SL/R107: Stalls when stopped or near-stopped - Need troubleshooting strategy
07-26-2014, 11:04 AM
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280 SL
Stalls when stopped or near-stopped - Need troubleshooting strategy
My 84 280 SL inconsistently stalls when stopped or sometimes near-stopped and won't start usually without waiting a couple of minutes, otherwise the car runs well driving at all speeds. The problem with greater frequency happens when temperatures are between 75 to 95 degrees, began over a year ago and started after an oil change & engine shampoo. Identifying the cause is like looking for a needle in a haystack and I don't know if the problem is fuel, electrical/electronic, vacuum etc. and would like to stop wasting money by guessing.
I'd be grateful for any advice identifying/repairing the defect myself or developing a troubleshooting strategy with a mechanic who has experience with older german, italian or british sports cars.
I'd be grateful for any advice identifying/repairing the defect myself or developing a troubleshooting strategy with a mechanic who has experience with older german, italian or british sports cars.
07-31-2014, 09:11 AM
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Heat-related issues can take many forms. My 560SL used to stall when the temp would climb at a stop light or extended slow driving. Turned out the fan clutch was just worn out and a replacement solved that particular problem. The next issue was the dreaded ignition control module - there was an intermittent issue of not starting when the car was hot after a long run. I think that the heat can cause some of the soldered connections that may have cracked over the years to expand and....no spark. I lucked out in that my mechanic had a spare that he sold me for the Ebay price. 
Next on the list is the crank sensor. They are made of dissimilar metals and if the sensor is faulty, those metals can separate under high heat conditions and again....no spark. I am going through this now. I have a replacement and fingers crossed that THIS does the trick. This time. The current symptom is a periodic no-start after the car sits for a while after an extended run. There could be a variety of other issues with thermal sensors, valves or whatever, but in the end I always ending up taking the car to my trusted independent shop. BUT....the guy there that really understands the R107's just retired!!! Good luck with your issues. I wish I could offer more diagnostic skills.
Next on the list is the crank sensor. They are made of dissimilar metals and if the sensor is faulty, those metals can separate under high heat conditions and again....no spark. I am going through this now. I have a replacement and fingers crossed that THIS does the trick. This time. The current symptom is a periodic no-start after the car sits for a while after an extended run. There could be a variety of other issues with thermal sensors, valves or whatever, but in the end I always ending up taking the car to my trusted independent shop. BUT....the guy there that really understands the R107's just retired!!! Good luck with your issues. I wish I could offer more diagnostic skills.
08-08-2014, 11:26 PM
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I began follow up on fuses, the Over Voltage Protection Relay and vacuum supply to the deceleration air system and it's component parts. I discovered that the decel shutoff valve is working and getting 20 inches of vacuum through the Switchover valve deceleration shutoff (43a) in the manual. Strangely enough, there is no vacuum (or minimal vacuum of 5 inches) through the four-way vacuum connector to the decel circulating air valve (11 in the manual) and through the Switchover valve air conditioning (43). Upon testing vacuum on consecutive start-ups, sometimes the idle is high even though the engine has warm-up and I am mindful that high idle results in lower vacuum.
The car runs fine when cold and previously idles well but the problem appears to occur on deceleration between acceleration and stabilizing idle. Most often after a stall, the engine won't start for 6 to 10 minutes and then starts up.
In two days, I will continue with testing to see if I can determine the reason for the high idle and low vacuum or no vacuum. Some of the vacuum lines branching off appeared to be at least partially plugged and where identifed have been unblocked however, that hasn't cured the problem yet and more testing is needed.
I welcome further suggestions as I continue and if anyone can comment on delayed re-starting, that would be helpful. Thank you everyone.
The car runs fine when cold and previously idles well but the problem appears to occur on deceleration between acceleration and stabilizing idle. Most often after a stall, the engine won't start for 6 to 10 minutes and then starts up.
In two days, I will continue with testing to see if I can determine the reason for the high idle and low vacuum or no vacuum. Some of the vacuum lines branching off appeared to be at least partially plugged and where identifed have been unblocked however, that hasn't cured the problem yet and more testing is needed.
I welcome further suggestions as I continue and if anyone can comment on delayed re-starting, that would be helpful. Thank you everyone.
08-09-2014, 09:40 PM
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The engine runs well when cold and idles well. The initial problem was stalling during deceleration and stablizing the idle after driving. If I keep the idle up when coming to a stop by shifting into neutral and driving with both feet, I can keep it running.
As reported earlier this week, I began troubleshooting by testing vacuum, etc. I removed blockages in a few vacuum lines within the decel system but that didn't address the problem.
A member on another forum suggested that I consider malfunction of the Auxiliary Air Valve not closing when warm causing the high idle and reduced vacuum. I will include that as I continue troubleshooting and will also investigate the cam sensor as suggested.
Testing the decel air circulating valve, the Auxiliary Air Valve and the Switchover Air Conditioning Valve is difficult because lack of access. Has anyone removed an AAV on an R107 280 SL with an M110 without removing the fuel injection from the top or the sub-frame and suspension from below. I am wondering if it is difficult but not impossible provided one has access to a hoist and the right tools?
As always, all advice is appreciated. Thank you.
As reported earlier this week, I began troubleshooting by testing vacuum, etc. I removed blockages in a few vacuum lines within the decel system but that didn't address the problem.
A member on another forum suggested that I consider malfunction of the Auxiliary Air Valve not closing when warm causing the high idle and reduced vacuum. I will include that as I continue troubleshooting and will also investigate the cam sensor as suggested.
Testing the decel air circulating valve, the Auxiliary Air Valve and the Switchover Air Conditioning Valve is difficult because lack of access. Has anyone removed an AAV on an R107 280 SL with an M110 without removing the fuel injection from the top or the sub-frame and suspension from below. I am wondering if it is difficult but not impossible provided one has access to a hoist and the right tools?
As always, all advice is appreciated. Thank you.
Last edited by Mboydsl; 08-09-2014 at 09:46 PM.
