catdaddy

I just bought this car: the tac, the cruise and the a/c dont work. Can anyone tell me how to start troubleshooting to fix these items. To get the car to crank you have to switch the ignition on and back off three times the the fourth time you can go all the way and crank the car. Can anyone help me with these problems!!!!!!!!! Thanks.

chomp_sticks

Are you letting the glow plugs warm up properly?

LawrieMB

There is always a difference in how people describe 'cranking.' When you turn the key the first time does the starter turn the engine over but the engine does not start, or does it take 4 times of turning the key to get the starter to turn the engine over?

catdaddy

yes, I switch the car on and let the glow plugs warm up 30 to 45 seconds before trying to crank the car.

catdaddy

The engine is turning over when I first turn the key, but will not start, so I turn the key on and wait for the glow plug lite to go off each time then after the third try the engine will start.

Floobydust

Sounds like you are missing your "tach" signal. Since oil burners don't have an ignition system, MB generates one via the Idle Speed Control Module (ISC) which takes a signal from a sensor on the flywheel. The ISC, the A/C system and your instrument tach all require this signal to function, so it's clearly the common element. The difficulty starting may also be related because without the "tach" signal, the ISC system has no way of knowing that the engine is actually running and a what speed.

I would start by checking all of the fuses, but check fuses 5, 6, & 7 in particular. Check them by removing, inspecting, and replacing - I have seen hairline cracks that are electrical opens, but visually look good until you take the fuse out.

Then, visually inspect your engine wiring harness - your car is from the eco-junk harness era, so if it hasn't been replaced, the insulation will be deteriorating. Look for cracked insulation around the engine sensor connectors. Anything and everything can happen/fail with a bad harness.

You may also want to check/replace the OVP relay as this supplies power to the ISC. You can check for + 12 VDC on pin 6 of the OVP with the engine running. OVP failure seems to be a right of passage with these cars.

Lastly, I would look into the speed sensor itself. I don't have the resistance value handy, but it should be in the several hundreds of ohms range. If it's near zero or open, the sensor is bad.

I have attached the engine control schematic for you car in case that is helpful.

Good luck.

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