Diagnose: Engine bogs down at 4K+ rpms on highway

[taylor192]

Pulled a bunch of codes that indicated the rough idle might be the MAF, so replaced the MAF and the car is much better yet still not perfect.

On the highway (60+ mph) @ 4K+ rpms the car "bogs down", like its starved for air or fuel, and just won't keep going.

Any ideas? I'm going to change the plugs later, they are probably filthy from the bad MAF dumping too much fuel and running rich at idle. Next would be an intake leak test maybe ....?

[Zenar]

Air filter, fuel filter, clogged injectors
An intake leak won't cause the car to bog, and would have some side effects at all rpms.

Also, I have heard about cats clogging up and not letting the exhaust escape.

[NemeSSis]

Pulled a bunch of codes that indicated the rough idle might be the MAF, so replaced the MAF and the car is much better yet still not perfect.

On the highway (60+ mph) @ 4K+ rpms the car "bogs down", like its starved for air or fuel, and just won't keep going.

Any ideas? I'm going to change the plugs later, they are probably filthy from the bad MAF dumping too much fuel and running rich at idle. Next would be an intake leak test maybe ....?

K let me get this straight, you are asking a question about a possibly one of the most advanced makes of car you can buy...one a site full of guys who own ten year old handas? you dont see me asking questions about my car and its nothign more than a glorified Nissan. IMO go to MB specific boards for this one.

good luck wiht your problem tho

[deebz]

Adding to Zenar's post, dirty plugs would usually affect the whole RPM range

[NoLimits]

What codes are you getting since you changed the maf?

[taylor192]

K let me get this straight, you are asking a question about a possibly one of the most advanced makes of car you can buy...one a site full of guys who own ten year old handas? you dont see me asking questions about my car and its nothign more than a glorified Nissan. IMO go to MB specific boards for this one.

good luck wiht your problem tho
There's nothign special about a Mercedes, its still a car like most others.

The problem with the MB forums is most don't work on their cars, so they have no clue how to fix them other than to drop them off at the dealer.

[taylor192]

Thanks guys.

Mike, problem is there's no CEL since the MAF change, I'll pull the codes anyways, maybe there's one that isn't causing a CEL.

I've had a rough idle three times before: once was dirty plugs, once was a vacuum leak, latest time was the MAF.

The car bogs at high rpms, ONLY on the highway > 100 kmph. High rpms < 100 kmph are fine.

Taylor,

Could this be a fuel pressure issue? A weak fuel pump, blocked filter, or failing regulator could supply enough pressure for normal operation under light load (such as cruising around town). However, once up to highway speeds and the demand for fuel increases, the compromised system may not be able to meet the demand, and rail pressure will drop as will, consequently, engine output.

This is just a scenario which fits the symptom - I am not very good at tracking down problems like this, and I suppose it is easy to suggest what it might be, but perhaps it is a good place to start.

Jim

[racerboy000]

universal code reader or actual scan tool?
you have a manual for the beast?

[deejay2000cav]

Thanks guys.

Mike, problem is there's no CEL since the MAF change, I'll pull the codes anyways, maybe there's one that isn't causing a CEL.

I've had a rough idle three times before: once was dirty plugs, once was a vacuum leak, latest time was the MAF.

The car bogs at high rpms, ONLY on the highway > 100 kmph. High rpms < 100 kmph are fine.

Chris,

I had 2 sensors go on mine and CEL's went off 2 x... one was for the O2 an the other was the Coolant Temp sensor... I would think if it was a sensor u would get a CEL... U aren't going into limp mode are ya ? I would still be betting on bad plugs man...

PS: still waiting on my BiX, Gaston Rey is still back ordered on the passenger's side one...

regards,

Marty

[Lealdade]

At 88mph the silver part of your car goes back to 1982 and the black part 2019.

[dwarrick]

i'd grab a fuel pressure tester, and see if it holds pressure, drops any, or if takes a while to reach the normal pressure.

