeply since it wasn't too bad and it was a lease. My point is they did it even when new, so it shouldn't be a carbon build up issue, and apparently it didn't do any harm since I see a ton of these rolling around with over 200k on them.

 

[Jimmy9190]

My 2001 Dakota had a pinging problem too. I had a fuel induction service done, tried other types and brands of plugs, Seafoamed it, used Regane and Lucas in the tank, nothing helped. It would ping at light throttle, especially when going uphill.

I put in a 180 degree thermostat and a set of Autolite 3923's. The 180 degree tstat makes the PCM think the engine has not fully warmed up yet so it advances the timing just a little. Between that and the 3923's being one heat range cooler than the stock Champion plugs, the ping is completely eliminated. Dodge engineers did a study some years ago and found that the Magnum engines made better power and performed much better at 182 degrees. But they had to use a 195 degree thermostat to meet the Federal Emissions standards. They also found that a plain copper core spark plug works best and provides the best power and idle in the Magnum engines too.

I don't know how it would apply in a 4.0 but you might look into a cooler thermostat, maybe that would help. At least in my case it improved power and my MPG actually increased a little too. Some who use a 180 tstat on Dodges see a decrease in MPG though.

 

[mechtech2]

Jimmy - A colder thermostat can be better for power, if the engine can take advantage of more ignition advance.

But using a stock 195 is beast for cruising fuel efficiency. The burning mixture does not have to constantly have to heat up the cylinder walls and combustion chamber as much, so more power is retained to drive the piston down.
195 thermostats are not so much for emissions, but real gas economy and a cleaner engine.

Plain steel plugs are great - they have less resistance than platinum. But they are only best when new and sharp. They lose their 'edge ' quickly.