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Discussion Starter #1
I don't know if you'll be able to help or if you'll just be put off because it's a 2.5-16 I'm talking about (don't be!) but I am hopeful for whatever suggestions people have.

The 2.5-16 drives and starts okay but my gut feeling is the throttle response and performance at low revs is not very good, it just feels flat. I checked out a lot including the throttle switches/position sensors and the temp sensors, and there seems to be no problems there. After a bit of reading on this board I went tweaking the EHA adjustment, and went even as far as 3/8 turn anti clockwise. At this position, the car really pulls well from low revs better than ever before, and I ran it like this for a week. It really brings a grin to my face how hard it pulls low down. Above 5500rpm it maybe tailed off a bit. Hopefully this would be the end of the story but no :(

It was such a big change I wanted to check the plugs to ensure it's not running really lean/rich, since it has no O2 sensor. It was obvious from the plugs it's running far too lean :(. Maybe it's a bit expected with that huge adjustment I made, but the mixture at the exhaust when at idle is in fact rich! Before I did any adjustment the plugs indicated a perfectly good mixture. So my question is, why is the low down performance only strong with the engine seemingly running on a really lean mixture?

The only other thing of note is the economy guage sits 1/4 way across towards the red when at idle (idles steady @1100 rpm).

Russell

PS In 'too lean mode' it also did 402 miles before the low fuel light came on! I am amazed and depressed both at once with this car.
 

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'85 2.3-16 '99 C280 '11 GLK350
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If the engine is running lean (more air in mixture than optimum) then I would immediately dial it back to normal, since the excess combustion heat can do serious damage to the valves and pistons, not inexpensive items in a 16 valve.

The 16 valve, although the 2.5 is better, is not a torque "monster" and it does require revving to get it to pull strongly. The good thing about the engine is that it does rev.
 

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2.5-16 (1990) SL500 (2000)
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With all this information it appears that your problem at the start was not that you had too much fuel, it was that you had too little air.

By reducing the fuel things are improved until revs get high and the engine can no longer get the gas fast enough.

I agree with the earlier comments that you should now reset the EHA back to where it was and
a) Clean the air flow meter
b) clean the ICV
c) check the air filter and maybe get a new one
d) adjust the idle mixture to get revs down to 750rpm

Where did your economy guage sit at idle before?
I think mine sits at less than 10% of max at idle
- on a level road at 80kph I can maintain speed with the economy guage at 5% or less
- around town I get 475km (295 miles) from full tank to first show of fuel warning light. (65litres)
- on a long trip I get 750 - 850 kms from 65 litres. (466-528 miles) from 65 litres.

Stick it on a dyno first then adjust followed by another dyno. It's worth it.
 

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Discussion Starter #6 (Edited)
When I discovered the leanness I reset the EHA to where it was and the power has dropped back off again to how it was before :(. I'm not going to drive the car until I can get somewhere with the issue, having experienced now how it could/should perform.

To the Aussie - does your 2.3 have the 70 litre tank? My light first flickered at ~380 miles, I filled up at 402 miles and it took 62.5 litres to brim it. This was half highway and half commuting work. 300 miles was more typical before adjustment. It costs around US$140 to fill up now :eek:.

I don't understand what can be cleaned on the AFM? I did however clean the ICV in an ultrasonics cleaning tank but not sure if it made a difference - would this affect the performance I'm experiencing and how? Does it introduce metered or unmetered air?

The plugs are 6000 miles old and the wires were on the car since I bought it. I don't know how wires would cause this problem so I haven't considered them! But there's never been a misfire so I've not paid much attention except the basic checks. However the ignition advance was checked and came out as it's supposed to according the idle/high idle timing figures I have. I will log up the wires in the back of my memory but am leaning to the fuel delivery side in my gut feeling.

The air filter is a bit dirty but was new approx 1 year ago, I didn't feel a difference when I fitted it despite hoping for a magical cure, so I figured it wasn't the cause!

I don't honestly think a dyno would solve my problem. My seat of the pants and then look at the plugs dyno (heh) says to me: when you tweak the EHA adjustment anticlockwise, the performance improves, but the car runs lean on the throttle. Also when holding a high idle of 2500rpm my Dad told me it was doing a 'lean misfire' and smelt lean. Obviously I reset the adjustment pronto but the performence dropped off again. I figure from this the fuel pressure seems to be relevant to the problem.

