Great48

Alright, the title tells my whole story. Before anyone says to search the forums i will list everything i have done to try and fix this problem.

I have a 1989 rx7. I was told the motor was replaced with an 1988 13b rotary that came out of an s4, im guessing cause it only has a single throttle position sensor as an assembly.

My problem is right at 3600rpms, not 35 or 37, and it will occasionally rev normally in first gear (probably about after 40 shifts). Once it hits 3600 the car bogs and wont pick up in speed but rpms continue to slowly rev. This is everything i have researched and or tried.

~First I tried re grounding my wires
http://www.nopistons.com/forums/topi...m-stumble-etc/
http://www.aaroncake.net/rx-7/grounding.htm

~Then 3800 RPM CUTOUT
http://www.teamfc3s.org/faq/FAQ.html
http://www.johnr.com/rx7faq/faq3.html
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/infamous-3800-rpm-hesitation-40609/

~Researched fuel pump pressure
https://www.rx7club.com/forum/showth...ion+rpm+switch

~Also TPS Adjustment
https://www.rx7club.com/newthread.ph...ewthread&f=256

I am a big hot rodder, chevy small block 350 is the love of my life, and i'm to the point where I want to drop one in my rx7, but I really want to keep it original!

eff_three_see_es

iTrader: (11)

have you tried testing your secondary injectors?

satch

iTrader: (1)

The ECU needs to see load to fire the secondaries. You can simulate load by disconnecting the vacuum hose to the Pressure sensor and plugging said hose in addition to unplugging the TPS. Doing so will cause the ECU to think there is load on the car. You could either drive the car or rev it in the driveway to check if the hesitation still occurs.

Great48

I am yet to check the secondaries!

But satch, the hesitation still occurs when i simulated the load

satch

iTrader: (1)

Both wires at the secondary clips should have 12 volts to them w/key to on when they aren't being used. The Black/Yellow wire always has battery voltage while the other wire, Light Green, has battery voltage until they are used and then the voltage drops. You could double check the voltage on these wires in addition to checking if the clips themselves are solidly connected to the injectors. Also, you could use an LED light at the ECU to see if the ECU is sending the proper firing signal to the secondary injectors or not.

Great48

The secondary clips have 12 volts running to them, but i do not have an LED light to check if it is firing properly. Any other suggestions satch?

satch

iTrader: (1)

As the secondaries kick on the voltage of the ECU wire which fires them would drop down to about 7 volts or so. An LED lights costs about two bucks at the local Radio Shack.

Great48

I'm off to go get an LED real quick, what should be my next steps?

satch

iTrader: (1)

Use the car battery to figure which LED wire is positive and which is negative. At the ECU pin 3H is the front secondary (Light Green/White wire) and pin 3F is the rear secondary (Light Green/Red wire). The smallest ECU plug located on the left side is the plug that houses these two pins. The negative LED wire goes into the back of one of these wires and the positive wire goes to pin 3I which is a Black/White wire. If you simulate load then you could check the trigger signal in the driveway as you rev the car. If the ECU sends the fire/trigger signal it will flash the light repeatedly.

3H is bottom row and second from the left.
3F is just to the right of pin 3H.

Great48

Scratch that, i hooked the LED up and it flashes repeatedly

satch

iTrader: (1)

I guess but if you were by yourself you would be able to see the light better perhaps if it were in the car plus if you wanted to do the test while driving that would require the light be in the car. Just depends. The positive wire needs to go to a constant voltage wire which could be the B/Y wire at the injector clip. If the injector clip is fashioned so as to accept the LED wires properly then I guess it could be done. You'll find out one way or the other.

Great48

I have me and my dad testing everything out, we hooked the LED up both ways and it seems to flash repeatedly, i found some small LED at my house so it wasnt the brightest flash, but it flashed!

satch

iTrader: (1)

Can you take an ohm reading of the secondary injectors? Some are low impedance while others are high impedance. If they are the wrong impedance that could perhaps explain the problem.

Was this car previously an automatic by chance?

Perhaps the injectors are damaged. Something to do with the coils located internally.

Your injectors are likely the same all across so if you wanted to switch them with the primaries that might shed some light on the cause.

Great48

Now that you mention it satch, we noticed yesterday that on my trailing coil
ignition box it seems when you have the car running and remove the plugs, with big welding gloves on of course, seems the coils are cracked and will jump from one to another. My dad believes something isn't firing at the right time, im not a technician and he has no clue on how to work on rotarys, so both of us have no idea what we are doing to this thing.

satch

iTrader: (1)

Actually, the coils I speak of are located inside the injector itself. The trailing coil is not needed to run the car. You could disconnect the two electrical plugs to the coil which has the B/Y wires and the other plug has 4 wires but I doubt it will cure your problem but you could try.

W/o the key just pull the clip off the injector and place both the meter leads on each of the injector terminals and get an ohm reading.

Great48

The readings i am getting from the injector terminals are around 2.2

satch

iTrader: (1)

Hmmmm... Low impedance injectors require resistors to run properly. The earliest S4's were all low impedance injectors and then it was later changed to high impedance. Perhaps you have the wrong injectors regarding the impedance such as high impedance on the primaries but low impedance on the secondaries. If this were the case and there were no resistors for the secondaries then this might be your problem.

RotaryRocket88

iTrader: (7)

The fact that the car has somewhat of an unknown history will complicate things, but here's what I can tell you. '88s did not use low impedance injectors, so there was no resistor pack attached to the EM (emissions) harness. '86-'87.5 cars used low impedance injectors, which is what you apparently have (2-3 ohm). High imp. injectors would show 12-13 ohms. So the question is what exactly you have for an EM harness. It could be a converted S5 harness (unlikely), an '86-'87.5 harness, or an '87.5-'88 harness. Odds are it's at least S4 ('86-'88), so what you should do next is check for a resistor pack. It's a little silver box plugged in around the airbox/AFM. There are pictures in this thread that show the pack: https://www.rx7club.com/forum/showthread.php?t=470664.

If you don't have this pack, you're likely looking at a circuit with too little total resistance. This means excessive current passing through the ECU, which can lead to damage. The only other way someone could have wired the car up properly is if they spliced aftermarket resistors into the injector wiring. This could have been done at ECU connector (LG, LG/W, LG/R, LG/B wires on plug #3), or at the injector clips.

Great48

My problem is fixed! There is a SMALL hesitation now around the 4k rpm range but you can only notice it if you really pay attention. I think my TPS has a flat spot in it, i messed around with alot of stuff today/tonight so i dont know what fixed it for sure, but thanks satch and rotaryrocket88 for the information!