hesitation at 4 thousand rpm
 

As the title says, my 7 has this slight hesitation at 4 thousand rpm while driving. The car is a 87 completely stock n/a, and it has 123,000 miles on it. This car has been doing this for a while, but since i seldom drove until a couple of months ago, i didnt really care. The car aslo has lost compression once before, and i was able to bring her back to life. I know that last statement will probobly be over a few heads, but its ok. The only reason i want to know why this is doing it is out of curiosity and maybe with a little bit of money and elbow grease, this problem can be fixed.

I was told by someone else that the reason the car hesitates at this rpm is because it has reached its peak. I thought to myself maybe he is right, but the nose of the car dips down at 4k, then picks right back up until i shift. Maybe he's right about the car reaching it's peak. But im tired of guessing, thats why im here. So, bring on some HELPFULL info........Don't wanna hear "trash it" or your "motor's done, dude!", unless, of course it really is. Thanks!

3,800 rpm is the injector transition point. The primaries cut down to half of the duty cycle they were at, and the secondaries come online at the same duty cycle to continue supplying adequate fuel.

A search for '3,800 rpm hesitation' will turn up many threads on this issue, but it generally boils down to the condition of the grounds used by the ECU and its sensors. Some have succeeded in fixing it, while others never get to go away altogether.

You should be able to get around the stumble when accelerating at full throttle however. I had a slight stumble when my car was NA, but it was never there if I was accelerating hard enough past the 3.8k mark.

NA rotaries make all their power at high rpms, so whoever told you the engine had hit its peak knows nothing about them at all. If anything, ~3,800 rpm is about where a 6-port NA engine starts making real power.

Thanks, but most of the time that it hesitates is when i am at WOT. It doesnt bother me as much as it used to, but i would like to fix it. I will look up what you said and hopefully it will lead me somewhere good.

Yeah i had this problem too when i bought my fc, First thing i did to the car is clean up and re do my grounds, ran 100 times better after that.

Ok. just a quick overview, what grounds should i check first? Are we talking battery ground cable, chassis to engine grounds or just anything ground related? I have looked this up and most have said that this problem I am having is ground related and most have been able to fix this problem quickly and without much much hassle. Thanks for the input.

http://www.aaroncake.net/rx-7/grounding.htm

The most important will be the ecu and pressure sensor grounds.

That Ecu ground is hard to locate.

Hey thats a awsome point of intrest the transition of injection at 3800. The ecu ground anyone know where that is located? on a 1986 13b 2 door coup 5 speed!

It's as shown in the picture on aaron's site http://www.aaroncake.net/rx-7/grounding.htm I'm in the middle of doing mine right now- I suggest you also pick up new secondary injector o-rings/seals/insulators (3 parts per injector.) One of my O-rings broke when I pulled the injector out of the rail, and the insulators were rock hard from sitting in there for 20+ years. It would suck to go through the trouble of pulling the upper intake only to watch fuel piss out when you start her up.