95 E320: Rough idle above 4000RPM - PeachParts Mercedes-Benz Forum

EricSilver · #1 08-09-2006, 12:25 PM

Car: 1995 E320
165K miles

While revving the engine in idle this morning, it became rough just after 4000rpm. From 0 to 4000 rpm, the engine is smooth and imperceptible. But as I ease past 4000, it behaves as if one or more cylinders are not firing in sequence.

Ancillary Observations:

* Check Engine light is on (has been for a long time – 3 years -- with no discernable cause – but I am hoping it is related to this discovery).

* Oil pressure needle, after a fast highway drive, hovers just above 0. Shifting into neutral puts it just above 1.0. (Planning an oil & filter change today).

Any ideas?

EricSilver · #2 08-09-2006, 12:47 PM

Also:

On hard acceleration in Drive, i.e. when merging onto the highway, there is no roughness at/above 4000rpm.

Arthur Dalton · #3 08-09-2006, 12:50 PM

<
Normal in P or N
Torque converter RPM safety cut-out.

Arthur Dalton · #4 08-09-2006, 01:06 PM

< >>

Why don't you just press the code button and see what code is stored that tripped ther CE
Search Code tool

EricSilver · #5 08-19-2006, 12:37 PM

Quote:

Originally Posted by Arthur Dalton

Why don't you just press the code button and see what code is stored that tripped ther CE
Search Code tool

While waxing the car I tried that.

Pushed button, LED illuminated, then went off when I let go of the button. No flashes returned. Held button down for several seconds and let go. No flashes returned.

I have not restarted or driven the car yet, but will see if the CEL is still on when I do.

Arthur Dalton · #6 08-19-2006, 12:41 PM

There is a specific retrieve LED/SW procedure.. check the archieves.
The trick is to hold the button for 2-3 secs for code ECU initiation.
If you have a CEL, you HAVE a CODE.

EricSilver · #7 08-19-2006, 11:55 PM

Quote:

Originally Posted by Arthur Dalton

If you have a CEL, you HAVE a CODE.

Not any more. The CEL is off.

Evidently, when I was trying to test it earlier, I held the button long enough to clear the code. Went for a drive a while ago, and the light was off. (I hope it is permanent.)

I am surprised that the previous owner, and his repair shop, were unable to clear it over the course of three years. Is the "holding the DM button" some obscure method that few people are aware of?

EricSilver · #8 08-09-2006, 01:18 PM

Thanks Arthur.

And look what I just found, and was about to post, after doing some more reasearch:

12-23-2005, 09:16 AM
Arthur Dalton
Location: Florida
Posts: 3,521

The car has a 4K rev limiter for P/N to protect the torque converter from operating at high RPM w/no load. It works by dropping a couple of cylinders. It is over-ridden by a speed senor when the car is moving.

You beat me to it.

Any thoughts on the oil pressure issue?

I plan to do filter and oil this afternoon and see if it persists. The car has been largely undriven since March, which is also when it had its last oil change (still less than 3000 miles since) and I suspect the filter may be mucked up a bit, even though the oil appears to be very clean.

Also, I have noticed that the oil pressure needle, at full, does not enter the white space of the 3-bar line, even though I know it is at max level. (On my previous car, I believe it did enter that space.) Also, on pre-start, before cranking, the needle moves to approx 0.1 or 0.2. I don't see why, since no oil is flowing -- or is that a diagnostic to show that it is working?

As for the CEL, I am new to this car, and that type of diagnosis, and still learning about both. I do have your LED diagram and code lists, however.

The previous owner told me that the Service shop (a really good one) that has maintained the car has not found any emissions-related issues connected to the CEL. That does not mean, of course, that other issues are not causing it.

Before I purchased the car, the shop's owner stated that they could not track down the specific cause. It went away after replacing the wiring harness, but then returned, and he said that codes sometimes refuse to clear.

I trust his knowledge, experience and judgment, however, if the CEL is illuminated, even for a mundane reason, it is like dirt swept under a rug and I cannot sleep soundly, knowing it is there.

I will search Code Tool to learn what to do. Thanks again.

Arthur Dalton · #9 08-09-2006, 01:48 PM

Car has a stored DM code if CE is on..
Te button for retrieve is in front of the battery

EricSilver · #10 08-09-2006, 01:56 PM

Quote:

Originally Posted by Arthur Dalton

Car has a stored DM code if CE is on..
Te button for retrieve is in front of the battery

OK. I will have a look there while changing the oil filter.

EricSilver · #11 08-09-2006, 09:38 PM

Changed oil (Castrol 20W50) and filter (Bosch).

When engine is hot (90C-100C) pressure is now between 0.5 to 1.0 with car in gear, and 1.5 with car in neutral. With engine at approx 83C, pressure is 2.2 in gear and 2.5 in neutral.

The old oil I removed ran very freely and quickly. I suspect it was a lighter, winter weight since it was last changed in March (car was not driven much since then). I also am wondering if lighter oils keep the engine generally cleaner, and if my 20W50 is too heavy....

To be safe, I will have the sender checked this Friday, and perhaps have the service shop change the oil yet again to whatever their standard is, since they have maintained the car in great condition for the past 7 or 8 years. I can live with the low pressure indication if I know there is not a problem.

gmercoleza · #12 08-21-2006, 11:37 AM

Quote:

Originally Posted by EricSilver

While revving the engine in idle this morning, it became rough just after 4000rpm.

I just noticed this. A little OT, but you should know that revving an unsprung engine to high RPMs can cause damage. RPMs of 4K, 5K, 6K, etc. should only be reached while the engine is under load. Again, sorry if off-topic.

Arthur Dalton · #13 08-21-2006, 12:06 PM

<
Time to clean the EGR pipe, one of the "most likely To Do" tasks on the list I made when I got the car.
>>

Don't assume EGR tube blockage until you have tested it. There are several other EGR faults on 104s that will bring u a code 5. Along with a Factory TSB part up-grade for EGR code. I will post a basic EGR flow test , if you are interested in diagnosing the fault before you go for a tube blockage repair.
Or go for the possible blockage and see if that solves it ..and if not, then repost you have the CE/code 5 again ant then you can do the flow test.

EricSilver · #14 08-21-2006, 12:34 PM

Quote:

Originally Posted by Arthur Dalton

Don't assume EGR tube blockage until you have tested it. There are several other EGR faults on 104s that will bring u a code 5. Along with a Factory TSB part up-grade for EGR code. I will post a basic EGR flow test , if you are interested in diagnosing the fault before you go for a tube blockage repair.
Or go for the possible blockage and see if that solves it ..and if not, then repost you have the CE/code 5 again ant then you can do the flow test.

I'll wait for your flow test.

My "clogged pipe" assumption is based on the "most likely" scenarios I've read in various EGR threads. If that turns out to be the problem, I'd probably prefer a tube replacement over a cleanout, since both seem to be equally tedious DIY jobs.

Arthur Dalton · #15 08-21-2006, 12:41 PM

Quote:

Originally Posted by EricSilver

I'll wait for your flow test.

My "clogged pipe" assumption is based on the "most likely" scenarios I've read in various EGR threads. If that turns out to be the problem, I'd probably prefer a tube replacement over a cleanout, since both seem to be equally tedious DIY jobs.

I will post the procedure as soon as I find it in the Archieves .. I did a complete DIYer article on it a couple of years ago..hold on, it's comin'..

.... and , Yes, If you do find you have to get into the blockage, you do want to go with the new tube as that eliminates the problem rather than just cleaning it every time...