Won't start. No power to Ecu

Fonzerelli_jnr

Forum User
IMG_20201108_094632.jpg IMG_20201108_094613.jpg IMG_20201108_094646.jpg IMG_20201108_094656.jpg IMG_20201108_094720.jpg Hi All,

I'm looking for some help with a 1979 (registered T plate) 280zx auto.

It has been sat for the best part of 25 years and this is my first bash at a datsun. I'm pretty capable with cars as I am in the garage trade and have experience with restoring an '81 celica and also own a 1950's commer truck, a' 91 supra turbo plus a load of other rusty vehicles too long to mention! Having said that I like everyone else can miss something obvious and also have limited knowledge with this model of car which is obviously quite idiosyncratic to say the least.

At the outset I had no spark and no circuit at the injectors. A new coil, and a good clean up has cured the no spark condition. I now have a spark, if a little weak, and the engine will fire and run on easy start. I do not however have fuel injection. I have a working fuel pump with decent pressure and power at all the injectors but no switching earth from the Ecu. Further investigation reveals that I have no power supply at pin 27 of the Ecu and this is where I require some help from someone more knowledgeable than me.

From the factory wiring diagram pin 27 is fed from one side of the EFI relay, the other side controlling power to the injectors and the relay is in turn fed by a circuit passing through 2 fusible links. My problem in chasing this through is that I'm not sure of the location of the fusible links or the EFI relay. The FSM suggests that the two fusible links for the EFI are under the black cover with the other links and I have seen various photos on forums to support this but both terminals are empty on this car. There are two wires in one connector right by the battery and I'm wondering if this is what I'm looking for. Second to this the EFI relay is shown to be behind the plastic cover in the inner wing on the driver's side. I do have two relays here one of which I think I have identified as the horn and the other doesn't fit as being the EFI relay as the number of terminals is incorrect and also there is no continuity between any of these terminals and pin 27 of the Ecu.

So, could someone please point me towards the correct location of the both the fusible links and the EFI relay? Perhaps someone could post a picture of two of what I'm looking for?

I will attach some photos of what I'm looking at in case that will help. I will also attach a photo of some wires that are on the driver's side of the engine bay that are not connected to anything in the hope that someone may be able to help me with identifying them. They seem to go into the original wiring loom but I have no idea what they are for.

Apologies for the long sprawling post I hope someone can be bothered to read it all.
 
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Huw

Club Member
Hi Pete.

The EFI relay is under a plastic cover behind the battery on the passenger side inner wing.

First picture is the fusable link housing and they are all there as they should be
Second can't quite see what that is for . It maybe the wiring harness for the EFI relay pulled out of the inner wing behind the battery.
Third picture is the horn relay and wiper control unit (under a plastic cover on the drivers inner wing)
Forth picture, those are spare connectors for other ancillaries depending on model (probably US) there are quite a few connectors like that for different model specs. So don't worry about those
Final picture relay (big one) is the fuel pump relay No. 2, there is another (No.1) fuel pump relay under the dash above the fuse panel. Other two relays in the picture are for lights.

Power to the EFI is supplied, once the EFI relay is energised, straight from the battery via the fusible links. The EFI relay is energised once the ignition switch fully turned 'on'.

Forgot to add. The FSM is probably for a US spec car. Things aren't always where the FSM says they are for UK and European spec cars. Just to make life that bit more interesting :)

Hope that helps

Huw
 
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Fonzerelli_jnr

Forum User
Hi Huw,

Thanks for the reply it's been a great help.

I've found the efi relay and that's working just as it should.

I was aware that there would be differences in the wiring diagrams but the more I look at them the more I see differences, particularly the ecu pinout which so far bears little relationship to the car itself.

I'm order to troubleshoot the issue further I could do with having a better idea of the ecu pinout. Is the pinout test sequence in the efi 'bible' more accurate? It would really speed things up if it was.

I am also wondering about another couple of wires. One is the single wire that has its own connector that splits off from the ecu plug connector. Is it an earth or perhaps the shielded signal wire from the coil? The other wire is a thin black and yellow, if I remember correctly, that is nestling by the battery. It does look like it has been connected to something at some point rather than unused. It also looks like part of the original loom rather than a later addition.

As usual, any help gratefully received.
 

Huw

Club Member
Hi Pete

The ECU pin outs are correct in the 1979 FSM (and Haynes) I can copy that section if you need it. I have a copy of the EFI bible and I don’t think the pin outs are correct for a 79.

