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D-Jet ECU's

Does anyone know the difference between the various 1.7 and 2.0 ECU's? I think there was something close to a half dozen different ones throughout the various years and engine sizes.
Old 02-17-1999, 04:29 AM
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Most of the differences are probably fairly subtle. However, there is one sizeable change that occurred some time in the 1971 model year.

Very early 914-4s cut off all fuel to the injectors on "overrun"--when the throttle was closed and the engine revs were high. The ECU detected this when the throttle switch read "closed" and when the signals from the trigger points were close together in time. All fuel was shut off until the RPMs dropped to a pre-set level. I forget the exact number, but I think it was around 2000 RPM. (Don't have my factory manual with me, sorry.)

In all the later D-jet 914s, the circuitry that performed this function was replaced with circuitry that allowed a mechanic to change the fuel mixture at idle. That is when the knob on top of the ECU was added.

In 1975, some of the pinouts on the ECU connector were changed. (See Haynes 74 D-jet wiring diagrams vs. 75 D-jet wiring diagrams.) This certainly meant at least some minor changes to the ECU.

I don't know what other changes happened through the years.

(Trivia If you look carefully, you will find that the 73 1.7 and the 73 2.0 used the exact same ECU. Same part number and everything.

--DD
Old 02-17-1999, 07:57 AM
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I have a 73-74 (?) 2.0L setup on my car right now. I also have the original 75 setup, but have to repair some wires that were chewed through by mice. Are you saying I must use the 75 wire harness with the 75 brain, I assumed this was so because of the extra connector on the 75 harness. The extra plug, I guess, goes to the air pump or EGR vavle (I have neither one thanks to a PO). I also heard that the 75-76 had a different TPS. Is this true? I've looked through all my manuals and can't find out anything about this 6 pin plug.
Old 02-17-1999, 08:28 AM
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That's correct. You have to use the 75-76 harness with the 75-76 ECU. It may be possible for the car to run OK mixing and matching--not sure of the exact pinouts right now. However, at the very least your cold start valve would not work quite right.

The extra connector is, I am told, for an external rev-limiter that cuts off the fuel. The earlier cars used a rev-limiter built into the distributor rotor that shorted out the spark. The fuel-cutoff one is probably more predictable.

Not all 75-76 cars had this extra feature. But I don't know which ones got them and which didn't.

I have one of these wiring harnesses as a spare. It might be the one with the banged-up connectors and a couple of broken wires, or it might be the one that's OK. (I have two 75-76 ones; one with the connector and one without. One kinda messed-up and one not. Not sure which is which.)

Let me know if you'd like to buy it. Click the envelope icon to e-mail me.

--DD
Old 02-17-1999, 03:18 PM
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Thanks!!!
Old 02-17-1999, 07:48 PM
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I installed a 75-76 2.0 ECU in my '72 1.7 (with original 1.7 harness) the day before I posted the original question. Everything seems to be working fine. The only reason I chose it was becuase I had it laying around and my 1.7 had a hole rusted through it.
Old 03-12-1999, 05:17 AM
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