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What is the scope of EHA adjustment??

8K views 18 replies 7 participants last post by  StreekG 
#1 · (Edited)
Hi all,


How sensitive are the adjustments on the EHA compared to the fuel mixture screw?
The story is important to properly explain why i ask.

Even though i've had my car fully tuned and it's running like an absolute champion with the big cams, FrankenCIS and race ignition [EZL Delete]

I've had some starting issues. Originally it was cold starting issues. I remembered that before the car had all the fancy equipment, the only way i could get it to idle with the cams was to adjust the accelerator linkage so it sits far from the stop, The fuel mixture screw was also set incredibly rich.Once i reset the linkage back to factory and used the laptop to adjust the idle control valve, she was cold starting ok.

After this the car didn't like warm starting. I've figured out the problem for this one and it's an easy fix.
After i had fuel control with FrankenCIS i was learning the ropes with software tuning and i did lots of tinkering just so i could learn. I managed to get the car running good enough but i leaned the fuel mixture screw too much and used the laptop to set the fuel requirements for driving situations. Back then i wasn't very knowledgeable on KE-JET compared to what i am now, so i thought all my starting issues were caused by other things like FRP and Accumulator[my whole fuel system is new now]

After i had Dkubus fly out to Melbourne, install his race igntiion and dyno tuned the car and went back home. I forgot that i had the fuel mixture screw infront of the fuel divider quite lean, way out of spec [i've had FrankenCIS installed on my car for well over a year and i was just chasing other culprits of starting problems]. This has lead to my starting issues. The car is fully tuned to this state, so while it runs great, it doesn't like starting

The cold starts are ok because of the Cold start injector spraying fuel. But during warm starts it takes up to 10-15 seconds of starter motor killing to start the car.

Solution:

We found a way to fix my problem without losing the fully tuned state the car is in.

I've marked around the air cleaner 8 points of a circle with green tape, so that i could write on it with a pen. I've also written down a few parameters of the cars running state in drive idle such as it's RPM-AFR-Duty Cycle-MAP/KPA while at operating temperature.
I've gradually turned the screw clockwise to richen the starting fuel mixtures, until the car would start fantastic in warm conditions. Now to bring it all back, i am going to remove the EHA and decrease the pressure on the 2mm allen key inside it until i'm back to the cars tuned running state. This saves us from dyno tuning the car again.
With all my parameters written down, this allows me to easily tune the EHA back to the cars good running state. FrankenCIS is pretty amazing for this.

I've turned the fuel mixture screw almost a full turn richer to make it start normal, is there a way of knowing from you gentlemen, how much would i need to undo the allen key on the EHA to bring it back, is it very sensitive like this??

 
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#2 ·
My reading and experience in discussion with others is that the EHA was not meant to be adjusted, but it certainly can. Removal will cause pressurized gas to force out, cold engine and shop rags and a fire extinguisher. I would go no more than 1/8 turn CW t get first adjustment. IIUC, the adjustment is to compensate for other items in the mix that are wearing or worn to the point of tolerance. SO EHA should be incremental turns only. Trial and error but with all your diagnostic work, you are used to that.
 
#8 ·
Yes i changed the EHA O rings recently due to a minor leak which seemed to fix the problem as it's not leaking anymore. So i know about the spray you get, luckily i was prepared for that.
 
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#3 ·
I did a little tuning with a wideband O2 sensor and the EHA on my SEC several years ago, but unfortunately I didn't write anything down and don't remember the specifics. I was going very lean on the top end initially (I think just over 15:1 - high enough to risk burning up the motor with lots of full throttle driving). I did two or three 1/4 turn adjustments that brought it down to 14:1 or just below; I coulda shoulda gone further, but I was concerned about throwing other things out of whack for the sake of an optimum high RPM mixture.

I'm not sure if Bosch intended the EHA adjustment to be a factory-only adjustment, but even if that's the case, I think there are many cases where it should be adjusted. In the year or so before I did most of the tinkering on the EHA, I'd installed a new EHA, Flowtech rebuilt FD, new FPR, new injectors, and a couple other fuel injection parts, so it hardly seems like a case where the adjustment was compensating for worn-out components. Bosch is fairly reputable, but I've heard of enough issues (plug wires, injectors, filters) with quality that I can say they're hardly an iron standard. It could be replacement EHAs (which most cars have had by now) are coming with sloppy factory settings. Or maybe there's enough variation in FDs and the rest of the system that it's not "one size fits all."

What would be really helpful, and I think what you're asking about, is if someone were to "map out" the effect of adjustments to the EHA set screw. For example, a 1/4 turn of the set screw produces a .x bar change in chamber pressure differential and a y% change in full throttle mixture ratio, lambda set screw was turned z turns to correct on/off ratio. I'm tempted to do such a thing, and I have the tools, but I can't promise anything. Last year the FD went out on my SEL, and after some mixing and matching with parts from my SEC it runs ok, but things are off and the top end is especially weak. So I need to check things over, and if I end up tinkering with the EHA again I'll copy down some numbers. One other thing, given the sensitivity of adjustments to both the EHA and lambda set screw, I think it'd be difficult to come up with an accurate ratio of adjustment between the two - maybe a ballpark figure, but that would give you an initial setting at most. With a factory setup, you need to check and set the on/off ratio; I've read into FrankenCIS and am interesting in buying it, but I don't know what number would be a good equivalent to the on/off ratio.
 
#6 ·
Thanks for the reply. I'm aiming to do the EHA adjustment tomorrow as i've found the sweet starting spot almost on the fuel mixture screw, which would be the factory setting most likely. I'll just do small incremental adjustments and see how i go.
 
#5 · (Edited)
Hi GreenT, my duty cycle is always displayed on the dashboard of my laptop tuning software for FrankenCIS. Before i started richening the mixture i noted down my Duty Cycle, AFR, Idle RPM, MAP/KPA load.

