1987 260E stumbles and stalls after warming up (after sitting over weekend)
 

My 1987 260E stumbles and stalls after it gets to temperature. This only occurs after it sits over the weekend. I have changed the fuel filter, OVP, voltage while running is 13.68 on the batter terminals. Seems like this might be related to a sensor problem. Seems like the battery is running low on voltage or something. The alternator was checked at my local parts store and they said it is good. I am stumped and so is my local garage.

Thanks, Bob.

13.6Vdc is plenty. That won't cause a stalling issue.

When you say stall, do you mean that while idling the engine shuts off??
Will the car re-start? Does it ever quit while driving? (foot on gas pedal)

The car starts to stumble while I am driving around 35mph, but it has not stalled unless I take my foot off the gas. Usually when it starts to stumble, I head for the nearest side street to get out of traffic. The last two times this has happened, the car stalls when I take my foot off the gas as I am turning the corner. This last time I was able to restart the car after around 10 seconds of cranking and pressing on the gas to keep it going. Once it restarted I did not have any problems driving home.

I am wondering if a failing crank position sensor would cause this problem.

Thanks, Bob.

Bob, I would attribute your engine's stumbling/stalling problems to a faulty Oxygen sensor. When was it replaced last?

I reviewed the vehicle records for the last 100,000 miles and I do not see where the oxygen sensor was changed. Is it possible it still has the original oxygen sensor? Thanks, Bob.

I checked the O2 sensor voltage today. The values were 0.36 volts when first started and .07 volts when the engine was warm. I disconnected the O2 sensor and I did not notice any problems. This leads me to think the O2 sensor is bad. Opinions? Thanks, Bob.

O2 sensor should not cause it to stall while driving, it will simply default to a fuel wasting rich setting if it gets an illogical O2 reading....

I'd bet on the crank position sensor....that's what it was when my 300E had those symptoms, only did it once warmed up (resistance changed from temp). On mine I have the california LED light code plug, so it actually gave me a CPS illogical code after it stalled a couple times.

Those voltage readings suggest it may be time to replace the O2 sensor. You probably already know this, but you should be seeing fluctuating readings between about 0.2v and 0.8v.

I am going to retest the O2 sensor by pulling a vacuum line to see if goes more lean and then forcing the engine to go rich. I am wondering if my mixture is way off. Also, is there anyway to test the crank position sensor? I hate to keep buying new parts before I test ensure they are truly bad. Thanks, Bob.

I disconnected the O2 sensor, drove it around town, and noticed zero difference. This tells me the O2 sensor is not working properly, so I ordered a new one. Thanks for all your help. Bob

Bump. What was the outcome? Did the sensor at least improve your fuel economy?

I hope to have the sensor installed this weekend. I will let you know after I drive it a few miles. Thanks, Bob.

I swapped out the old O2 sensor and so far my "seat of the pants" analysis says the car has more power. The voltage is oscillating between .1 and .9, which, from what I have read, sounds correct. I am hopeful my fuel economy gets better too. Now I just need to fix the rough idle and sporadic miss. Any ideas? Thanks, Bob.

The mileage has gone from 16 to 21.5 and I hope it will go a little higher after I adjusted the duty cycle from 10.8 volts to 6.2 volts.

That's a mighty impressive improvement in fuel efficiency! Is that "city" mileage or "highway" mileage or some blended average mileage? The EPA ratings on that car are 18/22 mpg.