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1990 500SL won't start. Ideas?

6K views 4 replies 3 participants last post by  jimdollar 
#1 · (Edited)
Hi Everyone

I came by a 1990 500SL which I'd like to get running. It's the CIS-E CFI M119 V8

It turns over but won't fire.

There was a Thatcham 1 immobiliser which interrupted the starter circuit. Now removed and purple wire reconnected. Car turns over.

We have fuel:
Turning key to position 2 I hear the fuel pump whirring for a second or two. There is plenty of fuel pressure.
Plenty of pressure to cold start injector.
Pushing the air metering flap down lets fuel out of the metering head to the injectors. Lots of fuel is getting through as turning the car over for a minute or so floods the spark plugs. The garage smells of petrol fumes, so it's clearly pushing fuel through

We have spark:
Pulling a plug out and shorting the plug body to the engine block produces a nice big fat spark. HT leads look to be almost new

The fuse was blown in the OVP relay, so I replaced first the fuse then the relay.
I tried a different MAS unit out of a working car.

Reading the codes with my code reader showed:

Pin 3 (CIS-E): 1 flash (no error)
Pin 8 (Distributor Ignition) 17 flashes (Crank position sensor fault)
Pin 14 (MAS engine control) 2 = fuel pump relay circuit not functioning, 3 = TN/TD RPM signal interrupted, 5 = Output for air injection pump defective and 6 = output for kickdown control defective.

I read somewhere that testing with the engine not running always gives code 17 for crank position sensor.
The fuel pump looks like it IS working since the fuel pump makes a noise as normal and there's fuel pressure.
I do not know what TN/TD RPM means.

Any ideas, anyone?

Does it look like the crank position sensor has indeed gone to meet its maker and if so, is it the one on the front of the engine by the crank pulley or the one by the flywheel by the torque converter

Any ideas appreciated

cheers

Dave
 
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#4 · (Edited)
OK. Crank position sensor replaced with a known good one. Still no sign of life.

Also reading the MAS again (after replacing the fuse for kickdown etc) I now have codes 2 (fuel pump relay) and 5.

The fuel pump is definitely working as the cold start injector squirts nicely as I crank the engine.
 
#5 ·
500 sl starting

If you are getting a strong smell of fuel you may have TOO much going in. Have you pulled a couple of plugs to see if they are wet? If they are I would disable the fuel pump by pulling the fuse if possible and try starting it, if all else is good it may well start and run for a few seconds on the excess fuel then cut out. Its often quicker trying it this way than removing all 8 plugs and trying to dry them or even put a fresh set in. Obviously if it does start and run you know its the fuelling system that needs attention.
If you had been getting backfiring on cranking you could have checked caps and rotor arms, but you may have done so already. HTH, Jim:smile
 
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