SLK320 Low Power
 

I have been looking for a manual transmission 2001 SLK320 for several years and bought one today. I don't pick it up until next week, but want to get input about the low power problem.

The car is absolutely pristine in every way. Everything works very well. Has 38,000 miles. No light on, and haven't been able to check for codes yet. The engine sounds great, runs smooth, but is noticeably low on power. My first thought was the variable length intake. My brother in law, a 25 year MB dealer diagnostic tech, said the mileage was so low that the intake runners are probably not the issue, but this was via text and I haven't talked to him in depth yet. I am anxious to draw codes, but I wonder if anyone has any experience with this problem.

I am excited about the car even with this problem. The car is outstanding in every other way and I bought it worth the money, so I am willing to work through this problem.

Thanks for the thoughts and comments from those familiar with the breed.

When you say 'low on power' are you referring to the acceleration or generally sluggish in general?


-Dmitry

Air&Road, it's possible a restriction in the exhaust system is causing the power reduction ... say a failed catalytic converter or dead rodents.

Idles great. Sounds great. Starts great. Cruises great. Accelerates like it has a normally aspirated four cylinder. I expect a 320 to accelerate like a solid fuel missile.

Since I don't get the car home until next week I am probably jumping the gun with this thread since I hanve not yet so much as pulled codes and done a basic inspection.

Given that this car has variable length intake runners and cam timing manipulation, I thought maybe someone knew of a common trouble spot that could cause this. Especially since the engine is used in so many other models as well.

Air&Road, an SLK320 has a V6 engine. If you have an SLK230 then it has an inline 4-cylinder engine. Which vehicle do you own?

Off the top of my head it sounds like the air mass sensor could be the problem. They common failure scenario is that they report less air than they should so the ECU trims the fuel resulting in loss of power on acceleration..........

As the thread title indicates, the thread pertains to an SLK320 that I bought Wednesday, but have not yet taken delivery. I also have an SLK230 that I wrecked about a year ago. I indeed jumped the gun with this thread, but I thought there might be a common Achilles heel with this engine that someone might be aware of. I am hoping that when I get my hands on it, a code will lead me directly to the problem.

The car is so pristine, that I think I will be good with whatever it takes to make it right.

My BIL the MB tech has been telling me since these cars came out in '99 that I should get a 320 instead of a 230 because it is so much faster. My 230 would mash you into the back of the seat, so I expected the 320 to feel like a rocket ship. Time will tell.

BTW, back when this car was new I was with my BIL while he was test driving my car. We entered a downhill entrance ramp that was a common route for his test drives. He said "an SLK320 will do 120 by the end of this ramp." I asked "how do you know?"

Also BTW, if my generic scanner doesn't retrieve a code that leads me to the problem, I will take it to my BIL and see if their are enhanced codes that will help. He will home in on it if I can't.

Air&Road, if the mass air flow sensor is bad the Check Engine light should be lit. I own a 1998 E320 with the V6 engine and it is very quick. As you mention an SLK320 should be as quick, if not quicker.

Surprised you didn't have your brother-in-law perform a PPI (pre-purchase inspection) and diagnose the problem before buying the car. That could have been used to negotiate a lower purchase price.

Hi Larry. Congrats on the new purchase. Didn't know you had crashed the previous SLK.

Two thoughts. On my old SHO the variable intake runners could be disconnected. You could tell the difference, but it was subtle, not dramatic. Mostly the lack of a switchover to the short runners at the designated rpm. I don't think a malfunction there is going to cost the kind of power you are missing.

Second. Not sure a 320 is much faster than a 230. It's approximately 215hp vs 190, and it weighs a bit more. More refined for certain, which of course makes it feel slower. So you may have to adjust expectations accordingly. That said, it definitely sounds like there is something to be chased down in the new car. Good luck.

The HP curve matters more than peak HP. I'd expect the smaller displacement engine to have more of a peak even with forced induction. ( less low speed power )

Was this car a garage queen? I've seen more than one seldom driven car with the air filter box filled with dog food. . . and I'm picturing a skinny dog in the corner.

I had a similar thought - physical restriction of the air intake path acting as a throttle.

It's been a long time, but I have hazy recollections of the supercharged m111 outperforming the 2.8 liter m104 despite a lower peak hp. But the m112 has quite a bit more power than the smaller m104. I'd expect it to outperform the slk230, but I don't think the margin of difference would be all that large.

Thanks for all the replies. I did indeed get this car for a very good price. I was happy to buy the car for that price even with the known shortcoming

The car is a long way from me, so I did not have the options that you would hope to have with such a purchase. I expect to go get the car Tuesday or Wednesday. I expect to get to the bottom of the problem then.

The CEL will light up only when the fuel trim correction reaches it's limit. This is why symptoms can appear before the light comes on. A proper diagnosis would include checking the fuel pressure and monitoring the air mass value while under hard acceleration :)

Air&Road, other possibilities would be a dirty fuel filter or restricted fuel lines. Best to follow ILUVMILS's advice instead of guessing and throwing parts at the problem.

