98 C240 starting issues (again)

[stargazerplus]

Many thanks to all who repled to my previous post. Have taken heed of your suggestions but I still have a starting issue.

The car starts and runs fine from stone cold and hot. However, after sitting for 6 - 7 hours it usually doesn't. The car has the autostart which continues to run the starter motor after turning the key briefly. The starter will spin and the car will attempt to fire but does not start. It usually takes about 2 or 3 attempts with autostart and eventually after long cranking it will catch and run perfectly.

The following have been replaced:

Fuel filter
Mass air flow sensor
CRANKSHAFT SENSOR
Coolant temperature sensor.

The car has been on Star diagnosis and shows no logged faults.

Has anyone got any suggestions? Help!

 

[Ultymate]

Some of the older Mercs had a one way valve in the fuel injection system it's sole purpose was to maintain whats known as residual pressure within the system to fascillitate easy starting. I used to work at a Renault Franchise some years ago and their one way valves were built into the pump hence you had to replace the pump if the valve failed, but we found out you could screw the Merc one way to the outlet of the Renault pump cost the customer less than a fiver and took minutes to fit, So it may be worthwile you finding out if theres any sort of one way valve fitted on your car as your symptoms fit with lack of residual pressure:idea:

P.S. I've found this schematic on the Russian site which I think is what you have on you car, I'd be interested to see if item twelve has a one way valve inside it as it looks very like what we used to fit on the Renaults http://www.detali.ru/cat/oem_mb2.as...GM=717.464&CT=F&cat=45H&SID=47&SGR=030&SGN=02

 

[stargazerplus]

Thanks for your reply and yes I think that there is a one way valve built into the fuel pump. However there also seems to be a valve built into the fuel filter which is why they cost £50 at a Merc dealer. Interestingly when I replaced the fuel filter the car started immediately! The fuel pump on these is over £150!!! so it is going to be a bit of an expense if the symptoms aren't cured after replacing the pump!

 

[Ultymate]

Wo I'm not saying to replace the pump please don't do that on my say so, what I am saying is there may be a one way valve inside fitting No. 12 in that diagram which will be available seperately from the pump. Another way you could check it is with a pressure guage on the fuel rail for a few hours whilst standing to see if your system is holding residual pressure. I have never come across a one way valve in a fuel filter:-?

 

[stargazerplus]

I have never come across a one way valve in a fuel filter:-?

No, neither have I! But I cut open the filter that I replaced and on one end there is a small cylinder which does appear to contain a valve. The filters for these models have four ports see here (diagram from 129 for illustration):

http://www.detali.ru/cat/oem_mb2.as...GA=722.607&CT=F&cat=44F&SID=47&SGR=045&SGN=03

 

[television]

I cant see how this is fuel pump related as the car uses a lot more when running.

Malcolm

 

[stargazerplus]

I cant see how this is fuel pump related as the car uses a lot more when running.

Malcolm

Thanks Malcolm.... I agree with you. The fault is very strange and relatively intermittent.

I suppose there is nothing to be done until the problem starts being utterly consistent!

My better half just started the car (instantly) and drove off. However yesterday after a 30 minute stay in Tesco it started with the usual struggle.... the car is immaculate and has only done 80,000 miles!

 

[Ultymate]

No I'm not asying it's a fuel pump issue once the cars running the pump will hold more than sufficient pressure I'm saying that the system may be losing residual pressure and therefore being hard to start after standing for a while ie fuel can run back to the tank to be replaced by air from the return side therfore the pump has to purge the system before the engine starts. Not a deffinate diagnosis you understand just a hunch

 

[television]

Do a google search,MB 240 poor starting, I saw lots a few days ago when looking for something else.

Malcolm

 

[stargazerplus]

No I'm not asying it's a fuel pump issue once the cars running the pump will hold more than sufficient pressure I'm saying that the system may be losing residual pressure and therefore being hard to start after standing for a while ie fuel can run back to the tank to be replaced by air from the return side therfore the pump has to purge the system before the engine starts. Not a deffinate diagnosis you understand just a hunch

I too thought about your hunch carefully. It doesn't work for me however. The car, for example, today has just been to Waitrose and the petrol station. Started fine after Waitrose, fine on cold, but churned for ages after five minutes in the petrol station. Seems to have changed its habits yet again!

 

[eric242340]

Fuel regulator

I dont know if this is causing your problem, but its very easy to check the fuel regulator. It should be located on the injector fuel rail and is operated by vacuum. simply remove the vacuum pipe and place your finger on the regulator pipe. If you find fuel on your finger then the regulator is no good. Some models have the regulator on the fuel pump but it can be tested in the same way.

 

[louisoliver]

bit of cleaning

I had an intermittent starting problem with my e280. Replaced no end of parts. Finally read a post regarding an old 190e and it worked wonders. I took off the throttle body and cleaned all the black gunk from round the butterfly. Starts on the button everytime.

 

[stargazerplus]

Resolved too - it seemed to be a combination of spark plugs and MAF even though this had already been replaced!