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NicholasKoenig

Front injector bank not firing (1976 280Z)

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Recently bought a Z and am sorting out the issues. 

It runs albeit on the 3 rear cyclinders. New fuel pump, new NGK wires and plugs, distributor looks like it was replaced not long ago. Coil looks original (new MSD blaster in the mail). 

I know it's getting fuel, spark and air. I know all 6 injectors are functional. Just not all at the same time. 

When I crank it, it starts almost instantly, when I place my screw driver to each injector, only the rear bank makes the clicking. Removing any of the front 3 injector pig tails doesn't affect idle. 

When i place the rear 3 injector connections on the front 3, once again it starts and idles the same. 

Is this a fault in the first bank wiring harness? A dropping resistor issue, faulty ECU? 

Currently I only have the FSM available on my phone and I'm diving through it but I feel overwhelmed. 

I checked the pins with a multimeter and each injector is getting current. Did I miss something simple? 

 

Thank you for reading. Hope to hear from you guys soon. 

 

PS, I bought all new injector connections, but that doesn't seem to be the issue despite them being worn. Haven't installed yet. 

Edited by NicholasKoenig

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21 minutes ago, NicholasKoenig said:

 

 

When i place the rear 3 injector connections on the front 3, once again it starts and idles the same. 

Is this a fault in the first bank wiring harness? A dropping resistor issue, faulty ECU? 

You were almost to a good conclusion.  When you put the 3 rear connections on the 3 fronts, did the 3 front cylinders start working instead of the back 3?  Or did the same cylinders work, just with different connections?  If the cylinders that work follow the connections, then it's a connection problem.  If they don't, it's a spark or mechanical problem.

These engines will start and run with the firing order of the plug wires backward.  They sound like they're running on 3 cylinders when you do that (by accident, of course).

Finally, history of the engine helps.  Did it ever run right, as far as you know?

Edit - sorry for the ad.  It came with the edit box.

 

Edited by Zed Head

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46 minutes ago, Zed Head said:

You were almost to a good conclusion.  When you put the 3 rear connections on the 3 fronts, did the 3 front cylinders start working instead of the back 3?  Or did the same cylinders work, just with different connections?  If the cylinders that work follow the connections, then it's a connection problem.  If they don't, it's a spark or mechanical problem.

These engines will start and run with the firing order of the plug wires backward.  They sound like they're running on 3 cylinders when you do that (by accident, of course).

Finally, history of the engine helps.  Did it ever run right, as far as you know?

Edit - sorry for the ad.  It came with the edit box.

 

The previous owner said it "ran 2-3 months ago" from the time I bought it. To my knowledge his son was wrenching on it and his work seemed lack luster but it appears as though he didn't alter any of the presumed electrical issues im experiencing rn. 

I reversed the bank connections. Placing the rear bank (the functioning one) onto the front and the front onto the rear. 

The front injectors began clicking and rear were silent. To me this rules it electrical but to what extent? Is it a wiring issue or something like the dropping resistor or ecu? 

Another thing I noticed, the part of the EFI harness that is in the engine bay looks untouched. But under the dash you can see electrical tape around the harness (didn't look that fresh but def not stock). That led me to the fuel / afm relays. The stock wires plugged into a Bosh black box that looked modern ( I doubt Japan used Bosch in the 70s?). Is this a clue? 

It seems like the harness is the issue but I don't want to mess with anything I don't need to. I'm learning along the way and any advice helps. 

Thank you for the quick reply. 

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You can check for power at the injectors with the key On, with a meter or test light.  I think that power is supplied in a set of two and four.  But it's grounded through the ECU in sets of three.  So you might have an issue with the ECU.

If you have a meter, going through the tests in the EFI Guide is the way yo do things.  It's what's happening at the eCU that really matters and most of the tests start there.

The 1980 EFI guide (in the Downloads section) covers all years up to 1981.  Use that one.

 

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12 minutes ago, Zed Head said:

You can check for power at the injectors with the key On, with a meter or test light.  I think that power is supplied in a set of two and four.  But it's grounded through the ECU in sets of three.  So you might have an issue with the ECU.

If you have a meter, going through the tests in the EFI Guide is the way yo do things.  It's what's happening at the eCU that really matters and most of the tests start there.

The 1980 EFI guide (in the Downloads section) covers all years up to 1981.  Use that one.

 

Ok I'll go through the ECU pins again tomorrow after work. I only get about an hours worth of tinkering each day max so process is slow going. 

Yes, looking through the FSM wiring diagrams I have saved, it looks like the the first four injectors connected to one dropping resistor and the remaining 2 are on the other resistor. From this I think it's safe to assume my dropping resistor is functional. Otherwise, only four or two cyclinders would fire by My logic and understanding of the diagram. 

