Engine REVING like crazy!!

[neema12]

After a this happening more than 10 times, I came to post here to find the problem. I started my car this morning, and it drops to around 500rpm, which isnt normal, then it jumps back and forth between 500 to 2000, up and down, every second. It sounds like the car is going to die, and sometimes it does, it just shuts off.

Last night the same issue happened, but I happen to have the lights on, so I saw the dash as well as outside lights lowering with the rpm, and going up with the rpm too.

I dont think its the alternator, but some sensor. But I have no idea. I want to fix this issue soon, as it does not sound good for the motor. Btw, I have not changed anything large like sensors, belts, alternator, or spark plugs, or anything similar to that in awhile, so it could be one of them. Thanks

[jnenad16]

if it was just the rpm fluctuating it would most likely be the MAS, but the dimming lights indicate a bad alternator, battery or a poor ground along with a few other things that I just cant think of. also check the OVP relay. CEL on?

nenad

[neema12]

CEL is on, but its always on, so I dont even look at that anymore. I bought a new MAS from mercedes about 7k miles ago, when I had the same reving problem, and it was not the MAS. Do you think I should clean this MAS? Also, I dont think its a bad ground, or battery, both are very good. I dont understand why it would be the alt, I have never put strain on it.

[vbrock1137]

It might be the battery, I had the exact same symptoms a few months ago. The dealership kept trying to tell me it was the MAS etc. when I told them it was a battery problem. Finally they figured out the battery was bad, replaced it. Since I had it for less than two years (length of battery warrenty) it was replaced for like half price.

If this is the problem you might have to tell them to check the battery, they didn't listen to me at first. MB batteries are under full warrenty for a year, then pro-rated after that.

Just hope you don't have the same problems I've been having...I think I'm on my fourth battery in the last 6 months, they tell me MAS and alternator are fine, but they're free so I'm not complaining. If one ever lasts two years I'll probably get an Optima or something.

[neema12]

I have an optima red top, with costco cash back 3 year warrenty. I can go and get a new battery tonight, but I have a strong feeling its not the battery. How do I know its not a sensor. What sensors can it be, so I can do some reading and searching for similar issues. Thanks

[NISMOPOWERED]

I had those symtons it was traced to the FPR. If your RPM's dip low enough the lights will dim and that is normal. The alternator is not spinning fast enough to make the power so they all dim.

[neema12]

Whats FPR? Something like Fuel Preasure Reader, lol.:rolleyes:

I kinda knew it wasnt my battery, and the alt as well because it gives less voltage at lower rpms. Let me know what that is. Thanks

[jnenad16]

Originally posted by neema12
Whats FPR? Something like Fuel Preasure Reader, lol.:rolleyes:

I kinda knew it wasnt my battery, and the alt as well because it gives less voltage at lower rpms. Let me know what that is. Thanks
FPR= fuel pressure regulator. its located at the front of the engine on the fuel rail. you can check the pressure by attaching the pressure gauge to the fitting on the rail. however, the problem might be as simple as a open vacuum on the FPR or the vacuum line might be cracked. that is if the fuel pressure in not within specs. the specs are 45+psi at idle and 50+psi at 3k rpm minimum.
as for the alternator, test the voltage while the car is running. it should be between 13.6V and 14.4V. anything above and below is bad. turn off the car, wait 5min, and check the battery voltage. if its below 12V the battery is bad. now, you said that the CEL is on, get it scanned, if you get MB codes like 107, 110, 111 then the most likely cause of your problem is a faulty charging system, meaning OVP relay, alternator, battery and/or poor ground.

nenad

[neema12]

OMFG, I have a vacume pump problem now and I use the key to open each door manually, as if I had no power doors. The pump dosnt even power, so it may not be feeding power to the FPR. Will these conflict, the vacume pump has been messed up since spring break. Thanks, lol, im happy, looks like I killed 2 birds with 1 stone.