Basically i'm just richening the mixture then leaning out the EHA to get me back to the duty cycle and AFR i have for it's best running state.

You are right though, the engine is modified to the point where factory numbers don't really mean so much. Mike from Dkubus and I have the car running very nicely with the cams, i couldn't ask for it to run any better. But to avoid having to re-tune the whole car, this is my solution. When i get the supercharger, i might replace the EHA with a new one because the car would need a re-tune by then.
 
#7 ·
I bet with the wide band, you will dial in with maybe 1/8-1/4 turn so two times. waiting for the car to hit temp, then waiting for it to cool sufficiently to remove the EHA is the time stealer. Careful of fire mate, use new O rings for the EHA.
 
#9 ·
Tjyak50 was all over this a few years back when he mastered the finer details in setting up the correct upper and lower chamber pressures via the EHA and getting the duty cycle correct in the process with the help of Jono at blueridge
http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1527280-cis-e-diagnostics-cel-3.html

http://www.benzworld.org/forums/w12...-560sec-baseline-dyno-tri-wye-install-12.html

Also remember back a few years ago one of the members installed a set of AMG spec 50:1 replica cams and then went about on a long mission (long thread too) in getting the fuel head and EHA set up correctly - it was a great thread as he documented the process in detail along the journey to finally get the desired result - i can't remember who that was but someone will - it was about 3 or 4 years ago (or longer when the thread started)
 
#10 ·
Ah yes, I remember the first thread, in fact I think that's the one that clued me in to tinker with my EHA. I still think of it a lot like tuning a carburetor: many fine adjustments, you make them on a (hopefully educated) guess and see what it does for you. A dyno and a wideband O2 are definitely helpful, although you can achieve the same results with a wideband. What would be really nice is an EHA that could be adjusted without removal or fuel loss - half the pain of tuning these is having to release the residual pressure and pull the EHA off time and again. Wintertime is a good time to tinker with it at least, less chance of a flash fire. Always have a fire extinguisher on hand though, keep those fire demons away!
 
#14 · (Edited)
You guys are bringing back memories!!! That was me a few years ago fine tuning my Gen II solid lifter conversion. Streek G, I thought that EHA was eliminated with the FrankenCIS? I first adjusted my duty cycle so it read low 40's with a AFR of 14.7 @ idle. I then enriched the EHA so the duty cycle dropped to low 30's @ 2500 RPM. This got me an AFR in the mid 12's at WOT (wide open throttle). This got me the best power set up. I never really solved my idle issue just learned to live with it and it has gotten better over the years. Not sure if the cams finally broke in. My biggest issue was trying to get the RPM's up at idle to generate enough vacuum to be streetable. I finally got there and have been happy the last couple of years. How is your fuel distributor? I had to get a rebuilt one by Flow Tech a couple of years back as well. I would have trouble starting sometimes and it would sputter for few seconds like it was flooded. It cleared after a few seconds. The new fuel distributor solved that problem.

Mike
 
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#15 ·
Thanks Mike for chipping - now i remember it was you as it was a while back and now i recall your not so smooth idle issues after the cams were installed.

The FrankinCIS plugs into the EHA direct by intercepting the factory plug and it then controls the EHA, but as Steve is saying his EHA should have been at factory setting or close before the custom tuning was undertaken- but he forgot to adjust the screw back to where it should have been (before he started playing with the EHA screw) prior to the install of the FrankinCIS kit.
 
#16 ·
Thanks guys.

Kim it's the other way around, my car was tuned on the lean setting with the fuel mixture screw in front of the fuel divider, hence why i'm having so much starting troubles. I've almost fixed it though, I've been slowly finding the right setting for the fuel mixture screw to be at, and then I will lean back the EHA slightly.
 
#17 · (Edited)
Thanks guys.

"I've been slowly finding the right setting for the fuel mixture screw to be at, and then I will lean back the EHA slightly."
Steve,
That is the secret i.e. small increments of fine tuning to get it into it's sweet spot. Somedays your will make progress, other days you will loose it. Mine finally got there. I haven't cracked things open in over 1.5 years. I will soon because it should be time to adjust the lifters.

The key to fine tuning is having a Wideband sensor to due the fine tuning. Just noticed that my video links don't work. Let me see If I can fix them.
 
#18 ·
The FrankenCIS kit contains a modern wideband O2 sensor that has to be plumbed into the down-pipe of the headers and the laptop screen of the software program mapping shows up exactly what is happening in real time when the car is being driven on the road (or on a dyno) and the laptop is being monitored and you can make software adjustments whilst the car is being driven by a 2nd person and you working the laptop sitting in the passengers seat.
The perfect way to fine tune the engine whilst on the road in driving conditions and load on the engine at various RPM
 
#19 ·
Thanks Mike, i think the fuel head is fine, unfortunately getting things like that rebuilt in Australia cost mega dollars, i've done some more richening on the fuel mixture and the car is almost starting right up while warm when usually if left for a couple of hours, it could take 15 seconds of cranking. The problem was as i said, before the car had the ignition upgrade and fully tuned, i did a lot of tinkering myself and i found the car to run OK at this point where i had the fuel mixture set very lean, unaware it could give me starting problems

My car is fitted with everything needed to tune. FrankenCIS is basically a complete setup for fuel tuning so it does include a wideband o2

Just so you guys know, this is my dashboard for my tunerstudio software.


I've had a lengthy discussion with Mike Dkubus about this and we've agreed that to not have to re-tune the whole car, we set the fuel mixtures where they should be via the mixture screw, this is probably also the factory spec that i'm chasing. Then we lean the EHA out to the parameters i have noted down from my laptop when it's running great
 
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