No Throttle Response/Bucking
11-22-23, 09:36 AM
#1
Junior Member
Thread Starter
No Throttle Response/Bucking
This will be rather lengthy, but I am deep into an issue that I do not have the solution to and am lost after doing so much; therefore I will give the full story to my situation as it may help for context. RHD 1997 RX7 Power FC TT 13B-REW bought in Japan sat for a while. Drove fine after sitting for like 6 months. Gunned it one day and immediately after it would not go past around 4-5k without bucking/jerking bad and backfiring. It has gotten worse. It now will not respond to the throttle at all ( loss of all power) after about 10% throttle and if I get up to it like 2.5k then no acceleration again. Therefore, I cant go past 10 mph or any grade of incline. Will backfire occasionally when this happens. Car only smokes on startup for a few seconds then good (read this was normal). Has been ran with only premium gas. Did attempt to premix recently in case OMP was bad. From what I've read, the Power FC will not go limp mode if this is bad? So, I was mixing to see if it would help and if it had helped I would have thought to block it off. But it did not. Will idle perfectly with just a few misfires very seldom. Revving when cold in neutral will go all the way through the rpm range, however after hot and driven will not. At this point it will stop like a rev limiter/governor almost at around 2.5/3k.
As a means to fix for the past 6months-year I have... new vacuum line to boost sensor, installed IGN-1A distributor-less coils, new spark plug wires, new spark plugs, new fuel pump (it is the cheaper MasterPro fuel pump from Advanced Auto Parts), new fuel filter, checked fuel relay, EVAP Purge Solenoid had 0 ohms replaced with new, all other Solenoids in vacuum chamber read 30-38 ohms, boost sensor when unplugged obviously car will die after chugging bad, removed catalytic converter to see if backpressure maybe was plugged? but no difference-reinstalled, and adjusted the TPS.
Final Questions: I read with a piston compression checker warm engine full throttle 60 psi at each bump for front rotor and back rotor consistent (however, if I kept the schrader valve in the tester it read 90 psi, don't think this matters from what I've read). I know this compression is low but it shouldn't run this bad right? It just means it is weak compression and sealing therefore eventually soon I could blow it correct? Power FC shouldnt have a limp mode but it is acting like a limp mode? PowerFC is on Normal PIM. PowerFC only has base map. Don't think I had one to begin with but maybe I deleted it? Don't think so though because the problem was instantaneous after gunning it that one time then got progressively worse. No blacked out sensor readings.
I know this was alot but hope you understand my situation. Any solutions or ideas would be of great help as you can tell I am lost. I was leaning toward maybe OMP or just need to rebuild. If rebuild is necessary, please send suggestions for cheap/good rebuild kits as I would be doing it myself to save money.
As a means to fix for the past 6months-year I have... new vacuum line to boost sensor, installed IGN-1A distributor-less coils, new spark plug wires, new spark plugs, new fuel pump (it is the cheaper MasterPro fuel pump from Advanced Auto Parts), new fuel filter, checked fuel relay, EVAP Purge Solenoid had 0 ohms replaced with new, all other Solenoids in vacuum chamber read 30-38 ohms, boost sensor when unplugged obviously car will die after chugging bad, removed catalytic converter to see if backpressure maybe was plugged? but no difference-reinstalled, and adjusted the TPS.
Final Questions: I read with a piston compression checker warm engine full throttle 60 psi at each bump for front rotor and back rotor consistent (however, if I kept the schrader valve in the tester it read 90 psi, don't think this matters from what I've read). I know this compression is low but it shouldn't run this bad right? It just means it is weak compression and sealing therefore eventually soon I could blow it correct? Power FC shouldnt have a limp mode but it is acting like a limp mode? PowerFC is on Normal PIM. PowerFC only has base map. Don't think I had one to begin with but maybe I deleted it? Don't think so though because the problem was instantaneous after gunning it that one time then got progressively worse. No blacked out sensor readings.
I know this was alot but hope you understand my situation. Any solutions or ideas would be of great help as you can tell I am lost. I was leaning toward maybe OMP or just need to rebuild. If rebuild is necessary, please send suggestions for cheap/good rebuild kits as I would be doing it myself to save money.
11-22-23, 12:23 PM
#2
welcome to the board. 
for your limp mode question, i've found threads where people who i believe to be credible and experienced have said both - it does and it does not. however, i found more threads that said it does have a limp mode. so take that for whatever it's worth.
other things worth mentioning from threads i searched are: MAP sensor and the PIM screen (i have no idea what that is). the boost sensor and TPS were pretty common as well, but it sounds like you have already eliminated them as possible reasons for your issue.
https://www.rx7club.com/power-fc-for...-reset-467911/
https://www.rx7club.com/power-fc-for...fe-mode-76966/
what i think is more important right now is your compression test. if you're using a piston tester, then the schrader valve should out, and if you're getting consistent 60s on both rotors, then that's a problem. i think it's also sort of odd though. recheck, making sure the engine is warm and that the cranking RPM is adequate and see what you get.
for your limp mode question, i've found threads where people who i believe to be credible and experienced have said both - it does and it does not. however, i found more threads that said it does have a limp mode. so take that for whatever it's worth.
other things worth mentioning from threads i searched are: MAP sensor and the PIM screen (i have no idea what that is). the boost sensor and TPS were pretty common as well, but it sounds like you have already eliminated them as possible reasons for your issue.
https://www.rx7club.com/power-fc-for...-reset-467911/
https://www.rx7club.com/power-fc-for...fe-mode-76966/
what i think is more important right now is your compression test. if you're using a piston tester, then the schrader valve should out, and if you're getting consistent 60s on both rotors, then that's a problem. i think it's also sort of odd though. recheck, making sure the engine is warm and that the cranking RPM is adequate and see what you get.
