Idle dying when warm

[Geoff's 240z]

Update on the continued saga...

Started out today with compression test (thanks O'Reilly for lending the tool) and got bad news. Results as follows:

Tested Cold/Warm

1. 60 / 70
2. 60 / 70
3. 100 / 120
4. 110 / 115
5. 90 / 100
6. 115 / 115

So now we have cylinders 1 & 2 to worry about. What's odd is that cylinders 4,5,6 are the ones making noise when I disable the front carb as posted in the video above.

Also checked for vacuum leaks with brake cleaner and did not discover anything.

Put in new plugs, results in the picture below. Seems like we're doing better on the color when compared to before, cylinders 6-1 as you look top to bottom.

Good news is that the idle seems to be holding now after the continued carb tuning. I'll drive again this afternoon to confirm this is the case.

Located in Laguna Niguel, CA for those local or who want to visit.

[Zed Head]

Those are terrible.  Are you positive that you had a good seal on the tester and the pressures are correct?  You didn't use the extension on #1 and #2 then take it off for the others did you?  The extension/adapter will give a much lower reading because it adds volume.

What is your ignition system?  Distributor and ignition module.  Your plug gaps seem pretty wide for a points system.

[Patcon]

Also did this engine sit for an extended period of time. I don't recall if that has been mentioned or not.

Those numbers aren't good. You need to double check those numbers and like Zed said make sure you do each cylinder exactly the same way. I don't really care about cold and warm. What I want to know is dry or wet. After you do the initial test squirt a little motor oil in each cylinder. If the numbers come up then it's a ring issue. If they don't its generally a head issue. I would also adjust the valves before I did another test

[Geoff's 240z]

I performed the same method for all cylinders, and double checked the front two cylinders given the variance. I was more focused on the variance than the actual values given that I don't know the history of the gauge itself.

Took the coil wire off, all plugs out, screwed compression gauge in as tight as possible by hand. No extension used. Full throttle and ignition for about 3-4 seconds for each cylinder.

No, the engine did not sit for an extended period of time after warm. Just long enough for me to do the procedures above.

I have a '79 280zx distributor. I gapped the plugs to .044, as I have a 280z bottom end. Interestingly, the NGK 11's came out of the box all gapped at .040.

Sound like anything else I'm doing wrong? 

[Zed Head]

Sounds like you're doing everything right.  Your engine is doing things wrong though.

I'd pop the valve cover and check the valve train.  As Patcon suggested, valve lash set wrong can affect cylinder pressures.  Although yours are way off for just a simple lash adjustment.  If you're lucky you'll find a rocker arm lock nut or two that is loose, causing the valves to open only partially.  If you're unlucky you'll find some damaged cam lobes.  Getting a new cam and rocker arms installed and broken in without damaging the cam lobes can be difficult on these engines. 

[Mark Maras]

  Time to adjust the valves and hope the compression improves on all of them. Be sure the throttle is wide open when conducting the tests.

[Patcon]

My question wasn't about sitting between the test, but whether the engine sat for a number of years before you got it. Some times the rings get stuck from sitting and can give low numbers like this. Doing a dry then a wet test can show this too.

[Geoff's 240z]

Sorry about the misunderstanding. No, the car has been driven consistently for at least the last five months.

[Mark Maras]

 While you're adjusting the valves take a good look at the cam and rockers. Pics of the cam would be good.

[Captain Obvious]

5 hours ago, Geoff's 240z said:

Started out today with compression test (thanks O'Reilly for lending the tool) and got bad news.

Well before you go and start looking into other more complicated possibilities, I would double check the results with another compression test gauge. Get your hands on one that you have confidence in. For all you know, it's a test equipment issue. Maybe that lent unit has been dropped one to many times.

4 hours ago, Geoff's 240z said:

all plugs out, screwed compression gauge in as tight as possible by hand. No extension used. Full throttle and ignition for about 3-4 seconds for each cylinder.

And as for the test procedure, everything looks good except for at the very end... What do you mean "3-4 seconds for each cylinder"?

Are you actually watching the gauge while you crank the engine, or are you just blindly cranking the engine for three or four seconds and assuming the cylinders have topped out in compression pressure by then? Reason I ask, is that in my experience, it takes three to seven compression cycles on the cylinder to top out at peak pressure. If you're just counting to "four one-thousand" and letting off the key, you may only be at half the peak "achievable" pressure.

Here's to hoping your having a test procedure or equipment issue and not really having a problem with the engine itself.  

[AK260]

Lots of good advice here.

 

With compression that low I'd be surprised that the car is starting and / or not smoking like a chimney. She would feel like a salted slug if true - I bet she doesn't, right?

 

I would question the test equipment first and foremost. The operator does appear to be somewhat intelligent and competent :p

 

This is what I use and have found owning one a very useful thing.

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F143013635153

 

One other thought, when doing this test I always hook up a battery charger on "start" mode to eliminate any effects of battery drain.

 

For comparison, my L26 that was burning a litre of 20w50 every 1000 miles ran with 155psi dry, 185 wet. My freshly rebuilt L28 with static compression of 10.5:1 and the 270 cam does 205psi wet or dry across all cyls +/- a nat's sigh.

 

 

 

I would be amazed if your car is genuinely running that low and not feeling massively sluggish.

 

Regardless of the absolute numbers, the variation across banks is a thing to consider. Cam clearances will of course have an effect and while you have the rocker cover off check head bolt torque too.

 

If you find after all this you still have the same readings, get a "leak down test" before tearing the motor down.

 

https://mobiloil.com/en/article/car-maintenance/car-maintenance-archive/how-to-do-a-leakdown-test

 

Oh the joys of owning old cars!

 

Good luck buddy.

 

 

 

 

 

 

 

 

 

[Geoff's 240z]

AK260, thanks for the support! Got back in the saddle today with new tool, and also increased starter time from 3-4 seconds per cylinder to ~10 seconds per cylinder to test. Here are the results:

1. 110
2. 125
3. 160
4. 155
5. 140
6. 160

So, feeling much better about things but still have something to investigate in cylinders 1 and 2. Any concern about cylinder 5? 

Lastly, bought a remote starter but wanted to make sure I hooked up correctly. Can you guys confirm? First, connect one cable to the smaller wire connection on the solenoid, then connect to the bolt on the solenoid that connects the positive battery cable. Do I need to disconnect any cables or can just bite onto those connections?

Thanks!