pre-detonation (pinging) on 87 octane

Hey all, I bought my 96 XJ 4.0 HO back in june. I have been using 87 octane since I bought it and have not had any pinging under load or otherwise. A couple weeks ago I put some cheap ( not just inexpensive) gas in and it was pinging like crazy. I added some octane boost and injector cleaner. Now even with quality 87 octane I get some pinging under load. Could the bad gas have messed up the timing. Isn't it controlled by the computer with a nock sensor etc. I am going to do a tune up sometime. I don't know if that would help. I know the principal is that the gas is detonating too soon and trying to expand while the piston is comming up still. This can be due to a dirty engine I suppose. Do others have problems running 87octane? Thanks for all the help. cheers

could try some gm top end cleaner.

What do you mean by or consider "cheap" gas?

AFAIK there is no knock sensor on 1991 and up 4.0's. Check your plugs to see if they're fouled, or have some debris. I'm thinking carbon buildup...

Of course, I'm no expert; just thinking cheapo gas might leave a lot of deposits.