My 1994 E500 has recently stopped pulling properly between 4000rpm and redline
No misfire or stuttering, it just goes flat from 4000rpm; worse in the higher gears.
I appear to be getting full throttle and car has recent (correct) spark plugs gapped at 1mm, air filters,fuel filter, rotor arms, caps, new upper loom and rebuilt lower loom, pcv hoses etc. The car ran fine after this work was carried out and still starts, idles and runs perfectly up to 4000rpm, hot or cold
I haven't had a chance to get the codes read yet but my local tuner did put his afr probe in the tailpipe and it showed approx 14.5:1 across the board which I understand is correct for the facelift cars and matched what was seen during a dyno run a couple of years ago before the current issue arose.
We also think we've ruled out the cats as an infrared temperature probe shows nothing unexpected on either bank, before and after the cats
Any suggestions on where to look next?