1990 2.6 stalls when hot, won't restart for 20 min

[outriding]

Hi all,
I've searched for hours and while I can find many similar situations, not really reflect the funny stuff my car does.
I should preface by saying I've owned this car for less than a month, and it's my first Benz.

• 197k kms (130ish Miles)
• 2.6
• regularly maintained
• good spark, good fuel pressure, filters are fresh
• battery is 12.6v = charging system pushes it to 14.4
• OVP is good, as best as I can tell
• There is no Fuel Pump Relay - this is the first year to incorporate it in the MAS computer.
• Car is without modifications, save a new stereo and speakers (and removal of the cassette holders

Car will always start, regardless of how long it has sat (ie: overnight, or for a week). When it is up to operating temp (roughly 80C) AFTER having sat for more than a couple days, the car will sputter, and will die unless you put your foot in it while either in drive or neutral.

If the car dies, it will not start for about 20 mins.

It will then run without any issue for the rest of the day - regardless of length of trip, or time between starts.

A new MAS unit is $400, I suspect I might find a used one somewhere. I have unplugged the EHA valve, and the car still ran...

I'm open to tips, I know with this car, a few days in the shop can easily double the initial investment.

Thanks for your assistance.

[321-GONE]

After the car stops, check to see if there is any spark. Should there be no spark, then I would immediately suspect the crank reference sensor (the one at the back of the engine, not the front).
Also check the satus of the fuel pumps with a test light. Check to see if there is any current reaching the fuel pump when the ignition is on (if not then the most likely culprit is the MAS relay.
I have a MAS relay that I could sell to you. Just make sure that it is the problem.
Regards
Fernando

[outriding]

Cool, will work on it in the morning and report back...thanks for the tip, fellow canuck.

[outriding]

Happened upon a MAS unit that was a working pull from a 93 2.6 and installed it...car still had issue starting after the conditions described above. My wife was driving it however so I was unable to run my tests.

I am going to this weekend - suspecting it will happen again...

I'm going to look at the sensor, and also spark, OVP and EHA further.

edit:
I should note that everything else functions on the car, however I do have an SRS light that is illuminated.
The prior owner said he bought the car from someone who was short and did not want the airbag to go off - and had it disconnected. I have checked the wiring to the airbag on the wheel, the brain behind the stereo and the box in the passenger footwell, and all are connected and in good condition.

I'm mentioning this in case there is some relevance to OVP relay or the like... I suspect not - but sometimes you never know!

[outriding]

So...

The car died twice on the weekend.

- Has spark
- I have swapped out a brand new OVP and no change
- I have swapped out a brand new EHA and no change
- I have swapped out a used working MAS unit and no change
- Crank reference sensor check (measured resistance)

Today when the car died (after running about 10-12 mins) I could restart it only if I held the key for over 10 seconds and floored the accelerator. The car would run at high rpms but would die if I asked it to idle.

I killed the battery and had to wait for about 25 mins for a boost, and when boosted, it started fine, and ran fine.

- Idle control valve?
- Coolant temp sensor?

What's left to check? I have access to a place that will let me swap in some parts before paying for them to see if they are the problem - which is very generous.

Thanks in advance for any tips.

[Chris Martens]

Check again the crank reference sensor at the flywheel.
Read this similar story.

It sounds to me like the crank sensor at your 190E 2.6 is shot more or less.

regards,
Christian

[outriding]

Thanks for the link. I have my multimeter ready to go (car is parked elsewhere right now) for tomorrow and will check it.

Still find it hard to understand why it runs the way it does or doesn't. Most notably - after the recent stall, I was able to get it start again after about 10sec of cranking, but had to have my foot on the accelerator. Car would not idle however...

Anyways, Will check it out - hope its something as simple as this reference sensor.

