Romak

K Im new here, hello, anyway I picked up a 75 and im having issues getting it running right, It has absolutely no power at all . Ive went threw all the tests in the FI bible. everything tested out ok except the AFM what a little off. Pin 6-8=200 Ohms (supposed to be 180) Pin 8-9=110 (supposed to be 100) and Pin 7-8=150 (supposed to be "Small Resistance") my question is, Are these numbers close enough that I should be able to drive the car without a noticable loss of power?

Ive checked for vacume leaks at the manifold TB and Boot, tested fuel pressure (30 at idle and moves), manifold vacume pressure (15 or so) , taken off and plugged the PCV system, brake booster, charcoal can, dash pot, and bcdd just to make sure none of those were a leak. Ive also sound checked the injectors and ohm checked them, all good. Ive also Removed the valve cover because there was no gasket on it, I put it at TDC and checked to make sure the cam was close to correct in position, which it is. Put a gasket back on it and it actually ran alot better but still no power. Checked ign Timing its on.

My plugs say Rich (fouled with carbon, Im about to change them just to check) but I think It is running lean because if I "Finger the AFM" to make it more rich it runs stronger, more lean runs crappier. The only other idea I have is that my injectors may be plugged up a little. any ideas?

zxguy1986

Welcome to ZDriver!

Great project you got there! Just remember that your Z was designed and built to run forever. Probably all you have to do is catch up on the regular maintenance your previous owners let slide, maybe for years... You will see.

If you don't have one already, pick up a freebie factory service manual [and other cool docs] at XenonS30 Great testing and inspection pages, easy to follow. Great almost-good-English from Nissan, too!

Our S30 pros will have some good input for you here. Check back and share info about your Z. Pics are always cool if you have them. Easy to post.

Thanks and welcome!

Romak

the car is fairly "fresh" when i had the cover off it looked like it had a new cam and it definitely had new chain and gear. looks like no miles on a reabuild. its got adjustable struts, drop springs, rear disc conv. strut bar, and energy bushings all around. it looks like it was well taken care of but it wasnt running right when i bought it. It would only idle and it didnt do that well. Im an ASE master tech so it didnt concern me much but ill admit im getting my *** kicked right now by a stone age fuel system. im not happy about it.

beg3yrs

IMHO those numbers, except for the "small resistance" are actually pretty good. Tolerances in resistance measurements typically can be within 15% and be within spec, unless otherwise stated. I doubt the electronics in these cars are any closer than that.

In the case of the "small resistance" of 150 ohms, that's a toss-up for me. If we're talking loudspeakers, 150 ohms is a large resistance, but we're not. I really don't know. Someone else with a FI car will have to chime in.

Your car looks sweet! Congratulations.

Steve260Z74

First off, THANK YOU for describing your testing and diagnostics.

Pins 7-8 are for the potentiometer in the AFM. This link may give you insight on its function: http://www.atlanticz.ca/zclub/techtips/afm/. (Blue's Tech Tips should be bookmarked IMHO. Read through his other tips, too.)

When you say the fuel pressure was 30 PSI, what did it do when someone pressed on the gas? The lack of power frequently indicates a fuel flow problem. Also what did you mean by "and moves" for the fuel pressure.

Also to cast a wider net for potential solutions, Google is your friend. Type in phrases like this into the Google Search box:
AFM potentiometer site:zcar.com
AFM potentiometer site:classiczcars.com
That will narrow down your search to those boards. ZCar.com was a much more helpful board 10 to 15 years ago. Read through the results.

Good luck and keep us posted.

Romak

if I force the pump to run with the motor off it goes up to 36 and the regulator hums like its working. with the engine running when I blip the throttle the pressure will come up with RPM. sorry I was trying to be thorough without leaving 6 pages to read.

that tech article is a huge help, I might try to adjust the wiper on the carbon trace to put it on a fresh track incase it is a little worn but I hate to start adjusting a factory setting in the AFM Without being 100% that's the issue. I don't want to fix one problem by creating another problem if you get what im saying.

Steve260Z74

Lots of details broken out is perfectly acceptable. You'll get better answers.

Your approach is logical. When you have time, do searches based upon my earlier suggestion. An hour or two reading may save you from many hours chasing down the wrong problem. I don't post many questions myself because I have searched & read through the major boards enough that I can usually find where someone had the same issue I had before.

You may want to post all of the details you presented here over at zcar.com and classiczcars.com. With your diagnostics, you will get some good responses from people with far more experience than I have with the factory EFI.

beg3yrs

Steve - THANKS! Although I don't have and AFM problem, from you I learned how to narrow down the Google search. That's really useful.

Steve260Z74

I'm glad I could help. Knowing how to use Google and knowing how to read wiring drawings make me look a lot smarter than I am.

Also, if you notice, the links in my signature block can help to answer a lot of questions, too. I just need to add the link to carpartsmanual.com

theramz

You might want to check for continuity at the ecu plug to make sure the ecu is getting the signals. If the cold start injector is stuck open it will give a seemingly rich condition but that doesn't mean the injectors are working good. Could be the injectors are clogged. If you very slowly open the throttle will the rpms go up? Make sure your dizzy advance is actually working. Observe with cap off and a vacuum pump, this is a very common failure.