1977 280z EFI Nightmare

[Zed Head]

1 hour ago, ckurtz2 said:

Interesting thing is at idle the timing read the same with or without vac advance.

The hose only gets vacuum when the throttle blade is NOT at idle.  When the throttle blade is closed the vacuum is shut off.  That's why you don't feel any suction at idle, but get more advance when the hose is connected and you give it gas.

Edited May 18, 2021 by Zed Head

[Zed Head]

1 hour ago, ckurtz2 said:

It is radial slop, so I can twist it about 1/4 in each way. I also can pull it further one way which I assume is the vac advance function. 

Actually that's the mechanical advance.  When you twist it the advance weights move out against the springs.

[Zed Head]

1 hour ago, ckurtz2 said:

surges when initially revving.

You should describe this in more detail.  Surging?

[ckurtz2]

Ok, those are all super helpful things to know.

Here is a video from yesterday when it was at 18 deg btdc. When colder it would idle and rev almost perfectly, and then this weird issue developed once warm. You can hear when I rev it that it almost surges. It will rev up, stop, then rev up again. Essentially its super jerky. It didn't do this as much on the test drive, but I definitely noticed it bucking in first.

 

[ckurtz2]

I am going to go ahead and do a hot valve adjustment. I have the car warming up now. Revs perfect cold with almost zero bobble. Warmed up a little bit and when I pumped the throttle it gave a nice intake backfire. I want to make sure it is not the valves fault. I will also take a photo of where the cam lines up at top dead center.

[Zed Head]

13 minutes ago, ckurtz2 said:

I will also take a photo of where the cam lines up at top dead center.

The engine sounds kind of "cammy".  Confirming cam timing and ignition timing will help.  I wonder if your damper is bad.  Your ignition timing might not be where you think it is.  Feels like this has been discussed, not sure.

Make sure that you pull the straight side of the timing chain tight when you set the timing mark on the damper to zero.  Get that tight then check your cam sprocket notch and groove.

[ckurtz2]

Just did a valve adjustment. A lot of them had way to loose of clearance. Only one I didn't need to touch. Weird cause I already did the adjustment once. I would say it was a warm adjustment. I also agree it sounds cammy, but I don't know why. Everything seems stock under the valve cover, but I don't know how to tell if it is an aftermarket cam. In addition, sometimes it smoothes out like when cold, so it makes me think it is just missing or stumbling.

I rotated the engine clockwise carefully until I got to TDC. I have it on mark 3, so obviously the chain has wear. However, it looks like at this position the cam is advanced still. Is that ok?

This is where the crank pulley lines up and how the cam timing marks look correlated to it. 

 

Edited May 18, 2021 by ckurtz2

[Reptoid Overlords]

I'm not entirely sure if yours is within acceptable parameters, but this is how i understand it is supposed to look. This is taken when reassembling my motor, which seems to be running just fine. 

Most people say turning the engine over with the cam bolt is bad, and it is better to use the crank bolt, or a remote starter.  I have used the cam bolt in the past, without causing any apparent damage, but since have started using a remote starter.

[Zed Head]

1 hour ago, ckurtz2 said:

A lot of them had way to loose of clearance.

How did the cam lobes look?  Did you check the wipe pattern after installing the camshaft?  You said "reinstalled and so on", but....

Your cam is in the "after adjustment" spot, which is good.  It does indicate that your chain is worn but cam timing should be right.

 

[ckurtz2]

What do you mean by wipe pattern? It definitely doesn't look amazing. There are some burn marks and light scratches to the eye, but over the finger everything feels smooth. I never did anything to the cam, just took it off and plopped it back in. 

I refired up the car.  Much quieter up front with less valve train noise. I definitely tightened it closer to the tight specs on the hot valve adjustment guide. I just let it idle and listened from the back end. The chop is erratic which leads me to believe it is not cammed. The plugs look great, except for plug number 2 and 1 which had a little bit more carbon deposits. I pulled the injector connector from cylinder 2 and I swear the car barely changed in behavior. Ran a tad worse, but not as much as the other cylinders. May just be placebo and me wanting to find the culprit though. 

So after letting it idle for a while I went to give the car about 3/4 throttle straight away. Essentially opening up the throttle body quickly to see how the car reacts. The only thing consistent I have noticed is that after sitting idling for a few minutes and I hammer the gas, there is always a pretty big missfire out the intake. This I think is the biggest clue we have thus far. 

Which leads me to believe it may be running a tad lean still? 

[ckurtz2]

@Reptoid Overlords thanks for the confirmation photo! My chain is definitely stretched, but the #3 cam pulley position compensated. Mine may be running a tad more advanced then yours, but it looks to be in spec as well. I wish my cam sprocket looked as clean as yours! 😎

[ckurtz2]

Ok so here is the plan. I am going to check the dizzy shaft tommorow and make sure it looks proper with the engine at TDC. Next, because my car is a 77 cali model I am going to disconnect the altitude switch under the dash and see by some miracle if that does something. After that I think it is time for the potentiometer magic to happen. 

Regarding the pot tweak, which pot should I get. I was looking online and there are so many options within the 1kohm limit I don't know which is best. In addition, do the bullet connectors have a certain size on the water temp sensor. I need to buy some connectors for the pot that match the water temp sensor's bullet connectors. Thanks for hanging with me over this tedious process thus far!