I am confused with your idea of 'not getting enough air'. I thought the air flow meter measures the air going in then it dispenses fuel? If the air getting in is limited, the fuel flow would reduce and the mixture would remain perfect, shouldn't it?

This is all the options I haven't ruled out:

An air leak: would result in a lean mixture?
My EHA looks to be leaking: I have tried another and there was no difference so..? My reading about leaky EHAs showed no coincidence with running problems
EHA connection bad meaning no enrichment: tried disconnecting it and the lag increased badly
Timing chain stretch: ?? visual inspection showed no significant stretch
Sticky AFM plate/plunger: not sure how to test. Would presumably also result in lean mixture?
Vacuum related problem: not tested. I read that a KE Jet fuel pressure regulator varies pressure based on vacuum load, does the 16v have this? That certianly is interesting and one to check next. What other vacuum functions may there be?
Fuel filter: Is this likely to cause this problem?
Fuel pressure: Not tested. I personally don't wish to think about rebuilding the distributor/metering unit as I've heard bad things on cost/effort/reliability/feasability. Would rather flog the car (a British term for selling off!). I could be swayed though if I was certain the problem was there, but only after ruling out everything else, I hope you understand why.

I should mention the car sometimes takes 3-5 seconds of cranking to start, hot or cold, but once going idles rock solid apart from a mild Subaru-esque burble to to the idle. I guess it's like a misfire which disappears above idle. This problem has always been present before and after my engine rebuild and it's only my Dad that notices it! Wander why that is.

Two final things:
How does idle mixture adjustment bring the idle down?
Isn't the economy guage supposed to sit against the peg at idle?
Is it worth me getting some spray to check for air leaks, and where do I find/what's it called?
 

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1990 Mercedes Benz 190E 2.5-16
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Interesting thread...And I shall give my opinions...
The symptoms you have are classic 2.5-16 symptoms...
It seems you have gone through the majority of Items...

The basics should be done first...

- Check the HT leads and more importantly the boots at either end.
- Check ALL KE-Jetronic hoses. Especially the two hoses that house the Injectors.
- The rubber boot underneath the AFM

Please DO NOT adjust the EHA valve. You cannot just turn it a quarter here and there. YOU MUST make sure you adjust everything else so its in sync.

Ideally you should have an O2 sensor. No matter if your car is pre 1992. You do not need to have a catalyst to have an O2 sensor.
Your car is already pre wired to accomodate an O2 sensor. The O2 sensor will constantly monitor exhaust gases and adjust enrichment and idle as necessary.

Your idle should be at 1,000...Nothing less than that.

If your EHA valve is leaking, replace it.
What condition is your fuel distributor in?

Your cold/hot start issues are more than likely down to a bad fuel accumulator and/or bad distributor cap/arm.

Lastly i just have a feeling you need to check the Ignition Control Module. This stores the various load maps for the car. Cold start enrichment to wide open throttle operation.
If this module is bad it will manifest exactly what you are experiencing...

Greetings...
 

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2.5-16 (1990) SL500 (2000)
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Of course, my 2.5-16 is automatic and the idle is
750 rpm in park
1000rpm exactly in neutral.

By adjusting the EHA anticlockwise I believe you are reducing the
differential pressue. Perhaps you have a slight leak so by reducing the pressure
the leak is resolved but at high revs you don't get enough fuel through.

The idle mixture control adjusts the resting position of the air flow meter arm
so it could give you more air at lower revs. The other possibility is the air flow
meter is sticky at nearly closed position but ok at higher revs (when it opens wider)

For a long time I had a leak in my fuel distributor and this caused the rubber manifold under the Air Filter/Intake to perish which then caused a vaccuum leak.
Actually the car was going really well at that point but you can't leave fuel leaks dripping through the rubber manifold.
It was only when we repaired the fuel leak we started to get problems.
So, it appears vaccuum leaks are not 100% serious, especially if you perhaps have an over-supply of fuel at idle (my leak)

Have you checked the exhaust gases at idle and various revs? that might give you a more definite idea.

Everybody told me it was the ECU but it wasn't.
We did replace all leads, Distributor cap, injectors, OVP, vaccuum tubing, cleaned ICV and check compressions and valve settings too.

You'll get there.
 

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Discussion Starter #9
Thanks for the post, I thought I wouldn't get a reply due to the slightly negative earlier post. Your thoughts make sense.

