running lean and the saga

[blackpaw]

Hello!

Long time stalker, first time talker.  I hope this is thorough, and let me know if there is something missing.

1978 280z 

Basically, my car is acting lean.  Front firing from the afm... I'll tell you how I got here, what i've done, and any seemingly relevant questions I can’t seem to get an answer on.  

Been chipping away at getting this car running well for a bit, passed smog (CA) last year. Car was running pretty good minus a rich issue.  I was modifying the car back to stock (previous owner put larger injectors/a number of things).  We are friends, so I was aware of these changes. Savvy Porsche guy leaned me out to pass smog car ran great all year.

I threw in a "fuel cleaning" supplement. One day in traffic here in LA the fuel pump got real loud (intermittently would get loud from time to time) shut down on me.  Waited 20 minutes then it started up, barely made it home. Seemed to only happen when the car was hot. When the weather was great (72F) the car ran great (besides the rich issue).  Hot days, the noise would return and then it would get sluggish, and the RPMs would get high. I thought it was fuel clogging since the cleaner was probably the culprit.  

I started with checking/changing Fuel pump, filter filter, and in the process unplugged the fuel rail to make sure the injectors were all spraying (new connectors and they were clicking with the screw driver test). I thought maybe the fuel dampener was clogged…did some research on here, and I had some extra fuel line, so I deleted it.  

Thermostat wasn’t really getting to the middle, and it made sense that the car was reacting a bit too much with the weather to me, cheap part. Swapped it.  Started working a bit better.

Did a starting fluid round on the hoses, nothing was really reacting to a leak, but there were some small cracks in a few things, just started replacing them. Intake boot, and PCV hose  

The air regulator was reacting properly, took it off to check the lil bean out, I thought maybe it was getting stuck open and sucking the pump off too much.

Popped off the vacuum of the FPR (which wasn’t leaking before), now it was leaking! Thought my fuel dampening choice was haunting me… I changed the FPR with one I had on a fuel rail from a part swap (maybe the culprit?) 

The car started running lean under load, but man that idle has never purred that consistent.  

While I was poking around, I made sure timing was at 10 degrees, replaced the coil (old one with no external resistor was 3.6ohm) with a 1.5ohm, and replaced spark plugs. 

I thought, well since it was running rich, this shop that helped me pass smog probably leaned it out on the AFM.  Did my research and marked my spots.  I was able to see the old glob on the black sprocket (must have been 12-13 teeth leaner) Tweaked it back to the glob, and it really doesn’t make a difference.

All along I’m going back n forth the FSM and here just checking around.  Did the AFM test at the ECU, all the testing reads fine! Except the continuity on 6-8, 7-8, 8-9.  Poked around and Zed head seemed to confirm its probably the AFM gone bad….

TOOK THE AFM OUT.  Did the bench test, it passed everything.  Cleaned contacts and connector put it back in.  Still failing those continuity tests.

Questions. 

Can’t seem to get a solid answer from a Z car.. Can the FPR make the car run lean ? When I unplug the vacuum line nothing changes. Figured it was a weak link since it was used.  

AFM continuity test, does that mean my wires to my ECU are funky? 

ECU itself is funky? 

Feels good to say this all out loud.  Thanks for your time and any advice you have.

[Dave WM]

did you check the fuel pressure? what were the numbers, engine off, pump on and engine on with a vacuum reading as well.

[Dave WM]

another question, does your car have a altitude adjuster for the EFI?

[siteunseen]

Here's some reading, stalking.  Welcome to the forum!

https://www.google.com/search?q='78+running+lean+classiczcars.com+site:www.classiczcars.com&rlz=1C1BOFA_enUS494US494&sa=X&ved=2ahUKEwjpv4iss__oAhVFgXIEHYzZBSUQrQIoBDAAegQIAhAP&biw=1280&bih=606

[blackpaw]

Dave,

I checked on this initially when I changed the pump, and I got good readings, but just to be sure I just rented a fuel gauge, and a vacuum gauge. I’m going to recheck in the next day or so and get back here.

thanks site! I did my fair share of searching, But I’ll read this again to make sure I’m not looking over anything. I think this ended with it running better, but he left for school. 
 