11-24-23, 10:20 AM
#3
Junior Member
Thread Starter
welcome to the board.
for your limp mode question, i've found threads where people who i believe to be credible and experienced have said both - it does and it does not. however, i found more threads that said it does have a limp mode. so take that for whatever it's worth.
other things worth mentioning from threads i searched are: MAP sensor and the PIM screen (i have no idea what that is). the boost sensor and TPS were pretty common as well, but it sounds like you have already eliminated them as possible reasons for your issue.
https://www.rx7club.com/power-fc-for...-reset-467911/
https://www.rx7club.com/power-fc-for...fe-mode-76966/
what i think is more important right now is your compression test. if you're using a piston tester, then the schrader valve should out, and if you're getting consistent 60s on both rotors, then that's a problem. i think it's also sort of odd though. recheck, making sure the engine is warm and that the cranking RPM is adequate and see what you get.
for your limp mode question, i've found threads where people who i believe to be credible and experienced have said both - it does and it does not. however, i found more threads that said it does have a limp mode. so take that for whatever it's worth.
other things worth mentioning from threads i searched are: MAP sensor and the PIM screen (i have no idea what that is). the boost sensor and TPS were pretty common as well, but it sounds like you have already eliminated them as possible reasons for your issue.
https://www.rx7club.com/power-fc-for...-reset-467911/
https://www.rx7club.com/power-fc-for...fe-mode-76966/
what i think is more important right now is your compression test. if you're using a piston tester, then the schrader valve should out, and if you're getting consistent 60s on both rotors, then that's a problem. i think it's also sort of odd though. recheck, making sure the engine is warm and that the cranking RPM is adequate and see what you get.
11-24-23, 12:02 PM
#4
i'm linking your other thread here so future searches will get all responses to your question: https://www.rx7club.com/3rd-generati.../#post12584587
11-27-23, 07:59 AM
#5
Junior Member
Thread Starter
welcome to the board.
for your limp mode question, i've found threads where people who i believe to be credible and experienced have said both - it does and it does not. however, i found more threads that said it does have a limp mode. so take that for whatever it's worth.
other things worth mentioning from threads i searched are: MAP sensor and the PIM screen (i have no idea what that is). the boost sensor and TPS were pretty common as well, but it sounds like you have already eliminated them as possible reasons for your issue.
https://www.rx7club.com/power-fc-for...-reset-467911/
https://www.rx7club.com/power-fc-for...fe-mode-76966/
what i think is more important right now is your compression test. if you're using a piston tester, then the schrader valve should out, and if you're getting consistent 60s on both rotors, then that's a problem. i think it's also sort of odd though. recheck, making sure the engine is warm and that the cranking RPM is adequate and see what you get.
for your limp mode question, i've found threads where people who i believe to be credible and experienced have said both - it does and it does not. however, i found more threads that said it does have a limp mode. so take that for whatever it's worth.
other things worth mentioning from threads i searched are: MAP sensor and the PIM screen (i have no idea what that is). the boost sensor and TPS were pretty common as well, but it sounds like you have already eliminated them as possible reasons for your issue.
https://www.rx7club.com/power-fc-for...-reset-467911/
https://www.rx7club.com/power-fc-for...fe-mode-76966/
what i think is more important right now is your compression test. if you're using a piston tester, then the schrader valve should out, and if you're getting consistent 60s on both rotors, then that's a problem. i think it's also sort of odd though. recheck, making sure the engine is warm and that the cranking RPM is adequate and see what you get.
I tested my compression this weekend. I am getting 90+ish on each face of each rotor. This was while hot and full throttle. I am getting around 248 cranking rpms each time as well. Therefore, my previous compression tester being a conventional rental and used quite often must have been losing pressure giving faulty readings. This is good news, showing a healthier motor than originally thought! With that being said, I bought a OMP block-off plate and am waiting on it in the mail. The next thing I have thought might be faulty is the OMP causing a limp mode type effect/ complete fuel cutoff? I do understand I will have to pre-mix after this is done. Any other suggestions?
11-28-23, 10:40 AM
#6
great news on the compression test! i'm really happy it worked out.
i'm afraid i'm pretty useless with your Power FC issues. i never worked with one and had no reason to really study them. what i will say is if your MOP idea does not work, then take heed to Akagi's White Comet's post in your other thread. in my opinion, it seems to be solid advice.
god luck with it. post your findings whenever you figure it out and get your car running well again.
i'm afraid i'm pretty useless with your Power FC issues. i never worked with one and had no reason to really study them. what i will say is if your MOP idea does not work, then take heed to Akagi's White Comet's post in your other thread. in my opinion, it seems to be solid advice.
god luck with it. post your findings whenever you figure it out and get your car running well again.
01-09-24, 11:42 PM
#7
Junior Member
Thread Starter
Gentlemen, the problem has been solved. I diligently worked and applied all the helpful information you all gave. However, after I got no results I decided to go back to my first assumption, the fuel pump. I replaced with an aeromotive 340 this time instead of a garbage autozone one. Nothing.... however the wiring from fuel pump to the adapter on the fuel sender unit was bad at the adapter. Multimeter read 0.2 ish ohms however I replaced anyways because it looked awfully messed up. That was it! I no longer have any acceleration issues! I am now only working on cosmetics and currently chasing a boost leak; im getting like 0.36 on the power fc I believe mmhg and a notable air leak noise entirety of time im building boost. I am so happy to have fixed the original issue now though. Thank you all.
The following users liked this post:
diabolical1 (01-16-24)
Trending Topics
Thread
Thread Starter
Forum
Replies
Last Post
Stussy
2nd Generation Specific (1986-1992)
4
06-25-22 08:31 PM
dimondjack
3rd Generation Specific (1993-2002)
50
07-10-11 10:46 PM