Full Version: CPU Overhaul
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?
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.
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
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
The Cap'n
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
Tom
QUOTE(76-914 @ Sep 10 2014, 07:09 AM)
Are you sure? Those are pretty much bullet proof in general.
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.
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.
" 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.
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.
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
#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
I seem to remember the ECU could also go bad if subjected to acid from a battery boil over.
I've had the same issue with the fuel pump not turning on.
.....It does happen!(CPU failure)but..........not very often. 
What do you see when you hook up the vacuum gauge? How much manifold vacuum do you have?
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
Good luck
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
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.
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.
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
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.
Hello everybody:
It wasn't the CPU! But a combo of vacuum leak at cold fuel injection and various other places. With the replacement of the fuel injection wiring harness. I rebuilt it. There is a store in El Cajon that has a complete set of elec contacts for the harness. Just save the plastic backshells. There is still a small hesitation in the acceleration. OK I'll order the TPS board from Dave Sprinkle. That should do it for a while. Hope, Hope
Replaced:
Hoses at intake manifold (Auto Atlanta) gasket CFI, gasket at throttle body new. New hoses, gasket at oil filler tower, cleaned and sealed with permatex, the blow by valve. New gaskets at fuel injectors, injectors checked.
Runs good.
Thanks again everybody.
Kpax914
It wasn't the CPU! But a combo of vacuum leak at cold fuel injection and various other places. With the replacement of the fuel injection wiring harness. I rebuilt it. There is a store in El Cajon that has a complete set of elec contacts for the harness. Just save the plastic backshells. There is still a small hesitation in the acceleration. OK I'll order the TPS board from Dave Sprinkle. That should do it for a while. Hope, Hope
Replaced:
Hoses at intake manifold (Auto Atlanta) gasket CFI, gasket at throttle body new. New hoses, gasket at oil filler tower, cleaned and sealed with permatex, the blow by valve. New gaskets at fuel injectors, injectors checked.
Runs good.
Thanks again everybody.
Kpax914
AA, There across the country. West coasters usually use Pelican or GPR for those parts. Check them out. Also add 914rubber.com to your list of suppliers. Good job!
QUOTE(kpax914 @ Nov 11 2014, 10:31 PM)
??
But a combo of vacuum leak at cold, fuel injection and various other places.
??
what is cold fuel injection?
QUOTE(type47 @ Nov 12 2014, 10:03 AM)
QUOTE(kpax914 @ Nov 11 2014, 10:31 PM)
??
But a combo of vacuum leak at cold, fuel injection and various other places.
??
what is cold fuel injection?
cold start injector mounted on the plenum
QUOTE(Racer Chris @ Nov 12 2014, 07:09 AM)
cold start injector mounted on the plenum
OK, cold start valve ... duh
QUOTE(76-914 @ Nov 12 2014, 06:29 AM)
AA, There across the country. West coasters usually use Pelican or GPR for those parts. Check them out. Also add 914rubber.com to your list of suppliers. Good job!
Yes the Cold Start Valve=Cold Start Injector, with a permatexed coated gasket. With Allen head cap screws from Lowes or Home Depot. Almost impossible to reassemble without taking out distributer. Precaution on torquing, not too much! I ordered a rubber fitting for the Deceleration valve ($20) to the intake manifold connection together with all the over parts. It was a disappointment. It doesn't do the job of the original, and I suspected the Decell valve was defective. So I connected the blow-by directly to the intake manifold. removing the Decell Valve from the car. Viola, smoother operation happened! I am going to travel to Hemet, QRS fibre glass,in the near future. To buy one of there front bumpers, perhaps we can meet up for coffee and talk 914?
I couldn't have done it without everybodys help!
Thanks again. Kpax
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