[DUFFS3169]

I would check and clean the Idle Control Valve my car had some of your cars symtoms when I first got it and that was the problem. Now this was for the 2.3 but it had the same symtoms where it would run then die and would'nt start then after I left it for a while it would but I had to floor it to keep it running. Then the idle got crazy and would not idle below 3 grand.

[Chris Martens]

funciton of the VR sensor at the crank shaft:
it produces an alternating voltage, voltage hight / signal amplitude depends on the revolution. Of course the frequency of the signal depends on the revolution as well, but that is not important in this case.

If the sensor passes away, the voltage peaks / signal amplitude at lower revs / idle is too low so the EZL ECU will not recognize it.
In case the ECU gets no revolution signal it stops the fuel pump and stops ignition because it assumes, the engine has died. It's a safty feature.

At higher revs (maybe over 3000 / min) the amplitude is higher / the signal is better (see above) and the revolution signal may come through, even if the sensor is half dead.

Furthermore, the hotter the engine is, the weaker the signal will be.

good luck,
Christian

[outriding]

Thanks for the info - I put the meter on it and am getting 15ohms...safe to say far from the 800 recommended.

I am sourcing a new and working pull of each - and hope for the latter to keep the price within reason. I can have a new one in 12 hrs, and the pull by the weekend.

This would be a pleasant fix! More shortly.

[danwatt]

If you are still stumped after replacing the vr sensor, do a search on vapor lock and see what you can find. But really, it sounds more like it only happens when the car goes into closed loop.

[outriding]

Ok, sorry for the newb diagnostics earlier.

I was checking something else near the MAS and OVP when I reported 15ohms - I was doing this without really knowing the part - and thought I had traced the right item.
I found a photo of the reference sensor online, and see it's plugged in on the driver's side of the engine bay. It DOES have 825ohms resistance.

On the way home the car died...it was dark and I confirmed right away that there is spark, having pulled the #5 plug.

Swapped the MAS unit for kicks - no start.

Took off the filter, and pushed on the plenum a bit, smelled gassy - but didn't have the tools to check the fuel line. Read somewhere that you can see if the pumps are running via the O2 sensor in the pass footwell, but couldn't get a reading off it.

I'll rig up a test light for the fuel pumps - but it smells gassy, and there is spark... a new twist to what I was reporting earlier. I'll search vapour lock - thanks danwatt - all this new benz stuff is fun if not a tad frustrating :)

[ppetracca]

To me it sounds like your car is getting too much fuel... maybe bad fuel distributor? When the engine gets flooded, it definitely takes some time before the car can be re-started. When you floor it, it lets a ton of air into the cylinders which will make it A LOT more likely to start quicker. Does your exhaust smell like fuel right after getting it restarted (after it cuts out)? You said that your intake smelled like fuel which really makes me think your fuel distributor is getting a bad signal from something (yes, could be VR sensor) and having some serious mixture problems.

Something else I would seriously consider is your Idle Control Valve. If it is malfunctioning, it might not open during idle, causing the engine not to get enough air to idle (and too much fuel) and stall. Try unplugging your ICV and cranking up your idle (to 1100-1200 or something) on the throttle body. Drive it around for a day and see if you have the same problem.

Now that I've reconsidered what I've written, I would lean more toward the ICV.

[321-GONE]

I would also think in terms of fuel delivery. Just to rule out that the engine does not die of fuel starvation. When it next stops. Take off the air filter housing. Then with the ignition on, press manualy on the AFM flap. There should be an audibly noticeable mechanical buzzing (hard to describe exactly) sound comming from the injectors. If the sound is produced, then this means that the injectors are spraying fuel. This is a rudimentary way to determine if there is indeed, any fuel pressure at the injectors. If there is no fuel, hence no pressure, then the injectors will not operate (they open when there is a certain build up of pressure, causing the mechanical valve to open), and there will be no noise created. Hope this helps.
Regards,
Fernando

[mde3]

sounds like a coil could be loosing ground...they sometimes do when the bond between the coil and the frame deteriorates...have you checked spark once the symptoms happen?