Hello everyone and thanks in advance for any and all help


I have been rebuilding an '86 RX 7 (na) and ever since the very first fire up i have had a bucking/shuddering when under load (2,500 - 3,500 rpm). It will even occur under light load on a slow "granny" drive. I have searched all over these forums and elsewhere but can not figure out the problem. The closest i have come was reading a thread about a boost sensor and it fit all of my problems. I unplugged my boost sensor and my car ran nearly perfect (under 3,800 rpm)! I then plugged it back in and unplugged all the other sensors associated with the boost sensor but the bucking was still there. I thought maybe i had found the problem and ordered a new sensor. As soon as i got it i installed it but the problem was still there. I also began to notice a pattern in the severity of the bucking in correlation to the humidity. I thusly began testing wires and double checking all vacuum line i could see. As far as i can tell it all is as should be. I am currently running my car without the sensor plugged in so i can drive it as it is my daily but i want to fix it asap as i have heard it is very bad to run the car without it.


So please if anyone can help any and all info will be greatly appreciated.

 

Test the voltage of each of the 4 wires at the boost sensor w/key to on and sensor plugged in. You have A Black/White wire which should read 12 volts. A Brown/White which reads 5 volts. A Brown/Black wire which is the ground and should read close to 0 volts. And the final wire is the output wire which reads 3.5-4.0 for the NA and for the turbo it should read 2.3-2.7 volts. The sensor has a vacuum line which needs to be ran to the proper vacuum source for not all vacuum sources are the same. Speaking of the vacuum hose, there is a restrictor pill located within the hose nearest the sensor. Do you have this in the hose?

 

I believe i have already checked for the voltage but i will double check my notes/maybe just retest. As for the restrictor i have none in my line. I actually have replaced all vacuum lines as they were all original to the 30year old car. I do not remember seeing one when i replaced the hose but what does it look like and can i get one from somewhere or do i have to order a factory hose if available? And where would a proper source be?


And thank you for the information i am looking for any leads.

 

The restrictor pill could be purchased through the dealer I suppose or you could come across one at the local auto store or make one yourself (using the advanced search feature will provide you all the info needed). Since it is contained within the hose it would then be found in the original hose (a wire through the hose would tell you one way or the other if you still have the old hoses).

And do the numbers on the sensor jive w/the type of car (turbo or NA), and year?

 

Well sorry for the very long delay life can get busy.


But i made a restrictor according to specs and it did not work. I also tested the voltage and it was all correct.


I am again lost but thanks for the help.

 

You could take the ground wire at the boost sensor and tap into it and run that wire to the engine block to help support the grounding of the engine sensors. You could also test the TPS, as it should read 1 volt w/key to on when reading the Green/Red wire after the car has thoroughly been warmed up (translates into at least a 20 minute drive). And when set properly, the range of the TPS should read from 1 volt at idle position to close to 4.5 volts or so at full throttle position. The sweep of the range should also be smooth (best to use an analog meter as a digital cannot accurately respond to the minute changes when testing the sweep).