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> CPU Overhaul
kpax914
post Sep 10 2014, 01:20 AM
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I have a 73, 1.7 liter with everything new or checks out OK on the Fuel Injection. One culprit left the CPU. I'm in El Cajon Area of San Diego. Any rebuilders, besides sending to PelicanParts?
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76-914
post Sep 10 2014, 08:09 AM
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Are you sure? Those are pretty much bullet proof in general. I'm in Temecula and will loan you one to confirm. It's off a 2.0 but should work to confirm or negate your supposition. If your not very well versed in 914's you might want to post up what problems your running into.
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boxsterfan
post Sep 10 2014, 09:14 AM
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Have you read this site?

http://members.rennlist.com/pbanders/djetparts.htm
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kpax914
post Oct 5 2014, 08:17 PM
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QUOTE(76-914 @ Sep 10 2014, 07:09 AM) *

Are you sure? Those are pretty much bullet proof in general. I'm in Temecula and will loan you one to confirm. It's off a 2.0 but should work to confirm or negate your supposition. If your not very well versed in 914's you might want to post up what problems your running into.

Thank you for your recommendo.
Yes I consult the site. Really first class and informative. I post because I have exhausted everything else that could be bad except the vacuum pressure sensor.
I might take you up on your offer. Because the local recycling place (Autobahn, in El Cajon) Let me hook up 2 CPUs that they have that are used. They cautioned me however about the similarity in malfuncton of CPUs. They sold one, which was defective and had to send a customer 3 more! Only one was good. Anyway I hooked up the 2 CPUs and same dproblem with the idle as mine. Advance the throttle and problem goes away.
Thankx
Kpax914
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Cap'n Krusty
post Oct 5 2014, 09:41 PM
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That story is a bit suspect. In the 40 plus years I've worked on Bosch D-jetronic systems, I don't think I've seen 3 bad ECUs. That would be out of thousands of cars.

The Cap'n
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Tom
post Oct 6 2014, 12:41 AM
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If it is running poorly at idle and more throttle causes it to run OK, I would seriously doubt that the ECU is the problem. Before I would buy an ECU, I would pull the injection harness and check all of the wires for good reading between the ECU connector and all of the connectors that go to the various components in the fuel injection system. The age of the wiring and the heat can do bad things to the wires' resistance. I had to replace several of the wires in my fuel injection harness, they were black in color and very brittle and read several ohms between several of the connectors to the ECU connector. Replacing the wires with new wires and reconnecting with new electrical terminals solved the problems I was having, ( poor idle and stumbling when giving throttle ).
Tom
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SirAndy
post Oct 6 2014, 01:23 AM
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QUOTE(76-914 @ Sep 10 2014, 07:09 AM) *
Are you sure? Those are pretty much bullet proof in general.

(IMG:style_emoticons/default/agree.gif)
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stugray
post Oct 6 2014, 08:19 AM
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QUOTE(kpax914 @ Oct 5 2014, 08:17 PM) *

Anyway I hooked up the 2 CPUs and same dproblem with the idle as mine. Advance the throttle and problem goes away.
Thankx
Kpax914


You plugged in TWO OTHER ECUs and the problem is still present so you think it is the ECU?

To ME that means that the ECU is NOT the problem, or my troubleshooting logic has taken a turn for the worse.
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pilothyer
post Oct 6 2014, 08:35 AM
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I think you nailed your problem in your post #4 when you stated.....
" I post because I have exhausted everything else that could be bad except the vacuum pressure sensor" The MPC could likely be the problem......test it if you know how, if not first see if it t's diaphragm is working by seeing if it will hold vacuum at the port...this can be as simple as suck on it and cover with your tongue tip the other test is primary and secondary coil check with an ohm meter.
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76-914
post Oct 6 2014, 08:40 AM
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I have a spare MPS also if you want to check that. I won't be back until the 15th but your welcome to drive up and we can see what the problem is. There are others closer to you that may chime in before then.
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Dave_Darling
post Oct 6 2014, 12:17 PM
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I have seen two failure modes so far from the ECU.
#1: The fuel pump switching circuit got flaky, and the pump would sometimes not run.
#2: An output transistor failed, causing the injectors to stay open. Impromptu CIS! And flooding--and a hydro-locked motor, actually.

Both of those were on the same ECU.

