Broken AFM...expensive part

[Zed Head]

Darn! I wrote a nice long post and this thing timed out on me. Hit Go Advanced and everything is gone. Any way for the admins to add a little time to that function? Do I set that somewhere?

SBlake, I thought about that, and I have read the same, but I have measured mine according to the procedure and the wires going to the injector all measured line voltage (12.6 V).

I think that dropping resistors actually drop current. This is what the manual states - "The dropping resistor is provided to drop electric current flowing through the injector and control unit."

(Edit - Not sure of my reasoning so removed it. Tests still worth doing)

(2nd Edit - My reasoning was wrong. Apparently both voltage and current drop when the injector is fired. Apparently to nine volts. But at zero current flow, voltage measured is line voltage.)

Funky-P, my comments are from the 1976 FSM. Your 1977 might have a different pinout but the test is still worth doing. If you have power, then you can focus on why the ECU doesn't fire.

Edited November 8, 2010 by Zed Head

[Zed Head]

The ECU doesn't control when the fuel pump comes on.

There is a 5 blade relay in the relay bracket. When you turn ignition on, it should turn the fuel pump on. Look for a white/black wire with 12v going to that relay. Test the relay.

The ECU gets power from the 6 blade FI relay right next to it. So you might as well test that relay while you are there. Test procedure for the relays is in the FSM under the EF section.

Cozye, just noticed your post. The fuel pump only runs when the motor is running (opening the Air Flow Meter flapper valve) or when the key is at Start. When the key is at On, you can make the fuel pump run, on 75, 76 and 77 cars, by opening the AFM flapper, which makes the contact for the fuel pump. Otherwise the fuel pump should not run when the key is at On.

This stuff is addictive.

Good luck Funky-P (I hope that's like a Married with Children ref or something and not an attribute...).

[Funky-P]

So some more information on what I've been doing/how I've been testing:

Based on page EF-22 I checked the Electronic Fuel Injection Relay: Fuel Pump Relay, by checking continuity between ECU pin 20 and grounded body metal. This checked out fine.

From the same page I checked the Air Regulator and Fuel Pump circuit by checking continuity between pin 34 and body metal. Again this was fine.

Based off of page EF-46 I checked the continuity of the circuit from fuel pump to air regulator to the ECU harness, connector 34. This circuit also checked out fine.

The fuel pump itself works when connected straight to voltage, so I'm at a bit of a loss as to why it doesn't come on at the START position. Unless the relay is bad, but the only test I see for that in the FSM is the ecu harness point test. Is there a good way to actually test this relay on its own?

I tested the injector pulse using the steps outlined on EF-52, where it describes connecting a small lamp to the harness of injectors 1 & 4 (not simultaneously) and cranking the engine to see if the light pulses. The light did not come on at all, and I tested to make sure the light functioned. Is there any other reason than a bad ECU for this issue?

A previous owner has messed with the wiring, there's a new ignition wired in and the connectors to the battery are rewired as well as some various other things, so its a bit more convoluted than it should be to try to get things tested individually.

I think it would be a bit more of addictive car if I could get it started, thanks for the suggestions though guys.

[FricFrac]

Yes the current limiting resistors limit the current. They do of course act as a voltage divider as well since your injectors have a resistance that is in series with the resistors so you will get a voltage drop across the resistor and across the injector.

Problems with AFM's (and current limiting resistors for the injectors) are often bad contacts. Make sure you have a good clean contact between the two and that the clip for securing the AFM is in place and you aren't just relying on the friction from the pins to hold the AFM connector on. The resistor pack can have the same issues as well will bad or broken connections.

Current won't drop when the injector is fired. It's the only time it will actually flow. Without the injector firing there is no completed circuit and without a completed circuit there is no current flow.

For the ECU there is an LED that lights up to give various fault codes as well IIRC. Check with the FSM at www.xenonS30.com or www.xenons130.com

You should typically be able to start the engine for a bit but it will sputter and stall if the AFM is completely disconnected. Poor running, stuttering, stalling, etc are AFM issues - not starting is likely an issue elsewhere. Got Spark?

[Zed Head]

Coincidentally, just saw this on Hybridz from a guy who had an ECU that wasn't firing the injectors. Said he had his coil wired backwards. Post #72. Also said his fuel pump wouldn't run because he had a bad EFI relay.

http://forums.hybridz.org/index.php/topic/91070-moderns30s-1972-datsun-240z/page__pid__904721__st__60#entry904721

[Funky-P]

Hmm I'll take a look its definitely possible with all the rewiring that has been done. Probably wont have time though until Friday.

[Funky-P]

Today was the first day I had to get to check out the relay due to school, work and the weather.

We tested the relay based off of the 280z fuel injection book. What we found was that the relay did not click when ignition is turned to start, so we checked the circuit between ECU pin 4 and ground for battery voltage when the starter solenoid and cold start valve were disconnected, and ignition was turned to start. We did not get the twelve volts, more like .7 to .01 volts. The fusible links appear to be okay.

So it looks like the power relay/fuel injector relay is not working, this relay is surprisingly expensive as well, I'm wondering if there is anything else we should be checking before buying one esp as it looks like it has been replaced before. The relay has 78 fuel pump relay written in sharpe on it is why I assume it has been changed before.

[Bruce Palmer]

I'm starting to get a better understanding for why guys are opting for the carb swap. BRrrrrr!

[Funky-P]

It looks like the relay has been replaced before (written on it in sharpe is '78 fuel pump relay) making me more skeptical that it is the problem.

[Zed Head]

I lam lovin' my EFI! It is smooth and clean running, and starts right up in the cold.

Funky-P, I was talking to a guy doing a V-8 swap the other day and he mentioned that he is using an inexpensive relay he picked up at the auto parts store to get 12 volts to his fuel pump.

Since you are deep in to your wiring diagrams, it might be a simple, cheap solution for you. I don't think that there is anything extraordinary about the Datsun relays. You could probably put together something that works for under $20.

[Funky-P]

I was wondering if that might be a possibility, I had to do that for my rx7 to get the wipers running. I'm going to check to see if I'm even getting power to the relay first, I don't think I did that yet for some reason.

[cozye]

Cozye, just noticed your post. The fuel pump only runs when the motor is running (opening the Air Flow Meter flapper valve) or when the key is at Start. When the key is at On, you can make the fuel pump run, on 75, 76 and 77 cars, by opening the AFM flapper, which makes the contact for the fuel pump. Otherwise the fuel pump should not run when the key is at On.

This stuff is addictive.

Good luck Funky-P (I hope that's like a Married with Children ref or something and not an attribute...).

I thought the 77 was the same as the 78 and they deleted the fuel pump cut off switch in the AFM ? If not, yeah my bad. There is that switch in the AFM on the older models. In any case he could jumper it on the AFM connector just as a test.