My friends rx7 we just put together is having a pretty strange problem where it stumbles and loses quite a bit of power after 5000rpms. the engine/ injectors were run in a prior car without issue, the ecu wiring harness, CAS and coils are all new to the setup

car is an 87 tII with a s4 n/a motor using a low impedance harness(resistor pack eliminated) high impedance injectors, as well as n/a MAF and pressure sensor


here are the mods: full headerback exhaust, msd wires, e-fan, cone filter, emmisions removed, running premix, simplified throttlebody, extra engine grounds, gasket matched intake manifolds, aux port sleeves removed, adjustable fuel pressure regulator set at 39 PSI at idle

we've tried: adjusting the fuel pressure both up and down
advancing/retarding the timing

thinking either bad plugs or fuel filter may be the problem, once we try those i'll post up again but any other ideas to the issue would be more than welcome!

 

bump someone give me some idea's before my buddy sells his car, this thing is too clean to go to someone else.

changed the sparkplugs checked the fuel filter. same problem. always have random stumbling in the exact same places in the top end of the rpm range. runs fine below it.. this problem is beyond me. could the ecu be pulling timing for some reason because it's a tii body harness and n/a ecu & body harness/sensors? (coolant temp sensor wire is different pinout)

 

you need an N318 Boost sensor...and AFM...TII stuff.
that is your problem.

 

..

 

The car is not turbocharged. It just started out as a tii.

 

Are you setting it to stock timing with the idle down at ~750 rpm?

There are a few differences in TII and NA wire harnesses, but overall, they are very similar.

 

idle is set at about 900, have tried stock timing, along with slight retard and slight advance, the car would run different but still have the same stumble. the factory coolant temp sensor guage is not working, however i believe this is due to the different ecu pinout between na and tii ecu's. does this mean the ecu is also not reading coolant temp? or is it just the pin OUT from the ecu that is different? if the ecu isnt reading coolant temp could that be causing the stumbling? or maybe a bad coolant temp sensor itself be the cause?

 

there are two coolant temp sensors, one for the gauge only and one for the ecu.

 

Well, I was hoping that was a possible lead. I suppose ill try swapping out injectors, afm and map sensor next. Would the ecu coolant temp sensor cause this kind of hesitation?