78 280Z - Finally got it driving - High Idle, will occasionally die (but restart), sound like it has a misfire

[Zed Head]

I used heater hose and it worked fine.  I think it was 5/8".  There is a metal screen-like thing in the factory hose used for flame arresting if there's a backfire in the intake system.  Dig it out and put it in the new hose.  

Since the top hose was cracked you should check the bottom hose also.  

 

 

[NocturnalEmber]

11 hours ago, Zed Head said:

I used heater hose and it worked fine.  I think it was 5/8".  There is a metal screen-like thing in the factory hose used for flame arresting if there's a backfire in the intake system.  Dig it out and put it in the new hose.  

Since the top hose was cracked you should check the bottom hose also.  

 

 

 

About that bottom hose, is it located on the accordion pipe coming off the afm as well? I was looking under the intake manifold and I couldn't see it easily, then again I could have just been looking in the wrong place?

 

Ordering that hose kit tonight and going to get busy changing out al the rubber air hoses/vacc lines, I don't think it would be a bad idea to assume they are all suspect at this point.

[Zed Head]

It's the hose connected to part # 7, the PCV valve, in the drawing on Page EC-2.  The Emissions chapter.  I'd post a picture but the function is broke.

It's underneath the intake manifold.

[NocturnalEmber]

I've ordered that hose kid I've mentioned, eta is on a Monday. So ideally I'll be able to get all the hoses replaced with healthy, fresh material.

 

Edit: Diagram on EC-2 was a bit interesting to read, but good enough to narrow down the location. I was at least in the right vicinity.

Edited March 1 by NocturnalEmber

[Yarb]

Pm sent

[Yarb]

Does it include the PCV hose?

[NocturnalEmber]

53 minutes ago, Yarb said:

Does it include the PCV hose?

I think it includes a certain amount of feet of each size hose on the car and I have to cut to length. I would assume they would include enough hose for the pcv hose, but as far as just a pcv hose itself, I don't believe so.

[Yarb]

It’s a formed hose that runs from the side of the block up beneath the intake.

[NocturnalEmber]

5 hours ago, Yarb said:

It’s a formed hose that runs from the side of the block up beneath the intake.

Gotcha. If the kit doesn't have the means for me to cut to length and run that specific hose (or any others I suppose), I'll buy them separately if available or the proper size and cut to fit.  The picture they have of the kit installed looks pretty comprehensive though, so hopefully I'll have everything I need hose wise.

I went with black hoses personally, but it gives an idea of what it replaces I think.

Uploading photos seems to not be working right now, so I attached the link to the kit below.

https://hpsimotorsports.com/collections/datsun-280z-silicone-vacuum-hose-kits/products/hpsi-silicone-vacuum-hose-kit-datsun-280z-and-zx-1978-1983

Edited March 2 by NocturnalEmber

[NocturnalEmber]

The plot thickens...

Honestly the more I work on this car, the more confused I get.

So, I replaced the hose in question that runs from the cam cover to the throttle body with a 5/8ths, making sure to transfer the flame arrestor as well.

I wanted to replace the hose under the intake manifold, being as how it had an entire side missing, but unfortunately it seems like the side that originates off the bottom of the intake manifold is way smaller of a diameter than bung it connects to at what I think is the BCDD according to the FSM. I started the car to check if either one of those bungs draw vacuum by attempting to plug them with my hand while the car was on and the end on the bottom of the intake manifold seems to do so (which I believe is the PCV valve?), while the other connecting end on the BCDD valve does not.

 Here's an interesting discovery I made:

The engine will idle and run on its own without dying (while continuing to feel like its misfiring) so long as that bung under the intake manifold (PCV valve?) remains open to just suck air in...weird isn't it?

If I plug it, the car will go back to what it was doing, running more rough than it already does, and eventually dying if I don't tap the gas when the rpm's get low.

The car still misses when you try to rev it WOT and breaks up the higher the rpms get.

 

Part of me decided to look and see if adjusting the distributor timing might help/hurt; I was looking for some kind of change.

 

However, with the car running, you can turn the distributor entirely to the left or entirely to the right and there's virtually no change in engine RPM whatsoever. I'm not sure how the L28's work, but on other cars I've had that had a distributor, making dramatic adjustments like that (full retarded or full advance on the distributor) while the engine was running would at least prompt a change in the idle. I didn't notice anything.

So part of me wanted to check and make sure I have the distributor on right, even though I've checked it before. Can someone verify I have the plug wires connected right? I'd think adjusting the distributor timing should at least prompt an audible change, but it didn't, so I want to verify I have the plugs connected right.  There isn't any line on the side of this distributor cap to aid in any markings of the cylinders.

Also worth mentioning, The car had been running a brand new set of plugs for maybe an extreme total of an hour runtime over the combined past few months of troubleshooting. I checked them and they were black, soot/charcoal black. Absolutely covered. I replaced them with a fresh set today.

Plug wires as they sit:

 

 

If anyone has any ideas on what to do further, I'd greatly appreciate it.

Edited March 4 by NocturnalEmber

[Zed Head]

12 hours ago, NocturnalEmber said:

unfortunately it seems like the side that originates off the bottom of the intake manifold is way smaller of a diameter than bung it connects to at what I think is the BCDD according to the FSM.

That's the PCV valve, not the BCDD.  

Yes, the PCV hose from the block to the PV is a specially formed hose.  Yarb referred to it above.  Small one end, big on the other.

When things aren't tuned well the engine will often be non-responsive to tuning efforts.  Kind of a vicious cycle, a rabbit hole.  The missing and break up at higher PRM are probably due to the massive vacccum leak through the PCV valve under the intake manifold and also through the hole in the block.  Air can enter the crankcase through the hole in the side of the block and travel through the engine to the intake manifold.

You can either block the two PCV holes, or get the proper hoses connected.  The EFI system will not work correctly with a partially intact system.

 

.  

Edited March 4 by Zed Head

[Zed Head]

13 hours ago, NocturnalEmber said:

However, with the car running, you can turn the distributor entirely to the left or entirely to the right and there's virtually no change in engine RPM whatsoever

 

13 hours ago, NocturnalEmber said:

Can someone verify I have the plug wires connected right?

Your firing order is correct.  One possible reason for no change might be that the timing is very retarded.  You need to get a timing light and see where it is.  You'll also be able to see if it's changing when you move the distributor.