1975 280z Electrical Issue

[Zed Head]

1 hour ago, Barefootdan said:

Injectors are in and working I believe. Still no start... I checked for spark again and do see it. 

Don't overlook weak spark.  1975 was the second year of electronic ignition.  Not the strong spark of later years, just electronified points level spark.  Make sure your plugs are gapped for it, around 0.029" I think.

[Barefootdan]

14 minutes ago, Zed Head said:

The other "extra fuel" thing is the cold start valve.  Somebody just had that problem.  Your resistance looks about right, chart below.  You can disconnect the fuel hose and plug it for a test.  It will have full fuel pressure behind it so be careful.

Something for the back of your mind - the ECU's often go super rich before they fail completely.

Too bad, no quick fixes for you.  Looks like you're on the marathon route.

Thanks, I'll check the cold start valve. I imagine this is probably shot too since all 6 of my original injectors were bad. But it doesnt hurt to rule it out! Im new to the classic cars, is there another way to verify running rich? Or is the fouled spark plugs a surefire answer? Just want to make sure I am not leading us down a wrong path! I like the testing layouts of the EFI manual, it helps me keep focused and methodical. 

[Zed Head]

Checking plugs and exhaust is the best way to see a rich condition.

Here's another thing I learned years ago.  The cylinders can lose their seal if they have surface rust and have dried out over the years.  You can squirt a big shot of motor oil in through each spark plug hole so that it runs down around the rings to give you a temporary seal.  A friend and I spent a day and half trying to get a 63 Bonneville started until an old farmer on a tractor came by and said "squirt some oil in the cylinders".  It fired right up after we did that.  It was a carbed engine but the same might apply here. Use one of those flexible nozzles or a piece of hose to get the oil up to the top of the cylinder so it runs down around the rings.

If I were in your situation, I'd pull the plugs, recheck gap, squirt some oil in and let the gasoline dry out for a little while.  Then squirt some starting fluid in each hole, put the plugs back in and give it a crank.

[S30Driver]

If you have a timing light, go down from 1 thru 6 on all cylinders one at a time and crank to verify that each plug is getting spark.  If they all do, it should run for 3 or 4 seconds just on the starter fluid, unless the timing is way way off.

[Barefootdan]

Well I have some good news and some bad news. Good news, perhaps I dont have anymore fuel/electrical problems (thanks @Zed Head for the help!). Bad news...

 

While I was waiting for the cylinders to dry out, I decided to run a compression test. I think you know where this is headed (pun intended).

In order, 90 PSI, 90 PSI, 0 PSI, 90 PSI, 70 PSI, 90 PSI.

The low overall pressure doesnt bother be since its been probably 28 years since it last was registered and the rings are probably dry as can be and the added fuel didnt help. But the dreaded 3rd cylinder is a dead...flat...zero.

I'll start by pulling the head...wish me luck! I may just need to start a build thread 🤔

[S30Driver]

Before pulling the head, remove the valve cover and take a close look at cylinder 3's valve train.  A lash pad or another important item may have come off.  I all appears normal, maybe have a assistant crank it and see if both intake and exhaust valves appear to be opening and closing normally.

Hopefully, you just have a inoperative valve on that cylinder or a stuck one.   The other option is a badly burnt exhaust valve causing no cylinder pressure. 

best of luck....

[Zed Head]

It should still start and run even with a dead cylinder.  

[Patcon]

I agree check the valve train first. Make sure all the valves have some lash

[Barefootdan]

13 hours ago, Zed Head said:

It should still start and run even with a dead cylinder.  

Should I continue to try to get it started in your opinion?

15 hours ago, S30Driver said:

Before pulling the head, remove the valve cover and take a close look at cylinder 3's valve train.  A lash pad or another important item may have come off.  I all appears normal, maybe have a assistant crank it and see if both intake and exhaust valves appear to be opening and closing normally.

Hopefully, you just have a inoperative valve on that cylinder or a stuck one.   The other option is a badly burnt exhaust valve causing no cylinder pressure. 

best of luck....

5 hours ago, Patcon said:

I agree check the valve train first. Make sure all the valves have some lash

Good idea. I ran out there and all looks okay from initial observations. No missing lash pads. I quickly grabbed my feeler gauge and use the .008" since I was short on time. But I did notice that cylinder 3 had one valve that even the .008" couldnt fit in. I'm hopeful that this is the cause! Keeping the valve cranked open would make sense...and a simple repair.

Edit: Even my thinnest, .004mm feeler wouldn't slide through

Edited March 23, 2021 by Barefootdan

[Zed Head]

If you've already been spinning the engine with the starter and had a few pops then starting it on 7 shouldn't do more damage.  Good luck with the lash adjustment.  There is something called "sunk" valves that could cause that.  Not good, but it might let you get it running for a short time if you readjust.  At least you'll know.

[Barefootdan]

I was able to get cylinder #3 lash dialed in. It looks like the rocker was sitting on the lash pad. Perhaps a very loose valve lash and high RPM caused it to jump on the side and get stuck? Well, all better now. Ran out of time on my lunch break to test compression. I'll report back soon.

[Barefootdan]

Still no go on the compression even after fixing lash unfortunately. Burnt valve perhaps?

Moving back to the starting issue. I think my ignition timing is 180 off. When I was adjusting my valve, i placed #1 at TDC (Bunny ears) and pulled my distributor cap. It was facing the cabin of the car, not the front (plug #1). Is it possible to install this 180 off? I thought they were keyed?