munoz4415

87 rx7 non turbo
Has spark but no injector pulse. Injector resistor pack tested ok and has power on the black/yellow wire. What are the ecu pinouts for the primary injectors?

RotaryResurrection

iTrader: (8)

Check ecu for proper ground. Since the injectors are triggered by ground pulse from the ecu, it stands to reason that if the ecu is seeing weak grounds, it may not be able to drive the injectors.

You could also have a bad ecu/injector drivers, perhaps due to a short or wiring issue, or the wrong impedance of injectors.

satch

iTrader: (1)

Pin 3C and 3E are the primary injectors. Both pins would have 12 volts w/key to on which indicates the plugs are secured to the injectors correctly.

RotorHappy

Also clean you injectors dirty injectors can give off a muffled pulse, and check with a mechanical stethoscope.

munoz4415

Ok. Now that I think about it, when I had a friend crank the car, I checked for voltage at the injector plug and I got about .3v. Ill check for grounds and let u guys know. The other day I borrowed injectors off a running rx7 with the same resistance and still nothing so im sure its not the injctors theselves.

Sgt.Stinkfist

iTrader: (6)

where in WI are you?

7thseven

I would definitely try another ecu maybe the one off the car u borrowed the injectors from just a thought...

RotaryResurrection

iTrader: (8)

Uhm...the injectors are all supplied with +12v via the thick black/yellow wires elsewhere in the harness, while each individual injector pin at the ecu (the light green colored ones) carry ground pulse from the ecu. Probing those pins at the ecu or the injectors will not give you 12v.

Even if you connected the + probe of your volt meter to a 12v+ wire and then checked those pins for ground, you still wouldn't see anything, because the ecu doesn't trigger the injectors at rest. IF you try checking the same way during cranking or running, you probably won't see any conclusive results because the injector ground pulse is so fast (milliseconds) that a voltmeter can't accurately pick up and display it.

You need a noid light to diagnose injector pulse issues.

Sgt.Stinkfist

iTrader: (6)

^ many newer DVOM's can measure duty cycle. if u get a duty cycle reading while cranking, it will indicates weather or not the ECU in trying to fire the injectors

7thseven

U can just use a test light to see if there working ...put the wire on a power source and put the test light to the injector pin and see if it lights up as ur cranking the engine ...it barely lights up but its enough to see if the injectors are getting a ground signal from the ecu

7thseven

Or just try another ecu to narrow down the possibilities ...

satch

iTrader: (1)

Sorry, but you are wrong as the voltage from the Black/Yellow wire passes on to the light Green wires that run to the ECU w/key to on, engine off. If the injector plug were pulled off of the injector then the light Green wires have 0 voltage at the ECU w/key to on, but when they are snuggly connected they have battery voltage. So if everything were good to go and one of the injector plugs were loose then it would be evident by the lack of battery voltage on the Green injector wire w/key to on at the proper ECU pin. W/no battery voltage on the Green wire w/key to on, and the injector could not possibly fire for the ground signal from the ECU would not be present in any form.

munoz4415

Im in milwaukee

RotaryResurrection

iTrader: (8)

No, you're incorrect. The green wires carry GROUND PULSE from the ecu to each injector. How else do you suggest that the injectors GET their ground signal?

There are two wires on each injector plug, go take a look. One is a light green thin wire, this is the same wire at the other end at the ecu. The other wire is a thick black/yellow wire. That B/Y wire carries +12v anytime the key is on. It is the same circuit that supplies the coils and other EFI/emissions harness components with power.

Let's take a look at the FSM wiring diagram, shall we? Injectors have been circled in red. Yellow shows the B/Y wire path, and represents 12v+ power. So then, those other 4 wires for each injector must be...



Here we can see that the 4 injectors are all connected to a common B/Y wire. Follow that B/Y wire backwards through the circuit. You'll find that it passes through the main relay, and is supplied by the battery positive terminal.

So, we've established that the thick B/Y wires supply each injector with 12v+ anytime the main relay/key is on. There is no way that the green wires can carry 12v+, because two wires with 12v+ will not trigger an injector coil...they need a ground to work.

So...I ask you again...where do you suggest that each injector get it's ground signal, to trigger the coil and actually fire?

From the light green wires, fed by the ecu. So you ask...where does the ecu get it's ground to supply those wires? From the 4 ecu ground pins, 2C, 2R, 3A, 3G. Looking again at our trusty FSM wiring diagram, we can see that these ECU pins all terminate at the same ground point. If that ground point has an issue, then all the grounds to the entire circuit will also be weak.

satch

iTrader: (1)

Why does the FSM list the injector ECU pins as having voltage w/key to on, engine off? Why is it if you measured the pins w/key to on the voltage would be 12 volts?

