Seat of the pants EHA adjustment - PeachParts Mercedes-Benz Forum

pentoman · #1 09-17-2007, 06:28 AM

Am I mad to be doing this?

I've just reconditioned the top-end of my 2.5-16 engine - the bottom end was fine. It starts and runs much better now, and makes a lot more low-down torque (no surprise since the compression figures were poor, 105-145).

However, after the rebuild it still had a poor pickup - the throttle response was not very clean, it ALMOST stuttered when you first got on the gas.
After checking the throttle position sensor plate adjustment and also the throttle position potentiometer, which seemed fine, I decided to try an EHA adjustment. I adjusted it a bit much at first - getting too rich so it misfired at full throttle, and then so lean that it wouldn't rev above 4000rpm. I've now settled with it at about 1/8 turn clockwise from where I found it.
The initial throttle response is definitely improved and there's less throttle lag. However it still isn't to my liking and the response still doesn't feel quite "right".

But I'm worried with my EHA set in a 'guesswork' fashion that I could be running too rich or lean under load - should I be careful? How might I know?

Also is my EHA adjustment just "covering up" for some other problem - maybe clogged injectors, or something in the fuel distributor, that is actually the cause of the problem?

The car is a euro without O2 sensor by the way. Fuel mileage is about 300 miles until the fuel light comes on.

t walgamuth · #2 09-17-2007, 08:00 AM

I have no real knowledge of these engines but I have driven one. It felt really doggy especially on take off. I only drove one car but I was really disappointed because I expected a really lively drive.

Have you driven other examples for comparison?

A timed acceleration test might reveal something too.

Tom W

A264172 · #3 09-17-2007, 10:06 AM

I think the propper adjustment is with fuel pressure gages on the upper and lower chambers... never done this myself... but you might want to find some one with the right test equipment or get it into a shop and do it right. Until then I'd just leave it alone or put it back to where you started from.

pentoman · #4 09-17-2007, 10:47 AM

Quote:

Originally Posted by t walgamuth

A timed acceleration test might reveal something too.

You mean like this?

I've driven a couple of others but only for short distances. They didn't seem enormously different but it's hard to know with short drives. I agree with what your experience though - it doesn't feel very lively and is disappointing - in spite of the fact that as seen in the graph above, actual measured performance is good.

But I don't think it should feel any less responsive than a 8v, since they run the same injection system - but it almost seems that way.

Quote:

Originally Posted by A264172

I think the propper adjustment is with fuel pressure gages on the upper and lower chambers... never done this myself... but you might want to find some one with the right test equipment or get it into a shop and do it right. Until then I'd just leave it alone or put it back to where you started from.

I have heard this not the quickest or easiest of jobs. Do you think it would cause my problem?

A264172 · #5 09-17-2007, 01:27 PM

Quote:

Originally Posted by pentoman

...I have heard this not the quickest or easiest of jobs. Do you think it would cause my problem?

I would doubt it with only 90,000 miles but you never know. Too bad you don't have an O2 sensor, you could get some feed back from they system on your mix. I think you may be right that the EHA tweak may be masking something but I have no clue what that may be. I'd say 300 miles per tank sounds decent so you are probably not far off on the mix. Do you know what the spark advance is on your engine, and have you replaced the plugs etc, and looked into the chance of a vacuum leak?

pentoman · #6 09-17-2007, 03:22 PM

Quote:

Originally Posted by A264172

I would doubt it with only 90,000 miles but you never know. Too bad you don't have an O2 sensor, you could get some feed back from they system on your mix. I think you may be right that the EHA tweak may be masking something but I have no clue what that may be. I'd say 300 miles per tank sounds decent so you are probably not far off on the mix. Do you know what the spark advance is on your engine, and have you replaced the plugs etc, and looked into the chance of a vacuum leak?

OK so the mix probably isn't too bad, that's good to know. It's got 105,000 miles now, and I can't even vouch for that mileage being accurate! Doesn't seem far off though based on condition/wear. However the car does have the odd sign of being fiddled with before (changed wires, missing bolts etc) so I wouldn't rule out the possibility of something that shouldn't be out being out, if you know what I mean!

No idea what the spark advance is, but I did get it tested as per spec, at idle and 'high idle', and it checked out right.

O2 sensors seem to make so much sense now, it's hard to imagine how cars even ran right (or at least efficiently) without them!

t walgamuth · #7 09-17-2007, 06:06 PM

I think the eight valve probably is more tuned for torque down low. Also it may have a more favorable rear end ratio or have shorter gears in the tranny.

Also the 16v has a beefed up suspension so it is so "buttoned down" that it may make the car feel slower than it is.

In short it may be normal to feel slower off the line than an 8v.

did you do timed runs in the above chart? sorry but I am too sluggish to see the method in the chart.

Tom W

pentoman · #8 09-19-2007, 03:18 PM

That chart is a single timed run. It shows the speeds throughout the run - so choose a start speed at the top, then choose an end speed down the left to see how long it took to get there.

Russell