Rudeney

When you run out of fuel, you get a very sporadic delivery and the engine can keep stumbling along for a while. I think this is what killed the injectors in the S500 as we did have to repair it. The salesman ran it out of gas driving about two miles from the dealership. Another one rescued him with a gallon, and when he brought the car back, he was complaining about it running poorly. I drove for the next week, about 100 miles, and it never got better, so I put it in service and they ended up replacing several of the injectors.

Like I said, this running out of gas would happen about once a week, but this was the only one during my 6-month "tour" that had this problem.

Russell Ormerod

Interesting one. Thanks for the info

I_am_Sam

Interesting discussion, a very fascinating read.

So, I've had the CPS changed on Monday 14th Dec. No issues so far, however we are having a run of hot weather now (35 C Today, 36 C, 39 C, 35 C) 35 C = 95 F, so this should be a good test.

However, I have MAF questions now - if someone wouldn't mind having a think on.

When searching my symptoms CPS and MAF always showed up, so it was always in the back of my mind, and this morning I had some strange readings on the digital temperature gauge which I always thought was air temperature and since reading on here I think it gets that from the MAF (correct me if I'm wrong).

Now this morning on commute to work, at about 8:30am, I'm in slowish traffic about 40-50km/h and I happen to be in a tunnel - it's short, only a few k's long, but I guess because the lights came on and the dash lit up I noticed that air temperature reading, and it was showing 37C (98.6F), and it seemed quite high to me. I opened my window to check and it didn't feel anything close to 37C - I'm sure it is much warmer in a tunnel than ambient temperature (phone reported current temp as 24C 75.2F) so I wasn't too concerned as I'm in a line of traffic all putting out heat.

But it got worse...

The tunnel heads up hill towards the last k, but traffic also speeds up and spaces out, so I'm now doing about 70-80km/h and the temperature gauge starts climbing, fast. I've never seen that before, it peaks at 57C 134.6F.

A minute or two later I leave the tunnel and I'm pretty much in suburbia, no traffic, back in the ambient air, but the car reported temperature is still at 57C. Probably takes about 5 minutes to start to decrease and it's quick. It hovers around the 40C mark but then settles back to 37C after another 5 or so minutes and doesn't go below. Again, temperature outside is actually about 24C.

So....
- Is this MAF related?
- If so, could it have caused my previous issues?
- Could it just not be reconnected correctly after mechanic installed CPS?
- If I do get another conk out, disconnecting the MAF and trying to start is the best way to diagnose?

Thanks again for any advice.

DanielFD

Thats unrelated to the MAF, your temp reading on the instrument cluster is called "ambient temperature" and its sensor is a 12$ sensor on the end of a plug the clips into the front bumper in the mesh next to the foglight. weird readings will most probably mean its loose in engine bay as it just clips into its place

Russell Ormerod

Correct. MAF reads intake air temp not outside air. Sometimes the sensor either falls out or was not fitted properly in the bumper and it could be laying in the engine bay picking up excessive heat

I_am_Sam

Awesome, thanks guys.

Quick post, new CPS did not fix the issue. Will post more later.

I_am_Sam

Hi all, happy new year!
So unfortunately changing the CPS has not solved the issue. First time I drove it, fine to work - 30 min drive. On return, lots of studdering and loss of power as described earlier. (Warm afternoon) but managed to make it home pulling over from time to time.
Second trip today, again fine on way to work, on return it just wouldn't start and stay started. So that is new. It would kind of start but then conk out. Then it might run a little but I could never get the revs very high - maybe about 4-5k. Then it would conk after a bit while it idled - somewhat rough.

Does this new info help you smart people diagnose this?

I plugged in my obd reader when it wouldn't start but it didn't give me any codes.

(Sorry about formatting laptop is in car which is still stuck at work, going to taxi to it later tonight and try to get it home)

Any help is always appreciated.

DanielFD

This sounds like a fuel pump issue, did u ever get a fuel pressure test from the fuel rail?

I_am_Sam

No I don't believe that was checked. Is it accurate to diagnose with the test? I mean, the issue is intermittent, would it need to be occurring for the pressure test to fail?

Cheers for the input.

DanielFD

Well somebody would have to chime in on that. weird that your not getting any codes.. usually without codes its something "un-electronic" though thats not necessary. could be the fuel pump not pumping correctly or it could even be oil residue on the spark plugs.

