I have this issue, sort of. 99 sport 2wd, 4.0 pushrod. Intermittent. Sometimes it's great, sometimes you think the engine is going to part company with the mounts. Best description is a death rattle, like a loose front end on my 1950 F-1. Fuel filter early this year, 6600 Mac's injector cleaner (every time), Autolites, Belden wires, single 6 port coil pack, air filter, cleaned MAF, had a mouse eaten wire to #4 injector, unable any more to do that myself, had it done, no change, shop changed the injector (their scope showed an occasional #4 misfire), no change. I did EGR test, normal. NO CODES except the P0401 for the road test with EGR unplugged to see if it was dumping too fast...no change. Did NOT light CEL. Transmission shop drove it with me, said not trans as tach did not even flutter when this happened....he said trains issue would have caused tach to flutter or move radically. DeOxIt5 cleaned engine gang plug, PCM gang plug, performed wiggle test on all wire bundles and plugs while running, no change. Fuel pressure at 60PSI, loaded st 2200 RPM, still 60PSI. Serviced trans....no change. Can start at 25, usually goes away at 40, but shop said still there at freeway speeds. Plugs on LH bank look normal. No oil, no burning, no pearly white. Thought PCM, but all the folks I know who do this or did say 99, no. Never the PCM. Plug voltage about 10K at each end, cylinder balance normal. Haven't done compression test yet (have to wait for pain levels to go down). Shop threw their hands up (they said exactly that), 35 years of wrenching and I am at a loss. Has to be simple. Thanks.
