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Help purchasing a project c230

2K views 28 replies 5 participants last post by  Benzyle 
#1 ·
Main question: Is this worth buying and fixing?

Sorry for the story, but here it goes:

So I went to check out a 2003 c230 supercharged 4cyl tonight under the impression that it had one misfire code (p0304). So I get there and car starts up and has an odd idle for a few seconds and then levels out. Normal idle, albeit, rough, but pretty steady. So I plug my scanner in and there's some pending codes. The car has no power and can barely go over 30mph before it no longer has enough power to keep pushing. Guy wanted $1400 before I went to check it out. After test driving, while I tried to accelerate, there was a rattling noise that was audible for a quick second at which point I let off the gas and it stopped immediately. Supercharger seems a little noisy at idle, not a good noisy. But it's not super loud. Under normal acceleration, shifting around 2-3k rpm, everything sounds normal. Anywho, here are the codes that I got.

p0101 "Mass or Volume Air Flow A Circuit Range/Performance"
p0108 "Manifold Absolute Pressure/Barometric Pressure Circuit High"
p0638 "Throttle Actuator Control Range/Performance Bank 1"
p0301 "Cylinder 1 Misfire Detected"
p0302 "2"
p0303 "3"
p0304 "4"

Could a bad MAF be causing all these issues?? When I clear the code, the idle smooths out for a little bit before returning to rough after the check engine light comes back on, usually after revving it a little bit. I cleared it a few times and will also post the sequence in which the codes showed up after a fresh start. Also, the owner said he changed out the Throttle Actuator to see if that would help anything, but now that is throwing a code as well and kills the accelerator in the middle of driving it or when you try to take off from a stop.

First scan at idle before first clear:
p0301
p0302
p0304

Second scan at idle after first clear:
p0101
p0304
p0301

Third scan after clearing and driving about 1000 feet:
p0101
p0638
p0108

Any help would be greatly appreciated.

I went to look at this car to make a purchase but just worried about what the issue(s) may be. The guy only wants $1400 because he said he wasn't going to put any more work into it. Mileage is 171,xxx all stock minus some hard piping.
 
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#2 ·
Without more hands-on diagnosis, and using SDS instead of a generic scanner, I can't say for sure, but none of that sounds too bad. My guess is that it's a few bad sensor and nothing major. But if you are serios about this project, SDS is a must-have.
 
#3 ·
I agree with rudeney above (particularly given his depth of experience). That being said, to play devil's advocate, misfire codes can be a pain to resolve. I chased one on my Jeep for months before it finally went away. Generally, if the engine is actually misfiring and there are no issues with the O2 or MAF sensors, the issue is caused by one (or more) of three things (i) spark, (ii) fuel delivery, and/or (iii) compression.
  • Spark - when was the last time the spark plugs were changed? If they were, did they use the correct type of plugs? Were they improperly gapped? Any known issues with the ignition coils?
  • Fuel delivery - this could be anything that delivers the fuel from the gas tank into the engine cylinders. E.g. fuel injectors, fuel filter, fuel pump, etc. Easy way to test this is to check the pressure coming from the fuel lines to make sure it is within spec. I've never performed this test on a Merc but I'm sure there are other, more knowledgeable people on the forum who would be able to explain it. It's pretty rare for fuel injectors to go bad on modern cars, a cheap way to test them is to swap them between known "good" and "bad" cylinders to see if the misfire code moves.
  • Compression - if a cylinder has bad compression (either at the valves or the piston) it will cause a misfire code. In my experience, the values themselves aren't that important, it's more important that all cylinders are +/- 10% of one another. If you're going down this road and you find an issue with the compression test, generally you hope it's a valve and not the piston.

I'm a long time lurker, first-time poster so please take the above with some salt. If you're mechanically inclined, this could be a good project. I'd change the MAF sensor first and see if that fixes any of the errors then move onto more in-depth diagnostics. $1400 isn't a terrible price but still more than I'd be willing to pay given that the car really isn't drive-able yet. If the seller has full service records and is up to date on maintenance (aside from the issues mentioned above), offer them $1000 cash and you'll pick it up that day and see if they jump on it. If they don't have full service records, offer $800 since you'll need to buy a few hundred dollars in fluids, spark plugs, oil, filters, etc. to get it up to date on service. This should give you a bit more money to test and replace parts without ending up too deep in the hole.

If you decide to pick it up, document your fixes, post photos and write-ups so that rest of us can follow along and learn!
 
#4 ·
Ok. So I ended up buying it for $1000. Came with tein lowering springs, axle back exhaust, weather tech window visors, aftermarket front bumper, aftermarket exterior trim, amg floor mats, custom seat covers, and some other goodies.

Anywho, i towed it home and dug into it. Checked the coils and spark plugs first. To my surprise there was a point where the coils were off long enough for mice to run around in there. There was droppings, pieces of food (seeds, nuts, etc), and debris keeping the coil from fully seating on the spark plug. For some reassurance, after cleaning out the spark plug holes, I moved the coils around. Plugged in my scanner, fired it up, and the misfire codes were gone! I also swapped the throttle body actuator with a m111 and that code went away as well. But very rough idle and won't rev passed 4,000 rpm. Another code pooped up, front o2 sensor. Found a crack in the header seam. So that's hopefully that. Maf threw codes so I started to check it. I thought I'd try to unplug it while it was running to see if it changed anything, but it did nothing. Is that normal? It runs exactly the same with or without the maf plugged in. I checked power and ground on the connector and I have 11.5v with the key on.
 
