ML430 Intermittent Starting Problem

[EPineda]

My 1999 ML430 would start normally but when I turn off the engine, say for gas, 2 out of 10 it will not re-start. It would take about 5-8 minutes to get the engine running again. The engine would crank, thanks for having a good battery, and there is no CEL light to indicate anything wrong. Most times, the engine would just run the first time I turn on the ignition and the car would perfectly. If I turn off the engine, sometimes it would not start, the engine just keeps cranking, no sputter, no nothing. After about 5-8 minutes trying, it would suddenly start again and run normally. I'm puzzled with this problem. This problem started about 3 weeks ago and it's happening more often now. Appreciate any help.

[azinn]

Sounds like a failing CPS (crank position sensor). Read all about it here > Crankshaft Position Sensor DIY

[EPineda]

Thank you, Azinn, I appreciate your assistance. I checked the link you provided and read the comments on the problem. It looks like it's the same problem I'm experiencing with my 99 ML430. I'll order the CPS (Bosch 0261210170-$39.12) and see if this would solve the problem. I'll keep you posted.

[EPineda]

Today, I replaced the Crank Positioning Sensor (CPS) on my 99 ML430 (original part is 003 153 2728; replaced with a Bosch 0 261 210 710 from ********** at $39.11). So far, all seemed well. My ML430 started every time but time will tell since the original problem is intermittent (engine will start 8 out of 10). However, I'm very confident the problem has been completely resolved with the new CPS.

Also, I want to add my experience with replacing the CPS from top (of the engine) is almost a nightmare (if not impossible) since there is very little room between the engine and the firewall, especially for someone with big arm and fingers. After several tries, I just couldn't get to the CPS bolt no matter what I did. So, I did the next best thing: jacked the body of my ML430 at the driver side about 2"-3". I raised the body just enough for me to be able to creep under the car from the front. This was definitely a better and easier way. Next I put a trouble light from the top so I would know where to look for the CPS. By doing this, I found the CPS to be just about 12" above me (in actuality, you cannot see the CPS itself but by following the CPS cable, you know it is there just above you). Also, there is much more room for your left hand to reach the CPS sensor. Yes, you'll need to use your left hand to position the E8 torx socket to the CPS bolt but it was much easier to get to the bolt. Since I still cannot use a ratchet for lack of room (from under the car) to the E8 socket, I decided to use the 1/4" ratchet extensions (2 of them) and universal joint in between, dropped from the top, position the end to the E8 socket and had someone turn the ratchet for me. The bolt came off easily and I pull out the CPS rather easy. Reinstallation was easier, again from the under the car, I had to coat the body of the CPS with very little engine oil (very lightly) to get it in place easily (without the oil, it was really snug fit). With the oil coating, I was also able to orient the CPS bolt hole easily, then start the bolt by hand and doing the reverse (using 2 extensions, u-joint & ratchet) from the top while holding the extension end to the torx bolt.

From under the car, it took me about 30-35 minutes to replace the CPS sensor. Trying from the top, I spent about 1hr & 20 minutes (just trying) to get to the CPS bolt and I was unseccessful. Very frustrating.

I hope this would help our DIY friends out there with CPS installation problems.

[EPineda]

On my previous posting, I forgot to add that I had someone help me turn the ratchet from above otherwise I couldn't have done the whole job in just over 1/2 hour. It would have taken me much longer to do it by myself. It pays to have someone to help you - in this case, someone to turn the ratchet for you.