99 Cherokee - engine predetonation

[jon1998]

My 99 Cherokee 4.0 5spd makes a noise that makes me think of predetonation, when driving in a hot environment I hear the marbles in a coffee can knocking when I accelerate aggressively. It revs smooth and builds power, but the pinging spontaneously appears. It used to be way worse when I got it, but three cans of seafoam in the tank and some premium gas really helped it. I have also replaced the plugs (gapped correctly) and wires, and it runs at 210 degrees. I checked fuel pressure and vacuum and both checked out fine. Any ideas on what it could be? Are these jeeps sensitive to 87 octane or something? I’m really starting to run out of patience for these 4.0s

 

By the way, love the forum, it has by far the most helpful jeep knowledge 

[Eagle]

I have two 2000 XJ 4 liters, and neither is prone to predetonation. If Seafoam helped, you may have a lot of carbon buildup in the combustion chambers and on the pistons. You definitely should not have to run premium gas. It sounds drastic but, if another treatment with Seafoam doesn't fix it, I'd consider pulling the head to de-carbonize it.

[HOrnbrod]

Try this heat shield (p/n CBXCB060) below. I was getting some pinging and preignition on the stroker in the hot summer after installing the later manifold like you have. The shield was only three bucks from the dealer and it did help. I also quit using fuel with ethanol a while after doing this little mod which helps even more. 

 

Quote

 

There are a couple of TSBs floating around dealing with injector heat soak causing hard starting when hot. The "cure" is an intake manifold heat shield or a wrap around the affected injector, usually #3. AFAIK these TSBs were for the 99 and up HO engines.

 

 

 

[jon1998]

Thanks for the replies, I’m already running a fourth can of seafoam through the tank but I think another can this time through the intake is worth a shot, I’ll also look around for that heat shield too.

[Sir Sam]

Where are you getting your fuel?

 

Only time I have ever heard pinging on an XJ the fuel came from the same station, at Cameroon AZ, and years apart.

 

Ethanol has a higher octane than gas, so higher running blend ethanol fuels will help, but at the cost of lower MPG.

[Dzimm]

Don't run anymore seafoam through your gas tank, you are really only cleaning your injectors.  For it to actually be affective, you need it to go through your intake. 

 

Step 1: pull your brake booster hose off the booster but leave the other end attached to the intake manifold. 

Step 2: start it and have a buddy run it at around 2000rpm (I used a penny under the throttle lever on the throttle body to keep a steady rpm) 

Step 3: slowly and steadily pour the seafoam into the booster hose so it can be sucked into the intake manifold.  Don't start and stop the flow, keep it constant.  Go slow enough that the engine doesn't die but fast enough you aren't there all day.  The engine will bog some. 

Step 4: after about 3/4 of the can, you will start to get heavy smoke out the tailpipe.  This is a good sign. 

Step 5: when the can is about empty, dump it all into the hose so it kills the engine.  Leave this to hotsoak for about 5-10 mins. 

Step 6: start the engine up.  You will get some more smoke for a bit but you will have gotten rid of most of the carbon in the engine and she should run much better. 

 

There are tons of videos online on how to properly use seafoam.  The whole process takes 10-15 mins. 

[jon1998]

I put some seafoam in it and zero smoke, it still seems to make the noise. Its a light tapping knocking, kind of like if you were to lug it near stalling. I’ll look around for some heat sheilds like Hornbrod said, it definitely seems to do it worse in hot conditions but perhaps this is some other noise like accessories or who knows. The gas I run in it should be good, its chevron, but I’ll try a different gas station just to rule out bad fuel. It accelerates smooth and drives great other than that noise

[Jeep Driver]

55 minutes ago, jon1998 said:

I put some seafoam in it and zero smoke, it still seems to make the noise. Its a light tapping knocking, kind of like if you were to lug it near stalling. I’ll look around for some heat sheilds like Hornbrod said, it definitely seems to do it worse in hot conditions but perhaps this is some other noise like accessories or who knows. The gas I run in it should be good, its chevron, but I’ll try a different gas station just to rule out bad fuel. It accelerates smooth and drives great other than that noise

What you may be hearing is a dieseling sound..............our 98 does and many others have reported it. 

[Eagle]

3 hours ago, Jeep Driver said:

What you may be hearing is a dieseling sound..............our 98 does and many others have reported it. 

 

Around here, "dieseling" is a slang term for predetonation. (Also for engine run-on after the ignition has been shut off -- usually caused by glowing carbon deposits in the compbustion chambers.)

[Jeep Driver]

33 minutes ago, Eagle said:

 

Around here, "dieseling" is a slang term for predetonation. (Also for engine run-on after the ignition has been shut off -- usually caused by glowing carbon deposits in the compbustion chambers.)

I'm referring to a sound. 

 

Countless threads and discussions. https://www.google.com/search?q=4.0+jeep+sounds+like+diesel&oq=4.0+jeep+sounds+like+&aqs=chrome.1.69i57j0l4.18291j0j7&sourceid=chrome&ie=UTF-8

[Jeep Driver]

OP, 

 

I would agree with those whom have come to the conclusion that it's either worn lifters or push rods. Since there is no way to adjust the valves............you live with it, until, well, the inevitable. 

[jon1998]

I checked out some of the videos and posts on dieseling, my noise is a lot more sporadic than what I saw. Its also only got 45k miles so I can’t imagine the pushrods are worn like that.  I’ve got the day off so might just drop it off at the mechanic today and see what they say, I don’t want to risk causing any permanent damage. Funny enough my 89 comanche made that exact same pushrod noise, it drove me nuts, I never knew what it was until now

[shelbyluvv]

What plugs are you using? If they are anything but Champion RC12ECC toss them and get new ones.

[jon1998]

26 minutes ago, shelbyluvv said:

What plugs are you using? If they are anything but Champion RC12ECC toss them and get new ones.

I know I should, but honestly don’t remember what I got, but it was factory spec. I’ll throw some champions in if it continues to make noise, plugs are easy enough  to change. I took it out this morning and did some hard acceleration and it didn’t make the noise, I’m thinking maybe it just needed a session or two of hard driving, usually I baby this thing. I’ll still keep an ear out for it, especially during the next hot day. Thanks everyone for all the suggestions and help, I really appreciate it.