1977 280z EFI baseline settings

[sboy79]

Hey all! This is my first post. I've been active in the Miata and BMW community for the last 20 years but am just diving into Zs

How I got here is a long story but I need some help with baselining my EFI settings. I have a wideband O2 sensor installed and am currently idling great at 13.5 AFR but I can't get the idle below 1100 RPM.  The idle speed screw is all the way in. The idle air screw on the AFM doesn't seem to do much. I did move my toothed wheel in the AFM to get where I am now (I marked the original position, though I'm not sure it was right to begin with)-- when I first got everything running it was EXTREMELY lean at 20 AFR.

My guess is I need to start with a predetermined number of turns out on the idle speed and idle air screws-- maybe half way through the full range of adjustment??? Then set the toothed wheel so I'm somewhere near 13.5 AFR and fine tune from there?

Any help would be appreciated!

[Zed Head]

15 minutes ago, sboy79 said:

I can't get the idle below 1100 RPM.  The idle speed screw is all the way in.

 

15 minutes ago, sboy79 said:

when I first got everything running it was EXTREMELY lean at 20 AFR.

Looks more like you had a vacuum leak from the beginning.  You should return the AFM wheel to its original position immediately.  The only reason to move it is to move it back to where it started at the factory.  It's not a tunable device.

One thing that gets overlooked often is that a leak in the PCV system can let air in to the air intake system.  Any air that does not flow through the AFM will lean out the mixture.  The hose from the valve cover and the one under the intake manifold are both possible leak points.  People sometimes use a smoke test to find vacuum leaks.

[sboy79]

45 minutes ago, Zed Head said:

People sometimes use a smoke test to find vacuum leaks.

Well, we're on the right path then. This car has been in my family since new and my uncle had it for the last ten years. He got halfway through replacing a broken exhaust stud and manifold and then sort of lost interest. It came to me with everything on intake/exhaust side of the engine in boxes. He purchased a Pacesetter exhaust (my research says the forums hate them) to replace the broken manifold. I got everything together with the header and felpro gasket and the car ran horribly-- lean backfire. Smoke tested it and the intake to engine seal was leaking badly. No amount of futzing could get it to seal. I ordered a remflex gasket and tried again and it's running better but not good.

Posted my question with Zed Head so kindly answered and then ran another smoke test. Still leaking but WAY less.

I actually tried to order an MSA header since the header flange is the same thickness as the original manifold and should seal much better but they are 2 months backordered.

I've replaced all vacuum lines, fuel lines and cleaned the tank and fuel pump out. I went through the EFI bible and bench tested every component and everything works. I also cleaned every electrical connector and tested at the ECU harness with no issues. When revved it runs GREAT so I think everything works ok.

Sooooo any tips on sealing a crappy Pacesetter header or should I throw it in the dumpster and wait for the MSA header?

[sboy79]

After scratching my head I think I’m going to grind some thickness off the stepped washers that came with the header kit. I think they may be bottoming out on the header flange before really compressing the intake flange. I’ll grind a 1/16” of an inch off and smoke test again. 

[EuroDat]

Hi sboy. Welcome to the club.

Checking vacuum leaks, you could try what was called the yogurt cup test. The original thread "Purs like a kitten" is unfortunately long gone, but this one describes the procedure well enough.

You basically block the afm and blow very low pressure air into the manifold and spraying soapy water on all the suspected areas. If it is tight and doesn't leak, you can move on.

Zed head is right with the AFM. It's an hands off device, it's not tunable. In fact these old efi systems are not very turnable en this JECS variant of the Bosch L-jetronic does have some known issues with leaning out over time.

Vacuum leaks and things like the AAR leaking air past the throttle body are your most likely issues. Mine 77 280Z was sucking air through the dip stick when I first got it. Changed hoses and even the injector seals before I found it with a simple yogurt cup test and soapy water.

[siteunseen]

I have it bookmarked. 

 

 

Edited July 30, 2023 by siteunseen

[sboy79]

4 hours ago, EuroDat said:

you could try what was called the yogurt cup test

From my smoke test, I know I have a intake leak at the gasket so I'm tackling that first. I'll do the yogurt cup test next. My smoke tester has a non-smoke, low pressure setting too that should work great for that. Reading about an actual hole corroded through casting between the intake and exhaust sections of the EGR in that quoted post is insane! Sounds like my engine is about to get real soapy.  Thanks for the help guys! I'll keep you updated.

[Zed Head]

Usually the exhaust system mounting plate is thin and doesn't seal when you use headers.  The intake manifold should seal.  You didn't really say if the intake was sealed with the new gasket or not.

12 hours ago, sboy79 said:

intake to engine seal was leaking badly. No amount of futzing could get it to seal. I ordered a remflex gasket and tried again and it's running better but not good.

EuroDat mentioned the electronics and running lean.  That problem is common.  Might be worth trying the fuel tweak on the coolant temperature sensor circuit if there are no obvious intake system leaks.  It's easy and it works.  Make sure you fix that AFM though.  

http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

 

[Zed Head]

Sorry, I missed your last post for some reason.  Looks like you still have a leak.  The other area that could confuse things is the injector seals.  They can leak also and might look like a manifold leak.

 

[siteunseen]

1 hour ago, sboy79 said:

From my smoke test, I know I have a intake leak at the gasket so I'm tackling that first. I'll do the yogurt cup test next. My smoke tester has a non-smoke, low pressure setting too that should work great for that. Reading about an actual hole corroded through casting between the intake and exhaust sections of the EGR in that quoted post is insane! Sounds like my engine is about to get real soapy.  Thanks for the help guys! I'll keep you updated.

That happened to my '77. Drove me nuts for 2 weeks. Finally got a hand held mirror and look at the underside of the intake. Golf ball size hole rotted around the egr connection. Look on the inside of your hood, passenger's side there should be a recall fix sticker about the egr clip upgrade.

[EuroDat]

3 hours ago, Zed Head said:

Sorry, I missed your last post for some reason.  Looks like you still have a leak.  The other area that could confuse things is the injector seals.  They can leak also and might look like a manifold leak.

 

Agrëd. My 77 was leaking through nr 3, 4 and 5 injector seals and the dip stick seal was gone.

[sboy79]

Update-- Took a 1/16" off the stepped manifold washers allowing a little more compression of the intake to the gasket and it's sealing much better. Still a leaking a tiny bit on two ports so I'll take the washers off and take off bit more. However, I was able to put the AFR toothed wheel back to it's original position. It's running a little lean and I can only get the idle (in park or neutral) to 900 RPM. However in drive it drops to about 700 RPM. 

I also took it for a drive and I think that's the first time it's been on the road in 10 years! That's a big win. Still tons of work to do. EVERY bushing needs to be replaced. (Should I be looking for urethane or rubber bushings?) Rear shocks are pretty much completely gone.  Making lots of progress. and am happy I found a good forum for help.  

I'm not going to cancel the MSA header order but that will be a fall install. I'm hoping I can get it running well enough to pass emissions testing so I can register it in the meantime. I've also got a 81 ZX 2+2  parts car in the driveway I'm using for a 5 speed and rear end swap.  Is there anything else other than engine and drivetrain I should keep from the parts car?