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Famous 3500rpm lag, replacing grounds didn't work

Old 03-10-19, 11:20 PM
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Famous 3500rpm lag, replacing grounds didn't work

My 1st post to this forum and new owner of a super clean 1986 RX7 N/A. So I bought this car 2 weeks ago and noticed it falls on its face right at 3500 rpm. If you keep on the gas it gets past that spot and rips in the high rpms and has plenty of power. I had found that post about redoing the grounds. I went straight for the computer ground underneath the intake manifold and resurfaced the metal parts and used dielectric grease on them. I also did the one at the back of the intake manifold that goes to the firewall because it was right there. I ported the throttle body while I was in there too.

Conclusion: The car still falls on its face at 3500rpm. I only redid the 2 grounds but isn't it the computer ground that causes this issue? What else could it be? Thanks.
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Old 03-11-19, 07:14 AM
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Originally Posted by DenCoRX7 View Post
My 1st post to this forum and new owner of a super clean 1986 RX7 N/A. So I bought this car 2 weeks ago and noticed it falls on its face right at 3500 rpm. If you keep on the gas it gets past that spot and rips in the high rpms and has plenty of power. I had found that post about redoing the grounds. I went straight for the computer ground underneath the intake manifold and resurfaced the metal parts and used dielectric grease on them. I also did the one at the back of the intake manifold that goes to the firewall because it was right there. I ported the throttle body while I was in there too.

Conclusion: The car still falls on its face at 3500rpm. I only redid the 2 grounds but isn't it the computer ground that causes this issue? What else could it be? Thanks.


Damn i cant for the life of me remember the name but im sure S4's had a sort of actuator that activates after a certain RPM. Dont hold me to it though as i have not wrenched on a s4 in ages
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Old 03-11-19, 08:38 AM
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Originally Posted by PnoyRx7 View Post
Damn i cant for the life of me remember the name but im sure S4's had a sort of actuator that activates after a certain RPM. Dont hold me to it though as i have not wrenched on a s4 in ages
You are correct, 5/6 port actuators. They may be stuck. It also might not be a bad idea to clean the rest of your grounds. The car is 30+ years old now. I've cleaned all of mine and added more to ensure it's getting the proper grounding.
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Old 03-11-19, 12:29 PM
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^ What they said. Clean the auxiliary ports.
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Old 03-11-19, 04:30 PM
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Nah its not the aux ports.

Probably something to do with the secondary injectors or fuel system related. Was the car sitting? Have the injectors been serviced? Have you changed your fuel filter? Original fuel pump? Fuel pump voltage at idle and WOT.

EDIT: I just read that you didnt fix all of the grounds. You need to do all of them. theres like 10.

This is one of Aaron Cakes write-ups. He knows what hes talking about. Do it.

https://www.aaroncake.net/RX-7/grounding.htm

Last edited by FührerTüner; 03-11-19 at 04:36 PM.
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Old 03-11-19, 07:17 PM
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Originally Posted by FührerTüner View Post
Nah its not the aux ports.

Probably something to do with the secondary injectors or fuel system related. Was the car sitting? Have the injectors been serviced? Have you changed your fuel filter? Original fuel pump? Fuel pump voltage at idle and WOT.

EDIT: I just read that you didnt fix all of the grounds. You need to do all of them. theres like 10.

This is one of Aaron Cakes write-ups. He knows what hes talking about. Do it.

https://www.aaroncake.net/RX-7/grounding.htm
Yes that's the write up I was following. I was going to do the rest of the grounds I just thought that in the write up he mentioned the computer ground being the main culprit of the 3500rpm problem. Maybe I'm remembering wrong. I will be doing the rest of the grounds. As far as the fuel pump, it is brand new along with the relay. I have a feeling the owner before me was trying to tackle this problem and throw parts at it and then got frustrated that he couldn't fix the problem. The car wouldn't start in the cold and he told me that. It did it 1 time for me, it would start rev up to 2500rpm, die instantly. It would do that 10-15 times then finally got warm enough to run. Well I don't know if it was carbon or not but being a new owner I took it around redlining it everywhere testing it out. It starts in the cold fine now. Injectors look original or pretty old. Car has 144k miles on it. Currently running a bottle of seafoam in about 1/4 tank of gas. So far hasn't done much of anything.
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Old 03-11-19, 08:09 PM
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What about your fuel filter? You could also check the wiring on your secondary injectors and check resistance
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Old 03-13-19, 07:22 PM
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I had this issue. cleaned all my grounds. check my 5th and 6th. replaced plugs, wires, and secondary injectors and nothing worked. I ended up replacing the trailing coil pack with a used one i got off ebay and that worked.
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Old 03-14-19, 12:20 AM
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You can always throw some parts at it which may or may not help. It never hurts to check your TPS resistance to make sure it's synced up. If you can get an analog dial-type ohm meter you can also look for dead spots doing a full sweep of the throttle. Most of these 30 year old sensors are starting to lose their integrity.
I'd go ahead and clean ALL grounds, only costs you a bit of time and energy.
If none of the above works, I'd say look into the secondary injectors.
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