280z with a L28ET motor running N/A on 280z electronics questions.

[Milenko2121]

Just found out my engine wasn't stock, and someone had put in a L28ET and attached all other parts from the 280z.

I'm wondering what can I do to try and help my fuel economy currently(getting 15mpg no matter how I drive). I understand the low compression isn't great for N/A, but I can't afford to convert all the way to turbo currently.

Is there a different way to set my timing, AFM adjustment, or even my valve lash to help until I get the other parts together?

[FastWoman]

Well, there are a few of us on this list whose electronics have drifted in their calibration over the decades. On mine, the injector pulses had gotten too short, resulting in a lean running condition. I determined this only by first going through every inch of my EFI system with a fine-tooth comb and setting everything right, including the AFM. When it still didn't run right, the unavoidable conclusion was that the ECU needed tweaking. I accomplished this by altering the resistance of the coolant temp sensor circuit. This is the most important sensor to the ECU, aside from the AFM itself. Its resistance impacts the pulse duration the same way under all operating conditions.

So my advice to you is to make sure everything is operating correctly (no leaks, proper timing, etc.) and then to adjust the CTS resistance to maximize your engine vacuum (to around 19 in Hg). To determine whether the engine is running rich or lean, you can remove the cover plate to the AFM and tweak the mechanism with your finger. If vacuum is maximized when you open the vane a bit further, your engine is running lean and needs more fuel. Remedy this by adding resistance to the CTS circuit (with a potentiometer in series with the CTS). If you find the opposite, that vacuum is maximized when you tweak the AFM a bit more closed, your engine needs less fuel. You would remedy this by wiring a potentiometer in parallel with the CTS. Then adjust the potentiometer to maximize engine vacuum and performance.

[Zed Head]

The engine might still have the high flow 265 cc/min turbo injectors. If it does, the 77 ECU will be dumping too much gas, since it is designed for the 188 cc/min NA injectors.

You might be able find some stock injectors at a wrecking yard that will get you by, if that is the case.

[FastWoman]

^^^^ Good point! I'd frankly buy new injectors if you can afford it -- about $150 for the set:

http://www.ebay.com/itm/75-76-77-78-79-80-81-82-83-Datsun-280Z-Fuel-Injectors-/160661473384?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3A280Z&vxp=mtr&hash=item25682b8868

I'm running this type of injector, and it seems to do just fine.

[Milenko2121]

The engine might still have the high flow 265 cc/min turbo injectors. If it does, the 77 ECU will be dumping too much gas, since it is designed for the 188 cc/min NA injectors.

You might be able find some stock injectors at a wrecking yard that will get you by, if that is the case.

well, my spark plugs are white which I assume is a lean condition.

would this rule out that it has turbo injectors or is there another way to know?

also,

how do you go about wiring up the potentiometer to the CTS? I've never played with one before.

and I've been getting 15mpg every tank mixing street/highway and 17mpg on the freeway only

Edited January 26, 2012 by Milenko2121

[FastWoman]

I wired a potentiometer in series with the #13 wire/connector to my ECU. The potentiometer is mounted just underneath the dash. It is a 20-turn variety that I heat-shrunk to the side of an electrical connector. Now I can adjust my mixture very accurately with the turn a very tiny screw. Details are in post #66 of this thread:

http://www.classiczcars.com/forums/showthread.php?40234-Purs-like-a-kitten/page3&highlight=purs+like+a+kitten

[Milenko2121]

I wired a potentiometer in series with the #13 wire/connector to my ECU. The potentiometer is mounted just underneath the dash. It is a 20-turn variety that I heat-shrunk to the side of an electrical connector. Now I can adjust my mixture very accurately with the turn a very tiny screw. Details are in post #66 of this thread:

http://www.classiczcars.com/forums/showthread.php?40234-Purs-like-a-kitten/page3&highlight=purs+like+a+kitten

could I do the same thing but mount it inside the engine bay instead(between the wires that connect to the wts) and have the same results?

[Willoughby Z]

FastWoman explains why in the linked thread:

"Anyway, that's the solution I propose: I'm going to put a resistor in series with the temp sensor to richen the mixture. I'm going to try a more refined approach than simply splicing a fixed resistor into the wiring harness. Instead I'm going to install a mixture tuning potentiometer directly inside the ECU housing, provided there's some good place to mount it. Before finalizing the mount, though, I think I'll run a couple of loose wires into the cabin of the car, so that I can play with mixture with the car in motion. I'll have my lovely assistant drive my car down the freeway, with her foot blocked against the transmission tunnel to keep a constant throttle opening, and then I'll tweak the mix to achieve the maxiumum speed. I'll note the resistance, and then set that value when I mount the pot back inside the ECU. Further tuning will be done on the basis of plug readings and mileage calculations.

BTW, I've also re-thought where to situate the series potentiometer. I think I'll put a little Molex pigtail connector on the ECU harness and make a little 20-turn potentiometer/plug doodad (incased in epoxy?) to plug into it. Then I'll make an extension cord that will allow me to make adjustments from a seated position (passenger or driver) as the car is moving. Once the correct calibrations have been determined, I'll remove the extension cord, save it in my "special tools" box, and have it available for future "while-driving" tune-ups."

[black gold man]

To get a good mpg test fill the car till pump stops by itself.

Drive 200 miles. Fill up again till pump stops by itself.

Divide Miles and gallons.

Do this test ten times and take the average. Then you will have true MPG.

[Milenko2121]

To get a good mpg test fill the car till pump stops by itself.

Drive 200 miles. Fill up again till pump stops by itself.

Divide Miles and gallons.

Do this test ten times and take the average. Then you will have true MPG.

I can't get 200 miles >_<

tank maxes out at 12 gallons and I usually see 180

[Milenko2121]

FastWoman explains why in the linked thread:

"Anyway, that's the solution I propose: I'm going to put a resistor in series with the temp sensor to richen the mixture. I'm going to try a more refined approach than simply splicing a fixed resistor into the wiring harness. Instead I'm going to install a mixture tuning potentiometer directly inside the ECU housing, provided there's some good place to mount it. Before finalizing the mount, though, I think I'll run a couple of loose wires into the cabin of the car, so that I can play with mixture with the car in motion. I'll have my lovely assistant drive my car down the freeway, with her foot blocked against the transmission tunnel to keep a constant throttle opening, and then I'll tweak the mix to achieve the maxiumum speed. I'll note the resistance, and then set that value when I mount the pot back inside the ECU. Further tuning will be done on the basis of plug readings and mileage calculations.

BTW, I've also re-thought where to situate the series potentiometer. I think I'll put a little Molex pigtail connector on the ECU harness and make a little 20-turn potentiometer/plug doodad (incased in epoxy?) to plug into it. Then I'll make an extension cord that will allow me to make adjustments from a seated position (passenger or driver) as the car is moving. Once the correct calibrations have been determined, I'll remove the extension cord, save it in my "special tools" box, and have it available for future "while-driving" tune-ups."

Yeah, I had read it, but I was wondering if I could just connect it directly in the engine bay where the temp sensor connects near the water neck.

[black gold man]

Do it with 100 miles you probably have more gas than you think when your on e.

When you think you have one gallon left drain the tank and see how many gallons you have.