Post #3 has the ECU pinout list as supplied by the FSM.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/88-rx7-wiring-diagram-968998/

RotaryResurrection

iTrader: (8)

Also, just to clarify for the OP, 86-87s had the B/Y supply wire running through the resistor pack, split there, and sent to each injector, otherwise the circuit remains the same. So you can test for B/Y 12v+ at the resistor pack input wire, and then again at each injector plug, to ensure that each of the 4 resistors have continuity. Once you've verified that path, all you have to worry about is the ecu ground path continuity, both into and out of the ecu. Normally the issue will be getting ground into the ecu itself, since the 4 green wires are usually in pretty decent condition unless the harness has been "doctored" by an engineering type previous owner.

RotaryResurrection

iTrader: (8)

Believe it or not, the certain aspects of the FSM are not always fully accurate and/or do not give you all the info you need. IN this instance, it's my guess that if you were using the correct equipment, they assume that the dealership tech would know to apply +12v to one probe and then check for ground pulse...which would then give you 12v as described.

One thing about it, the wiring diagrams are always the most accurate part of the manuals, so there's no disputing what I've said.

satch

iTrader: (1)

W/key to on and engine off the voltage on the B/Y wire will pass on to the Brown wire which runs to the ECU and can be measured there. If the 12 volts did not occur then either the plug is disconnected or wire(s) in the plug are pulled back. If these wires had a ground then the injectors would fire. Wouldn't they? And you don't have to guess about anything as the facts speak for themselves. Any working RX7 will have battery voltage w/key to on, engine off on the injector wires leading to the ECU.

RotaryResurrection

iTrader: (8)

Brown wire? what brown wire? What circuit? What ECU pin?

How about we make a bet.

We each walk outside and pull an injector plug off an FC with the key on. We take two pics: one showing a volt meter with the ground probe grounded to the chassis or battery terminal and the red probe connected to the B/Y wire on the injector plug, and let's see if we get 12v (indicating the B/Y wire carries the + half of the 12v signal).

Then for test two: plug the injector back in and start the car. we probe the green wire (for one of the primary injectors, since we can be sure they are firing at idle) this time except at the ecu end (since obviously we can't get at the primary injector plugs while the engine is running)...ground probe connected to chassis ground, positive probe connected to a green primary injector wire. See if you see any + voltage on that wire.

Then we post the pics of our VM readings for both tests.

How sure are you of your position on this? Because again, it's already been proven that the B/Y wire carries the + 12v to each injector anytime the key is on, there's no disputing that fact...so unless the ground fairy magically comes in the middle of the night and slips the other half of the circuit electron flow under each injector connector while we're not looking, that ground pulse has to come from some wire, and guess what...the only remaining wire for each injector is the green wire.

Coincidentally, this is also how the ignition coils work. Check it out...key on, the B/Y wire carries 12v+, while the small green/black wires carry the switching pulse signal from the ecu/igniter to trigger the coil to spark.

Sgt.Stinkfist

iTrader: (6)

too bad you arent in the madison area. i was goin to suggest u supply the beers , i could come over with a known good working ecu and my snapon vantage and help u get to the bottom of this issue

satch

iTrader: (1)

From the get go I said w/key to on and engine off and not a situation of when the car was actually running. I never stated while running.

You have a car that suppposedly does not have primary injector firing while starting the car. Now the problem might be created by numerous possibilities, but one of them deals w/the plug not being connected properly or either one of the two pins being pulled back within the plug thus not making good electrical contact and so on. So, one very easy check is to see what voltage you get at the proper ECU pins w/key to on, engine off that relate to the injectors. If you get a 12 volt reading w/key to on, engine off, then you know that the injector plug is connected properly and that the B/Y wire is powering the plug properly as well.

Now this car is an early 87 w/the low resistance injectors. The two wires running to each individual injector is Brown and a Green as opposed to a B/Y and a Green.

RotaryResurrection

iTrader: (8)

I see. So you're advocating checking for or diagnosing an injector ground pulse issue by looking for 12v+ signal being backfed by the injectors on the wires that the ecu would normally pulse ground through...under conditions when the ecu will not pulse ground to begin with...correct?

The brown wires on 86-87 models carry the same 12v+ current from the thick B/Y wire that all the 88-91's get.

satch

iTrader: (1)

The original poster claimed his injectors were not working and asked what the primary injector pins at the ECU were. I replied, "Pin 3C and 3E are the primary injectors. Both pins would have 12 volts w/key to on which indicates the plugs are secured to the injectors correctly." There is nothing wrong with what was stated. Nothing.

RotaryResurrection

iTrader: (8)

<sigh>.

Whatever. You go on checking for injector ground pulse by looking for 12v+ on the ground wires, and I'll keep doing it the correct way.

satch

iTrader: (1)

Could the injectors possibly work if the ECU pins did not read 12 volts w/key to on?