MaxN

1986 Rx7
n/a (as all 86s are)
manual transmission
base model (no ps,ac, or cruise control)
mods:
air pump delete
racing beat Prescilencer
egr delete
omp delete
electric fan

Okay. To preface, yes I know this has been talked about a zillion times. And yes I have read most of the threads on the subject. Now the background on the car. I purchased it non running around the start of summer 2022. Rebuilt the engine replacing all hard and soft seals and all three irons. All other parts were within spec. When doing the rebuild i also removed the egr and omp because they were non operational. Additionally I replaced the fuel filter and fuel pump. I also cleaned the diffuser plates and i am sure that they were installed. The car ran great after the rebuild but would not exceed 3500-4000 rpm. I drove it like this for several months because i had to keep it under 4k for the break in anyway but recently ive decided to dig into it. I have calibrated the tps so im pretty sure its not that. I figured it could be a clogged cat and i was planning on going with a RB Prescilencer anyway so I installed one and while it did make the car run better it didn’t fix the issue. I tested the positive lead to the secondary injectors and confirmed that they are getting power when the key is on. I tested resistance in the injectors, solenoid resistors, and CAS as recommended by the fsm. All were within spec. I hooked up a noid light to the secondary injector leads and when driving confirmed that the secondary injectors were not being grounded when they were supposed to. Next i backprobed the front secondary injector’s ground pin on the ecu and ran a jumper wire to the injector. This allowed the engine to smoothly rev through the rpm range while in neutral but under load it still topped out at 3500. I checked pin fitment on the ground wire connectors and found no issues. So i replaced the ground wires and the car still wont rev past 3500 under load. My solder is good and all of them are properly heat shrinked. There was some improvement as the engine now revs to 7k in neutral sometimes. At this point im pretty lost but it could be a mechanical problem in the injectors or possibly a fuel pressure issue. Please advise.

TLDR: I have tried almost everything and no dice.

thank you so much for reading.

Brice_Brice

Not an NA guy, but if I remember right the air pump delete may affect your 6th port from opening (i cant remember if it was both s4 and s5)... try a search using 6th port, VDI, air pump

Brice_Brice

https://www.rx7club.com/2nd-generati...m-help-919893/ ​​​​​​​according to Aaron cake in 2009, it's the 6th port and VDI that are inop.

MaxN

that only applies to the s5. On the s4 the 5th and 6th ports are controlled by exhaust back pressure. Also this problem has been going on since before the air pump delete. Even then the 5th and 6th ports only come on when the car is requiring torque off the line. Not for high rpm. Thanks for your response though.

WondrousBread

If the noid light shows the secondary injectors aren't behaving as expected, I would start there. Fuel pressure could do it but the noid light tells you there is a definite issue there.

I would check the injector resistor pack. This sits under the airbox bolted to the wheel-well, and has a connector shaped kind of like the Chevy emblem. Disconnect it and make sure there is no corrosion inside.

Otherwise some people find adding a ground to the pressure sensor helps. In my case it did nothing, but it's worth mentioning.

DR_Knight

iTrader: (23)

Check spark? You didn’t mention it in your post so just asking.

I did some work on my t2, drove around and the rpm’s wouldn’t go above 4K. Ended up being I left the leading coil unplugged.

daritto05

Hey boss, I got a 88 na vert. Had the same issues for the longest, replaced lines, fuel filter, pumps, tried a lot of ****, changed the secondary injectors, the upper ones that are visible from left top side of the motor under the throttle body and once I replaced that the issues was resolved and I also re sauder my mass air flow sensor bc I figured the prongs were damaged or torn, I was correct and they were torn so either replace it or do what it did and re did the connections. Doing these 2 things got rid of the 3500 load issue. Update me if it gets resolved, if not, RIP

rlynchster

One things for sure, you don't have a condition where you have too much air. You are either O2 limited or fuel limited.

Things that can cause O2 limited condition. . .

1) Bad Air Mass Meter
2) 5th or 6th ports not opening. (check ports per manual and make sure the line from the last cat is not clogged or cracked and is actually pressurizing the line to open the port actuators.)

Things that can cause Fuel limited.

1) secondary fuel injector resistor pack bad
2) secondary fuel injectors bad
3) fuel pressure not at 64 to 85psi

Hope this helps.

MaxN

Thank you all for your responses. I haven’t had a chance to work on it in a few days but you’ve given me more things to try so I appreciate that and will keep you updated 🫡

MaxN

Alright. Its been a while but if anyone still cares I believe ive figured it out. Im a dumbass so when I went to check the ground off of my vacuum sensor I found that it was unplugged. Unfortunately plugging it in did not fix the issue. I then found that my 5th and 6th port actuators were stuck. Fixed them but the problem still persisted. Only unchecked part was the function of the injectors themselves. As mentioned before they are electrically sound but I found that the pintles were stuck closed. I was able to find some 12 ohm injectors off of a late year 87 and i am bypassing the resistor block to run them. Waiting on one to arrive so I will update when it gets here.

13bfd3s93

I deleted the omp on my car, it put the car in limp mode wouldn't Rev above 3500 rpm. Plugged omp in and zip tied it up in engine bay ran perfect afterwards. Hope this helps

GtiKyle

iTrader: (5)

Just a note, this applies to S5 only, the s4 is purely mechanical and has no fault for disabling the OMP.

R_PROWESS

iTrader: (3)

I had a bad resistor block once on my s4 keeping my secondarys from coming online, swaped it out for another and all is well. It took me years to figure this out.