EFI question's

[my900ss]

1977 280Z 5spd is failing the CA emissions test for both HC and C0.

 

The 5 & 6 cylinder plugs appear to be running much richer than 1-4 due to black soot on these two plugs not found on the other 4.

 

Compression reads between 130psi and 135psi across all 6 cylinders.

 

I have replaced the plugs, plug wires, rotor, distributor cap, coil, fuel filter and EGR valve.

 

I ran through the "poor mileage" xblshooting section of the 280z service manual and everything passes except the air regulator DC voltage check.

A. A continuity check at the sensor on the air regulator tests good.

B. When I initally pulled the vacuum lines from the regulator I could see the valve was 1/2 open. After running the car, I pull the vacuum lines and the valve

is closed.

 

Looking through the fuel injection bible pdf on page 56 Test #1 - (8) there is a part labeled "Relay". Where is this physically on the car?

 

I am looking for where and how to adjust the air fuel mixture, but I have yet been unable to locate a mixture adjust screw or instructions on the suggested means to do so. Any input or guidance on the where and how?

 

Thanks,

 

Troy

[ModernS30]

I can't really help you with those parts but I can say maybe you should get like an exhaust adjust valve. Like one that you turn to try to fool the emmisions? I don't know how well those additives work but you could try something. Car looks clean.

[my900ss]

I can't really help you with those parts but I can say maybe you should get like an exhaust adjust valve. Like one that you turn to try to fool the emissions? I don't know how well those additives work but you could try something. Car looks clean.

 

Thanks for the compliment. I choose to buy this car because it was a clean unmolested example. I would prefer to fix the issue vs. fool the emissions.

[19762802+2]

I believe the air mixture screw is on the AFM but I'm not sure so search about that, also the reason you might be running richer on cylinders 5 & 6 could be clogged or dirty injectors. You could run some fuel injector cleaner or take off your fuel rail and look down the hose connected to the injector to look for small pieces of gunk or etc. Go over all your connections and make sure they are clean and in good shape. I am not sure which relay you are looking for but the EFI relay is under the dash above the computer on the left side. It is a small silver box with to square connectors in the side.

[Geking]

On a 78' Z the FI relays are under the black panel thing that the fuseable links are mounted to. Not sure about the 77's, I would assume they would be in the same location.

Some may say that the spring in the AFM has gone soft with age and needs to be tightend. This is done by popping the black cover off of it and tweaking the screw in the upper left a bit. Also would be a good idea to make sure that the throttle switch is not sticking to the idle position.

 

Good luck.

[my900ss]

I am going to give the BK44 fuel system cleaner a try. I have been pulling and spraying contact cleaner in the sensor connections as I come across them. The attached jpg shows the relay I am looking for on the schematic. My hunt for the air fuel mixture screw continues, I will look into the possibility it is in the AFM.

 

Another semi simple question... the 4 fusable links on the inside fender well just forward of the battery. What amperage are they rated at?

 

Thanks,

 

Troy

Edited April 29, 2010 by my900ss

[19762802+2]

here is a fusible link upgrade that also lists the different amperages.

 

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

[MONGO510]

With 2 plugs black and sooty I would be looking at bad injectors.

[my900ss]

Injectors would seem like a logical step given the symptom. However they have good continuity and using the screw driver test I can hear them pulsing. When I get to it I will most likely swap the #3 and #6 injector to see if the sooting issue follows the injector and then replace if needed.

[my900ss]

I have new injectors on order. I am still looking for where and how to adjust the air fuel mixture, but I have yet been unable to locate a mixture adjust screw or instructions on the suggested means to do so. Any input or guidance on the where and how?

 

Thanks,

 

Troy

[ModernS30]

here is a fusible link upgrade that also lists the different amperages.

 

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

 

Do this, makes the car run 100% smoother!

[rossman]

There is no simple screw to adjust the mixture. The Air Flow Meter (AFM) determines the mixture. You have to tighten the spring on the flapper inside the AFM to lean out the mixture.

 

I have new injectors on order. I am still looking for where and how to adjust the air fuel mixture, but I have yet been unable to locate a mixture adjust screw or instructions on the suggested means to do so. Any input or guidance on the where and how?

