2004 ML 500 Hard Starting
 

Hi All, We've had this ML for 13 years and have encountered the hard starting problem before. I replaced the fuel filter at 64,000 miles and again at 87,000 miles. Now we are at 105,000 miles and the car has the hard starting problem again.

This time I replaced the fuel filter, but it did not resolve the issue. I put a pressure gauge on the fuel rail and it tests fine. It runs steady at 55 psi and holds 52 psi for a good 1/2 hour. I was able to recreate the hard start with the gauge in place and it seems I've ruled out fuel as the issue.

I then replaced the crank position sensor. This did not fix the problem.

It started out as an occasional problem where the car started fine when cold, but once it had been sitting hot for 10 minutes or so it wouldn't start on the first try. The starter would spin the engine over just fine, but the engine would not start. I'd turn the key off, remove the key, try again and it would start fine.

Now it is having the hard start issue when cold or hot, and may take 3-4 times to get it started. Once running, it is very smooth and runs normally.

I tried the second key. Same problem.

Any suggestions? I don't have a scan tool, but I will buy one and check for codes. Are there other obvious things I should check? I will add that the plugs and wires are original. I plan to change them and use Bosch wires and plugs. But it runs great once started, and unless that is very likely to be the problem, I'd like to get the starting issue resolved first.

Thanks!

Have you checked the resistance on the Camshaft sensor? That's most likely the culprit.

No I have not checked that, but I will do that next.

Thank you!

I wanted to report back that the cam position sensor was the culprit. I had it scanned for codes at Autozone and got the P0341. I went ahead and bought a Bosch sensor and replaced it and it's been 10 days and dozens of starts, hot and cold. All Fixed!

TX76513, you called it! Thanks!!