'69 250 CE ECU

[L-Vez]

In the process of trying to determine why the injectors on my new CE (thank you Michael Schroter) are pulsing full volume, I feel I have eliminated the temp sensors, the TPS, the MVS and am now left thinking that the ECU must be at fault. The manual suggests substituting for a known good unit. Now where am I going to find that? Is there anyone who can repair or test these ECU's? Buying a scrap yard unit is difficult as these cars weren't sold in NA and then there's the problem of knowing if a used unit is any good. Suggestions?

[JPMOSE]

If you are left with no choice but rebuilding your unit, it is approximately $450 at ProgRama Inc. | 3500 NW Boca Raton Blvd Ste 501 | Boca Raton | FL 33431 | 800-668-8843.

http://www.programainc.com/

They are highly regarded for their work and are often seen on part sites for Cruise Control, Ignition and Climate Control components. I have purchased a spare ECU for my 1970 280SE 3.5, in case some of the electronic components become NLA someday. I have seen used units on Ebay sell for quite a bit more than simply rebuilding you own!

I wish you good luck in your diagnosis....I know how frustrating it gets!

[cth350]

First make sure the trigger points are delivering a signal to the ECU. The brain box modulates that signal into the signal sent to the injectors. -CTH

[L-Vez]

Thanks very much JP. That's the kind of info I was hoping for !
Charles you are right, I do need to make sure that it's the brain at fault. That's the trouble with electronics...making assumptions based on what you CAN"T see. Having inspected the interior of the ECU it strikes me that it's all straight forward components but without a schematic it's not easy to verify anything and I didn't find any burnt resistors or obvious damage.
More sleuthing required.

[JPMOSE]

According to ProGramma...these units can last for decades without any problems. The typical problems are cracked solder joints, internal wiring and corroded connectors. I know they always replace any components that are trouble prone (if any), solder and all internal wiring. Of course the connectors are rejuvenated as well. The cracked solder joints can cause intermittent operational problems.

[cth350]

You can "see" the circuit, you just need a different set of eyes. In this case, a duty cycle meter. -CTH

[L-Vez]

OK Charles, now you've peaked my interest, what's a duty cycle meter and where does one find said meter? Is this an MB service tool that "used" to exist?

[cth350]

duty cycle meter == more general purpose dwell meter.

100% duty cycle is full on. 0% duty cycle is full off.

You can use a dwell meter set to "v8" and map with pencil/paper from 0-45 dwell == 0-100 duty cycle.

I have long forgotten what the "correct" duty cycle reading is, but you should have something between 0 and 100% for each trigger point circuit and all three (I think it's three for a straight 6) circuits should have the same value, give or take a few percent.

-CTH

[L-Vez]

OK I understand. I thought you were referring to a test of the ECU. I haven't tested the trigger points but the previous owner determined that they were pretty close, though maybe slightly worn. He came to the conclusion with help from folks here that it was probably the ECU and my own tests so far seem to verify that. Apart from trying a known good unit there doesn't seem to be a way to determine if the ECU is functioning correctly. I don't have a copy of the appropriate shop manual however and I'm sure that would be helpful.

[bwostosh]

Try this

http://members.cox.net/bostosh0/Fuel%20injection%20troubleshooting.pdf

[L-Vez]

Hi Brian
Thanks for that ! That's a nice little troubleshooting guide, when I can free up some hours I'll try applying it.
The Benz Dr. is going to help me with an ECU loaner ! A temporary heart transplant...we both know what that's about !

[Benz Dr.]

Yeah, I'll see what we can do. My car ran perfectly until the fuel pump quit working. The 250CE is kind of rare and I've only seen three of them in the past 20 years.
The ECU on the 4.5 cars almost nerver fails so I'm wondering why they do on this model. The 2.5 FI engine puts out 170HP so it should pull nicely.