1976 280Z Replacement ECU Issues

[Captain Obvious]

Well if you did check the oil that frequently and it really IS disappearing, that's unfortunate. I was just hoping it might have been a non-problem.

A quart in 100 miles is really a lot of oil. At that rate, I would have expected you to crop dust a mosquito fogging blue cloud behind you. Especially without a catalytic converter.

[Dave WM]

check to see if the PCV valve is not stuck. Just remove it and give it a shake, should hear a rattle.

[DD76]

Thank you guys. I replaced the PCV valve when I thought this was a fuel injection issue. After your post, I took the valve out to double check. It moves freely and looking in the motor end, it's nice and new looking. Something that did cross my mind is that my last oil change was with Lucas Hot Rod/Classic High Zinc 10W30 and the weather both times I took it the car out was in the 90 plus range and very humid. The dash temp gauge was a little high, picturing the pointer like a clock hand, it was at 5:30. Today it finally dropped to the low 70's so I got it out for a thirty mile ride. The temp gauge pointer "clock hand" was steady at 6 and, measuring tonight, it looks like I only used 3 or 4 ounces of oil. Not great but a big improvement. I'm thinking, as the car rarely is on the road when its under 60 degrees, that changing to heavier oil going forward after the valve seals replacement would be a good move.  Would 10W40 make sense or something else?  Thanks again for all the help.

[Zed Head]

Four of your plugs look great and two look terrible.  The fact that your pressure numbers look good but you're losing oil and have two dirty cylinders suggests that the oil scraper rings in those two cylinders are damaged, or the intake valve seals on those two cylinders aren't working.  Valve seals is the easiest place to start.  Changing oil won't help.

You might be able to see by eye if the intake valve seals on those two cylinders are different than the others.  Worth a look.

I wouldn't be surprised if the engine is only firing on four or five cylinders.  Those plugs are filthy.

On 7/7/2024 at 1:13 PM, DD76 said:

Outside of fuel injection, the engine has 150 compression in each cylinder. A leak down test showed 96 per cent retention in 2 cylinders, 93 in two and 90 in the other two.

 

[Zed Head]

You'll have to look very carefully through the valve spring.  Bright light, magnifying glass, or camera with close-up shot.

Here's a shot of an exposed one and link to the guy's video.  No idea who it is, found it by Google.

 

[Zed Head]

p.s. since you only have two bad cylinders it might be worth the time to just replace valve seals on those two.  If it was mine I'd probably just do the two intake valves.  Why mess with the others that appear to be just fine?

[DD76]

Thank you. That’s a great idea to just concentrate on those two cylinders. Definitely seals would be an happier fix than rings. Are you thinking that oil entering past the exhaust valve would more likely be going straight to the headers and not so much burning as the reason  to center on the intakes? Thanks again.

[Captain Obvious]

2 hours ago, DD76 said:

Are you thinking that oil entering past the exhaust valve would more likely be going straight to the headers and not so much burning as the reason  to center on the intakes?

My understanding is that the reason exhaust valve seals are less of a concern is... The cavity where the valve stem passes through the exhaust port is never under vacuum like the intake port area is. It's less likely you would ever pull oil INTO that area because you just don't have the vacuum differential like the one you see on the intake side.

[DD76]

That makes good sense. Thank you.

[DD76]

Following up to thank everyone for their assistance. I was away from the garage for a month with a hip replacement.  I did go ahead and replace both valve seals in cylinders 3 and 6 as they were the obvious places to start. It actually made no difference. A couple of things I learned in that process (1) filling the cylinder with rope and then turning the cam just a bit further to TDC was a great suggestion (2) whacking a spark plug socket set on top of the spring unit is a very effective way of releasing the keepers and (3) removing the rope after reassembling the spring makes it a lot easier to reinstall the rocker. After doing those with no benefit, I was pretty much resigned to getting professional help with the rings. I decided to try soaking the pistons for 36 hours with Berryman 12 and then, as they direct for an engine flush, I added about 10 ounces to the oil through the dipstick tube and then ran at idle for about 15 minutes. I then changed the oil and filter. I took it for a 100 mile ride. Checking the oil afterward, it had used a half quart, not great but an improvement. I then changed the oil and filter again to make sure all the Berryman was out but this time, used 10W-40 instead of 10W-30. I've now driven the car 200 miles since this last oil change and have used no more than a couple ounces of oil, if any, and no smoke. I have to assume I had one or more oil control rings stuck in the two years it was off the road for the fuel injection rebuild. I'm guessing, as it's been driven more this year than it has in the last 5 years combined and its been improving in oil usage over the summer, and maybe with the Berryman help, that the ring(s) broke loose and started to function correctly again.  Anything I'm missing? Thanks again.

New question...In the following photo of the plugs today. Plugs 3 and 6 are still dark compared to the others where the ceramic still is white. All the plugs were changed at the last oil change so I assume I have a second issue of imbalanced air/fuel mixture. There has always been carbon buildup on the back bumper. Is this an injector issue? They are Standard brand and all new. Would a temperature range change on those two spark plugs be a thought? All the usual culprits like AFM, Temp Sensor, etc. would seem to be across the board items not individual cylinders but what do I know.. Any thoughts would be great. Right now I'm just thrilled that the oil problem seems to be fixed.

Thanks again to everyone.

[dutchzcarguy]

18 hours ago, DD76 said:

I have to assume I had one or more oil control rings stuck

My 240z smoked a bit and my garage had the tip to put some (about 150mL) ATF in the oil and... after about 200km there was much less smoke!

He remembered this from the old days where he always did this when old mercedes 6 cyl. cars did this and he always did this standard to old mercedesses! It works!  

I think the pistonrings get stuck and the ATF frees them up!  Use ATF from the auto transmissions.

[Dave WM]

old fuel injectors can def cause issues. only sure way is to pull them and test. beware of buying "new" replacements, better to do some research and see if you can find someone to test and if needed clean.. You may end up with a dud that will not come up to spec, hopefully if that happens whoever you find to service them can get a replacent core.