Tuning with CIS - PeachParts Mercedes-Benz Forum

pentoman · #1 02-24-2009, 11:35 AM

All,
I'd like to state that I've found some success in changing the running of a 1990 190 16v by fooling the management system to control the EHA as per my wishes.

If you're interested in this then read on.

At its launch the 16v was criticised in the British media of the period of 'lifeless low rev performance' and in the strongest examples I even read something akin to 'the worst throttle response I have ever experienced'. I can only agree. People who have fitted EFi (electronic injection) and done a custom fuel map have reported big improvements.

I wanted therefore to have a rudimentary attempt at seeing what effects the fuel system's componenets have.

Air mass sensor position signal (or the throttle potentiometer)

Well, so K(E) jet CIS Mercedes have real no throttle position sensor. Instead there's a signal for the position of the air flap. When the air flap moves down the ECU knows it should supply more fuel using the EHA. Why, I am not sure because the movement of the air flap itself injects more fuel anyway. I guess this is what they call 'acceleration enrichment'.

I tried disconnecting mine to see what effect it has. This made the throttle response really bad. There was an even bigger delay before pushing the throttle and getting the engine to do work. However if you get jerky acceleration then disconnecting this seems to fix it.

Wide open/closed throttle switch

All it does actually is signal WOT and Idle positions. It makes no difference to the throttle response in all the in-between scenarios (i.e. 99% of driving) so I have ignored it apart from testing that it is working correctly.

Coolant temperature sensor

This important sensor signals engine temperature to the ECU, and the engine will run richer if the engine is cold (and raise its idle rpm). But you can abuse this by faking a signal at this sensor to fool the ECU to run the car richer. This is what I tried. I got the engine nice and warm but fitted a resistor to make it think it's only 60 degrees C. At low revs the car responds really well. At high revs... well... it was really jerky. Really horrible. I am not sure why. All over the place whenever you moved the throttle position. But then I had an idea, I disconnected the air flow sensor position potentiometer. Wow, the jerkiness went away and I was left with a great performing car that had staggeringly much better throttle response low down.

So I am convenced there is some basic tuning that could be done by changing the fuelling to improve the low-down response. However it would be important to understand what other effects doing this would have, just for example of fuel consumption. It's possibly the factory set up sacrifices response for fuel economy (all the Mercedes brochures boast about the economy of the 16v engine). If true then this would mean that there is room to retain the stock Jetronic CIS system but also to change its behaviour to the benefit of response and performance. My vision is of finding an effective way to force the ECU to richen or lean the mixture. Then it is necessary to apply some tuning work so as to translate that ability into the desired improvements. The ideal solution would be a mappable system such as Megasquirt used in conjunction with the stock ECU system to adjust the fuel map as desired. This would allow mapping on a rolling road.

The EHA:

I fitted a spare EHA and changed the hex screw adjustment on it - nothing good could come of it

. Therefore I ruled out EHA adjustment as a sensible tuning method for performance gains.

My car has been returned to standard after this experiment but it has given me food for thought.

JayRash · #2 02-24-2009, 12:40 PM

hey, i have never tried disconnecting the voltage out of the sensor plate, but disconnecting the wot switch does 2 things, first it stops the function of the over run fuel cut which might be why u felt the car respond better.
second, it stops the full throt enrichment.

as for the fooling of the temp sensor, well it will help lots more if u fool the timing box too. thats where the real power is, and its strange that ur car was not smooth on the enrichment for i have driven a 2.5-16 modded that way and the diff was stunning. i could tell cause that car had 2 switches which put it in stock factory mode.

my guess is on a proper tune and no cats you should be at abt 220hp,
as for beter low down feel , if after the fuel enrichment by foolin the temp still not as good as u want, try shorting pins 2 and 3 on the WOT switch u disconnected before. but keep it connected as well this time that way you will still have fuel cut on over run which helps ur MPGs.

hope you try those and tell us what you think.

i wish i have one of those cars, am trying to push a guy here to sell me his EVO2, would be a dream to own that car. the car is super clean but have been told it doesn't have the EVO2 engine, a stock 2.5 in place. still i'll take it and push the price down.

pentoman · #3 02-28-2009, 06:52 AM

The 2.5 is pretty good, just has the torquey to be okay daily, but when you rev it it's great.

I went out to clarify what I'd said here just in case. I couldn't repeat the improvement

. So it looks like it's back to the drawing board.

Why do you say you think there's more improvement possible from the ignition timing? My car has a 7 position switch for the ignition timing.

JayRash · #4 02-28-2009, 07:10 AM

cause when u set it at say the s position or plug out and then do the mod i did it will pull more timing more than u can think. Just keep a notch down from where it pings
Try it man wont take more than an hour of fiddling. I swear it should make alot of difference. Check the other thread where i posted some
Values as a start point.
Hope u try them

pentoman · #5 02-28-2009, 08:52 AM

Hmm I couldn't find them. I do remember seeing the figures once a long time ago (I think) - can you point me to it? Will let me do some research before having to go and take the switch apart to get the values.

JayRash · #6 02-28-2009, 10:00 AM

Quote:

Originally Posted by pentoman

Hmm I couldn't find them. I do remember seeing the figures once a long time ago (I think) - can you point me to it? Will let me do some research before having to go and take the switch apart to get the values.

