77 280z Water Temp Sensor Issue, Runs Very rough

[Samson]

I think that your HC numbers are pretty close. Small changes will probably get you there. Do you have the vacuum hose connected to your fuel pressure regulator and does the FPR work correctly? Fuel pressure should be ~36 psi with the hose disconnected and 28-32 psi with it connected, at idle.

I have a gauge hooked up inline with the filter it shows a about 32psi at idle. What do you mean by vacuum hosted connected to FPR? The hose from FPR is going into the intake manifold, yes.

[darom]

Samson, did you get your car to pass smog and what kind of numbers did it post?

[Samson]

Samson, did you get your car to pass smog and what kind of numbers did it post?

Hey Denis, nope.. still haven't gotten a call from the shop. Still waiting..

[EuroDat]

I have a gauge hooked up inline with the filter it shows a about 32psi at idle. What do you mean by vacuum hosted connected to FPR? The hose from FPR is going into the intake manifold, yes.

Hi Samson,

Just a quick run down on how the fuel pressure works.

The fuel pressure regulator controls fuel pressure by reading the vacuum. That way the injectors always have the right differential pressure over the nozzles. Eg: At idle you have high vacuum and therfore you need lower fuel pressure, at full throttle / full load you have very little vacuum and therefore higher pressure in the fuel system. The system wants to maintain around 35 psi across the injector nozzles.

The ecu works on a time basis pulsing the injectors. A higher differential pressure will give more fuel, but the ecu cant calulate this because it doesnt read the fuel and vacuum pressure.

Thats why you do an initial test with vacuum hose disconnected or turn ignition on and open the afm via the aircleaner the simulate air flow. The pump will then run and should read around 36 psi.

Chas

Edited January 4, 2013 by EuroDat

[Samson]

Hi Samson,

Just a quick run down on how the fuel pressure works.

The fuel pressure regulator controls fuel pressure by reading the vacuum. That way the injectors always have the right differential pressure over the nozzles. Eg: At idle you have high vacuum and therfore you need lower fuel pressure, at full throttle / full load you have very little vacuum and therefore higher pressure in the fuel system. The system wants to maintain around 35 psi across the injector nozzles.

The ecu works on a time basis pulsing the injectors. A higher differential pressure will give more fuel, but the ecu cant calulate this because it doesnt read the fuel and vacuum pressure.

Thats why you do an initial test with vacuum hose disconnected or turn ignition on and open the afm via the aircleaner the simulate air flow. The pump will then run and should read around 36 psi.

Chas

This makes so much sense. Thank-You. Now, the FPR is also a possibility that it's adding more fuel at high engine load thus giving me a rich mixture? I was going to get an adjustable FPR (have it set at 36 psi?) and change the fuel rail to an aftermarket unit. Can't do any other tests now since i took the Z into the shop.. Denatured alcohol also came up when i was talking to some friends about having the Z pass smog, they say get the car to about 1/4 of a tank and pour a gallon of the alky in there and should pass with flying colors just pump full tank after the test to dillute the alcohol ..but idk.

[siteunseen]

I did this http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html to my '77 instead of the adjustable fuel pressure regulator and it fixed my problem. ZedHead suggested putting it inside the car for adjusting while driving and that worked out really good. My mechanic friend kept my car for 4 weeks and couldn't figure out the problem, ZedHead and Fastwoman got it in 5 minutes. He clamped off the return line to increase fuel pressure in the system and thought raising the pressure to 45lbs would fix the stumble. $5 from Radio Shack and it runs better than ever now.

[EuroDat]

Hi again,

Like Stieunseen mentioned in post #42. The resistor tweak in the temp sensor loop is a great way to adjust the fuel air ratio on the OEM efi.

Some people play with the spring in the AFM to richen the mixture. It works well a low to medium air flows but leans out when the flap fully opens too early and you haven't reached full throttle.

Unfortunately your problem is a rich mixture and the resistor tweak is to compensate a lean mixture. THe injector open time decreases as the resistance decreases. Therefore if you increase resistance you will increase injection time and richen the mixture.

You will need to find the problem first and then use this mod to fine tune your mixture to pass smog.

Chas

[Samson]

Hi again,

Like Stieunseen mentioned in post #42. The resistor tweak in the temp sensor loop is a great way to adjust the fuel air ratio on the OEM efi.

Some people play with the spring in the AFM to richen the mixture. It works well a low to medium air flows but leans out when the flap fully opens too early and you haven't reached full throttle.

Unfortunately your problem is a rich mixture and the resistor tweak is to compensate a lean mixture. THe injector open time decreases as the resistance decreases. Therefore if you increase resistance you will increase injection time and richen the mixture.

You will need to find the problem first and then use this mod to fine tune your mixture to pass smog.

Chas

Okay, Just got done talking with the shop and he said that the computer is shorted, said it was showing 12volts on both sides of the computer? Didn't really understand him.. He told me to not throw a computer in there till I redo the EFI wiring. He's not going to charge me either for Diagnostic and told me to just come pick it up..

[EuroDat]

How are you going with the computer? Im not sure what your mechanic meant by "12volts on both sides of the computer" ?

Have you done the tests in the FSM and Trouble Shooting manuals?

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

http://www.xenons30.com/files/280zfuelinjectionbook.pdf

Chas

[Samson]

How are you going with the computer? Im not sure what your mechanic meant by "12volts on both sides of the computer" ?

Have you done the tests in the FSM and Trouble Shooting manuals?

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

http://www.xenons30.com/files/280zfuelinjectionbook.pdf

Chas

At the injector connectors on both pins it showed power when It's suppose to be power and ground, correct? Therefore its shorted somewhere in my wiring? I've noticed that my computer is also a A11-601 which is off a 78 if I'm not mistaken.. 77s should have A11-600?

[EuroDat]

My computer is an A11-601-000 with Lot nr. 7511 for a L28. The car is from 5/77 and as far as I know the unit is original.

[Zed Head]

Coincidentally, today I was looking at a few ECU's I've collected to see if they had the "altitude compensation" pins. All of them are A11-600-000 and they come from cars from 76-78. While checking the FSM's I saw that only the California cars came with altitude compensation. I wonder if the -601- ECU's have the altitude compensation circuit? Samson is in CA, Eurodat, where did your car, or ECU, come from?

The switch is described and shown in the Engine Fuel chapter, it drops the fuel supply through the injector duration by 6% when the switch closes due to low pressure from high altitude. It wouldn't affect operation unless the switch was shorted, causing a lean condition.

Samson, your mechanic doesn't understand how the injection system works. The injector connections have 12 volts on both sides due to the way the transistors operate (I confess that I'm not clear on why that is either, but it is). The injector solenoids don't activate until current actually flows when the transistor circuit allows it to. 12 volts on both sides is good.

As I said in an earlier post, you're pretty close. I had to adjust my idle air screw and install some new plug wires on my last DEQ (our emissions checkers) visit here in Oregon. A miss will spew unburned fuel (bad), and the idle air screw can lean up the idle. I wouldn't do anything major and I would find a mechanic who knows old EFI.