Front injector bank not firing (1976 280Z)

[Zed Head]

The 11 600-000 number looks right.  You have what might be a second source ECU, or a replacement, from Bosch, with a "K" instead of an "A".

You got a picture of the bottom of the transistors.  They're above the picture I cut out of yours. You can see the ribbons.  The screw heads are of the screws holding the transistors.

Here's a copy of the ECU guide, showing the Nissan "A" numbers.

 

[NicholasKoenig]

18 minutes ago, Zed Head said:

The 11 600-000 number looks right.  You have what might be a second source ECU, or a replacement, from Bosch, with a "K" instead of an "A".

You got a picture of the bottom of the transistors.  They're above the picture I cut out of yours. You can see the ribbons.  The screw heads are of the screws holding the transistors.

Here's a copy of the ECU guide, showing the Nissan "A" numbers.

 

I had a suspicion it was a replacement because when I took off the metal box shell, there was already one screw missing, one that secured the green electrical plate down. 

The K11-600 000 sticker is on the outside of the box and another exact one on the inner workings of the ECU. 

The connections on the transistors looked together, they didn't seem broken after my once over look. I put it all back together and started up the Z. Unfortunately the symptoms remained exactly the same. It started right up though! I put my ear to the injectors and confirmed again that only the rear bank is working. 

This brings me to another question. If this ECU was replaced, am I just unlucky or is there something else that has caused at least two ECUs to fail? 

[Zed Head]

Did they fail in the same way?  

CO knows his stuff.  I'd take him up on his loaner offer.  Maybe he'll swap that transistor for you just to see what happens .

I'm not sure but I think that the transistors should have a direct connection to the injectors.  You should be able to take a meter and see voltage on the "C" leg, I believe.  It should be hot when the injectors are, and the "E" leg should be connected to ground.  "B" is the activater, controlled by the timing circuitry.  (Give me a grade CO...).  So you can check C and E by plugging in the ECU and turning on the key.  Be careful with the meter probes.

Edited November 17, 2016 by Zed Head

[NicholasKoenig]

37 minutes ago, Zed Head said:

Did they fail in the same way?  

CO knows his stuff.  I'd take him up on his loaner offer.  Maybe he'll swap that transistor for you just to see what happens .

I'm not sure but I think that the transistors should have a direct connection to the injectors.  You should be able to take a meter and see voltage on the "C" leg, I believe.  It should be hot when the injectors are, and the "E" leg should be connected to ground.  "B" is the activater, controlled by the timing circuitry.  (Give me a grade CO...).  So you can check C and E by plugging in the ECU and turning on the key.  Be careful with the meter probes.

After reading this I couldn't wait. Opened the Z back up with flash light in hand. 

I used my dmm on the E and C legs of each transistor, key on. They both read 12.15V! Now I'm confused, I thought for sure this was the issue. 

 

[Zed Head]

Actually, the C voltage fits what you saw at the ECU connector.  The E voltage might be through one of those resistors CO mentioned in that other thread.  You can see full voltage if very little current is flowing.  Did you check for continuity to ground on the E pin?  You can do that with the key off.

Anyway, the reality is it doesn't work.  The very last thing that Nissan says after all of the other tests fail is "replace ECU".  Try a loaner first, then you'll know if you should buy.

[NicholasKoenig]

8 minutes ago, Zed Head said:

Actually, the C voltage fits what you saw at the ECU connector.  The E voltage might be through one of those resistors CO mentioned in that other thread.  You can see full voltage if very little current is flowing.  Did you check for continuity to ground on the E pin?  You can do that with the key off.

Anyway, the reality is it doesn't work.  The very last thing that Nissan says after all of the other tests fail is "replace ECU".  Try a loaner first, then you'll know if you should buy.

I didn't check for continuity, does that mean, red probe on E and back to vehicle ground? What would the results be? Still learning these terms as I make my way through electronics. 

Ok, thanks for the reassurance. Hopefully CO and I can plan something soon and try his loaner. 

[Captain Obvious]

Hi marks Zed.

The "B" leg is the actuator signal
The "C" leg is connected to the injectors. Three injectors connected to each C.
The "E" leg should be tied hard to ground.

The voltage readings you got with the same voltage on both the C and E legs doesn't make sense, but I suspect it's a measurement method issue. Or maybe there's an intermittent ground issue. I don't remember the details of the ground scheme, but depending on how they actually did it, you might be able to drop three injectors with a carefully placed ground fault. I'll dig into that a little more when I get a chance.

Just be very careful poking around in there with power on. One slip and you can let the smoke out. 

Nicholas, I'm about a half hour from you in the burbs. Send me a PM and we'll chat.

[Captain Obvious]

Took a look at the prospect of a ground fault taking out three injectors. It is possible, but very unlikely. And the fault would have to be inside the ECU itself, not a harness issue.

[NicholasKoenig]

27 minutes ago, Captain Obvious said:

Hi marks Zed.

The "B" leg is the actuator signal
The "C" leg is connected to the injectors. Three injectors connected to each C.
The "E" leg should be tied hard to ground.

The voltage readings you got with the same voltage on both the C and E legs doesn't make sense, but I suspect it's a measurement method issue. Or maybe there's an intermittent ground issue. I don't remember the details of the ground scheme, but depending on how they actually did it, you might be able to drop three injectors with a carefully placed ground fault. I'll dig into that a little more when I get a chance.

Just be very careful poking around in there with power on. One slip and you can let the smoke out. 

Nicholas, I'm about a half hour from you in the burbs. Send me a PM and we'll chat.

Not sure if I did anything wrong, I'll explain my method. I placed the one probe on C and one on E and got 12.15V, both transistors read the same. 

Ok, I'll send you a PM now! 

[Zed Head]

I probably planted the wrong seed in your brain when I said C and E.  You want to check voltage on C, and continuity to ground on E.  Which you did, directly, and in one step with your method..  The voltage was on C and the path to ground was on E.  So those numbers look right.  But they don't tell you about the "B" circuit.  You're at the point where you'll probably find that a replacement ECU will get you running.  Then you'll have to decide if you want to try to fix the ECU.

Yours is the first 3 injector problem I've seen.  It implies that one of those transistor "B" traces is bad.  It seems like the "B" timing circuit should be common to both, otherwise there would be two complete sets of timing circuits, which seems overkill and redundant.  So, tracing the two transistor "B" circuits back should find a break, I'd think.  My inner engineer is curious.  Don't throw the ECU away if you get a good one.

[Captain Obvious]

Yup. Measurement technique error. Measuring 12V between C and E makes perfect sense. I was figuring it was something like that.

Zed, Both transistors bases are driven from the same source and I highly doubt there is a problem with that base drive circuitry. My guess is that the output transistor went belly up open circuit.

[NicholasKoenig]

Thanks to the generosity of CO, we got the Z running on all six cylinders today. Swapping in his loaner ECU seemed to have solved the issue. 

As a secondary perk, I got to see his 280 and it's a beaut!!