Problem starting when at operating temperature
 

Hi All,

I've been in search of a solution to an intermitent problem starting my 1990 300D 2.5 Turbo for some time now. The problem I am experiencing goes something like this:

When I've been driving and am up to operating temperature, and it is above say 80 deg outside, and I shut down and sit for anytime over say five miniutes, I have trouble starting. Never have a problem staring cold or in moderate heat, even at operating temperature. It acts as though the fuel system is air bound or priming or starving. It can take anywhere from a few seconds of turning over (more than normal) to turning over for up to a minute as done when the fuel filters are changed. The problem seems to be worsening as over the last couple of days I've found it very difficult to get started again (IE wait for the car to cool and prime it a few times).

The fuel filters have been changed w/i the last 3000 miles, I do not see any fuel leaks, I do not see any air visible in the clear fuel lines adjacent to the fuel pump when running, the injectors are new/rebuilts (tested before installed).

I've read of others having trouble starting, although w/ different particulars, changing the o-rings in the fuel system (fuel delivery valve seals). I am inclined to change these out in search of a solution but am not confident they are the fix. It would seem to me that if I had a leak in the system by way of the o-rings I would see fuel leaking. Also, I have not checked the prefilter in the tank and feel that may also be worthy of inspection/cleaning. Again, not confident has any bearing on whats happening.

If anyone has any ideas for trouble shooting this problem or recomendations to solve it I would greatly apreciate the input.

My car had the exact same symptoms... ended up simply being the starter. Have you checked that?

While I can't speak from experience on the newer MB diesels, on the older diesel cars hard starting when hot can be caused by a bad starter (shorted windings/burned enamel insulation). Sometimes you can verify by spraying water on the starter, then try to start it a few minutes later.

I haven't considered the starter as it turns the motor over like a champ. Also there is no change in the rate at which it is turning over even after a minute of engaging the starter and it seems it is cranking by the movement of the engine. Veloce, Was there any noticeable difference in the cranking when your starter issue showed up?. This is my first MB, but with other vehicles I have owned there has been noticeable changes in the cranking (IE drained the battery, spinning noise, didn't engage). Palangi, I'll give cooling the starter a go.

Thanks, Brian

just a thought..
 

try taking the fuel filler cap off when your car is turned off and hot to see if there is a vaccum built up in the fuel tank.

Re: just a thought..
 

I would second that recomendation.

Checking the cap was my first thought too but nobody has mentioned valve adjustment. Could that be possible? When a motor is shut off when hot the temp will actually rise considerably and if the valve clearance is too loose it will be exagerated the more heat that is applied leaving the engine low on compression.

Of course check the easy stuff first--

I'm no expert--what do you guys think of my theory??

Good luck and let us know what the problem was.

Cheers,

Bill

I also noticed this problem with leaky injectors, but usually it happens cold too.

hmm...
 

I checked for a vacuum on the tank and found there was not and still trouble starting. Pulled the tank filter this evening for my own piece of mind, cleaned it and replaced. Nothing appeared to be wrong.

I've gone and ordered delivery valve o-rings to change out. I have read posts for other models that have had issues with taking on air near the filter/IP at these and getting similar symptoms. Parts Changer!!!!

Bill, I believe there is no adjustment to be made to the valve clearance with this model (engine 602.962). My service manual has a method for 'CHECKING AND RENEWAL OF HYDRAULIC VALVE CLEARANCE'. Perhaps checking the clearance is in order.

Phantom, I thought leaky injectors as well. That is how I ended up with new ones. Actually had to have the new ones serviced after I bought them. Turns out three of five of the new ones had problems (One wide open and two poor spray). Go figure, should have had the originals serviced. Either they came to me with dirt in them or I did it during installation. Had them cleaned and brought up to snuff and installed them. They seem to be working fine and problem not solved.

Thanks for the help,
Brian AKA (PartChangerGuy)

Brian I believe you are right--I don't think there is valve adjustment on this model but I'm not sure as this is a "late" model car to me! I saw the "300d" and didn't pay attention to the year, so I agree with you guys--check injectors. Run a strong dose of cleaner in your tank to see if that helps before removing / replacing them.

Cheers,

Bill

Fuel Primer Pump is the Problem
 

Its been a while with this. I believe I have gotten to the bottom of my hot start problem.

Turns out after much investigation and some parts changing that the fuel primer pump (PP) is the culprit. This model MB has a high volume primer pump operating in series with the IP. The clear fuel lines I was inspecting along the way were not clear enough to see that there was air making its way to the injection pump. On an occasion I was able to see small bubbles of air in the clear return line from the IP and began tracing back from the IP to determine where the air was getting in.

I worked my way back to the tank. Starting with the CLear bit of fuel line (which was not so clear by the way after 15 years of diesel) connecting the PP to the fuel preheater and the associated rubber lines. Still had air. inspected and changed the hose clamps. Changed fuel tank feed line and cleaned tank prefilter. Still after all this took determined it must be the primer pump cavitating creating air. Changed out pump and it was definately shot.

The air was gone but would be back. This version of PP does not like 100% biodiesel, eihter b/c of the viscosity or the methanol as the pump began to degrade and back came the air entrainment. Note that imediately after the pump change I did notice very very small quantities of air showing up.

I am in search of a cure to keep this car, however my expectations are not good. I have retrofit with a 4psi facet pump (4psi not enough MB spec min 12 at IP) in series with the mechanical PP with decent results until the POS electric facet pump burned up after about 2000 miles. Looking to Bosch for the spec on the pump to see if the seals are all Viton.

Have a 12 to to 14 psi facet pump ion the bench to install a electric pump powered loop to the engine compartment so the fuel is lifted up to the PP. Also in search of VW.

Moral to the story so far as I am concerned is this model MB (W124 w/ 602.962) can not handle bio at the quantities I am running it.

Thanks

THank you for following up...really helps to have the thread closed out for others having the same problems. :)

Does anyone know about the high volume primer pump that bkg was talking about back in 2006?

As far as I know now, my 124.128 only has the fuel pump that is mounted to the IP and the IP itself. If there is another fuel pump I want to know about it, especially if it is sensitive to biodiesel. I haven't seen a reference to it on any of the fuel system schematics I have looked at so far. Thanks.