And since it gets fuel, spark, and air with working injectors, the only thing left is faulty harness (the first 3 injector wires) or ecu? 

Going to look over your attachment now. Ill let you know how I do with the multimeter tomorrow! 

 

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Turns out I have a similar attachment to yours. Instead mine is soley for the 1976 EFI trouble shooting instead of the broader range of yours. 

But looking through it helped me find the name of the black Bosch part i was questioning. It's the fuel injection relay. (Photo attached)

Perhaps this Bosch replacement is faulty. Which leads me back to the harness that was retapped under the dash. Maybe that's hiding some shoddy soldering work or other gremlins. 

 

IMG_3816.PNG

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That looks like the replacement relay for the original JECS relay.  Which is actually based on the Bosch system.  It's actually two relays in one, EFI and fuel pump.

Despite all of the pins it's a fairly simple relay.  If you get the readings that you should at the ECU connector, don't worry about it.  Many people "assume" and replace, it's hard to resist. 

If you get tricky, you can ground the injectors individually at the ECU connector, just like it would, to test the complete circuit of wires, power and injectors.  I made some male pins to use in the connector from a flattened piece of solid core copper wire.  Makes it easy to get an alligator clip connected to supply power and ground.

Forgot to say - there's a procedure for testing the EFI relay, if you get odd numbers.  In the FSM, Engine Fuel chapter, and probably in that EFI book too.

Edited by Zed Head

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I'm thinking ECU. The ECU has two big output transistors that fire the injectors in banks of three, and if one of those transistors burns open, you will lose those three injectors.

There aren't a lot of other things that could cause you to drop three injectors like that at the same time. As you already noticed, the dropping resistor does four and two so that's probably not it. And while it is  possible that the wiring to the front three of the injectors is screwed up inside the harness, I consider it unlikely. Why? Because each injector gets it's own independent wire from the ECU to the injector. So sure... It's possible that a PO cut three of those wires, but I consider it more likely that the ECU is the root cause.

I'm in the Philly area if you get stuck. I'm no FI expert, but I know some stuff. PM me if you need a hand.

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Hey guys, thanks for the replies. I just got done using my dmm on the ECU pins. Injectors plugged in, key on; all six injectors read 11.92V!!! 

Does this rule out my harness and point to the ECU? 

 

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If you got 11.9 on all six injector pins at the ECU with the ECU disconnected, then yes... It points away from a harness issue and towards the ECU.

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41 minutes ago, Captain Obvious said:

If you got 11.9 on all six injector pins at the ECU with the ECU disconnected, then yes... It points away from a harness issue and towards the ECU.

Gotcha. This is a relief because I am likely close to the solution instead of scratching my head at this. 

Id rather not buy an ECU from eBay, they are cheap but probably risky. I saw this one available, once the core charge is accounted for it seems like a good deal ($124).

Any vendors you guys recommend for an ECU? 

IMG_3822.PNG

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I would put an add in the classified section of this forum, never know what you might find. I had one that got another member out of a jamb. You might be as lucky.

I like MSA but sometimes their prices are.......

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Just for fun, you might take the ECU cover off and make sure the transistor wires are intact, and/or not shorted.  The ECU location can get moist if a leak develops at the windshield.

I actually have some part numbers for a replacement transistor and did replace both on a bad ECU.  But probably for the wrong reasons, they tested okay afterward.  It was probably something else.  Your situation though, with three dead injectors, looks like maybe a single transistor or its wiring.  

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29 minutes ago, Zed Head said:

Just for fun, you might take the ECU cover off and make sure the transistor wires are intact, and/or not shorted.  The ECU location can get moist if a leak develops at the windshield.

I actually have some part numbers for a replacement transistor and did replace both on a bad ECU.  But probably for the wrong reasons, they tested okay afterward.  It was probably something else.  Your situation though, with three dead injectors, looks like maybe a single transistor or its wiring.  

It's worth a shot, although I wouldn't really not what to look for. Burned connections, corrosion? I'll take it out tomorrow.

Could you send the part #? May be a better alternative in my situation as you mentioned. 

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53 minutes ago, rcb280z said:

I would put an add in the classified section of this forum, never know what you might find. I had one that got another member out of a jamb. You might be as lucky.

I like MSA but sometimes their prices are.......

Although I'm new to Zs, I've already done some shopping around for parts and what not. I too noticed their prices are jacked. 

That considered, once you deduct the 200$ core charge, the re manufacturered ECU comes to $125. And that is cheaper than other remans I've found which seem to go for 200-250. 

Thanks for the classified tip! 

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13 minutes ago, NicholasKoenig said:

It's worth a shot, although I wouldn't really not what to look for. Burned connections, corrosion? I'll take it out tomorrow.

