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Old 11-04-2013, 05:33 PM
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Join Date: Nov 2013
Posts: 17
no start when hot

Hello gang. Thanks for responding to my thread. I have a 1985 Mercedes 300sd 126 model. The car starts up ok in the morning when its cooled down. I do live in Puerto Rico. When the car gets up to operating temperature (approx. 80 degrees) then it idles at a little higher rpms. Also when I shut it off when hot it will NOT start. It turns over ok. But I have to wait an hour for something to cool down. I am almost certain that I have good compression at all cylinders. The car has great power in the Puerto Rican hills. I have recently tuned in all of the valves. I have checked the resistance on the glow plugs and wires. It does read higher when hot. Then when it cools down the resistance changes from 4.3 to .8. I maintain pressure at all times at the manual pump. I do have to press on the pedal 10 seconds to keep it running in the morning. I have replaced the gold plated idle plug on the injector pump. If I push hard on the pedal in the morning the rpms rev up then quickly fall. When hot, the rpms fall very slowly after I press on the pedal. I have cracked the lines at the injectors. Each spit out fuel while running. I have run the car with the fuel cap off. I have taken the vacuum hose off of the shutdown valve. Again, the car runs great even when hot. But, it stalls when I place it in drive from P and at idle. I have to press on the fuel pedal when I put it in drive to keep it from stalling. I obviously have not seen this dillema posted on the forums. Please Help! Luke you are my only hope! Thanks....

Last edited by goldveg; 11-04-2013 at 06:09 PM.
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Old 11-04-2013, 07:40 PM
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Join Date: Oct 2012
Posts: 5,429
You might want to try pouring a couple of buckets of cold water over the injection pump when the car is hot. Sometimes injection pumps are well worn.

Also try to get some voltage to the glow plugs or check to see if there is any there for a little time before the engine is turned over. The occasional diesel that runs well in general etc. Just does not like to restart hot without some glow plug participation. Had a volkswagon diesel engine that was not interested in starting hot without some glow plug activity. Never knew what it was as that engine started well at even very cold temperatures otherwise. So it was not unreasonable the compression was decent.
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Old 11-06-2013, 09:52 PM
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Join Date: Nov 2013
Posts: 17
still high idle

Thanks for the reply. I have tried the cold water on ip. It worked when it was hot. My idle is really high when hot and the car won't stay running when hot unless I keep my foot on the pedal. It does run great even when hot. It stalls when I put it in gear. The rack dampener bolt does not seem to be making a difference even if I screw it in a lot. I am thinking that it could be the bolt with the spring in it that regulates the pressure. Please help my dilemma. Otherwise I will be stranded soon. Car is super hard if not impossible to start when hot. And is easy to start when cold. Thanks everyone?!
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Old 11-07-2013, 07:38 AM
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cho cho is offline
diesel power
Join Date: Dec 2011
Location: Europe
Posts: 933
worn IP


bolt with the spring is overflow valve,..if bad you would be having
starving issues hot or cold,you can easily pinch the line to test it
if the flow is increased...

....if water test on IP proves that car starts fine
I'm afraid that you have a well worn solution to that one
at least no cheap one... good used one can do the trick for you.


w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered
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