I have done lots of engine performance troubleshooting, so once I get it home, give it the once over and connect a scanner, I will get to the bottom of it. My reason for starting the thread was to probe into what known or common problem might exist with the breed.

I go get it tomorrow and will report what I find. Can't wait!

Thanks very much for the responses.

If you're scanner can read actual values post the fuel trim numbers so I can take a look........

I found two things. There were fuel trim codes for both banks. I found the air filter/engine cover not fitted to the mass air flow sensor such that it was not sealing properly on both ends of the sensor allowing unmetered air. It also was slow until warmed up. With no money spent it is now a rocket ship! I figured it would be something simple. The car is just too slick and low mileage for anything serious to be very likely.

Air&Road, glad to hear the fix was that simple. I expected the SLK320 would be very quick. Congratulations on your purchase. Post some pictures if you get a chance.

Well I am not done yet. I drove several hundred miles in the rain on secondary roads with no trouble whatsoever. Started it Friday afternoon while warm and got a light. Started it cold in the evening and when accelerating the power came in and out abruptly as if I were turning it on and off with a toggle switch. Once home I connected the scanner the next morning. Had P0171 high LTFT AND THE COMPANION CODE FOR THE Other BANK.

The air filter and MAF were tight. Started it up cold and had 34.3 LTFT both banks. STFT was normal at virtual zero. I did not run it to warm up. I am driving it to town this morning. I will report any other symptoms or codes.

I drove it 20 miles to town. The LTFT on both banks seems to be stuck at 34.3 but it never set the MIL. STFT seems normal. IAT was about 25 degrees higher than normal.

Okay, I want to post my final resolution in case it can help someone in the future.

The IAT was high and the MAF values were high at 1.09, so I took a chance on the MAF and it solved the problem. The car is now a rocket ship and the LTFT has come back down.

This car was low mileage, well cared for and always garaged. I have been looking for a stick shift V6 car for a very long time, so when I found this car I bought it perfectly willing to sort through the power problem. My gamble has paid off and I am absolutely tickled to death to have this car. Thanks for all the replies.

Sounds good. How about some pic's. I'm interested in that generation SLK myself as a possible purchase one day. Have you experienced any noticeable quality problems with your previous one in comparison to earlier generations of Mercedes? A lot of opinions seem to indicate poor quality interior materials from what I've read.

- Peter.

Pj, the one I ran through the fence was a ragged car that I bought and fixed up on the cheap. It didn't look bad, but it was not absolutely pristine like the 320 I just bought. These cars don't have some of the high end gadgetry as do the sedans. Even the C class has more in the way of electronic wizardry than the SLK. The build quality overall is pretty good though.

The interiors are indeed a problem. The ragged car I had actually had portions of the dash that were broken. In 2000 or 2001 they introduced what they called the facelift version with some subtle improvements. I think the interiors are a little more durable in the facelift version. The most common interior problem on all of them is that they have a paint coating on top of a black plastic base. As it gets chipped and scraped the black plastic shows through. If the paint on top is white or red or something other than black, it looks ugly when the black starts showing through. My newest car has a black interior, so the chipped spots don't show up very badly. If you can find a car with a black interior it will make it look much better as it wears. This is the worst problem with the interior.

Mechanically the cars are pretty decent. The supercharger wears out if the oil in the gearcase is not kept changed. The odd thing is that MB does not indicate the need for the SC oil being changed. It is a special oil and is a little bit of a hassle to change, but if you have a good SC you should keep it changed. The V6 eliminates the need for this of course, and the V6 car is a more refined car. It is not only smoother, but it delivers very nice torque from idle to redline. This makes it wonderful with the six speed manual, but I expect is quite nice with the auto box as well.

The other issue to investigate before buying one is to see if you fit in it. I am 6'1" and barely fit into it. If you are taller than about 5'11" make sure you are comfortable in it.

Overall I really like the little car. It took me a really long time to find a stick shift 320, but now that I have it nicely sorted, it was well worth the wait.

I am leaving on vacation tomorrow, but I will try to post a picture before I finish packing and leave.

Thanks for the reply. What about the mechanical top? No problems there?

- Peter.

The top works very well on these cars. It is not uncommon for the cylinders to leak. The cylinders are very expensive from MB, but there is a very competent cylinder rebuilder in the NW US that will make a cylinder like new for a very reasonable fee. The cylinders are not super simple to replace, but within the capability of a serious DIYer.

Sounds like Air&Road got a really nice 320 stick. I purchased my 2001 SLK230 new in Sept. 2000. No problems with the hydraulic top, but I rarely ever put mine down. It has 72K miles and has been garage kept since new. Mine is red with charcoal interior, the interior peeling has been an issue with these models, as you can see on the console in my picture. But with the charcoal interior it's not as bad as others. Overall it has been a very reliable car and I still get compliments on the condition.
IMHO, a 2001 SLK has to be one of the nicest, cheapest to purchase, used cars on the market. I just backed mine out of the garage and took a few pictures.

Good luck if you decide to purchase an SLK.