m271

What should happen if any of these sensors are unplugged? I'm still trying to figure out what's wrong with my car. Last night I unplugged my front adjuster magnets while the car was running and nothing happened. I shut the car down and the car wouldn't start after. I plugged them back in and the car fired up fine.

Today I went to go try the cam position sensors located on the side and the top and noticed the bolt was missing for the exhaust cam sensor. So while the car was running I pulled the cam sensor out of the hole it sits in real quick and nothing happened, no idle change or anything. I didn't try to leave it out while I started it so don't know what it'll do. Should these sensors shut the engine off while running if removed, or do they only send info on the initial start? I'm also debating on replacing my crank position sensor, even though none of the symptoms match the symptoms that I am currently having.

Thanks for any help in advance.

 

Please never ever do that type of stuff again.

Fwiw, no ECM/PCM is designed to allow sensors to be plugged in/out while the engine is running or on.

If you kill/ruin the ECM, then you're semi-screwed. The car gets towed to a dealer, and the dealer would put in a new ECM and program. You might get away with $2,000+ in charges.

You can not just plug in any ECM and have it work. The ECM has a unique code that is married to the tranny and the key-system.

So, again, please do not risk blowing your ECM, or an input, by unplugging or plugging stuff in while the engine is running or on.



As for removing the cam position sensor while the engine is running, you risked mechanically ruining the cam and the engine by removing the cam position sensor while the engine was running.

There is very little space between the cam position sensor and the index bump on the cam. If the sensor hit that bump-out, it would likely flake-off metal. Any loose metal in the valve covers could then ruin the cam bearings, lifters, piston rings, cylinder walls, etc.

Also, the M271 has ECM controlled spark and fuel. By moving any position sensors while the engine is running, you risk the ECM misfiring the spark and/or the fuel. The code and algorithms used are not publicly available. So, it's a guess as to what the ECM would do as you're removing a position sensor and the engine is turning over ~10-20 times a second.

 

Thanks for your input. The car is trash to me at this point, just curious as to what the problem was this whole time before I junk it. Pretty sure my ecm is already gone.

 

I checked your old posts.
Did you ever pull or replace the head?
Your compression numbers for all 4 cylinders were bad.

https://mbworld.org/forums/c-class-w...n-numbers.html

https://mbworld.org/forums/c-class-w...any-codes.html

 

No I didn't. I got too many conflicting answers and the Mercedes repair manual said my numbers were fine. Also my problem only happens after I get on it once. Meaning when I first take off after the car has sat for a few hours I have full power and I have full use of my rpm range. Only after does it start to limit me to 4k rpm. And it does the same whether the car is warmed up or not. So I'm convinced it's an electrical issue causing my problems.

 

Very unlikely. If the engine is running, the ECM is likely good.

The exception would be if there was a bad input or output. And, a DTC would show that very clearly.

For your car, from what I can tell, the outputs all seem fine.
Any bad input would show up very quickly in the codes. Other than the MAF input, it seemed like there was no other possibly bad input. And, MAFs go bad all of the time. The MAF input is one of the only inputs that may have more protection on it. That's because MAF connector may be yanked-off and put-on many times when the engine is being diagnosed.

If the only problem is the engine, then it seems like a head swap and timing chain replacement would be a good place to start. You could do it all for ~~$2,000.
Imho, if you were planning on keeping the car, I'd suggest spending more and replace a little more stuff.


Buying any used car is a risk.
I always suggest to people that they buy a used Camry from a dealer with at least a 1-6 month warranty. Imho, that's the safest used car to buy in the continental USA.
Note, I have never owned a Camry, nor even a Japanese car. In fact, my C230 is the first non GM/Ford/Chrysler that I've ever owned.

 

Well I do have plenty of codes, none making sense. After unplugging and messing with the cam sensors and magnets, no code came up. Which leads me to believe an ecm issue more. Timing is dead on and the car runs fine, idles fine most of the time, and doesn't overheat. I drive it everyday since I bought it. When it acts up, a simple restart fixes it and I'm on my way again.

 

????
What "Mercedes repair manual"???

I posted the pdf from the real Mercedes service manual. From a real pressed DVD that came from Mercedes.
Your compression numbers are bad.

If you don't have a DVD that was pressed (not burned), and it doesn't look like the picture below, then you you do not have the real Mercedes service manual.


I have two DVDs like the above, for my 2005 C230 W203 (I keep one as a backup).


The reason the engine is limited in rpms and in speed is because the ECM is programmed to limit the engine and car speed when a misfire is detected.
Mercedes has done that for many years. I know that the C, E and S class all do that.

You're getting a misfire because your head and compression are cr*p.
Imho, there's no big mystery, other than how bad is the head, the pistons & rings, and the cylinders.

The cats can also be bad/clogged. Simple pressure tests will confirm.
For the main cat, with the exhaust manifold and cat off, it's very easy to see how clogged or how clear the cat is. Mine looked almost like new. Still, I replaced it and the secondary cat.

 

It's been posted many times how the "head" on the American M271 "goes bad" (from oil).

The seats on the intake valves get caked with carbon. This is very common with all boosted (supercharged or turbocharged) engines.
That eventually causes misfires. There are a ton of factors that go into when a particular boosted engine will have issues. Some may have issues in 60K miles. Some may have issues in 190K miles.

Withe the intake valves not seating properly, you'll have compression and other problems.

If you did an leak-down test, you would be able to hear air escaping from the intake valves (if you took of the intake manifold). With the intake manifold off, and an good inspection scope, you could see the carbon build up on the seats of the intake valves.

You may claim your engine problems are "a big mystery". Rain is a mystery until we learn what causes it and how to predict and track it.

Imho, you have a common M271 engine in a C230, where the owner got rid of the car because they found out that the engine need a new head ($6K++ at dealership).

Fwiw, I expect that to be happening a lot. That's why I asked a while back "what's your budget for this car".

The purchase price of my car wasn't even near half of my overall budget for my C230. I knew before I bought my car that the head and timing chain were garbage on an M271. Heck, I found that out very quickly using Google.

I spent over $500 just on catch cans for my restored engine.
A used car with a supercharged or turbocharged engine is always a very high risk! Fwiw, I also bought a new supercharger. I was going to get the original rebuilt. But, I decided to buy new, and keep the old one as a spare.

 

I spoke to a tech at the dealership, he said the numbers were within spec. Unfortunately he said I needed to bring it in to see what was wrong with it and couldn't tell me much else. My cats are both clear and flowing good. My speed isn't limited, only my rpm. I can sometimes go over 4k but it increases the chances of a rough misfire. I'm gonna start parting it out soon once I sell my other cars. So at this point, just curious what is gonna make this the last Mercedes I ever own.