--DD
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Johny Blackstain
post Oct 6 2014, 12:20 PM
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I seem to remember the ECU could also go bad if subjected to acid from a battery boil over.
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dknechtly
post Oct 6 2014, 01:02 PM
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I've had the same issue with the fuel pump not turning on.
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Drums66
post Oct 6 2014, 01:15 PM
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.....It does happen!(CPU failure)but..........not very often. (IMG:style_emoticons/default/idea.gif)
(IMG:style_emoticons/default/flag.gif) (IMG:style_emoticons/default/bye1.gif)
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Jacob
post Oct 6 2014, 01:46 PM
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What do you see when you hook up the vacuum gauge? How much manifold vacuum do you have?
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Chris Pincetich
post Oct 6 2014, 04:33 PM
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I just replaced an ECU for my 1972 914 1.7 with D-jet. It wasn't sending the ground signal to the relay board and my fuel pump wouldn't run. Due to parts availability, I had a "022 906 021 B" ECU and now have a "022 906 021 E". Problem solved. Mine was running OK off the bad ECU with the fuel pump ground "jumpered" to a good ground wire. Thanks again to Capt Krusty, Tom, McMark, and bdstone for all their help! It took three weeks of testing almost everything before we concluded to swap the ECU.

Good luck (IMG:style_emoticons/default/beerchug.gif)
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worn
post Oct 6 2014, 08:50 PM
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QUOTE(Chris Pincetich @ Oct 6 2014, 02:33 PM) *

I just replaced an ECU for my 1972 914 1.7 with D-jet. It wasn't sending the ground signal to the relay board and my fuel pump wouldn't run. Due to parts availability, I had a "022 906 021 B" ECU and now have a "022 906 021 E". Problem solved. Mine was running OK off the bad ECU with the fuel pump ground "jumpered" to a good ground wire. Thanks again to Capt Krusty, Tom, McMark, and bdstone for all their help! It took three weeks of testing almost everything before we concluded to swap the ECU.

Good luck (IMG:style_emoticons/default/beerchug.gif)

Were you able to identify the cause of the failure, or in all else send it to Jeff Bowelsby? I am figuring these little gems ought to be saved if possible. They are amazing transistor analogs of the fuel map of the engine. Like a bumblebee shouldn't oughta fy, but they do.
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JamesM
post Oct 6 2014, 10:53 PM
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QUOTE(kpax914 @ Oct 5 2014, 06:17 PM) *

...I have exhausted everything else that could be bad except the vacuum pressure sensor.



Its your pressure sensor then. They are about 1000x more likely to fail then the ecu.

If it starts and runs on all 4, but just runs badly, its most likely not the ECU

Failure of the diaphragm would mean the ECU already sees full load (or close to it depending on how bad it has failed), meaning that at idle/part load it would be super rich but under some throttle it would be closer to running correct.

Not going to guarantee anything though as idle issues can be quite a few different things, but it is unlikely the ECU is bad.
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Chris Pincetich
post Oct 7 2014, 01:49 PM
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QUOTE(JamesM @ Oct 6 2014, 09:53 PM) *

If it starts and runs on all 4, but just runs badly, its most likely not the ECU

(IMG:style_emoticons/default/agree.gif)
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kpax914
post Oct 7 2014, 06:14 PM
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QUOTE(JamesM @ Oct 6 2014, 09:53 PM) *

QUOTE(kpax914 @ Oct 5 2014, 06:17 PM) *

...I have exhausted everything else that could be bad except the vacuum pressure sensor.

Thanks everybody for the advise.
Yes I am going to try all the alternatives to CPU replacement. I didn't know you could check out the pressure sensor so simply!
I am retired and I have to watch my budget. I am restoring this great and underrated car. I love this car except for the engine. I am tempted to convert to an AC electric drivetrain.
thanks again everybody for the help

Kpax914

Its your pressure sensor then. They are about 1000x more likely to fail then the ecu.

If it starts and runs on all 4, but just runs badly, its most likely not the ECU

Failure of the diaphragm would mean the ECU already sees full load (or close to it depending on how bad it has failed), meaning that at idle/part load it would be super rich but under some throttle it would be closer to running correct.

Not going to guarantee anything though as idle issues can be quite a few different things, but it is unlikely the ECU is bad.
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