Could you send the part #? May be a better alternative in my situation as you mentioned. 

I'll dig up the number.  The connections from the transistor pins to the board are fairly fragile looking metal ribbons.  Very easy to see, the two transistors are on the top edge of the assembly.  ~Quarter-size.  I could see one of the ribbons getting damaged if somebody poked around in there.  You never know.  

Besides that, you'll want the part number for the ECU.  There are several.

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1 hour ago, Zed Head said:

Post #37 here has the part # for the transistor - http://www.classiczcars.com/topic/56143-super-rich-plugs-fouled/?page=2

You can also read our past ramblings, insights, and conclusions about ECU problems.  Might be entertaining.

 

Thanks I went through the thread. 

Part # for the transistor is "NTE247", for the convenience of any readers out there with a similar situation as myself. 

Now I know what it looks like, I'm actually exited to take out the ECU tomorrow and see what is going on in there. 

Attachted picture for reference. 

IMG_3824.PNG

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That is a good price actually for the ecu from MSA if you end up going that direction. I seem to always forget about the core charge.

Hopefully you find its a simple repair and don't have to buy a ecu. I on the other hand am ignorant when it comes to electronics. But it does sound kinda exciting to open one up just to look inside, hmm....

Looking forward to see what you find. Good luck.

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Hey Nicholas,

Welcome---glad you are here!

A good friend of mine, and fellow www.classiczcars.com member, S30driver (Jim Smirlies---one of the many Jims) contacted me about your problem.

I may have a good ECU at the NWA south garage in storage.

Jim has offered to do a test of the ECU on his 280z to ensure that it is functional.

If your exploratory surgery of your ECU and the pending transistor transplant doesn't pan out, give me a shout and we'll try to get you going.

Just post up the number from the case of the faulty ECU so we can check it against the one's we have in storage.

Edited by Zup

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27 minutes ago, Zup said:

Hey Nicholas,

Welcome---glad you are here!

A good friend of mine, and fellow www.classiczcars.com member, S30driver (Jim Smirlies---one of the many Jims) contacted me about your problem.

I may have a good ECU at the NWA south garage in storage.

Jim has offered to do a test of the ECU on his 280z to ensure that it is functional.

If your exploratory surgery of your ECU and the pending transistor transplant doesn't pan out give me a shout and we'll try to get you going.

Hey, thanks for the outreach. 

I will keep that in mind as I'm definitely heavily considering getting another ECU anyway. 

Not selling myself short but I have some reservations on my ability to fix the ECU and have it remain fixed haha. 

Edit: I'll be able to take the ECU # down tomorrow for sure 

Edited by NicholasKoenig

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30 minutes ago, rcb280z said:

That is a good price actually for the ecu from MSA if you end up going that direction. I seem to always forget about the core charge.

Hopefully you find its a simple repair and don't have to buy a ecu. I on the other hand am ignorant when it comes to electronics. But it does sound kinda exciting to open one up just to look inside, hmm....

Looking forward to see what you find. Good luck.

Thank you. I predict I'll pop the cap off. Wiggle some stuff and stare at it for a few minutes. Pack it all together and see if it starts again! 

Im on the cusp of getting all 6 cylinders to fire, I can feel it. Can't wait to hear what it sounds like when all of them actually fire.

Nearly had the Z one month! 

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I would try to source a replacement ECU before I would try a component level repair on the old one. Those kinds of repairs sometimes spiral into unexpected complications and I wouldn't try it unless you had verified the failure first and had a backup plan in place.

I've got a spare ECU (from a 77) if you just wanted to try one to see if it fired all six injectors. I was told that it gets squirrelly on hot days after it heats up, and I have verified that it tests fine on the bench when cool. Would work at least to confirm that your ECU is the problem.

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6 hours ago, Captain Obvious said:

I would try to source a replacement ECU before I would try a component level repair on the old one. Those kinds of repairs sometimes spiral into unexpected complications and I wouldn't try it unless you had verified the failure first and had a backup plan in place.

I've got a spare ECU (from a 77) if you just wanted to try one to see if it fired all six injectors. I was told that it gets squirrelly on hot days after it heats up, and I have verified that it tests fine on the bench when cool. Would work at least to confirm that your ECU is the problem.

Awesome. I'm in NE Philly myself. 

Took the ECU out to get some photos and take a peak. I don't know what I was expecting but I popped it off and instantly realized I have no idea wth I'm looking at haha. 

Nothing seemed loose or disconnected. Maybe some dirty stuff that built up by nothing stuck out. The transistor connections looked ok but they still may be at fault for all I know. 

ECU Part # K11-600 000

IMG_3825.JPG

IMG_3827.JPG

IMG_3828.JPG

IMG_3829.JPG

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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.

 

transistors.PNG

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