kujiro414

hello all i have an 86 rx7 fc s4 n/a.
Im having really hard time trying to figure out what is wrong with my fc.....

here is the issue. she has the 3800 rpm hesitation/wall but only under heavy acceleration.
NOW here is were it gets tricky...
i have checked and re checked everything.. but still no go.
what i have done:
-i have checked timing.
-i have replaced the pcm ground and the engine, chassis and battery grounds
-tested the secondary injectors, come to find out they were bad so i replaced them
it worked until i turned the car off and restarted it.
-tested the tps. i got 1k closed and 4.4- 4.5 WOT....
- tested the pcm to see if it was sending signal to the secondary injectors.. and yes, that works..
-checked the catalytic converters, they were not clogged, i did replace them with a cat/delete pipe. ran a lil better. then after i turned the car off and back on.. yup still hits rpm wall...
-checked the injector resistor and im getting 12 volts there and for the secondary, resistance test im getting 4 ohms.
-checked the MAP and the is working fine....
Ive really done all i can to try to fix my fc all except replace the pcm. (as stated before, i tested it and it checked out.)
no matter what i do. it runs fine after i do anything to it untill i turn it off and re start it

im at a loss here... please if anyone can help it will be greatly appreciated.

thank you all again.

satch

iTrader: (1)

How did you replace the ECU grounds?

kujiro414

i had cut the old eye hooks and replaced them with new ones. and the fastener was replaced with a stainless steel. the new eye hooks have been soldered on.

satch

iTrader: (1)

Unplugging the boost sensor and TPS allows the secondaries to come on line while free reving. This can allow you to test some things. Do the ECU pins (ones w/the Green/striped wires) for these injectors read about 6 volts when they should be triggered?

kujiro414

will do that.

satch

iTrader: (1)

And how many engine/ECU ground wires have eyelets besides the main engine ground?

kujiro414

the 2 that i replaced were the ones under the intake manifold. (granted those were the same ones mentioned in Proper RX-7 Grounding Procedures

i unplugged the boost sensor and i checked the voltage at the ecu. 5.5 volts.
so i then got curious and unplugged the secondary injectors, nothing, no volts no ohms.
so i looked for the injector resistor, 12.4 v and 4 ohms for the secondary injector circuit...

so i went back to the ecu and i got nothing. though i still had the secondary injectors unplugged at the injector.

satch

iTrader: (1)

The Green wires at the ECU have 12 volts w/key to on only when the injector plugs are connected to the injector. The wire which sends 12 volts to the injectors are Brown and this voltage is passed to the Green wires only when the plug is secured to the injector. What you might want to do is check the Brown wire at the secondary injectors have 12 volts w/key to on. The resistor box takes a B/Y wire from the main relay and sends 12 volts to the injecors w/key to on. At the box the 12 volts is then passed to the Brown wires that leaves the box and ends up at the injectors. Besides checking for 12 volts at the secondary injectors at the Brown wire there is another thing you can do.

The AFM's ground wire is notorious for being bad on 86's such that Mazda released a service bulletin pointing out this problem. They suggest taking the ground wire at the boost sensor and tapping into that wire and running it to the engine. I did this and my hesitation which I had since I bought it back in 86 finally disappeared. This was done after having the car for about 17 years or so and the fix has never failed.

And the injector ohms can only be accurately measured at the injector itself and not downline. It should measure 2 ohms.

kujiro414

I thank you!!!!! The problem ended up being the boost sensor and that ground. Previous owner grouned. The boost sensor ( the brown wire) to the chassis. I re grounded it to the block still had a slight issue. Swapped the boost sensor and no more problems. She reves high with no hesitation underload.

satch

iTrader: (1)

Good news!

misterstyx69

iTrader: (142)

Your car has officially been "Satched"..lol!