#5 ·
Checked the coils and spark plugs first. To my surprise there was a point where the coils were off long enough for mice to run around in there. There was droppings, pieces of food (seeds, nuts, etc), and debris keeping the coil from fully seating on the spark plug. For some reassurance, after cleaning out the spark plug holes, I moved the coils around. Plugged in my scanner, fired it up, and the misfire codes were gone!
Nice!

Another code pooped up, front o2 sensor.
More mouse POOP? :wink (Sorry, I couldn't resist that hilarious typo!)

Found a crack in the header seam. So that's hopefully that.
That would be my guess in why it throws an O2 error.

Maf threw codes so I started to check it. I thought I'd try to unplug it while it was running to see if it changed anything, but it did nothing. Is that normal? It runs exactly the same with or without the maf plugged in.
If it runs rough either way, then it probably is the MAF sensor, but if it runs smoothly either way, then probably not.

I checked power and ground on the connector and I have 11.5v with the key on.
Try charging, but you may end up with a new battery.

This all sounds very promising - keep us posted on the project!
 
#6 ·
I think you'll have found a good car which hasn't been well looked after. Of course when you start a thread like this, you are going to have to keep our curiosity well fed with updates.

Good Luck with it, it sounds like you know what you are doing, which helps enormously, for us Mechanically challenged types.

Give the throttle body a good clean...for some reason that has something to do with the cold start idle.
 
#7 ·
Oh also forgot to add that I can drive the car fine, as long as I don't boost too much. If I shift early, it drives almost like normal. Just very weak if I try to give it too much gas. Doesn't overheat or anything. Just rough idle, and it's weak. No smoke either.
 
#9 ·
I read on another forum about a car losing power as the gas was applied and it turned out one of the hoses from the Supercharger was split and when the pressure was applied, it caused the split to open and so the pressurized air was escaping, hence the Car was getting asthmatic.



I don't really know how anything works and where it connects, but the explanation seemed to make sense. Suggest if you get the chance to have a look around down there, to look for cracks, holes or splits. It could also mean the MAF sensor is not faulty but actually doing its job (perhaps). :confused:

Good Luck.

Hutcho
 
#12 ·
Yet another update... New maf came in. Maf code is gone now. Idle is normal sometimes, doesn't shake at idle now but still jumps around from time to time. Definitely smoother acceleration, but still limited to 4k rpm while idling. Had the p0120 code so I ended up changing with gas pedal with no luck. BUT while driving today I noticed I could go a little above 4k. At that point (~4200 rpm) I heard a rattling coming from the intake side of the engine. So I'm led to believe my still standing p0120 may just be a bad throttle body. I'm going try to get the throttle body tomorrow if I get out of work early enough (complete 2003 c230 at the wrecking yard). Has anyone ever experienced the throttle rattle? I can't have someone rev it while I search for the noise because it doesn't do it without actually driving. On a side note, if I clear my codes the cel stays off. As soon as I rev it or drive it I get a misfire code, from one cylinder to all cylinder misfiring. Still driveable, just rough. I simple restart will go back to normal until I try to accelerate over 4k rpm. What I'm gonna do is have someone floor it with the key on, not started, and see how far the throttle actually opens.
 
#16 ·
Sure thing


Ok so I've now got a "cl fault" on my fuel system in live data. Found a missing vacuum line that came out of the supercharger so I reconnected that. Still no change. Pulled the cat and started the car, still no change. Removed the precat and header combo and checked inside, the honeycomb all looks good on both sides (pictures below). I noticed something new, when I first drive the car I can exceed 4k rpm in first gear but it'll still throw misfire codes on all 4 cylinders and then lose power in 2nd and revert back to the 4k rpm limit. Gonna watch my live data on startup today and see when the cl fault comes into play.
 

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#18 ·
just did a smoke test and a fuel pressure test. No vacuum leaks and my fuel pressure held at 54psi with fuel pump on, not running. After starting it, fuel pressure stayed the same. Revved it to 4k rpm (limp mode rev limiter) and pressure jumped a little but still 54-56 psi. Psi drops to 50psi at about 25-30 min when I turn the key off.
 
#21 ·
What are you thinking? I don't leak coolant, will never overheat (driving not while idling), no mixture of coolant and oil, and no smoking while driving. I've seen compression tests yield 170's for the m271. Leakdown is my next test probably on Wednesday.
 
#24 ·
Why do you think 115-126 psi is too low? The actual steps for checking compression indicated by WIS are not to use a gauge for a specific psi, but to pressurize the cylinder with compressed air and make sure it holds.
 
#28 ·
OK, using those document numbers, I found this:

http://benzbits.com/M271/CompressionPressure.pdf

The lower limit is 8 bar, or 116 PSI. Giving a range of accuracy on your gauge, I'd say you're within spec. Besides that, when you have compression problems, there will be other symptoms - buring oil, leaking coolant, dirty oil, etc.
 
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