91 560SEL Hard Start in the morning

[BENZ TEK]

Hello all!! I have a 560SEL in here that has a hard time starting in the morning and after it has been sitting for a while. I changed the normal stuff like Fuel pressure accumulator, check valves at the fuel pumps, EHA and distributor cap and rotor button. I checked to make sure that I had 75ma flowing thru the EHA with the key on and I did.I did notice that at first crank of the ignition that the milliamps shot up to 105 then leveled off at 22ma. These reading were taken at the EHA while the car was cranking but not starting. I also checked to see if I had enough current flowing from the ignition switch to the EZL. Everything checked out good but now I noticed another problem. I was test driving the vehicle and I noticed a little hesitation pulling off from a stop. I also noticed that while stopped the car jumped as if it lost spark for a split second. The longer I left it in drive with my foot on the brake the more frequent it was occuring. So I shifted the car into neutral and waited for the light to change. The light changed green and I shifted into drive and the car died as I pushed on the gas pedal. I then shifted the car back into neutral and the car started right back up. I brought it back to the shop and I noticed that the car seem to idle better but I am thinking that I might have a intermittant problem with either the crankshaft position sensor or the overvoltage relay but I never seen a crank shaft position sensor work intermittantly nor have I seen a overvoltage relay give full power at times at not at others. I don't believe its a fuel related issue but maybe a loss of power to the computer, or bad ignition coil. Any help would be greatly appreciated!!

Melvin

[stevebfl]

Coil is a possibility. But these things can be tested. It obviously would have been cheaper to pay a professional than to throw parts at it.

[zcc]

I'd try to clean the coil first and check for dust and oil on it (inclusing the spark/coil wires).

[ctaylor738]

Does the '91 have a cold start valve? If so, have you checked its operation?

[BENZ TEK]

Originally Posted by stevebfl

Coil is a possibility. But these things can be tested. It obviously would have been cheaper to pay a professional than to throw parts at it.

How do you test the coil?

[BENZ TEK]

How do you test the coil!!

[stevebfl]

With a secondary ignition occiliscope. If done will running one pulls a plug wire and views the open circuit output. If it won't start one would just look at available voltage. it needs probably 10-15kv to start.

[BENZ TEK]

Originally Posted by stevebfl

With a secondary ignition occiliscope. If done will running one pulls a plug wire and views the open circuit output. If it won't start one would just look at available voltage. it needs probably 10-15kv to start.

That was one of the first test I performed and according to the scale that you state this car is on the low end. I only have 9k max at the plug wires and 10k on the coil wire. Are there any resistance test for the coil like going from the two post on the coil to the center and getting a resistance reading? And if so what are the proceedures for testing and what are the values that I am looking for? THANKS IN ADVANCE!!

[just-n-time]

Originally Posted by BENZ TEK

Hello all!! I have a 560SEL in here that has a hard time starting in the morning and after it has been sitting for a while. I changed the normal stuff like Fuel pressure accumulator, check valves at the fuel pumps, EHA and distributor cap and rotor button. I checked to make sure that I had 75ma flowing thru the EHA with the key on and I did.I did notice that at first crank of the ignition that the milliamps shot up to 105 then leveled off at 22ma. These reading were taken at the EHA while the car was cranking but not starting. I also checked to see if I had enough current flowing from the ignition switch to the EZL. Everything checked out good but now I noticed another problem. I was test driving the vehicle and I noticed a little hesitation pulling off from a stop. I also noticed that while stopped the car jumped as if it lost spark for a split second. The longer I left it in drive with my foot on the brake the more frequent it was occuring. So I shifted the car into neutral and waited for the light to change. The light changed green and I shifted into drive and the car died as I pushed on the gas pedal. I then shifted the car back into neutral and the car started right back up. I brought it back to the shop and I noticed that the car seem to idle better but I am thinking that I might have a intermittant problem with either the crankshaft position sensor or the overvoltage relay but I never seen a crank shaft position sensor work intermittantly nor have I seen a overvoltage relay give full power at times at not at others. I don't believe its a fuel related issue but maybe a loss of power to the computer, or bad ignition coil. Any help would be greatly appreciated!!

Melvin

Look up sights under my name for the procedure to EHA testing,you need to be sure that the O2 is ok. You also need the fuel mix to be set, you will find the info in the sights all over the forum

[BENZ TEK]

Originally Posted by just-n-time

Look up sights under my name for the procedure to EHA testing,you need to be sure that the O2 is ok. You also need the fuel mix to be set, you will find the info in the sights all over the forum

Thanks for the help guys. I found the problem to be a intermittant one with the overvoltage protection relay. I had checked the fuse and it was ok but what tipped me off was that I checked the EHA VOLTAGE AGAIN but while under cranking I found that the EHA voltage went up at first but fell to 22ma and the car wasn't started. So I changed the overvoltage relay and everything worked fine. I also changed the coil and tested the voltage again and found the kv voltage went up into the range of 12k to 14k.Thanks for all the help.