spartan

iTrader: (2)

Hi guys, I am having a problem with my 87 NA RX7. I have searched on here extensively and tried a bunch of things, and I am getting pretty frustrated.

Engine idles fine at 750-800 rpm when warm.
Runs great between 1000-3000 rpm
Bad hesitation/ stumble between 3000-5000 rpm
Runs great 5000-7000 rpm

Went through all the grounds, new plugs, wires, fuel filter, clean air filter.
I have adjusted the TPS numerous times using all the different methods. It always changes every time I drive it, and even after adjusting the TPS to near perfect (1k ohm) cycling the throttle and going for a drive it will run bad. Sometimes the car will run great through all RPM's, then the next drive without touching anything it will struggle to make it to 5k.

Do I need to try and find another TPS sensor, or should I look for something else?

DaBrkddy

The RPMS you're having problems in are around when the secondary fuel injectors come on, and when the auxiliary ports open. If you can't make it past 5k rpm, you have a serious issue. I'd re-check the ground underneath the intake manifold on the rear rotor housing, and the engine ground.

Check/replace spark plugs, and test fuel pressure. If you're suspecting the TPS, unplug it for high rpm testing and fix it last. The computer will default to WOT when you unplug it. (no deceleration fuel cut.)

Edit: check your auxiliary port sleeves/actuators for free movement after you do everything else.

NCross

iTrader: (18)

Aftermarket exhaust? Make sure the auxiliary ports move freely and getting proper back pressure from the exhaust.

My 0.02 cents on a consistent lack of power at a consistent RPM or power band is to check the following...

-TPS has dead spots (you won't be able to detect them with a digital multi meter)
-Aux ports are dirty or not getting enough back pressure
-Secondary injectors are lazy (clogged, dirty connections, incorrect resistance)

Hockley Comet

iTrader: (2)

Had the same problem on my S4 NA. Check your injector resistor box and what DaBrkddy said. Sounds like your secondary fuel injectors are not firing.

spartan

iTrader: (2)

I will check those things, it does seem to have full power after 5k rpm's, it's just getting there that can be a problem.

satch

iTrader: (1)

Can you free rev w/o a problem? You could unplug the TPS and remove the vacuum hose to the pressure sensor and this replicates load on the engine thus when idling you can rev the engine and get the secondaries to kick in.

NCross

iTrader: (18)

Not all 87 models had a resistor box.

spartan

iTrader: (2)

So I took it for a drive again tonight and I believe it is a secondary injector problem. Cannot free rev without hesitation/ cut out. It was stumbling really bad while trying to go 3-7k in second gear. Hoping to get out and check the voltage and resistance of the secondary injectors before I head out of town for a while. Thanks for the help thus far.

satch

iTrader: (1)

The secondary injectors should not be coming on when just free reving as the primary injectors are only used.

And the TPS value should not change if you're measuring it properly. It should always be measured w/the engine as hot as it can possibly get (20 minute drive should do). If you measure the engine at various temps then that changes the reading of the sensor.

spartan

iTrader: (2)

OK, guess I was wrong on that one then...

TPS value was still good (1k ohm) when I checked it after driving last night. Would the actuators for the 5/6 port cause the issue while free reving also? I had them checked last year and the shop said they were opening as intended. I guess I will do the grease check on the shaft and see if that is still the case. Anything else I should try?

NCross

iTrader: (18)

Make sure the thermowax cam is on the hot mark and the idle is as close to 750 as possible when setting the TPS.

satch

iTrader: (1)

When you went through the grounds did this include the engine ground which grounds the ECU? If not then you should, and you could add an extra ground to the ground wire found at the pressure sensor (you ground that wire to the engine).

spartan

iTrader: (2)

Just to follow up on this. I had gone through the battery grounds, and re-grounded the ECU in the cabin. I made a new ground wire for the engine to chassis, found a bolt to the engine and ground off some paint on the chassis around a strut bolt. Hesitation is gone, thanks everyone for the help.