I never checked vacuum with a gauge, so I’m looking forward to check that off when I check fuel pressure again. 

 

[siteunseen]

A vacuum gauge will tell a lot diagnostic wise.

 

[blackpaw]

5 hours ago, siteunseen said:

That valve pic is super handy.   Thanks!

Alright.  

Dave, re altitude switch: I don't see one... The book seems to have a dotted outline. Is it out of sight? I've googled and some of them are on the BCDD?  I didn't see it, but I did see a circular type empty spot floating next to the vent opener.  

Fuel pressure - Engine off pump on 40 psi

Pump off hangs at 34psi, very very slowly drops. 

Engine on about it has a tight flutter 34/35psi.

Vacuum test! Very telling... Fast flutter  at 12.5-14.  Looks to be loose valve guides and not enough vacuum?  

When I quick throttle it jumps from 0 to 21.  Gotta get one of these.  They are pretty cheap. Any recs, will the $25 one on amazon suffice?

 

5 hours ago, siteunseen said:

 

 

Quote

 

 

[Dave WM]

OTC is nice, harbor freight is cheap, sure either is fine. you have to let the engine warm up some, same with compression testing, warm engine will give better results. Typical to be 16-22. Altitude effects it as well, higher alt, lower vacuum. I don't think you have a smoking gun yet. Try smoking the engine for a leak test. I prefer this to the spraying flammable fluids around it. Block off the throttle body with a foam cup, get a stogie and blow smoke into a pipe connected to the intake manifold (brake booster fitting works well). look for smoke. Sneaky things like PVC or EGR and create lean runs. missing or damaged fuel injectors rubbers, cracked hoses around intake. Smoke will find them the best. For EGR you may have to remove the valve and just make sure its clean and that the diaphragm is operational.  

[Powerglide1956]

Bump initial lead to 15 degrees BTDC. Check vacuum again with HOT engine. Report back.  Bet you see 18 inches of mercury on the gauge. 

[blackpaw]

Dave,

Smoking it is,  all the signs always lead to just doing it the right way the first time. I have a fogger (I'm a music guy) that I can rig up to smoke it out. Also, I didn't mention it because it wasn't a part that I changed during the lean saga, but my EGR is new.  I was chasing those legs during the smog saga of 2018-19.  I'm going to get the car hot to redo the vacuum reading.  I mentioned before that the car acted weird when it got hot (i.e.. loud pump) , but what I forgot to mention for clarity is that since I changed the thermostat and FPR the car no longer gets loud.

re: altitude I am at 350' 

Actually, just to be sure on my vacuum test.... The hose that came on the vacuum pump was too small for the brake booster inlet on the manifold.  I unplugged the FPR and used that one since it fit, would that get me an adequate reading?  Just wanted to make sure.

Also, while I'm at it I read somewhere that their brake booster was leaking internally.  I'm going to try to rule that out as well.

2 hours ago, Powerglide1956 said:

Bump initial lead to 15 degrees BTDC. Check vacuum again with HOT engine. Report back.  Bet you see 18 inches of mercury on the gauge. 

Powerglide -  Does "Bumping initial lead to 15" refer to advancing the timing another 5 degrees? It's seems to me that the car "ran" for a good year, but now I'm getting to the grit with making it run really well.  If you are referring to a timing tweak..... would this be somewhat of temp fix? Is running that advanced common? 

 

[Powerglide1956]

Yep. Don’t trust the balancer. Trust the vacuum gauge. 

[blackpaw]

Hey guys,

I’m back... I advanced the timing and got way better vacuum (19). It’s pretty advanced though, could that be future problems, or sounds good though....  I did a smoke test and no leaks!  I enrichened the AFM like 12 teeth. Seemed like a lot, but I passed smog, and the car is running pretty good on the low end but loss of power on the high end. I was reading around about the temp sensor mod and how some were saying that a 78 ECU could run lean with age... considering doing the mod to try it out. 
 

Also, on another note.. I tested the afm, and it is giving me readings within spec.