Wire that splits off the ECU plug is the coil -ve I believe (should be pin 18). The wire by the battery is for the battery electrolyte level sensor. The original battery wasn’t a sealed cell and the sensor screwed in one of the cell top up caps. With modern battery now being sealed the sensor is redundant so has probable been clipped off at some point.

It would be useful to understand what happens when you turn the key. For example does the fuel pump spin up then cut out after a bit? Does the engine turn over but not fire etc?

Most issues to be honest are corroded connectors or bad earths. Probably best first step is to methodically clean all the connectors on the EFI harness and all the body earthing points. If it’s been stood up for a long time corrosion is going to be an issue with the EFI system. Air leaks are another headache.

Let us know how you get on

P.s love to see a piccy of the Celica, another favourite of mine :)

Huw
 
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niroshann

Club Member
With Huw advising, you are in great company Pete! I can’t add anything useful at this stage but will see how you are getting along.

I haven’t seen one of those large fuel pump relays for a while - Reminds me of when I was back at uni. I used to have a 79 280zx and given I loved the car and couldn’t afford an immobilizer, I used to take that relay with me to uni when I had to leave the car parked far away!
 

Fonzerelli_jnr

Forum User
Hi Huw,

Once again thanks for the decent info.

Progress is slow I'm afraid as I'm just so busy at work and it doesn't help that the car is there so I can't fiddle with it later in the evening.

I do have both a Haynes manual and a pdf copy of the FSM but both suggest that the main ecu live is on pin 27 with ecu grounds on pins 19,20 and 22. Unless I'm being an idiot, and that is always possible, I don't have this. Pin 27 has no continuity to the efi relay on any pin and is not live with ignition on. I do have another pin that is live with ignition on from memory it is pin 9 or 10. Am I going mad or just looking at the picture incorrectly? Perhaps I'm misinterpreting the drawing.

To answer what happens when you turn the key. The fuel pump runs and if I pull the hose from the filter it delivers a decent amount of fuel. The engine turns over at a decent speed and the starter isn't lazy. I now have spark and the engine will run on easy start. It would seem that something is preventing the injection system from working. I have a live feed at the injectors with ignition on but nothing changes at crank. With this in mind it seemed to me to be prudent to ensure I had power and grounds at the ecu and to work from there. I did think that I had taken a photo of the ecu harness connector but it would seem that whilst I thought about doing so I didn't actually follow the thought through! I'll grab a photo tomorrow.

Whilst the car has been stood for nearly 25 years it has been in a warm dry garage and it's me who has now had to dump it outside in the rain. I think nearly all the corrosion is from before that time. The engine bay is clean and tidy and when I first lifted the bonnet I found that it had been covered in polythene. The previous owner did care about it for sure but not enough to stop his cats ruining the interior. Despite this I will go through the earth points again.

I will try to dig out some pictures of the celica. It's an '81 1600st with the square headlamps. So not one of the more popular' baby mustang' earlier versions and not, alas (from a value point) , a gt. Despite this and despite the rather woolly steering box set up it still ranks as one of the most enjoyable drives I've ever had. Great fun to thrash with a solid engine that will take any abuse you try to give it. At the moment it is wrapped up under a tarp with no interior and no glass waiting for my friend to finally get around to painting it for me. He keeps putting it off as he won't want to charge me and won't let me give it to him as a paid job. He's brilliant at his job so I'm happy to wait for him even if it takes years, which it has so far. I see it as I've done all the hard work and really I've only got to refit and refresh the interior, decide if I go with or without the vinyl roof, and fit the glass and it's done. Somewhere around are a load of photos documenting the work I've done and I'll try to dig one or two of them out if you are interested.

Thanks again,

Pete.
 

Ped

Club Member
Hi, below is a photo from my 1979 FSM. Have a look and double check it matches yours, I know the Haynes manual is different as it is for US cars. Also if you see any unattached wiring in the loom which has light blue electrical tape on it, it means your car was never fitted with that accessory at the factory, eg air con, electric mirrors etc.

Let me know if you need the full diagram. Hope this helps.

wiring_280zx_1979.jpg
 

niroshann

Club Member
image.jpg image.jpg image.jpg Adding to reference from Ped

last photo should help see if you can trigger injectors to narrow down further

Before you do all this, do you get power to pin 27 of the ecu now? You had mentioned that it wasn’t earlier. Could there be an old aftermarket immobilizer cutting into this line? Your fusible links look good. Is the relay showing continuity when it is triggered outside of the car using 12v on the coil pins?
 
