Rx72Die4

An 87 TII with 89-91 Jspec motor(all s4 wiring and computer). I am trying to diagnose a "3800 rpm brick wall" symptom, and upon my research i have found that at my secondary injectors(Greddy 720s), on the one closest to the firewall i am gettin like .5v at one pin and 1v at the other??????on the one closest to the radiator im gettin 12v at both pins. Just a bad ground affecting one injector??? How can i check this stuff at the ECU???

1SxyRXy

i would just check the wires from point A to point B or just check out the grounds.

Rx72Die4

where would point B be? i can ohm resistance check the wires but i need to know which pin on the Ecu or where else in the harness.

Rx72Die4

oh also what would cause my car to stay running after the key has been turned off?

HAILERS

Go to RADIO SHACK. Buy some wire taps. Pull the rug up to uncover the ECU. Go to the small plug on the ECU. Tap into the LIGHT GREEN wire for the front primary. Then tap into the LIGHT GREEN AND BLACK wire for the rear secondary wire.

Both should read approx 12v or battery voltage when the key is turned to ON. When the car is started and idling, they should read b/t 11 and 12volts. As you drive the car and step on the pedal some more the voltage will decrease when you are ON IT. The more you're on it, the bigger the voltage drop.

The front secondary is a LIGHT GREEN AND WHITE wire and the rear secondary is a LIGHT GREEN AND RED wire. Those will read approx battery voltage until you hit 3500rpm AND are heavily ON IT. Then the voltage will drop. If you are not on it, those two will read battery voltage all the way to six/seven grand/until engougn load is applied.

The primay injectors are the two down on the intermediate housing. The front primary is in the front and the rear primary is.....where??????

The secondary injectors are located up higher above the primary injectors. The front secondary is towards the front of the car and rear secondary is....where??? Towards the rear of the car. There. Done.

Almost done. Early 1987 cars had low impedence injectors. The JAP motor has high impedence injectors. The two, 1987 and 1990 whatever are not compatable. To tell if your car has a early injector setup, Remove the afm and look down. A early 87 will have a thing callled a solenoid resistor. It will have an aluminum cover on it. Its is approx four inches long and an inch wide. It has a round connector going to it. It is held on the fender with two 10mm wrench size nuts.

HAILERS

Car runs when the key is off? Have you done some electrical work on it lately? Say you removed and replaced your alternator and had a busted two prong connector that goes on the back of it. If you put the wires on the alternator *** backwards, i.e. in the case of a 87 car, the black/white one where the white/black one should go, then the car will run with the key to off, UNTIL you stall the car by dumping the clutch with the brake on. Then the car will die. In that case it would have been the voltage of the alternator keeping the car running with the key to off.


There are othere scenarios where a person ties a hot wire where it should not be a going. Same results more or less. So undo what you have done whatever it was.

Rx72Die4

Hailers your dead on with the alternator, one of the wires was coming apart so i redid it, must have just got them switched tryin to hurry to fast. And thanx for the injector tip ill try some of that testing as soon as i can.

Rx72Die4

oh and i knew about the jspec injector resistance so i kept with the S4 ones

Rx72Die4

Ok, finally the results of the testing...the alternator problem is fixed...and i am getting battery voltage at ECU on the Light Green and Black wire and the Light Green and Red wire, a friend suggested to me that it may be a broken wire from the ECU to the injector, or/and broken wire from the resistor pack???? sound logical??? ground???

HAILERS

Yes, a broken wire at the resistor pack would ruin your day. That's good for the Light green/black and the Light green/Red. Now the Light green/white is the Front secondary and the plain Light green is the Front primary. See: https://www.rx7club.com/forum/attach...postid=1449483

If it's a early 87 it has the resistor pack below the afm/filter assy, attached to the fender. It has one power wire going into it that feeds four resistors and from each resistor a wire goes to its respecitve fuel injector.

So at each fuel injector, one wire should have 12v anytime the key is on. The other wire at each fuel injector goes to the ECU. The ECU pulses a ground to the injector in milliseconds. So what you would see on a meter attached to a primary injector wire at the ECU, would be batery voltage of appox 12 volts and as you stomp the pedal, that voltage would DROP on down to around 3-4 volts until the engine reached 3500 rpm upon which the voltage would go to somewhere around 7 or so volts. Also at that 3500rpm the secondary injector voltage would go from a solid 12v approx, to the same voltage as is seen on the primary wire, then if you kept your foot in it, both voltages would drop to??????got me.

Yeah, resistor pack....not ground. The ground is put on it by the ECU in millisecond span ranges. One wire on the injector should see 12v with the key to on and your meters negative lead on a good ground, like the battery negative post...or on the block or a clean bare place on the chassis.

Do not put your meters positve lead on one wire at the injector and the negative lead on the other wire on the injector. It don't hardly work like that, never ever. It also does not hardly work like that. Just more fun to say don't hardly.

Rx72Die4

OK here is an update and a correction, (correction - Lg, LgB, LgW all reading battery voltage, LgR reading approx. 5v -- got these same reading on 2 different ECUs, an N332 and a N333) and upon checking the wiring from the Resistor pack i am only getting .5v at the BrY wire, so i will be purchasing some new resistors from radio shack, what spec resistors should they be?? What you think about the voltage from ECU?? do i just have 2 with the same problem???

HAILERS

Something is honked up in this discussion. The battery voltage originates at the Brown/Yellow wire, passes thru the Solenoid resitor thru four resistors, TO the injectors.

So if you can't read 12v at the injectors and have only .5 volts at he brown/yellow wire. Comprende????

The voltage goes thru the resistor, to the injector, and finds a ground when the ECU decides to pulse a ground to the injector. That ground is in milliseconds, and drops the voltage down from 12v to ?????what ever load the ECU puts on it. Something like that.

Nope. PUll the small plug off the ECU. Put a meter on each of the injector wires. They all should read the same, approx battery voltage. If the brown/yellow has but .5volts....then all the injector wires will have approx .5volts on them. Look at the picture https://www.rx7club.com/forum/attach...postid=1449483 Be sure your putting your meters negative lead on a good ground when checking things out.

Rx72Die4

I believe you are talkin about the Black/Yellow wire that goes into the resistor pack... i was referring to the BrY one that comes out of the resistor pack to the Rear Secondary but i have that fixed, there is now 12v goin from it to the injector, hence the resistor pack is good. On the other end however i am still getting 12v on all wires at the ECU except the Light Green/Red wire, on that i am getting only 5v?? what is the cause for this?? Just to make sure with KOEO i should be getting 12v on both of the wires going to the injector if i check them at the injector??? I apologize for being such a headache, i realize there is somethin i am not catching here.

Rx72Die4

Its Fixed!! It's Fixed!! Thank you HAILERS

HAILERS

Oh poop. I see I wrote brown/yellow when I should have written black/yellow. Oh well. Thanks/your welcome.