Carburetor Question

[Mike D]

I had toyed with the thought of just dropping a GM ECU into my wife's 250C with a M115 engine installed. I ran into problems trying to configure a "road speed sensor" or "engine speed sensor". There were a couple of different sensors available but they all involved hanging magnets on the driveshaft and using a pickup for the signal. I was leery of this because of the "floating" driveshaft Mercedes uses. I couldn't figure out a safe place to mount the pickup.

It is definitely workable but I think the Megasquirt ECU is the way to go.

I'm thinking, and this is just MY thinking, you'd have to reflash the EEPROM to compensate for the higher rpms and different air flow characteristics of the inline M110 6 cylinder which is vastly different from the GM V-6.

The Megasquirt doesn't need the RSS, has an on-board MAP sensor and is programmed using a laptop via a serial port (something to keep in mind since most of the newer laptops dont have a serial port). More expensive than the use of a existing GM ECU (yeah, I had to struggle with that also since I had the GM ECU just lying there begging to be used and it was FREE!) but eventually I conceded "ease of use" over "ease of wallet abuse" and went MS.

Keep us informed on the GM ECU conversion because I still think it is viable. It would make for a much cheaper conversion.

Oh yeah, on the M110 automatic, you have to take into consideration the transmission shift point linkage. I doubt you could turn the TBI unit "around" without getting into some really wild linkage adaptations.

So the Holley pump mounted on the fender works fine? Cool, I'm glad to hear that. My concern on mounting the pump that far along in the fuel system was the possiblility of it running dry because the Mercedes tank doesn't have a baffle in it. Did you mount your fuel filter before or after the pump? If the pump works there then that is where I am going to mount mine. There would be no changes to the existing fuel lines required which means nothing to change back to revert to the original. I'm ALL about not making non-reversible modifications!

[Richard Wooldridge]

You might possibly be interested in looking at my conversion web pages for the '82 300D/4.3L V6 - I show how I took care of the vss there - There are vehicle speed sensors that mount inline with the speedometer cable, and that's what I used on the '82, works great, and cost less than $50. I also used a cable on the throttle shaft, which eliminates the problems of mounting location. I notice that on my '75 the transmission shift linkage is connected before the throttle arm, so a person could just leave that portion of the linkage as-is so it wouldn't be affected.

Take a look at:
http://www.freewebs.com/rwooldridge/mercedes.htm

I believe that the vss sensor is only used to control the locking torque converter, and could be eliminated if you are using a different transmission.

I installed the fuel filter before the fuel pump, ie on the input side, so that it didn't have to be an expensive high pressure filter.

[Mike D]

Hmmm, I was under the impression the RSS-VSS-ESS also controlled the behavior of the TBI when the engine goes to idle. I do believe it allows the engine to differentiate between "stationary" idle and when you de-accelerate from say, coming off the interstate on an exit ramp. Just makes a smoother engine speed transition. I've talked to a couple of guys who said their engines would stall or bog (rarely but it would) when they tried to go from full throttle to idle back to throttle.

Here's a couple of pics from some of my efforts.
#1 MS ECU mounted behind the glove box (Box is removed and so is the lower "kick panel). No reason why the GM ECU wouldn't fit in the same spot.


#2 The Holley 41-17 TBI to Rochester Quadrajet conversion kit.


#3 The MB phenolic gasket/adapter sitting on the plate for machining purposes.


#4 The rear mounting holes drilled and an outline of the spacer drawn on the adapter. I can and will probably remove most of the excess metal, yeah, SOMEDAY



p.s., The glove box and lower kick panel/shroud are out simply for the photo.

[Richard Wooldridge]

Thanks a lot for the pictures! It looks like the Holley adapter plate is drilled so the TBI unit could be installed either direction - is that right?

I'll have to check out the wiring diagram of the GM ECM to see what all the vss actually does go to - I printed the diagram off a few years ago and have it somewhere around here.

[gerardoparedes]

is this topic dead, i am interested in seeing how far anyone did go on this issue. Seems like installing a TBI unit a M110 looks like a hot topic but nobody has done this stuff.

[wolf_walker]

Originally Posted by gerardoparedes

is this topic dead, i am interested in seeing how far anyone did go on this issue. Seems like installing a TBI unit a M110 looks like a hot topic but nobody has done this stuff.

It's not totally dead. I'm studying up as we speak.

Looks to me, seeing what the GM guys are doing with the 2.8, that a 4.3L throttle body unit with a 2.8 ECM should be a good way to go. The stock 2.8 t-body is restrictive on a motor that makes 50hp less than the M110 does. An adjustable FPR should be able to tweak it enough to run alright it looks like.

[Mike D]

The M110 TBI conversion is next in line. I'm trying to wrap up my wife's M115 TBI project this week. The M110 is going to be a piece of cake after that!

[gerardoparedes]

I have decided it, i do not wish to fight with the solex a minute more. i Have put and order to Diyautotune for a kit. If anyone have a GM TBI in good working order i intend to pay some $150 for it with all the connectors included.

[gs sparhawk]

Mike, keep us posted on the 110 conversion. I have one waiting as well.

Steve

[wolf_walker]

I still hate my solex. I replaced it with another one that sucks slightly less, but only slightly.
The center section is visibly, to the naked eye, warped on the corners. It's just silly.