The way they explained it at Chrysler tech school was that if the normal production tolerances in the engine parts stacked in a way that the compression ratio was raised, then there might be pinging on regular. The reflash doesn't retard the timing, it just allows the interface with the DRB-III scan tool, which allows the timing to be retarded in 2* increments. If you have it reflashed, there are many other improvements possible in the programming. All of any applicable updates are included with the new program.

Chrysler uses knock sensors on other engines, the 4.7 v8, 5.7 Hemi V8, 3.5l and 3.8l V6s, and the turbo 2.4l come to mind.

I was just meaning Chrysler dropping the knock sensor on the 4.0L, not everything. I would think there could have been performance gains to be had, even if they were minor, from optimizing the ignition timing with the knock sensor. Obviously the engineers at Chrysler had their reasoning, maybe it was cost, maybe the gains in performance were negligible verses the set up we have.

So from what you are saying Marty, it sound like the TSB reflash is to compensate for worn parts.

Still good info.

Oh also to note that TSB 18-24-98 only applies to '96 and '97 model years.

Ok, so here's the update. He just filled up with Mobil high test this morning, and when I saw him this evening he said he hadn't really noticed it pinging, but he hadn't really tried to make it do it again yet either. And the good news he said it does have an OBD2 port even though its a `96 and its the boxier body, which surprised me, so next week I'll bring my laptop and hook up the scan tool, and take a look at things.

I believe I can look at ignition timing too, it will be interesting to see if there is any difference between his '96 and my '99.

I did mention the TSB and noted this was an optional update that could be made for cause, but told him of the drawbacks of retarding the timing as well. He replied the previous owner was meticulous and always had it serviced at the dealer, so most all of the updates were likely done. To which I replied this update was optional and would have only been done for cause, so it might not be there, and it might not be required.

The current plan. Run it as is with high test for this tank, which is looking good so far. If ping is gone then add in some carbon cleaner for the next tank. Any other recommendations on a cleaner other than the Mopar, or is the Mopar cleaner the best choice?

unfortunately, I wont be able to hook the lap top up to his until next Tuesday.

<img src="/forums/images/graemlins/cheers.gif" alt="" />
Sean

Somebody makes the combustion chamber cleaner for Mopar, so I would suspect that Wynns, Chevron, etc. have the same product available at a parts store or service station.

If a PCM update was performed, there will be a grey sticker near the emissions label, and also a small white one on the PCM itself, showing the revision number (if the tech followed the instructions)

'96 was the first year for OBD-2 on Jeeps.