Interchangeable Brains??

[alex9s]

I recently rebuilt a 74 2.0. I couldn't get it to start and replaced the 2.0 brain with a late 72 1.7 brain. The cars runs fine. I read somewhere that they could be swapped. Is this true?? The 2.0 brain had a place where it had been smashed slightly and after opening looks like it MIGHT have broken a circuit. Does anyone know about the Brains???? I would very much appreciate any info.
ALEX

[pbanders]

Originally posted by alex9s:
I recently rebuilt a 74 2.0. I couldn't get it to start and replaced the 2.0 brain with a late 72 1.7 brain. The cars runs fine. I read somewhere that they could be swapped. Is this true?? The 2.0 brain had a place where it had been smashed slightly and after opening looks like it MIGHT have broken a circuit. Does anyone know about the Brains???? I would very much appreciate any info.
ALEX

The ECU's (Electronic Control Units - "Brains") are often more interchangeable that you would normally suspect. I'm surprised the combo you describe works, but if it does, great! If you want to know more about which ECU is the right one for your car, take a look at my D-Jet parts web page at:

http://members.rennlist.com/pbanders/djetparts.htm

The ECU's are at the top of the parts table. I also have a section that describes the exact set of components for a '74 2.0L setup.

Brad Anders

[Dave at Pelican Parts]

The short version is that only the 73s are interchangeable between the 1.7 and 2.0. They had the exact same ECU from the factory. You can swap around many or most of the D-jet ECUs and the car will work, but it is highly probable that the mixture will be wrong under most conditions. If it's only a little wrong, then things are OK.

--DD

------------------
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[Roland Kunz]

Hello

Most brains are interchangable some will run very poor but run.

http://members.rennlist.com/pbanders/ecu.htm

Grüsse

[HarveyH]

Why did I immediately think of Young Frankenstein when I saw the title of this string???

Harvey

[Dave at Pelican Parts]

That's "Frohnken-steen"!



--DD

------------------
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[BKOMAR]

Better than interchangeable Brians....although my wife would probably like that! Brian

[bowlsby]

Dr. Anders-from your excellent ECU page:

"However, measuring the injectors in my car at the ECU socket gives values of R between 2.8 and 3.8 ohms. "

In measuring many original FI harnesses before they are rebuilt, with my $50 DMM, I regularly obtain wiring resistance values...across the harness wires only...of 2-5 ohms per wire on the original harnesses. Should I be concerned about that value, especially in light of injector values of only 2.5 ohms? Wouldn't this value taint the effective ohmage that the ECU sees?

Secondly, do you have a table of the 'differences' between the various 914 D-Jet ECU's, year by year? e.g. I think the only difference between a 73 and 74 ECU, is that the ballast resistor at TS2 is internalized into the 74 ECU, so if I needed to use a 73 ECU on my 74 car, I'd want to be sure to add the ballast resistor.

Thanks as always

Roland, your posts are phenomenal. Thanks for taking an active role and giving us deeper insight.

[pbanders]

Originally posted by bowlsby:
Dr. Anders-from your excellent ECU page:

"However, measuring the injectors in my car at the ECU socket gives values of R between 2.8 and 3.8 ohms. "

In measuring many original FI harnesses before they are rebuilt, with my $50 DMM, I regularly obtain wiring resistance values...across the harness wires only...of 2-5 ohms per wire on the original harnesses. Should I be concerned about that value, especially in light of injector values of only 2.5 ohms? Wouldn't this value taint the effective ohmage that the ECU sees?

Secondly, do you have a table of the 'differences' between the various 914 D-Jet ECU's, year by year? e.g. I think the only difference between a 73 and 74 ECU, is that the ballast resistor at TS2 is internalized into the 74 ECU, so if I needed to use a 73 ECU on my 74 car, I'd want to be sure to add the ballast resistor.

Thanks as always

Roland, your posts are phenomenal. Thanks for taking an active role and giving us deeper insight.

Jeff, I think that values of 2 to 5 ohms are way too high. Most likely, there is some problem with your meter, or else you've come across some really crappy wires! I would expect less than an ohm. I'll measure some of the wires on my harness and report back later.

I'm still working on a a table of ECU differences. Dave Darling is shipping me a couple (or is it just one) that I don't have so that I can compare it. BTW, I think there are a few more differences in the '73 and '74 ECU's that you mention - I'll try to check it out.

And like you, I really like Roland's posts!

Brad Anders

[Roland Kunz]

Hello

Now is my question did you like my short posts or prefer the longer ones ?

Grüsse

[bowlsby]

I enjoy them all.

The longer ones give more detail and are more informative.

Still trying to figure out if you write your messages in German and then translate them on a translator like babelfish.com before posting, or if you enter the posts directly.

Either way, you have a wealth of knowledge of these cars unobtainable elsewhere and we appreciate your involvement.

Grusse


[This message has been edited by bowlsby (edited 07-18-2001).]

[bowlsby]

Please check your harness wiring for internal resistance and lets compare notes. I assume you have a good meter...mine is only about a year old.

The fuel injector wires are only about 3-6 feet long, 18 gage. I was really surprised when I started measuring the resistance of them, related to teh injector winding resistance. Maybe its degradation/oxidation/wire weakening (reduced section) at the wire terminals?

What effect would you guess too high of a resistance might have on the FI system and engine performance?

[pbanders]

Originally posted by bowlsby:
Please check your harness wiring for internal resistance and lets compare notes. I assume you have a good meter...mine is only about a year old.

The fuel injector wires are only about 3-6 feet long, 18 gage. I was really surprised when I started measuring the resistance of them, related to teh injector winding resistance. Maybe its degradation/oxidation/wire weakening (reduced section) at the wire terminals?

What effect would you guess too high of a resistance might have on the FI system and engine performance?

Jeff, if you go to the Belden web site, I think there's a table there that you can use to calculate the expected resistance of a wire, depending on the gauge, stranding, and material. Check it out.

Resistances in the range you describe would have a lot of negative effects. Lower system voltage to the ECU, trigger contact resistance, voltage drops to the injectors, etc. I doubt that 3 to 5 ohms would have any noticible effect on the temperature sensors.

Brad Anders

[bowlsby]

Velly intelesting...

Per the Belden site, an 18 gage stranded copper wire has 6.92 ohms per meter!

http://bwccat.belden.com/Bimages/TechInfo.htm

[Roland Kunz]

Hello

OHH i just think in my low ability english and type it in. If I would work an other way I couldn´t do so much mails.

I testet several translateors but thy are not to usefull as the screw up the sense even more. Right now everyone will see that I have to strugle and talk around things as I miss the correct word. If I use a translation machine it will sound like a oxford language professor talking about engines.

If it goes on that quality my brain will be flushed empty. However as I have a liver necrosis my liftime seems to be very much limitet and this is some way to "clear" the head.

Grüsse

[pbanders]

Jeff, you'll note that was a maximum resistance. I'll check some of my leads in the next couple of days. Who knows, maybe your meter is doing fine!

Brad Anders

[Roland Kunz]

Hello

The used wires are a lower resistance typ but the didn´t withstand oxidation.

Very anoying are the grond contact connectors. Also the cables get hard and brake under vibration.

Most sender have a high resistance reading only the Vacuum unit wires are important.

Higher resistance will rich up the system and can be adoptet by turning the CO screw on 72 on cars.

Grüsse