I reported a problem here a week or so ago that I thought was related to the addition of a can of snake oil in the gas(Berryman's Chemtool B-12). After 30 mi. or so of highway driving in near 90 degree heat, the car would not restart after sitting in the driveway for about 10 mins. After 10-15 mins of cooling off, car restarted, but idle began bouncing up and down from 300-1500(approx), then would die. Once fully cooled off, the car started fine and ran ok.

Last night on the way home(another 30 mi. drive on the highway), the car began to cut in & out after about 20 mi. of driving. I suspected the car was going to stall when I pulled off my normal exit, so I chose one a little further down with less traffic & that was a good idea as the car died when I came to a stop.

The vehicle did as before when I cranked it - nothing. Engine would spin quickly, but no hint of wanting to start. I walked home and returned and hr. later. Car fired up and I drove home(3 mi. drive). Once inside the garage and at idle, the idle speed began to jump up and down and the engine died.

OVP and MAS controller(contains fuel pump relay) were replaced about 1 yr. ago.

I realize there are a maze of things to check such as:

- Throttle Valve Switch
- Idle Control Valve + hose
- Vacuum hose under int. manifold
- EGR
- Crank Position Sensor
- Air Flow Pos. Sensor
- Decel Switch

In both cases this has occurred when it was warm outside - car had been sitting in near 90 degree heat all day and driven home in temps not much lower than that. On cooler days in between the first occurrence last week and last nights reoccurrence, this has not happened. In all cases, the temp gauge never goes much over 80C.

I'll check the list above, but am somewhat doubtful it's vacuum related. If I had a leak, it seems the problem would occur irrespective of the ambient temp?

I've read that heat can affect the secondary side of an ign. coil - suspicious of this part and was wondering if it could also impact the single fuel pump my model has? This unit is the original Pierburg pump. Fuel filter changed about 10,000 mi. back.

Have also noticed that I'm getting much better gas mileage than I usually do. The tank is just a little less than 1/2 full, so I haven't refilled & calc. mileage, but after hitting the 1/2 way mark, I had driven about 250 mi.. Normally I've driven about 210-230 mi. when the 1/2 way mark on the fuel gauge is reached. This would indicate a lean condition or a miraculous improvement brought on by the snake oil.

Thanks for your time.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

I can only confirm that I have had a few ignition coils in different vehicles that acted as you described when they went bad. The fuel pump relay in my Benz had the same symptoms. Once they cooled off they were fine. I didn't feel they where affected by ambient air temperature much though, just from the heat of operation. If you had someone with you when it failed you could have them turn the ignition on while you listened for the fuel pump which should run for a few seconds.

Jorg

Friend,
If your fuel pump check valve or fuel accumulator are leaking your car may
exhibit that "hot soak" symptom.

MB Tech:

Thanks for the reply. Would the accumulator & or check valve also cause the bucking at highway speeds once fully warmed up?

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Mike,
I know this is a long shot... but I recently had almost identical symptoms that were driving me crazy. Larry Bible suggested the O2 sensor as a possibility which seemed like a long shot to me at the time (it was less than a year old... and I had never had a bad O2 sensor cause those symptoms)
After lots of reading and preping for a long frustrating investigation I ended up pulling the O2 sensor cable while stalling on the freeway and 'wala' no more stalling or stuttering. It is such an easy fix/test that it's worth a try before you go a more exaustive/expensive route.
1½ ¢

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Marty:

I don't think your idea is a long shot at all.

After digging thru the archives, I've placed the O2 sensor high on the list, along with the fuel pump.

The fuel pump may also be tested easily. On my model you would pull the MAS controller that houses the fuel pump relay(and other circuits); then jumper port 1 & 2. If the pumps run and the car starts, the fuel pump relay is bad. If the pump does not run, then the pump is bad. Had to replace the MAS last year -> fuel pump relay was bad. I need to make a jumper wire to carry in the car for the next time. Sure hope that $500.00 FPR is OK.

Thanks for the O2 how-to. I'll pull my passenger side carpet tonight and get a jump on where it's at for the next time.

I suppose the snake oil could be clogging the injectors, but I'm not sure how a 1 hr. rest would "unclog" them.

The ign. coil would remain a suspect, but the surging idle would be more fuel/air related than ignition. I came across a post by psfred that associated a failing fuel pump with a surging idle. Investigation on the WEB showed heat being a factor in fuel pump failure and in both of the situations I've experienced, the ambient temp was much higher than it had been.

Summer's coming - definitely need to get this one resolved.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Hi Mike:

I had the same problem on two of my 260E's and both times it turned out to be the crank position sensor.

Hope this helps. Let me know what your fix turns out to be.

Aloha,
Eric

__________________
1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles

Where is the CPS located on the 260E?

__________________
joel

Prayers bring forth enlightenment.

Hi Joel:

It is located I believe on the top of the bell housing of the transmission towards the back of the engine. The easiest way to find it is to trace it from the EZL (the smallest plugin next to the vacuum hose) located on the drivers side fender. Just follow the cable that runs along the fuel distributor in a track towards the back of the engine. You can't miss it.

Hope this helps.

Aloha,
Eric

__________________
1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles

Some CPS are located in the bell housing area; some more toward the front near the crank pulley. It's model dependent, but following the line from the EZL as mentioned in prev. post may be the way to get you there.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

thanks, mike and eric.

__________________
joel

Prayers bring forth enlightenment.