Hello guys

I have not found anyone who describes a problem like I experience, so I ask for your input. The car is a 1991 RX7 S5 Turbo.

Between around 2000 and 3000rpm I experience hesitations on partial or even full throttle as long the manifold pressure around zero or on low boost.

I have a wideband installed, the AFR in that manifold pressure range is typically around 13 but then it starts jumping between AFR 13 to around 15 and back again in around half a second interval. You can hear the engine sound change and depending on RPM it will jerk back and forth quite violently.

It is quite annoying since this is the RPM range mostly used on the highway for cruising. Also I really have no idea what could be causing it. The car has no codes indicating what it could be. I checked the knock sensor and its connectivity to the ECU, the oxygen sensor and its wire but all was ok. Also around 6 months ago I II adjusted the TPS after I got a code for it. This code is now gone. Also back then it did not seem to have any death spots.

The problem exists for years now. It gets worse when it’s hot outside, I just try to drive around the issue but I really want to fix it.

Thanks for your input in advance.

Sam

 

Check for any vacuum leaks.
Also check the grounds and clean them up. That is a common problem for 3k RPM hesitation.
That's the only advice I have, sorry.
Good luck

 

I'd check all the grounds, clean them, and see if it improves the situation.

This is a bit of an unusual issue. Normally these cars hesitate at 3800rpm from bad grounds (or sometimes other issues). A hesitation between 2-3k is less common.

Anyways, grounds cause 99% of the problems on this car. Aaroncake has an excellent guide on his website on servicing the ground points. You can measure resistance too; there should be zero ohms of resistance between the ground atop the engine and the negative post of the battery. This is the main (only) ground for the ECU and its sensors. That one is the main suspect, but all the grounds are important.

Good luck, I hope that helps. Otherwise the culprit is almost certainly electrical, but tracking it down will be more complicated.

 

Check the port actuators. . . . .the line that feeds them on a S5 comes from the air pump I believe. . . .

Make sure that line does not leak. .. .Might want to change the air pump if you feel it is older than 10 years.

sometimes the ports just get harder to twist... .. I also have a little hesitation problem on my S4 and I'm pretty sure it is that.


http://www.foxed.ca/rx7manual/manual..._non_turbo.pdf

page F1-42

 

An S5 Turbo doesn't have "port actuators."

I had a similar issue twice early on with my first S4 N/A. (Back in about 2007 or so.)

The first time the problem occured, it was a faulty TPS.

The second time I had the issue it was a faulty IAC (BAC) valve.

Both are easy to diagnose per the FSM.

YMMV, good luck.

Edit: If none of the above are the issue, I'd lean toward manifold pressure sensor.