 

Thanks,

 

Troy

[Leon]

Get the FSM and study how the EFI system works. The Tech Tips link also has a lot of good info.

 

http://www.xenons30.com/reference.html

[Daeron]

There is no simple screw to adjust the mixture. The Air Flow Meter (AFM) determines the mixture. You have to tighten the spring on the flapper inside the AFM to lean out the mixture.

Ross is right, there is no user-serviceable "adjustment" for the mixture. The stock L28E EFI is un-tuneable, if you go by-the-book, and anything that isn't by the book is guesswork. It is only guesswork to the same degree you depart from the book's line, but it goes something like this:

 

-Tweaking the AFM wiper can move the enrichment curve further up the line of air volume consumption. In other words, this simply jumps the "air flow" input to the computer by a set increment, across the board. SOMETIMES the spring can be weakened, but this can only be determined by calibration using weights and a good ohmmeter. This process is laid out in the Techtips, along with more advice on why you should only use these AFMs at factory spec. If the spring has weakened, it needs to be replaced. Tightening it may make your car run better, but it still isn't right.

 

-Looping into the CTS/Cold Start enrichment input loop with a potentiometer (to replace the thermistor that told the ECU when the engine was cold, which provided a minimal fuel enrichment at all times, but not indexed in the same way the AFM was linear.) This knob essentially acts as an "over-rich" knob.

 

-Some have replaced the AFM with a hybridized AFM from a Toyota Cressida, using the guts from the original Datsun AFM. This modification, along with some other "breathing" mods like possibly minor head or manifold work, a cam with more lift and/or duration, or a larger throttle body, should be useable to tune the stock EFI to some more power.... BUT...

 

..All of this is guesswork, trying to fool a 35 year old "computer" that is less complex than a knockoff free ipod from the bank. That "computer" was tuned for a combination of efficiency, cleanliness, and long-term reliability, and those components are VERY simple. You can only fool it by shifting this curve up an axis, or by adding this non-linear, non-regular tweak to richen up the fuel, or adding fuel pressure to help keep up with the air demand at a more "stock-like pace," or anything else that could be rationalized. Sure, maybe you can make the car feel more powerful, maybe it IS, but this kind of tuning is ALOT of guesswork and takes much repeated failure before you learn how to do it right.

 

I haven't done much of this stuff to the stock EFI, but I researched it and started thinking hard about it, before I realized it simply wasn't worth it for the likely minimal gains.

 

 

 

All that is an extremely longhand way of saying: don't tweak your AFM in any way other than the calibration method laid out at blue's TechTips page. It isn't healthy, and nothing that would do would effect two out of six cylinders.

 

Chances are something is causing those two injectors to seep slightly, and not close. Have you put a fuel pressure gauge on it? Try pulling all the spark plugs, carefully stuffing a paper towel into each cylinder, turn the car on (to make the fuel pump prime; hotwiring the fuel pump may be simpler? If you aren't 100% clear on how to make your pump prime I can check and make sure I am 100% positive I know what your year does and let you know.) Anyhow, see if more fuel seeps onto the rags in the problem cylinders. If you don't want to bother, I don't blame you; You are probably on the right path and new injectors will likely fix this problem, IF the emissions issue is that tied to the black sparks on #5&6.

 

Good luck, and I hope I was able to paint you a decent picture of how the EFI can (but maybe shouldn't) be modified and tweaked.

[rossman]

Nice writeup Daeron! I was being lazy and just answered the question. Years ago I messed around with the FI on my old '76 Z. One thing I learned is that the AFM and FI temperature sensor are the most important parts of the system to determine mixture. I agree with Daeron, don't mess with the AFM unless you really know what you are doing. Make absolutely sure the temp sensor is working correctly and that it's connector and the bullet connector before it are clean and free of corrosion. The system works off resistance readings. Corrosion increases the resistance thus making the computer think the engine is cold. If the computer thinks the engine is cold, it dumps more fuel causing the engine to run rich. Also clean all the other connectors in the system. Deoxit is a good cleaner. I used and a small piece of fine grit sand paper shoved between the contacts in the connectors to help removes some of the thick corrosion.

 

Good luck.