[jnenad16]

no the vacuum pump has nothing to do with engine vacuums. damn, still no luck with the locks? like I said, try replacing the pump.

nenad

[neema12]

danm, danm!!

Alright, so you suggest changing the FPR? I am looking around online and cant find the part at german star, and dont know where the part is in the engine bay. You said the front, is it on the left, right, what color? I got this tho, that it?

http://www.autopartsworld.com/1995_mercedes-benz_c-220_fuel-pressure-regulator_parts.html

Let me know, Thanks

[jnenad16]

like I said, test the fuel pressure first to make sure its the FPR. anyways, here is the link to it.

http://mercedes.thebenzbin.com/?year=1995&make=MB&imageField22222.x=51&imageField22222.y=12
go under fuel injection, and you will see fuel pressure regulator listed on the right

nenad

[neema12]

Yes, I got a c220. I will take the car to a mechanic tomarrow to check the preasure. I popped the hood today and looked at the small engine layout on the inside of the hood in the bottem left, but dident understand where the FPR was. Ill check it out tomarrow, until then I will take bus to school, this motor dosent sound good.

[fastmayte]

hey, a vacum line on my purge valve came off, it was reving up and down. the purge valve is next to the washer bottle labeled MOT

[neema12]

I will check it out tomarrow. BTW, does it have a valve you can turn on the top of it? Thanks

[NISMOPOWERED]

When my FPR went out the prussure was ok but there was fuel in the vacuum line that went to it. Thats very easy to check, pull the line if gas comes out its bad.

[98c43amg]

Originally posted by jnenad16
FPR= fuel pressure regulator. its located at the front of the engine on the fuel rail. you can check the pressure by attaching the pressure gauge to the fitting on the rail. however, the problem might be as simple as a open vacuum on the FPR or the vacuum line might be cracked. that is if the fuel pressure in not within specs. the specs are 45+psi at idle and 50+psi at 3k rpm minimum.
as for the alternator, test the voltage while the car is running. it should be between 13.6V and 14.4V. anything above and below is bad. turn off the car, wait 5min, and check the battery voltage. if its below 12V the battery is bad. now, you said that the CEL is on, get it scanned, if you get MB codes like 107, 110, 111 then the most likely cause of your problem is a faulty charging system, meaning OVP relay, alternator, battery and/or poor ground.
nenad

You Rock man! :D I'm not having a problem with my car, but if I have one I already have some idea of what causes result in what symptoms! :classic:

[jnenad16]

Originally posted by 98c43amg
You Rock man! :D
Thanx, I'm here to help.

Nenad

[neema12]

I went to a shop to take a look, he said he can take a look tuesday. I will check out another shop this weekend and let you all know. :(

[swank]

Originally posted by fastmayte
hey, a vacum line on my purge valve came off, it was reving up and down. the purge valve is next to the washer bottle labeled MOT

Yea those plastic valves i hate with a passion. Why in the hell.. an amg of all things and they went with plastic instead of aluminum or something more durable. Ive replaced many valves for my water pump and its not cheap.

[J Irwan]

One easy and fast way that I would to right now ...

to make sure it isn't the MAF ...
( I know you said you replace the MAF about 7K ago.
Just word of advice to you or everyelse on this board to never bought a USED MAF. It would be a waste of money IMHO. Since MAF is a wear and tear electronic part).

when you start the car, and the car running idle..
unplugged the connector to the MAF unit..

If after you unpplugged the MAF the idle drop to around 700 rpm and steady.. (like it's suppose to) then it is definitely a faulty MAF.

But if it doesn't do you any good then it's most likely the fuel pressure regulator.


Hope this helps.


Regardz,

Regardz,

[neema12]

I got it figured out. I took it to a mech who ran the codes. It came out to be the O2 sensor, and he changed it. I will pick it up tomarrow and once I get back I will let you know how it came out. He also changed the bushings too, but thats another story. Thanks;)