I meant regarding the fooling of the temp sensor, sorry, here is the post but u can try higher values than those:

there are a few tricks to fool the ecu into some good timing advance and a bit more fuel as well.
IIRC find the engine temp sensor that has 4 wires into it, this one feeds temp input into 2 ecus, the ignition and injection. usually it should have 2 grounds and 2 live wires. the one that feed the injection should terminate at pin 21 in the ecu just do a connectivity test. once located cut it and fit a variable resistor. now the second one terminates in one of the wires going to the ignition ecu located on the left fender. also cut this and reconnect with a variable resistor.

Good values to start with should be abt:

450 ohms for the injection
and 750 ohms for the timing
and then adjust as u like.
let us know how it goes, it should give u a good power increase.
to see the diff just wire 2 switches the would bypass the variable resistors (short them no need to cut the connection to the resistors since electricity takes the shortest least resistant route)

duxthe1 · #7 02-28-2009, 01:56 PM

The biggest problem I see with fooling the ecu's temp signals is that the feedback from the O2 sensor that will cause the ecu to pull that enrichment back out. That's pretty much the reason I put the effort into building my Lambda controller. Modifying the input signals may show small improvemnts but the feedback is constantly trying to undo them. Gain control of the feedback and the world is your oyster.

JayRash · #8 02-28-2009, 02:23 PM

Quote:

Originally Posted by duxthe1

The biggest problem I see with fooling the ecu's temp signals is that the feedback from the O2 sensor that will cause the ecu to pull that enrichment back out. That's pretty much the reason I put the effort into building my Lambda controller. Modifying the input signals may show small improvemnts but the feedback is constantly trying to undo them. Gain control of the feedback and the world is your oyster.

Very true, and thats the reason i had it removed on my 300, but it only does that in closed loop, open loop and full throtle will be running like intended by the fooling.
if u dont care much abt the closed loop running response u can leave the o2 on. i know u have it there to pass the emissions, here in lebanon the test is not that strict for the time being at least.

400Eric · #9 03-01-2009, 01:23 AM

Quote:

Originally Posted by JayRash

I meant regarding the fooling of the temp sensor, sorry, here is the post but u can try higher values than those:

there are a few tricks to fool the ecu into some good timing advance and a bit more fuel as well.
IIRC find the engine temp sensor that has 4 wires into it, this one feeds temp input into 2 ecus, the ignition and injection. usually it should have 2 grounds and 2 live wires. the one that feed the injection should terminate at pin 21 in the ecu just do a connectivity test. once located cut it and fit a variable resistor. now the second one terminates in one of the wires going to the ignition ecu located on the left fender. also cut this and reconnect with a variable resistor.

Good values to start with should be abt:

450 ohms for the injection
and 750 ohms for the timing
and then adjust as u like.
let us know how it goes, it should give u a good power increase.
to see the diff just wire 2 switches the would bypass the variable resistors (short them no need to cut the connection to the resistors since electricity takes the shortest least resistant route)

Great thread everybody. Jay, could you please post that link again? Thanks.

JayRash · #10 03-01-2009, 08:40 AM

Quote:

Originally Posted by 400Eric

Great thread everybody. Jay, could you please post that link again? Thanks.

As soon as i find it my self man, if it is the link to the post where the values for the 7 position switch are listed!!!

anyway here they are as i have them on my phone

just dont ask y

:

7. -No resistor = no retard
1. -1.4Kohm resistor = 2 degree retard
2. -1.3Kohm resistor = 4 degree retard
3. -750 ohm resistor = 6 degree retard (standard in US car)
4(S)-470 ohm resistor = 8 degree retard
5. -220 ohm resistor = 10 degree retard
6(N)-0 ohm resistor = 12 degree retard

Chlippo · #11 03-01-2009, 02:42 PM

PS: everything is on that phone

JayRash · #12 03-01-2009, 02:54 PM

Quote:

Originally Posted by Chlippo

PS: everything is on that phone

Haha ha ha
Well at least this post is thru my phone

lol

RBYCC · #13 03-03-2009, 09:18 AM

Quote:

Originally Posted by pentoman

All,
I'd like to state that I've found some success in changing the running of a 1990 190 16v by fooling the management system to control the EHA as per my wishes.

I've always been curious about this device devopled for VW KE-Jetronic.
Theory sounds workable.
Should be adaptable to the Merc CIS-E

http://www.autotech.com/prod_engine_pwrmod.htm

JayRash · #14 03-03-2009, 10:55 AM

Quote:

Originally Posted by RBYCC

I've always been curious about this device devopled for VW KE-Jetronic.
Theory sounds workable.
Should be adaptable to the Merc CIS-E

http://www.autotech.com/prod_engine_pwrmod.htm

well in theory it should, just need to tap into the correct wiring. but the diff is in the autotech the device reads the plate voltage and thus determines when to activate.

but don't think its doin anything to the timing side of things. more timing will really give good mid range pull.

RBYCC · #15 03-03-2009, 12:13 PM

Quote:

Originally Posted by JayRash

well in theory it should, just need to tap into the correct wiring. but the diff is in the autotech the device reads the plate voltage and thus determines when to activate.

but don't think its doin anything to the timing side of things. more timing will really give good mid range pull.

The only thing the Autotech does is increase fuel delivery at wide open throttle position via the EHA.
It does so without tampering with any stock settings which is important.

I know of no single device that controls timing and fuel as these are in essence two discrete systems on the KE-Jetronic III equipped vehicles.

To modify fuel delivery at a point other then WOT on a stock engine would really not accomplish much.

Pulling more timing advance would give a better low end response.

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