Sorry ~ strike EGR comments ~ I had M112/113 engines on the brain.

Air pump relay should be in front SAM relay cavity "O"

 

OK so I ran out to MB and picked up a relay as I didn't want to have to wait until Monday. I swapped in the new one, had the car started (33f ambient- still started bad), and I don't think the air pump ran at all. It should be fairly obvious right? If I recall it sounds a bit like a jet engine for a few seconds to a minute or two? I didn't hear or feel anything. I pulled off the big air pump intake tube from the air box and didn't feel anything. Is there a fuse for this or just the relay? (Edit I checked a 40 and 50 amp fuse near the relay and they are both good)

Checked and no stored or pending codes. All monitors ready except catalyst. With more than a few bad cold starts I hasn't thrown a code in more than 2 weeks (last was 420,175,172)

So I guess I need to see if there is voltage being sent to the pump next. Can anyone tell me which of the wires/pins I need to check on the pump connection, top or bottom? Is there a length of time that the car needs to be off to check it or just coolant below a certain temp? If I want to supply the pump with 12v to see if it runs do I give one pin 12v and the other gnd or is it grounded separately and I just need voltage?

I'm curious about this, as I understand it the car is supposed to run a bit rich for cold starts, the air pump is supposed to run for up to 2 1/2 min (the colder the longer) pumping air into the exhaust ports increasing post cylinder combustion, thus warming the O2 sensors and cats.

Now I don't know about the start itself, but the way this car runs stinky rich for a bit when it's cold out- the colder the longer, seems to correspond with how long you might expect the pump to run.

So am I barking up the wrong tree or could this actually be the problem?

 

I do not have a useful wiring diagram for the excess air pump.

Fuse should be in position 65.

I can certainly hear the pump running on my CLK with the window or door open M272. On my W203 C240 it was even more obvious. Sounds like a turbine.

I am helping you from basic principles. We don't experience your sort of temperatures. In my global job however I have driven Benz cars in very cold conditions in places like Harbin in NE China at minus 50 deg C. The V6 engines start well. The M271 I4 has always been a bit of a rough starter in these conditions. Too rich is as bad as too lean in cold starts.

I think the pump might be part of the problem. I'm not sure that it is all of the problem. I worry about the temperature sensor accuracy. This car seems very rich indeed.

 

I just checked during a start and the pump is not getting 12v. When you directly supply the pump with 12v it turns on. I suppose next would be to see if there is 12v at the fuse during start. But, I think the car may be too warm now.

 

OK so this afternoon I replaced the coolant temp sensor and removed the throttle body for a thorough cleaning. TB had a pretty good ring of nasty on it.

Put it all back together and started the car (46f). The air pump DID run for 30 sec to a minute. So, not sure what was up before. 46f is a temp the car always starts/runs fine so I put it outside to wait till AM and a cold start to see if it's fixed or not.

 

Here's hoping! I wonder if you have a poor connection somewhere on that pump.

I meant to remind you to clean the electrical traces on the TB actuator while you had it out

 

If you are talking about the little contacts and tracks in the electrical portion of the TB, I did use some contact cleaner on them.

I don't know what's up with the pump. I'll pop the hood for the AM start and see if it runs. We'll see, fingers crossed.

 

Good man

 

Well it's not fixed. Started it this morning (18f), wouldn't start/come to a smooth idle without throttle modulation. Bumble/stumble started and then cleared right up. It appeared that the air pump did NOT run...

I logged data with DashCommand while I took it for a 30 or so minute test drive, some stop and go neighborhood and some highway. Still has crazy -27/-29 long term fuel trim and popped a P0175 near the end of the test drive.

I'm thinking of taking it to the dealer it's starting to frustrate me.

 

Sometimes without the benefit of a Star things can be hell to track down. One is forced to go methodically through every item and sometimes we simply don't have the time or inclination to do that.

I'm running out of ideas!

You are not logging any 300 series misfire codes which means the ignition system seems fine.

I have no idea why the excess air pump does not start reliably unless there is corrosion in a plug somewhere. This must be rectified.

You are getting no O2 sensor codes so they are cycling properly.

You might have a faulty or dribbling injector or two but it is rare & usually just requires a clean up with Techron. Injector replacement is rare.

