95 E320 M104 poor idle and flat spot - Page 2 - PeachParts Mercedes-Benz Forum

W124coupe · #16 06-04-2006, 08:43 PM

Ok so tomorrow (its 1:35 AM here now...) I will do the vac tests and try to persuade the other E320 owner to let me steal his OVP for a while.

If that doesn't show anything then I will plan to go to the local indy (who did the coils and ECM refurb for the last owner) to get a scope on the car to see if we can narrow the problem to one/two cylinders?

kth286 · #17 06-06-2006, 01:26 PM

Steve

I was the guy that pointed you in the direction of knock sensors last time.

I am just wondering whether the ECU had the original code deleted whilst it was being fixed, and therefore subsequently not had the correct code inserted again.

The correct code is dependent on vehicle spec and is critical to correct running.

Whilst driving your car will it easily rev well past 5000 rpm say ???????????

Regards

zafarhayatkhan · #18 06-06-2006, 02:17 PM

Around that RPM, Intake length is changed, so you will notice a change in performance.

W124coupe · #19 06-06-2006, 06:00 PM

All I did after the knock sensor lead was repaired was a reset for the code 32 and then a reset adaptation to avoid possibly waiting for the "10 trips".

Spent some time today checking all the vac lines - all hold vacuum and none of them affect the O2 sensor once reconnected (using Arthur's test).

Still need to check around the manifold and injectors for a leak - will use some carb cleaner and the O2 sensor tomorrow.

I am also going to re-clean the throttle flap with the carb spray to be sure its
closing off cleanly (re the wobbly idle).

Zafar, I did just check the intake flap - you are right it does get activated at about 4k RPM. I thought the flap was mainly meant to increase low end torque while closed?

Do either of you see a definite step in power at 4,000 RPM after a "dip" at 3.5k or so? (the other E320 I drove just climbed in power linearly).

Once past the 4k mark, mine howls strongly to slightly past the redline on full throttle before changing up (although I rarely treat it that way).

W124coupe · #20 06-08-2006, 05:21 AM

A/C low speed fans was corrosion in the pressure switch connector dropping the trigger volts too low for the relay to operate.

Rough tickover was dirty throttle butterfly (I obviously wasn't aggressive enough with the carb spray the first time I cleaned it - there was still some crud right up at the pivot points holding it slightly open).

Flat spot was the dreaded OVP. Must have not liked the resonance at 3.5k revs?

Anyway, OVP now the current part number and we have a clean running straight 6 that stays cool in traffic. Since the fans are responding to the A/C pressure they have not been on at high speed at all today.

Took till 3am today - my wife thinks I'm mad to bother with the old car but to me making it work properly again is the best antidote to workday stress I have found.

Arthur Dalton · #21 06-08-2006, 05:28 AM

<>

Hate to keep mentioning the OVP as a possible fault source, but there you go...

Your high fan won't come on now b/c the low fan, being operational again, keeps the cooling system high thermal load of the a/c in check ....

JayRash · #22 05-28-2009, 01:58 PM

i know its an old thread, but on my 36 amg M104 i have the same flat spot at 3400 and then its fine at abt 3700 rpm.
I have changed the resonance flap, its relay (is that the OVP) and have changed the electronic throttle along with full service.

so what is the ovp and how can it affect the faltsopt?

Ortolan · #23 07-26-2010, 10:44 PM

I guess it's my turn to revive this old thread.

My dyno guy is trying to diagnose some issues with the aftermarket ECU connected to my engine. Can someone please post a pic which shows where the connections are for the intake resonance flap and variable valve timing on a 3.2L M104 HFM engine? Not sure if they're electrical or vacuum operated. Do they both use a simple on/off signal? Thanks!