[evil haze]

maybe a mouse built himself a home in your inlet tube while you were in calgary!
thats what you get for bragging

[-=M=-]

I just had that happen on my golf, the car would not go over 4000rpm, it was my crank position sensor.

[Andre]

Also, I have heard about cats clogging up and not letting the exhaust escape.

Actually that may not be far off...

My dad's Grand Prix had similar symptoms when this happened. What's the mileage on the car Chris?

[b18c]

when my last motor was bogging down below 4.5k RPM i found out i had bent intake valves and piston rings with a possibility of a cracked head :oops:


i'm sure your situation wont be near as bad but you should make sure to check over everything.

[taylor192]

Mileage: 125K kms

CEL came back on today with a slight rough idle at startup. Once warm idle was fine.

I noticed this: my gas mileage is usually 10-11L/100km on the display, when it started it went to 22L/100km then slowly while I drove to work it went down to 11L/100km.

I don't think its anything as serious as the crank position sensor or valves, probably a bad O2 sensor, the information from the MB forums said it was most likely the MAF, oh well, at least I have an extra MAF now and the car is running better with a new MAF and plugs.

I doubt its a clogged cat. I had a 4-1 header for the last 8 months and the problem developed over that time. The stock header is back on. (cat is attached to the header) unless the secondary cat is clogged...

your crank sensor is full of hair.

[AWDGuy]

I'd start with the obvious...start with the plugs and ignition. I had similar problems where the car would start hesitating after 4k, my problem was all my wires going to th coil pack were brittle and falling apart. Bought a new pig tail kit from Ford, and I was back on the road with no issues :)

[taylor192]

Thanks Nate, did the plugs this morning and inspected the coilpacks and wires, all looked good, no cracks.

This is an odd problem, I'm ordering an O2 sensor and will try swapping the downstream one since it usually goes faulty first.

Fred is going to help me read the codes tomorrow.

[taylor192]

Definitely going to try the O2 sensor next, since when they go bad they typically read lean, which makes the car run rich to compensate and thus the P0172 code (rich) I got before and my terrible gas mileage. O2 sensors work better when heated up, so that could explain my car running better when warm.

Can you measure the output voltage on the O2 sensors with an ODB reader?

[lurkingknight]

I've heard of a cat dislodging in the exhaust and rotating to prevent exhaust flow causing a bog above certain RPMs as well.

[carlos11]

Definitely going to try the O2 sensor next, since when they go bad they typically read lean, which makes the car run rich to compensate and thus the P0172 code (rich) I got before and my terrible gas mileage. O2 sensors work better when heated up, so that could explain my car running better when warm.

Can you measure the output voltage on the O2 sensors with an ODB reader?

Mine couldn't. Maybe there are more "advanced" ones that can?

[AWDGuy]

Definitely going to try the O2 sensor next, since when they go bad they typically read lean, which makes the car run rich to compensate and thus the P0172 code (rich) I got before and my terrible gas mileage. O2 sensors work better when heated up, so that could explain my car running better when warm.

Can you measure the output voltage on the O2 sensors with an ODB reader?

Mine can, and from what ive read, Fred has more advanced software than me...

Unfortunately, mine is being used by a freind right now...

[AWDGuy]

Chris...buy this

http://www.myscantool.com/ <= its what I use.

I use EasyObdII (freeware), only complaint is that it doesnt have logging capabilities.

[racerboy000]

how much does a manual cost you because if you keep throwing parts at ... the manula will have a diagnostic chart in it for the problem

[-=M=-]

Did you figure out what the problem was, im still not convinced it isnt the crank sensor

[Low4dr]

do you get the same thing under hard acceleration? I had a symptom like this long before i understood cars, turned out to be a bad electrical connection that kept rocking back and forth and lead to the engine wanting to stall/die. anything over 3000 rpm made the car studder and die. sad part was it was on my battery and i just kept a wrench in my car to keep knocking it back into place. 10 bucks later, problem solved. new terminal.

I was such a newb.