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Loss of acceleration

4K views 14 replies 5 participants last post by  Jostep 
#1 ·
Hey everyone, new to this forum and would love to contribute in the future. Quick question, so i have a 96 c220 and recently as id drive the car would momentarily lose acceleration for a few seconds and then it goes back to being fine but happens many times during drive. Its getting pretty scary when i drive on the freeways as id unnecessarily slow down. I changed the fuel filter but no luck :( have any of u experienced this before? If so what was the problem?
Thanks
 
#3 ·
Welcome to the forum! For future purposes, please fill out your profile with the model and model year in your profile. As for your loss of acceleration, do as george said, start by getting the codes scan, if there is a check engine light on, we will need to know what's happening with that!
 
#4 ·
Yep scan for codes first...

My 95 c220 did that right off idle, mashed the gas and it would sit there like the throttle was not connected, didn't even rev.
My problem was the dreaded wiring harness issue in the throttle body wiring...basically the insulation rots away letting all the bare wires touch...new TB and it was fixed.

Swing by an autozone, oriellys, etc..... they will scan your codes for free, write down the actual code (example P300) and let us know....I don't think there is anything this forum hasn't covered or experienced so no worries. And welcome to the forum...the M111 is a tank!
 
#9 ·
Jostep, Thank you for the detailed explanation. I think i will go ahead and change the spark plug wires.

What is TB?
Throttle body. If you start getting codes about idle circuit, that's it.

I think at your mileage, the new wires would most likely pay for themselves soon with increased mpg.


Thanks for all the help guys, i took to my friend whos a mechanic and got him to scan but no error codes came up except for FUEL RICH which was my doing as i was testing the car without the MAF. In regards to wire i will have a look again so cant comment on that. But i had a temrorary fix. I cleaned the TB and it worked perfectly for 2-3weeks. One other problem which could be contribiuting to it is the fuel pressure regulator. It is leaking fuel into the vaccum tube so ive ordered a replacment.will update on outcome once recieved and installed. With that being set the big metal tube bit on the TB where there is three vaccum plugs is missing two of the vaccum leads and i have one loose vaccum tube in engine bay which not sure if it connects there or otherwise. Would any of you have a picture of that area so i can use as a reference.
Ps my apologies about the late reply as i hadent recieved any notifications wrt this forum haha. I have to set my account up properley lol.
 
#5 ·
I seem to be having a similar problem but very seldom. Is the wiring harness same thing as the spark plug wires? I have the original spark plug wires and coils on my car and visually they look fine. With 18 years old and 190K miles should I change the spark plug wires?

Thanks in advance for your advice.
 
#6 ·
Don't know the actual specs....but I think Mother Benz calls for a swap at 100k. I tested mine with a simple multimeter. Set it up for ohms reading (resistance), bright colored finger stabber at each end and took a reading. 3 of the 4 wires were at, 1.8k, and one was almost 9k... (should be 2k max).

The plug wires are not the same as the TB wiring harness. Coils seem to work until they don't...on your 280 it's way easier to change them out than the 220. You should be getting P30x codes for misfire if it is a coil.

Wiring harness for the TB is the actual plug in lead, covered in a thick plastic insulation with an oval plug on one end, other goes into the idle control side of the TB. Looked perfect externally, inside was a mess.... should only effect 1995-1996 years where they used biodegradable wiring insulation on purpose...

Pics of the carnage. FYI rockauto.com has them for $425 new with the new revised part#. Working perfectly now with new TB and cleanup. Car was a dead C220 given to me for hauling it off.
 

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#11 ·
There should be a vacuum diagram as a sticker under the electronics flap (where your ECM is).

Basically, the 3 plugs are for: 1 will have a rubber Y-splitter, that splitter sends vacuum to the fuel pressure regulator and the vacuum solenoid on the front of the engine (under the plastic cover). One of the lines from that solenoid goes back to that same area and connects to the EGR valve (it's at the very back of the engine, mounted directly to the intake manifold). Another line coming off that solenoid goes to the secondary air injection check valve (it's close to the solenoid, mounted near the exhaust manifold).

Back to those 3 plugs on the intake manifold, you now have 1 that is accounted for. Another line goes from the intake manifold to the electronics area, where it plugs into a plastic vacuum splitter with many plugs and lines going to it. That then powers the rest of the vacuum accessories on the car (folding headrests, central locking, HVAC actuators, vacuum reservoir, and whatever else needs vacuum). If you see an open plug on that vacuum splitter, don't worry, it's not leaking, any open port is automatically shutoff internally. However, that plastic splitter is known to crack and cause a vacuum leak, so inspect it for that, particularly at the ball bearing.

Back to those 3 plugs on the intake manifold, you now have one plug left. That line goes to the PCV (positive crankcase ventilation) solenoid, which is located under the windshield fluid reservoir.

So, how to get your car back up to its former glory? First, replace that leaking fuel pressure regulator, that's what is causing your rich fuel problem. You need some circlip pliers to remove it, but otherwise it's really easy. You just remove the circlip and pull the regulator out, pop the new regulator in, and reinstall the circlip.

Next, reconnect all your vacuum hoses, and do a general inspection of all the vacuum lines in the engine bay. After 21 years all the rubber gets stretched and starts to leak. Go to your nearest dealership, they sell the rubber vacuum line crazy cheap, I bought 3 meters for 20$. You can use that rubber line to replace any rubber lines, and make yourself new straight connectors for the hard plastic lines (the plastic lines will be fine). Elbows and splitters will have to be bought, but I'm sure they are also super cheap.

With all that done, you should be good to go! Your probably thought your car was fine during those few weeks because you had just enough vacuum leaks to offset the unmetered fuel leaking past the regulator. Anyway, it will make a world of difference once you do all that. The C220 isn't a slow car, it's just usually they have some age-related maintenance that needs to be done to get them back running strong.
 
#12 ·
Thank you for the detailed resonse. I have had a look for the valve that connects to the PCV solenoid but cant seem to find it :s. I have attached the areas. the two vaccums connected are the fuel pressure and the other is to the electronics area. the second picture is the area below the windshield fluid resorvior and the only vacum line i found was the one that connected to the throttle body.
 

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#14 ·
Ive had a look it's not there. the entire module is not present there it doesnt even have a mount for it but theres space under the washer tank . It seems like the Australian models aren't ment to have it as it was a regulation matter or previous owners have tamperred with it? Ive emailed my local dealer and asked them confirm this.
 
#15 ·
Thank you for the compliment, worked hard to polish up years of neglect. Kind of a thing if I remove a part (had a small leak around the spark plug seals) I'm cleaning it and putting it back together fresh.

Patman nailed it, and actually mine was doing the same thing with the pressure regulator. backfilling the vacuum line and creating a seriously rich condition. In fact, I would swap in new plugs as they foul out quickly like that. And I got sick of chasing the elusive vacuum leak and bought a Mityvac per recommendations here.. best 49 bucks i've spent so far. I bought 10 feet of new vacuum tubing, tested each component to verify that it was functioning properly with the Mvac... stuck on a fresh hunk of tubing whether it needed it or not and never looked back. 35 minutes later I was buttoning up the motor for the last time, and getting 28 mpg with a lot more performance. 2 months later, still going strong!!

Once you get that pressure regulator swapped out (takes 3 minutes) you will not believe the difference.

I have the diagram also of the vacuum routing if you need it for the motor. it should also be on a sticker on the hood insulation by the grille.
 
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