alan860

Hi,

I recently managed to fix my transmission problems by putting some fluid into the transmission dipstick tube (later got the fluid renewed and no probs since). However at around the same time I started having starting problems (when I put the fluid in, and continued beyond when I got the fluid renewed). The problem appeared worst during hot weather.

When I try starting the car (2002 C180) it turns over no problems and if the car has not moved in a while (few hours) it will start before the car gives up this first time (it seems to try to start for around 5-10 secs before stopping). If however it hasn't been parked for very long it will try this first time then stop. On the second attempt it normally starts ok (once it didn't).

I've read that this could be indicative of a cam or crank shaft sensor, now given that i spilled some fluid (i did clean it up though) on top of the engine when replenishing the transmission fluid, i'm thinking perhaps some has migrated into the camshaft sensor. Does this sound likely or can someone suggest an alternative fix?

I have checked for codes and despite the problems starting the car there are no codes stored (OBDII, not sure about other computers).

Any help is very welcome as this thing is becoming more and more problematic, but i'm sure its something simple and once fixed the car will be a good one.

Thanks,

Al

johnand

CPS is definitely possible, as is a bad pressure regulator in the fuel filter (Have seen a rash of bad filters lately.), or lazy fuel pump I would put a fuel pressure gauge on and verify fuel pressure is in spec (3.7-4.2 bar) before proceeding further.

alan860

Thanks John,

I'll try to get a pressure guage from somewhere. The car was just serviced last week and the garage couldn't find anything wrong (worked ok when they tried it), but as you say worth checking everything out methodically.

When you say the CPS are you referring to the Cam Position Sensor or Crankshaft Position Sensor. I'm tending to err on the Cam sensor purely because of spilling the fluid in that general area (not a lot of fluid but problems started around the same time.

Also when the car starts if left to its own devices the rpm hunts a bit to start with if that helps any (800-1200 rpm).

Alan

Glyn M Ruck

Listen to John. Please note that you need a minimum of 3.8 bar fuel pressure WHILE CRANKING. Check pressure while cranking.

Good luck!

alan860

Thanks everyone. Found a cheap fuel pressure guage so will give it a try once it arrives.

Alan

alan860

OK, I checked the fuel pressure (using basic tyre pressure guage at the end of the fuel rail). Prior to inserting key there is next to no pressure (first thing in the morning), while cranking pressure rises slowly (clocked at around 25 psi), and once the engine starts pressure shoots up to above 55psi (guage maxed out).

Any ideas?

A

Glyn M Ruck

You have insufficient pressure while cranking. s/b 55 psi. Check filter as Johnand suggested & fuel pump might be on it's way out. Also check fuel pump relay in rear SAM. Relay is in position "A".

alan860

Thanks everyone, the car is going in to the garage on Monday so hopefully i'll find out for sure then. I had almost convinced myself that the cam position sensor was faulty as playing with th connector seemed to make the car start every time, and then later on it reverted to normal.

Could probably do with finding something detailing how everything interact on the fuel and ignition system for any future faults, things just aint as simple as they used to be are they.

A

Glyn M Ruck

The 4 cylinder engines use a different injection system to the 6 and above engines. With the 4 cyl you have the electric circulation pump to provide rail pressure for priming & starting, then you have the HP pump which is engine driven & ramps up pressure as the supercharger increases boost. That's why you went off the gauge after starting.

alan860

Thanks Glyn,

Is it worth trying the filter first, this was changed about a year ago. The problems started when the wife let the tank get pretty empty and appears to be harder to start when fuel level is below 1/4 tank?

A

Glyn M Ruck

Yes - do filter first. The system might have sucked a load of gunk from the bottom of the tank. We have also had recent filter failures as John said. I hope no dirt got to the pump. They can tolerate very little - especially magnetic rust because the pump runs flooded. Remember CPS remains a potential problem but get the fuel pressure up to spec first.

alan860

Glyn,

Do you mean Crank Posit Sensor, or Cam Posn Sensor? I've already changed the Crank Posn Sensor.

A

alan860

Also, i've been told the fuel pumps should be changed as a pair, is this just because if one goes the other is likely to go shortly too or is there another reason?

Glyn M Ruck

I mean crank position sensor. Its done - great!

Regarding pumps. The engine driven pump seldom gives trouble. There is only one electric pump in the fuel tank. Two hatches under the rear seat, two level sensors in the saddle tanks. Only one contains a pump. Only replace that if necessary. Don't replace what you don't need to. The dealers would love to charge you for another sensor unit!

alan860

Hi folks,

Problem solved. Fuel filter was bust. Something to do the the PRV in it.

Thanks for your help.

A

Carsy

I would be glad to know what PRV means .Pressure Relief V/V ?

Glyn M Ruck

The bloody pressure regulator in the filter again!!! Why Benz ever integrated the pressure regulator with the fuel filter I will never understand. We keep having failures with relatively new filters.

Pleased it's fixed!