wont run when hot...72' 280SEL - PeachParts Mercedes-Benz Forum

jkeith72 · #1 06-07-2010, 09:59 PM

Well, just when it seems all is well with the way my car is running (72 280SEL 4.5), another issue arises. This time the car runs great until it warms up completely. I drove it about 3 miles, parked it, had dinner for about 45 minutes (above 100 degrees in AZ). I started the car and it did not want to run. I was able to limp it home, and by the time I got there....it would BARELY idle then die. This has happened to me the last time I drove it, but I had since replaced the old fuel filter thinking it was obstructed causing a lean condition. It does seem that when it runs like this, the fuel pump makes a whining noise...although im not sure if its a sign of distress or not.

Im not sure where to go with this. I will check fuel pressure first off. I just replaced the vacuum lines from the throttle body to the switch and to the distributor...so that should be ok. I was thinking the idle may be set too low, but it seems to just lean out and want to die when you give it gas....

Thanks in advance! Jason Keith

ctaylor738 · #2 06-08-2010, 10:19 AM

Classic signs on fuel starvation especially the whining pump, suggest you check the fuel tank outlet screen.

Graham · #3 06-08-2010, 10:55 AM

Sounds to me like typical D-Jet hot start problem.

Check out this thread

Usual cause is that mixture goes very lean, probably due to gas flashing to vapour across injectors.

Other links:

http://mbca.cartama.net/showthread.php?t=35260

http://mbca.cartama.net/showthread.php?t=34446

Good Luck!

jkeith72 · #4 06-11-2010, 06:57 PM

Not to ask a silly question, but is the fuel pump strainer at the pump, or part of the tank outlet? I have not had a chance to troubleshoot my issues yet. I will be back in town tomorrow and will perform some maintenance. I need to buy a fuel pump pressure gage. I was looking at Harbor Freight, and looks like theirs doesnt have the fittings for a Bosch system....can probably rig it to work right?

Im sorry Im such a rookie. I have always owned newer Japanese cars, and rarely do more than change fluids on them.

Jason

Graham · #5 06-11-2010, 07:47 PM

Quote:

Originally Posted by jkeith72

Not to ask a silly question, but is the fuel pump strainer at the pump, or part of the tank outlet? I have not had a chance to troubleshoot my issues yet. I will be back in town tomorrow and will perform some maintenance. I need to buy a fuel pump pressure gage. I was looking at Harbor Freight, and looks like theirs doesnt have the fittings for a Bosch system....can probably rig it to work right?

Im sorry Im such a rookie. I have always owned newer Japanese cars, and rarely do more than change fluids on them.

Jason

Strainer is in tank. Have to drain tank to remove it. I would do a fuel pump flow test before messing with strainer. Should be 1l in 30sec. Fuel filter is after pump and easy enough to change.

You can make up a temporary fuel pressure gauge using a simple water pump gauge (0-50 psi), a tee and a few pieces of injector hose. Something like this:

Graham · #6 06-11-2010, 08:02 PM

Quote:

Originally Posted by ctaylor738

Classic signs on fuel starvation especially the whining pump, suggest you check the fuel tank outlet screen.

Chuck - There is a modification of the fuel hoses in the engine manual to stop whining. MB dealers used to change out whining pumps and even the new ones whined. They moved the pump slightly and then added a longer hose run with a larger hose over top of the actual hose, presumably to deaden the vibrations.

I hoped to post a link to the pdf, but the w116.org site seems to be down.

My SL pump whines even although everything is clean. Keep meaning to fix those hoses!

ctaylor738 · #7 06-11-2010, 10:43 PM

Well, a key piece of my long distance diagnosis was that the pump whines when the car dies. That suggests that it's running out of fuel. This is consistent with a car that does a lot of sitting.

I agree that the volume test is the more important test to run.

Graham · #8 06-12-2010, 01:20 PM

Quote:

Originally Posted by ctaylor738

Well, a key piece of my long distance diagnosis was that the pump whines when the car dies. That suggests that it's running out of fuel. This is consistent with a car that does a lot of sitting.

I agree that the volume test is the more important test to run.

You could be right about the cause of the noise. But I know my SL does it and the screen is clean. The pump is original and has been dismantled for cleaning, with rollers not necessarily back in same place

. So noise could be just the pump itself or the hose routing.

The pdf on fuel hose routing actually only refers to 107s. Maybe the sedans already had this mod? I have attached the pdf file this time.

Jason's car dies only when hot soaked, so he more than likely has the common d-jet hot start problem.

jkeith72 · #9 06-13-2010, 04:49 AM

I bought a gage kit today and will try some pressure readings Sunday. I will also do the volume check....once again, great information from the Mercedes gods on this forum!
As for the hot start issue, I like the solenoid fix so far. In theory when it decides to act up when hot, I should be able to relieve pressure (very carefully) to fuel rails, reconnect, and the fresh fuel should alleviate the vapor issue right? Im thinking I might try that next time it decides to misbehave...shouldnt be long in the AZ heat.

Thanks!
Jason Keith