m104 low power when hot

[dcurbet]

Hello all
looking for some advice on an m104 w463.

Drives nice and fairly agile when cold but once it warms up becomes underpowered (agility and responsiveness is gone) and has a hard time keeping speed even on the lightest hill. I can tell its acting different because the shifts become more jerky as if vacuum changes as well affecting the modulator.
No issues otherwise really maybe some low idle sometimes... the cat is really hot as well.
Is it just running way rich? EGR still in place. Maybe it is to blame?

thx for any pointers.

 

[dcurbet]

is there a better place to post this question? just looking for a place to start...
thx

 

[dboz]

Sounds like retarded timing when underhood temperature is higher. Are you getting any fault codes?

 

[dcurbet]

not sure how to check and no lights are popping up on the dashboard.

 

[dboz]

Non-MIL codes are often stored, i would recommend searching for how to retrieve fault codes (either here or other sites) the forums here are primarily about W124, however.

 

[dboz]

My E420 behaves in similar fashion to what you're describing, and the primary recurring fault codes is defective knock sensors. Since that job is a PITA, I've been deferring(procrastinating) until I'm able to do the major dismantling work which includes transmission overhaul, motor mounts, drive shaft, exhaust, and more. For now I deal with the issue by stopping, turning ignition off for 30 seconds or so, then starting again. This bandaid appears to temporarily reset the condition.

 

[dcurbet]

interesting... i didnt hear or know about knock sensors. I was sort of focused on the ecu temp sensor or maybe some combination of o2 readings feeding the wrong info. It is obviously running rich to me. The cat is wildly hot i think and the mileage is abysmal.
Maybe also the throttle body? Not sure.

 

[dboz]

Hot cats might be caused by retarded ignition timing, but could also be clogged (might wanna check exhaust pressure) I've learned that at least 2 things make the EZL retard the ignition, knock sensors (for obvious reasons) and the transmission overload switch (to help during full throttle shifts). Just sharing what the gurus on this forum have taught me (many thanks to GSXR, Gerryvz, Klink, Sheward, Terry & many others!)

 

[dboz]

Also don't underestimate the value of installing a new OEM crankshaft position sensor (aftermarkets are all 100% ) . My car continually ran like crap intermittently while I chased ETA, EZL, vacuum lines, temperature sensors, wiring, LH module, TLL/R, fuel delivery and more. The right CKP solved 90% of my issues, now the only recurring fault code is defective knock sensors

 

[dboz]

PS I was in denial of the knock sensor issue for a long time because they're a rare failure item. My motor mounts are quite collapsed however, so as soon as I can arrange for a backup daily beater, that's all getting fixed. I look forward to driving my poor man's 500e (E420 with lowered rear diff. ratio) when it consistently runs like it should. No other car in my experience balances reliability, performance, comfort and the fun-to-drive factor better than the W124's.