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niroshann

Club Member
41E7E198-1003-4281-A77D-8F2C20E79586.jpeg The location in the manual for the EFI relay doesn’t seem to apply for the RHD cars. I looked at mine during my lunch break and here are the photos - car ran briefly And stopped then didn’t start when I removed the relay. Worked fine when I plugged it in. This was tucked away by the battery (passenger side). Ignore the switch with the rubber boot. That is not factory and is the bonnet switch for my alarm. Also my car is an April 1980.
 
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niroshann

Club Member
Also out of interest the items in your photo are the same as in my car (taken on the brake master cylinder side). Looks like horn relay and wiper motor controller to me that sit behind that plastic cover.60D33346-AE01-4456-A951-D7CBA90E23BE.jpegCF14DA27-361C-48FA-8369-A7DF3EC103FC.jpeg
 

Huw

Club Member
Hi Pete

I gave you some duff info, apologies I was looking at the wrong FSM I got a US and UK. Pin 27 is to the air flow meter so no volts on that. ECU power from EFI relay is pin 10.

8CC5AF60-3762-4861-B01C-839B107EFEB2.jpeg

Pretty much the same as the image from Ped. Other things to check that will stop it starting is the cold start injector ( just after the throttle body.) easy to check just remove it from the inlet manifold, leave the fuel pipe connected and put 12v across it. Make sure it’s in a jar or pointed away from you as it should squirt petrol. Check the injectors are clicking, listen with a screwdriver on the injector body or connect a 12v build across the connector. Water temp sensors, check continuity. Lastly the ignition module on the dizzy can go bad.
 

Fonzerelli_jnr

Forum User
Hi All,

Firstly, I'm overwhelmed by the response. In all my years of posting on forums this one has to be the most helpful and genuine I have ever experienced. It's so refreshing to find a community so welcoming and non-judgemental.

I have only managed a small amount of time on the datsun but I'll share what I've done/discovered.


I found a online a scan of a page that listed ecu connector pin changes on a '79 and showed these against the pins from '75-'78. My pinout seem to match the '75-'78 and this matches the wiring diagrams posted by both Ped and Huw. Thanks both for posting those, they will be a great help.

I have:

Pin 1 continuity to coil negative terminal.
Pin 10 12v power supply
Pin 18 continuity to power supply terminal on throttle position switch.

Furthermore, the ecu has a power and ground circuit as with ignition on there is a power supply from the ecu to the throttle position sensor therefore I assume that the ecu is not completely dead.

I have spark, fuel pumping out in what I believe to be sufficient quantity (I removed pipe before the fuel filter to check this) and the engine will fire on easy start. I have power at injectors with key on but with a test light connected to injector no 6 loom plug I have no circuit on crank. As I have continuity between ecu pin 1 and the negative coil terminal (I know that I haven't load tested the wire but I think it unlikely that its hanging on by a strand as the loom appears OK) and I have spark I am assuming that the ecu is receiving the timing signal. If this were true would the injector circuits not be operating or is it that on cold start the injectors do not operate and its only the cold start valve that operates until the engine is actually running?

Perhaps there is another condition on this system that I have missed that prevents the operation of the injectors? I seem to remember that on the mk 2 golf and also the 16v corrado (I know that they used a k-jetronic rather than a l-jetronic) a bad temp sensor or cold start valve would prevent starting and we used to disconnect or short the pins on one or the other to get them going. I must admit that it's all so long ago that I'm not totally sure what we used to do!

This is as far as I have got for the moment. My next step is to try grounding the coil wire repeatedly and see if I can detect the injectors operating.

I hope that some if this makes sense to you all and if and if anyone has any thoughts please let me know.

On another note, the recent somewhat inclement weather has led me to believe that the windscreen is leaking like a sieve. Or more likely that the frame is pretty rotten all round. The recent driving rain has left me with water dripping off of the interior mirror, water all over the dash and a passenger footwell that is only missing a few ducks. Huw did warn me in a previous post about the windscreen frame area being a problem and it would seem these fears have been thoroughly realised. I must admit that the longevity of this car is becoming a worry to me but despite this I need to get the car running as only then can I get it up in the air and really see what I'm into.

Cheers,

Pete.

Meant to add that I will be pulling the cold start injector to test that too as I was advised to by Huw. I will also check the temp sensor.
 
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Ped

Club Member
Hang in there, I guess you will just need to go through it methodically.
 
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