Cappadocie - My car is 'EZL' which I thought didn't have an O2 sensor? The wire is there under the driver footwell but connects to nothing. This is how I thought non-cat cars were configured?

PaulE your post makes much sense. One thing I don't understand is which rubber boot was perished - the one between the AFM unit and the throttle butterfly part? I read a thread here of problems solved by replacing that. The thoughts on a possible fuel leak are interesting - if I had a leak of fuel into the engine, reducing the pressure would have improved things, although not sure it should have made it so lean? I have checked exhaust gas at idle and revs while in 'lean mode' it showed slightly rich at idle, but holding it at 2000-2500rpm was clearly lean already, I didn't check other revs though.

One for your thought pipe I don't understand: if my mechanical parts were giving me too much fuelling then the throttle enrichment would make it even worse. Yet disconnecting the EHA to prevent enrichment from occuring just makes the response worse; doesn't affect power noticeably though.

I'm positive I'll get there, eventually!
 

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1990 Mercedes Benz 190E 2.5-16
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For different cars its a different solution.
I'd take it to someone who know's what they are doing...a bit tough in the UK since there is next to no one who knows how to work with and diagnose KE-Jetronic issues...

Good luck...
 

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'85 2.3-16 '99 C280 '11 GLK350
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..a bit tough in the UK since there is next to no one who knows how to work with and diagnose KE-Jetronic issues...
If looking for Jetronic expertise, don't limit oneself to Mercedes dealers or independents. Check for shops that have older Porsche, VW, Audi customers as well. ;)
 

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2.5-16 (1990) SL500 (2000)
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Hi Pentoman,

The rubber manifold was part No. 59 in the digram below.

We noticed it because there was a strong smell of fuel and using a mirror you could see drips when the engine had been run for about 1 minute from cold.
Hard to detect if the engine is warm.
 

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So, from your exhaust analysis it seems that the problem at high revs is you are too lean and the problem and at low revs too rich.

a) Perhaps your fuel pump cannot handle maximum flow.
There are tests you can peform to check fuel flow
Remember, messing around with fuel is dangerous. Follow proper procedure.

b) Perhaps your idle mixture is very rich and reducing the differential pressure
balances it for low revs.
With the EHA back where it was or even a bit more clockwise you would need
to balance with much more lean idle mixture to resolve the mix for low revs
 

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Discussion Starter #14
I looked and the 16v does indeed have a fuel pressure regulator thing, comes off the distributor and has a really short vacuum feed from, oddly, the air pipe going to the idle control valve?? I can't imagine that a lot of vacuum is created in here (?) so don't imagine it does a huge amount. I disconnected the vacuum pipe and went for a drive; made no difference. Could be that mine is bust in which case disconnecting the vacuum would do nothing - anyone tried this before to confirm?
I am keen to chase this one up since it's fuel pressure related and fuel pressure change made such a difference to the car.

When the engine's cooled I'll check for splits/blocks in this and other vacuum pipes.

I also noticed while there that the black rubber pipes on top of the injectors - 2 of them each feeding 2 injectors - have slight splits in them. Not split right through from what I saw, but I want to remove/inspect them as an air leak here would be unmetered.

PaulE I hear you on the poorly fuel pump - will log it up as an option. I have the afternoon off so may go play now, bit low on energy with it as I'm going to China for 2 weeks on Thursday..!
 

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If it is any help, I have checked the economy guage at idle and
- Idle cold in neutral revs 1,000rpm economy about 8-10% of max
- idle warm in neutral revs 1,000rpm economy 0% of max.

This is an automatic so if you put it in Drive but stopped engine warm
- revs 800rpm
- economy 8-10%

The vacuum hoses get really hard and brittle so I found it was easiest to replace absolutely all of them.

Not sure if there are any 16Vs in China ...
 

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Discussion Starter #17
Crumbs that's rather different to my vacuum setup. Looks like an 8 valve motor that one?

Mine has:
front of engine: double pipe fitment, one pipe to throttle body (connector hidden), one pipe to front wing T-piece. That then comes back to the carbon canister too in a thicker black vacuum pipe.

Back of engine: Y-split piece - one goes off to headlamp high adjustment passing by brake booster. Other goes to ignition ECU.

Also very short vacuum lead from idle air control valve to what I believe to be a fuel pressure regulator.

Think that's it!

Just checked it all and doesn't appear split/blocked. Did drive with vacuum pipe disconnected from ignition computer and seemed to make no difference. It does suck your finger if you put it on it!
 
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