From what you say as soon as it clears the flooding/over fueling the engine settles down. This spare temperature sensor you had lying around. Is it new & known to be good?

I really doubt an ECU gremlin. One last thing you can try is unplugging the MAF & see what happens. While the MAF has no influence on fuel trim in enriched open loop, unplugging it does force the ECU onto a default fixed map where everything is roughly right.

Give that a try or get the car onto a Star.

Good luck!

 

Thanks Glyn, the car is at the dealer now so we'll see what they say. It's supposed to be close to zero f tonight and I suggested that they leave it outside the door, push it in, hook it up and then go for a start. Don't know if they'll heed my suggestion. If they leave it out and drive it in they will at least witness the bad start but won't have diagnostic data about it as subsequent starts will be fine until it cold soaks again.

Confusing thing is it's appearantly not just the cold starts as it wants to run rich all the time with LTFT near -30 on both banks.. Don't know if it's same problem or two different problems.

The temp sensor was purchased a month or so ago just had not changed it as looking at data suggested it was fairly accurate.

 

Man do you have an intake obstruction or something? fuel trims that out of whack are very rare without throwing a rich correction code.

very odd.

 

I hope they listen to you. They should have a portable Star.

 

Well they called today; Said that they were definitely able to reproduce the fault when started in single digit temps (f) yesterday AM. Said it started quite badly.

Told me they did a software update to the ecu, changed and adjusted some parameters in the ecu, and put it back outside overnight. When they started it this AM (8f) it started fine and normal.

I spoke to the service writer not the tech so I don't know exactly what they did ecu wise but he said just a couple hours labor and no parts. In the past 2-3 months it has NEVER started "fine and normal" when the temp was much below freezing. So they must have accomplished something..

I asked him to park it out overnight again and start it (should be 15-20f) in the AM. If its good to go I'd come get it.

 

It's strange though. I thought there was only one "software update" campaign for this car, and I thought this car already had it judging by the under-hood writing.

 

Wow! I look forward to hearing your views when you get it back.

I'm sorry if I steered you away from an ECU software gremlin but I really doubted it could be that simple. Maybe there is a lesson there somewhere.

 

Glyn, I really didn't think it could be an ECU software issue either other than a plain bad ECU. If that's the case I would haver never found it, just slowly ruled out everything else while pulling my hair out and bleeding time/money. So if it's truly software related I'm glad I gave up when I did.

I didn't really think the software could corrupt, or that there were many significant operational parameters a tech could actually adjust. I thought when they went bad it was usually down to a part on the board going bad and you were out of luck and in for a big bill. But, I admittedly don't know much about MB ECU software and what is possible with star.

My fear is that they did something like a hard reset on the fuel trims or other parameters, didn't road test it, and it's only had a couple of starts and idle/just off idle operation. Once on the road for a few trips things work out of whack again and the problem returns.

Let's hope my worries are unfounded.

 

The EEROMS used in automobile ECU's are rather susceptible to gamma rays. Those from space usually penetrate the package and pass through the IC without disturbing any of the programmed junctions. At a microscopic level there is wide open spaces between the memory cells.

If you live in a more Northern latitude exposure to random gamma rays is more frequent. Reflashing the memory will usually fix the bad bits.

Put away your tin foil hat, they won't help. The rays are not always from space. A good close lightning strike often generates a lot of rays.

 

Well picked up the car yesterday after the dealer reported another trouble free AM cold weather start. Didn't talk to the tech but paraphrasing here the write up basically said;

Problem reproduced, car would not start in 1(f) deg weather. Had to be pushed inside to warm up for a start. Started and ran diagnostics running rich several fuel trim and misfire codes. Checked plugs-OK, installed updated software to ME, left outside overnight, started next AM in single digit weather without problem.

No road test as mileage was basically same.

I hadn't observed misfire codes before unless they were pending and went away. It might be that they didn't give it any throttle modulation and just let it try and start on its own ultimately failing to do so. As I said before it's never failed to actually start but if you don't give it some pedal it will bumble/stumble along on the verge of started but not.

Sooo anyway, I had them keep it an extra morning start and picked it up yesterday. Drove a short highway/city trip home and all was fine. Son drove it to class and back (city) and it popped a P0170 on the drive home.

Weather is warmer today and for the next several days so no info on the cold starting. Otherwise appears to run fine he said.