Loss of power - restart fixes it. - PeachParts Mercedes-Benz Forum

brewtoo · #1 08-29-2007, 10:41 AM

Since my car did this three times already this morning, I figured I'd start a new thread and see if I can get any input.

1991 124 will suddenly lose power just driving along. It even does it sometimes just sitting at a light. It will suddenly start to idle rough, the idle speed will drop under 500 and when you try to move, the power is gone, like you've got five ACs running. You can tell when it happens while in motion because the car starts to feel really heavy, the slow idle makes it slow down more quickly and when you stop, the tach is showing less than 500, rather than the usual 700 or so.

For a while now, the car would lose power sometimes but you could "fix" it by flooring the accelerator for just an instant and it would be cured. This new (?) problem feels different somehow and the floor-it trick does not work. But turn off the key, restart and poof! It's back to normal. For a few minutes, anyway.

What do ya'll reckon this could be?

lee polowczuk · #2 08-29-2007, 10:55 AM

Sounds like the beginning of a bad OVP. At least that's what happened to me.

A264172 · #3 08-29-2007, 12:40 PM

Those symptoms happened to me. In my case it was a flakey oxygen sensor (nobody ever believes this.)
I diagnosed it by pulling the connector wire under the passenger carpet while stalling on the interstate... (not a method I would recomend)

A264172 · #4 08-29-2007, 04:30 PM

One more note: A restart takes the computer out of loop for a few seconds when warm... so any 'leaning' fault in the mix might be temporarly overridden or be forced to find another intermitent window.

david s poole · #5 08-29-2007, 06:11 PM

have you replaced the cranksensor pickup at the flywheel thru top of bellhousing? they are known to operate intermittently when going bad.

juribe2 · #6 08-29-2007, 06:31 PM

it sounds like a bad coil to me.

John Plut · #7 08-29-2007, 10:19 PM

My '88 260 hesitated badly and was finally cured with a new EHA.

In my case the car ran fine when first started cold, would hesitate as it warmed up, and ran okay but had a rough idle when warm. Your case sounds a bit different - more like an intermittent hesitation.

One sure symptom of a bad EHA is leaking, there will be a slight gas smell under the hood after driving.

brewtoo · #8 08-29-2007, 10:33 PM

Today I replaced the O2 sensor and the OVP with spares that I had. You accumulate this stuff when you own two of these cars for years.

The coil and EHA have been replaced within the last year.

I also washed the car today...that always seems to make them run better.

We'll see what happens tomorrow.

Thanks for all the input!

brewtoo · #9 08-30-2007, 12:43 PM

Oh, well. No change at all.

Any other ideas?

Thanks

A264172 · #10 08-30-2007, 01:26 PM

How often does it die? Might be time to hook fuel pressure gages up to see what's happening in the distributor when it stalls...

Oh one last thing before that... un plug the EHA (you probably know that that's the black box on the back of the distributor under tha air cleaner) and see if it runs without stalling... that would narrow it down to a mix problem if it continues to stall.

brewtoo · #11 08-30-2007, 01:38 PM

Well, it never has actually stalled. It loses power overall and the idle speed drops from the normal ~700 to ~400. If I happen to be at a light I can shut it down, start it right back up and it's normal again.

ASaltyDog · #12 08-30-2007, 02:27 PM

Mass Air Flow - maybe? Or the aged wiring to/from

brewtoo · #13 08-31-2007, 09:28 AM

I wonder if the Arthur Dalton Radio Shack code reader would reveal anything?

I'm really wishing for OBDII about right now.

jhodg5ck · #14 08-31-2007, 10:07 AM

My 560SEL was doing right about the same thing..no power and a re-start would fix it for a little while.. Turned out to be the KE control unit...it's open loop/regulated had lost it's mind, no longer able to provide worthwhile info to the EHA etc.. Re-starting kicked it into closed loop/unregulated and it could run OK that way.

Finding a 300E KE shouldn't be hard @ all..know anyone in the area w/ the same car? You can make the swap in a matter of minutes.

Jonathan