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ML350 with low compression, will not start. Any help appreciated.
Hello all,
We have spark, and 56PSI pressure on the fuel rail. Spark plugs and coil packs all replaced with OEM equipment 2 months ago. Daily driver. Here is what happened:
Wife started truck and backed it up about 3 feet to make room for something. Next morning tried starting it and sounded funny, like it had no compression. I just did a compression check in cyl 1 and it got to 40 PSI before the battery was no longer wanting to turn the crank. Battery was at 25% when I attached my charger. It's charging now. But battery was much higher when I first started performing tests.
From what I understand if there is fuel pressure in the fuel rail, I've got fuel. If there is spark then the fuel injectors are also given the signal to open, so it appears my crank pos sensor is okay. I'm at a loss...could it just be a bad battery? I would love to hear your thoughts. Thanks in advance!
The first thing you must do is update your profile to include the year, model, is it gas, CDI or Blue and where you live, which tells us you have right or left hand drive.
I went ahead and updated all of the fields in my profile and included that my vehicle is a LH drive.
UPDATE: After fully charging the battery she started fine. If I could have tested the alternator I would have, but since I could not get her to start I could not get a reading. The battery SEEMED fine, so I went through the process of testing for fuel pressure and spark. While testing compression the battery got low so I decided to charge it FULLY before continuing, and after doing so BAM! Started right up. I am about to test my alternator, but at this point either the battery or alternator seems to be the culprit.
I have never worked on a vehicle that sounds like it has a broken timing chain when the battery is low, but now that I know ML350s do that, I'll look into the battery next time I test for fuel and spark. I just hope I didn't foul my plugs by flooding the engine, I just put those NGKs in, they were NOT cheap. Hope this post can help someone at some point. Stay safe everyone, and thanks!
Last edited by TorchHypnosis; 12-07-2020 at 09:17 AM.
You have to consider that the battery was drained because either your wife left interior lights on or there is a parasitic draw draining the battery.
Slow charge the battery overnight and take a reading of the battery, which should be 12.7v, reinstall the battery. Key out of ign. & leave the hood open and every 2 hrs. check the voltage at the jump start points under the hood.
If there is a noticeable drop in voltage, then there is a draw on the battery.
Thanks Maj., The alternator is putting out 14.10VDC, diodes and voltage regulator check out. I just tested the battery and it is indeed bad. I will check for a parasitic drain on the battery, but I'm certain that my wife didn't leave anything on, when it wouldn't start she immediately gave me the key and asked me to fix it. Nothing is on, and it kept its charge overnight fine after I trickle charged the battery to 100%, started right up this morning 12 hours after I disconnected it from the charger.
I will trickle charge the battery to 100% today, then check the percentage full in the morning. But won't a bad battery lose a charge anyway, regardless of if there is some kind of drain?
I performed some tests. I checked battery levels periodically and it did not really lose any charge. Then I let it sit for three days and she started up just fine. I believe you were right. Although nothing was left on, per se, I believe my wife did not completely shut the door so the interior light remained on. She parked during the day so did not notice the interior light was on, and by the time dark happened the light was already dim, or we just did not go outside. Just wanted to conclude this post. Moral of the story is, "A Mercedes can sound like a vehicle with no timing chain present when starting if the batter is low".
I performed some tests. I checked battery levels periodically and it did not really lose any charge. Then I let it sit for three days and she started up just fine. I believe you were right. Although nothing was left on, per se, I believe my wife did not completely shut the door so the interior light remained on. She parked during the day so did not notice the interior light was on, and by the time dark happened the light was already dim, or we just did not go outside. Just wanted to conclude this post. Moral of the story is, "A Mercedes can sound like a vehicle with no timing chain present when starting if the batter is low".
12-06-2020 | 07:13 PM
