SL/R129: 1990 500SL Hard to start after engine has warmed up
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
JDwilson from 3 years ago. Post#1. The nightmare lasted a year because no one measured the EHA current during cranking.
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1995 SL500
My 1990 MB 500SL starts perfectly when it is dead cold but once the engine has warmed up and you turn the engine off and let it sit for more than 10-15 minutes, the car is difficult to start. The starter spins but the engine doesn't want to ignite for 6-8 seconds. I have had two MB shops look at the car and neither can find the source of the problem. Fuel line is holding pressure, distributors are almost new, spark plugs and wires have been replaced. Coils have been tested. Car has a rebuilt fuel distributor, a new accumulator and other new parts. It will do this for hours after the engine has been turned off until the engine has totally cooled down and then, it will start perfectly (when dead cold; like it does in the morning after it's sat all night). I'm very frustrated because I've never had an automobile (or motorcycle) that has exhibited this behavior. One of the mechanics who checked it out (30 years experience as a MB mechanic) told me that he's seen this before with some other MB of this vintage and that I should just accept this as the way the car is going to behave. I have a problem with believing that statement. Am I wrong? Has anyone else experienced this problem that supposedly can't be fixed?
Pull the vacuum hose off and if fuel comes out that is your issue. Sometimes mine did, sometimes it did not but after a 5 minute swap to a new one, she has never once had a hot start issue again.
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Starting problems SL280 ONLY after +/- 15 minutes
I am having similar issues with my 1995 SL280. It starts immediately when cold or hot but after a certain pauze in driving - around 15 minutes- it takes also 6-8 second to start. I can get around this by turning the keer back off and then it always starts immediately on second try. I've also had 2 mb mechanics look at this but without success. No issues on the computer, engine cable & control valve replaced
Last edited by Kahuna76; Dec 31, 2024 at 05:09 AM.
MBWorld Fanatic!
Joined: Mar 2016
Posts: 1,369
Likes: 195
From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
I am having similar issues with my 1995 SL280. It starts immediately when cold or hot but after a certain pauze in driving - around 15 minutes- it takes also 6-8 second to start. I can get around this by turning the keer back off and then it always starts immediately on second try. I've also had 2 mb mechanics look at this but without success. No issues on the computer, engine cable & control valve replaced
Your theory supports too much fuel. But to check it out one can unplug the vacuum line that leaks the FPR back to the intake incase of a ruptured diagram and see if it is dry or if it has fuel coming out.
Another theory is that the Fuel Pump Relay maybe starting to fail. The most energy/current is needed when the fuel pumps are starting up. I read in this long trail somewhere that one of the mechanics claimed the fuel pressure is dropping when the engine is warm started. So to check that out, one can hot wire the Fuel Pump Relay and see if that helps the matter. I should add that the fuel pressure should never drop during cranking, if it is that would be the culprit and needs to be resolved.
If my memory serves me correctly a 1990 comes with a control unit that includes the Fuel Pump Relay in the MAS instead of a stand alone one and 1990 is the year MB switched to this set-up.
I have not heard of this issue on pre-1990 cars. Both of mine are pre 1990 (1989 and 1988 M103 engines). Most people have the other problem. The car will start on a dime on warm start but immediately die because of a vapor lock.
Last edited by dolucasi; Dec 31, 2024 at 12:25 PM.