Russell Ormerod

Connect a fuel pressure gauge with a long hose with the gauge laying near the wipers so you can see it while u drive. When the fault occurs see what the pressure is doing. If it's the pump you will see it fall to 1 bar or less then the motor will die. A bit of pressure fluctuation is normal as you accelerate or lift off. But should not fall below 3 bar.

I_am_Sam

Firstly, the car drove fine home in the evening when I returned.

Secondly, thanks for the info on the fuel pump, I will give it a test next warm weekend and drive around the neighbourhood until it I get the issue.

Would anybody know the size of the pressure testing valve?
I have found this test kit on ebay - http://www.ebay.com.au/itm/Universal...-/201496776834
Looks suitable?

Thanks again.

claudioz06

Damn, why running a Mercedes low on gas so frequent? Your fuel pump needs fuel to lubricate itself and to keep it cool. When you drive low on gas the pump will suck it air very frequently loosing lubrication and running hotter and burn. So you either burned or damage your fuel pump of got too much air in the fuel line. My advise is to fill it up and put some lukas fuel additive if possible and keep trying to start it up.

Rudeney

I replaced my fuel pump and in-tank filter/sender this weekend. I ran it down to one "bar" on the gauge and was very surprised to find how little fuel was left in the tank. As designed, the left side (sender side) was empty, and the right side where the pump sits had maybe just over an inch of fuel in it. I added another gallon after the job and first start-up and drive was terrible as there was air in the system. After a shutdown and fill-up, all was fine.

BTW, the pump pulls fuel from a small reservoir in the bottom of its housing. Fuel "seeps' into the reservoir through a sponge-filled mesh "pillow". After 80K miles, the inside of my tank was spotlessly clean - no sludge or sediment. Probably 60K miles of that used Costco gasoline, the other 20K is name-brand Chevron, Mobil, BP, Shell, etc.

I_am_Sam

You guys are amazing. Special mention to Rudeney & DanielFD.

I had the fuel pump replaced on Tuesday, and have driven it every day since (now Sat)..... and it's running great!

It has been hot here (Melbourne, Australia), I've gotten stuck in stop-go traffic - all the things where it died, and not an issue....well I was crapping my dacks and looking for places to pull over the whole time, but apart from that, all is well.

Additional:
I didn't check the fuel pressure I just organised for a mechanic to come over and do it (I would have liked to do it myself but time is precious these days). However he did spend 45 mins saying the CPS I had replaced must have been faulty and to do it again - also calling about 5 other mechanics for their opinions, who all said change the CPS but then didn't have a follow up suggestion. He just didn't think it could be the fuel pump and was trying to save me the money.

More thanks:
So thank you all again, those who posted suggestions and also those that took the time to read my post.
My wife also extends her thanks as I am now able to drive our 18month old son around again, we all went to the Zoo today...and she is thankful that I will always keep the tank topped up! It used to drive her crazy.

Conclusion:
Having the car low on petrol and hitting the train tracks super hard caused a problem with the fuel pump. My frequent low petrol indicators may have weakened the pump.
I promise I will fill up with fuel more regularly and keep my pump lubricated....

gixxerboy

Glad to hear you got it fixed

DanielFD

Forum has helped me more then i could ever give back

Rudeney

I replaced my fuel pump a few weeks ago. I ran the car down to one "bar" on the gauge and the "distance to empty" screen just showed an icon of a car at a gas pump. When I checked the tank, there appeared to be just over a gallon in the there. The pump is made to stay surrounded by fuel even on an nearly empty tank. The pump motor itself is less than 2 inches in diameter. It's suspended in a larger housing, basically a canister, that's about 4 inches or so in diameter. When the tank is full, fuel enters the canister from the top. It stays full, but can also draw in new fuel from the bottom with a check-valve. Fuel coming from the bottom passes through mesh "sponge" inside the canister that acts as a large particle filter. Basically, the canister is designed to stay full of fuel even as the tank level drops, and thus keep the pump cooled.

My guess is that the failure was overheating of the pump. The impact of the tracks on very low fuel probably caused the fuel inside the canister to slosh out. After replacing my pump (and in tank filter/sender) I left the back seat cushions out to check for leaks. Hearing the pump run as I drove around, it works HARD! At highway speeds, it sounded like an outboard motor running.