SL/R129: 500 SL - MISFIRE WHEN HOT
10-19-2011, 03:46 PM
#1
Junior Member
Thread Starter
500 SL - MISFIRE WHEN HOT
Hi, my 500 SL, 1990 model has a misfire at low RPM when hot. At high RPM its fine and has loads of power, but on acceleration it misfires and splutters and runs rough until 3500 RPM then its fine over 3500 RPM. When it is cold it is perfect. On start up and for the 1st 4-5 mins until it gets hot, it revs without any hesitation and runs smoothly through all gears, no problems at all. I have tried the process of elimination - have changed all the spark plugs, then both distributor caps and rotors, and lastly I have changed all HT leads. All the electrical side is new other than the coils. Could this be fuel problem, is it maybe running too rich hence when its starts its fine. Has anyone else had this problem? I am at a dead end now...
10-24-2011, 02:52 PM
#2
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Join Date: Aug 2007
Location: Atlanta
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95 SL 500, 08 Infinity FX35
My problem was similiar. It ran fine when cold, then it seems to stumple at idle when warm. After changing the MAS, plugs, rotors & caps, crankcase vent hoses, vacuum lines, oxygen sensor, and one of the computer module with no results, I decided to test my fuel injectors using a 12 volt harness that I made.
After lifting the fuel rail with the injectors intact, noticed one injector had a leak, some sprayed a weak stream of fuel as opposed to a strong mist. I just replaced them all and it's now running silky smooth. they cost about $37 a piece with a $10 core return
After lifting the fuel rail with the injectors intact, noticed one injector had a leak, some sprayed a weak stream of fuel as opposed to a strong mist. I just replaced them all and it's now running silky smooth. they cost about $37 a piece with a $10 core return
11-04-2011, 02:40 PM
#3
Junior Member
Thread Starter
UP DATE - A this point in time, I have changed all 10 x HT leads (8 for plugs 2 for coils), all 8 spark plugs (bosch), both dissy caps and rotors, all 8 x fuel injectors. Guess what, its still doing the same. Whats next, mmmm - o2 sensor...? It couldnt be the camshaft sensor or it would run rough all the time - yes or no? Could it be the crankshaft sensor sending the wrong signals..??
I will try the o2 sensor first. The is a process of elimination task or what...!!!!
__________________
I will try the o2 sensor first. The is a process of elimination task or what...!!!!
__________________
11-20-2011, 04:25 PM
#5
Senior Member
My problem was similiar. It ran fine when cold, then it seems to stumple at idle when warm. After changing the MAS, plugs, rotors & caps, crankcase vent hoses, vacuum lines, oxygen sensor, and one of the computer module with no results, I decided to test my fuel injectors using a 12 volt harness that I made.
After lifting the fuel rail with the injectors intact, noticed one injector had a leak, some sprayed a weak stream of fuel as opposed to a strong mist. I just replaced them all and it's now running silky smooth. they cost about $37 a piece with a $10 core return
After lifting the fuel rail with the injectors intact, noticed one injector had a leak, some sprayed a weak stream of fuel as opposed to a strong mist. I just replaced them all and it's now running silky smooth. they cost about $37 a piece with a $10 core return
