Engine misfire after washing V12 biturbo
 

Good morning, I have a 2004 CL600 (I know, this is the S-class forum, but you guys have more activity and I'm sure the causes would be similar.) The car went through the car wash and after a brief stop at the store, it was misfiring badly. After a short time, it was running well enough to make the 2 mile trip home. After another two hours, it was running fine.

It did the same thing 2 weeks ago when my brother tried to test drive it, and they took it to a mechanic who said the culprit was wet coils from washing. I'm not so sure of this diagnosis, what do you guys think? I'm irritated because I bought it because I though they had taken care of the problem! It's a large dealer, not one of those corner joints.

If you want to investigate this yourself, you can get a spray bottle that will create a fine mist. Fill it with water, and carefully mist a small area on top of the engine with the engine warm and idling. Wait a minute to see if the idle becomes rougher. If not, mist a different area. When the idle become rough, you have found your problem area. It might be cracked insulation on spark plug wires, dirt build up, etc. Hopefully, it will be something that you can fix yourself, or at least you can tell the mechanic what the problem area is...

The coil packs are sealed. No wires to crack. Wally's idea is good, but I doubt that will trace your problem.

More likely, you got enough water in the spark plugs wells to short a couple coils. The wells are deep, the coil tubes go down a long way and it would take a while to boil water off. I could see washing getting water down in there.

I would wash the engine by wiping it down with a damp rag...take the plastic covers off and clean them separately if you like. But just spraying water and/or soap on this engine would make me very nervous...

Yesterday it was not washed under the hood, just a regular car wash with an underflush. Will water get on the engine that way? I had thought the dealer might have opened the hood to spray it down, but now I'm not sure.

Just drive it around for an hour or so, it should clear on its own. I had this happen at the car wash about a month ago with my S65. After three 15 minute trips it cleared. Despite the best maintenance occasionally things happen. The dealer looked at it last week during the B service, said everything was great and could not find any maintenance items to add to the service.

Underflush is a no no on these. Cars

Hand wash /low water wash only

There is a lot of plastic shielding on the underside...hard to imagine much water got into the engine, but it would depend on the angle and volume of the "underflush" I would think...I think it's more likely that water was applied from above, and it would only take an ounce or two to travel down one of the spark plug wells towards the front of the engine to cause the grounding that would make it misfire.

The wells were not visibly wet, and I have since been corrected that it never had an underflush(I wasn't the one that washed it.) I'm a little stumped at the moment, and more than a bit irritated that the dealer did not solve this issue like they were supposed to prior to sale.

Yeah - this is the culprit. I had the same problem after washing...misfired, smelled bad. Checked codes and had misfires....cleared codes - all good.

The engine was not washed. Is it a common problem for these things to get wet from an exterior wash? How would the water be getting there?

Jack - I've never had a problem with the M275 engine in rain, or after an exterior wash. I did get a misfire after washing the engine, and I was careful to use low pressure, but that's a mistake I'll never repeat.

I'm not certain what the dealer did to your car...sounds like you're not certain either...after all, you weren't there.

The way to "wash " a Mercedes Engine is to spray degreaser with a spray bottle then wipe down with a dampened towel , so no excess water droplet hits any part

I would not discount the car wash being the culprit. I owned a 1993 BMW 325i- the early E36's were notorious for running poorly after a car wash. And ther was an actual fix, thus it was not an anecdotal diagnosis

Another thought came to mind. The only two times I know of the issue being present is also the only two times I know of that the car was restarted while warm. It should also be noted that an additional problem exists, namely the car intermittently triggering a low coolant light despite being topped off, and running at above normal temperature when not at freeway speed. Shop thinks that may be cooling fans not coming on, but no word yet.

So, update. Shop says it's that the auxiliary cooling fan has failed and the over temp resulted in misfires. What I don't know is if replacing the fan will completely solve it. How high is the risk that the coils have been permanently damaged? Also, I'm getting some pushback from the dealer, they don't seem to eager to cover the repair and I'm frustrated because the issue was supposedly taken care of before I bought it. Meanwhile, the shop wants just shy of $1200 for the repair. And I'm in Maryland, while the car is still in Michigan. I flew home to pick it up, and ended up borrowing my brothers car to get back home, and trying to handle it from here is a bit of a pain...

There's no telling if the temp has damaged the coils
If you need a fan you'll need to get it done then see what problems remain

These s600 can easily cost $10k a year in repairs

I had planned on doing work myself, where possible, but I need to have the car to be able to do that. I was supposed to be buying a working car, not a project. I haven't even driven it yet. :(

Sounds as if it is time to talk to a Michigan attorney.

it experienced problems during the test drive so you knew it had issues

Just undo the deal if you can . This isn't the car for you

The car experienced problems during the first time it was looked at and was unable to be driven. The second time it was looked was at the third party shop after the dealer said the issue was resolved and it ran fine. So after taking it home, the problem showed up on the way back from the tire shop(the only place it had been since purchase.) My issue with the dealer is that the problem they said they have solved wasn't, and I want that fixed or them to take the car back, at this point. This wasn't an as is sale, they do have a warranty of sorts, alledgedly, but I don't know what that covers or how much. The paperwork is with the car, apparently. I'll keep this updated as I go. Wish me luck.

I genuinely wish you luck Jack.

I love my V-12, but haven't seen anything like this. FWIW I've spent about $5K for maintenance over the four years I've had it. Mostly parts and my labor. So, it's no the horror show that folks make it out to be.

It's worth something, Astro. At this point, I'd just rather give the car back and find a different one. I feel like this one wasn't supposed to be. Problem is, I can't seem to get anyone on the phone at the dealer.

Alright, seems like I finally have forward motion. The dealer didn't seem to keen on the idea of buying the car back but didn't take it off the table either. They are paying to replace the aux cooling fan and want to see how that goes first. I'm terrified that I don't know how often or how badly it had been overheated in the past, so if I'm to keep this car, I'm going to have to lean hard for a warranty for the underhood components. I've seen overheated cars quickly develop serious issues, even from one overheating. That said, it could have never overheated by much and not have any real damage(other than the coils, I suspect,) I have no idea.

Did the temp gauge ever go too high?

I think the aux cooling fan is a red herring. Personally, I think MOST of them don't work, and nobody realises.

Nick

I have no idea. It didn't get too much over temp when my brother drove it. But other than driving it to the tire shop, driving home from the dealer was the only trip it took, where no over temp was noticed. So far, it's only been on restart it's misfired. I think the temp rises just enough in the few minutes it was sitting to cause the miss upon restart, but I'm not sure. The shop says there is no doubt the fan was not working, and that's what they're starting with.