rx-7 obsessed

hey guys have a really odd dilemma for u and ill try my best to explain my situation first a list of all mod's to the car to help.

86 GXL body with:

87 turbo 2 ECU, motor, tranny, rear end. NA wiring harness remade (i call it a hybrid due to the fact it works with the knock sensor and my cluster is the t2 cluster so the boost gauge works on dash even though i have aftermarket)

mods to motor:
all stock its a Mazda reman with 60k on it or 40k miles (Canadian car)
stock injectors all stock intakes. and when I dropped the motor in 10k ago it was stripped down to the block and rebuilt (never opened the motor up) it has all new gaskets, injectors have new gourmets, pintail caps, and new injector clips.
all emissions removed. BAC valve and thermo wax still on car.

and yes i know the pulsation damper was replaced with a banjo bolt but the car has only done this lately not when it was first running.

symptoms:

when its cold in the morning (12 degrees C) the car will start and idle at 1500 rpm until it drops down to a nice idle of 950 (that's where i set my idle) as soon as you touch the gas the car will rev to about 1500 and then it seems like it misses really bad...its hard to explain. its smooth revving to 1500 then just does a shuddering noise almost, like an extreme lean is about all I can explain. at this point the car is parked and not moving

so now the car is warm and it has stopped doing the shudder i just spoke of above. we are driving and as soon as my boost pressure reaches 0 (manifold vac and boost pressure equal) the car will do the same shudder thing.....now if you just put your foot to the floor it will continue to do this until it reached 5psi of boost then it will go just fine...back of , shift and it starts all over again. after a couple times of this it will go away most of the time.....it has done it once when it was warm but that was it (by warm i mean as hot as it gets 1/3 of temp gauge)

things I have done:

tested my AFM with lab scope. tried setting my TPS using both LED tester and ohm setup with no change. I have swapped both leading and trailing coils, plug wires, and plugs. (using NGK breq7s and 9s) new NGK wires (8mm thick) with no change. i have checked and recheck all vac lines (also all redone 10k ago). when the injectors where out i tested them for flow and checked resistance(diesel shop in my area did them they do good work) tested good. changed my boost pressure sensor with no change. i am at a loss and sorry for the long post. i am just so confused. i cant think of what it is.

o yes and last but not least my compression is good 100 psi pulses all rotor faces using a piston gauge with the valve removed so it could not hold pressure. anything else just ask!

misterstyx69

iTrader: (142)

sounds like a vacuum leak.when the car is cold it will have the vacuum leak.As it warms up the Hoses get more Pliable and seal.
I would try a. vacuum/pressure test on the Engine
www.fighters-garage.com they are about 30 bucks,and work good.It saved my ***.

rx-7 obsessed

im not sure what the vaccume should be when its cold but im around 20 psi of vac when cold

one more thing i forgot to add it has a brand new o2 sensor

Mattax487

On my 91 TII I had a similar problem when the car was cold. It turned out to be the Thermal Wax Sensor. After I replaced it the problem went away. But returned about a year later. It seems that the TWS is a POS. Not sure if your year has one or not.

Hecubus84

iTrader: (1)

There is a section in the fuel and emission section of the fsm that gives a voltage range for each pin in the ecu, you can use this to help you backprobe the computer and find bad wiring/sensors while the circuits are hot.

rx-7 obsessed

ok first off i ment 20 in lbs not psi just to clear that up

its getting worse i have had to park the car becuase now even after a 40 minute drive on the highway the problem still presists. on a side note while i was driving i was playing with my fuel cut switch (i know not a good idea) when off it seemed like it problem came instantly and then went away when i turned the switch back on. i tested my pump for votage and its 12.76 (was trying to read while driving so it might be slightly more). fuel pressure test came back fine but seems to me it might be running lean? any way to test underboost

SecondGenPat

Possible failed ECU?

Do you know somebody else in your area that you can swap ECU's with to check?

another item to swap with a know working car:
boost pressure sensor

If neither of those cures the problem then I would check the knock sensor / knock sensor wiring circuit out. Again, something else to try swapping. (make sure you torque it down correctly)

That's all I can suggest. Best of luck!

Hecubus84

iTrader: (1)

Try rigging up a fuel pressure gauge inside the car and see if your issue goes along with a drop in pressure. Fuel pressure and flow are very important and you need to rule out pressure problems before you continue any further with your diagnosis.

rx-7 obsessed

alright guys another update since i still cant figure this thing out. bought a welbro 255 and installed. car stated right up and then did the same thing. best way i can describe the symptom is it feels like hitting the fuel cut. i have one guy that i can swap with but his is a JDM motor so i know there are some differences. im really starting to get fustrated. i check knock sensor curcit and voltages are correct. check timing yet agian no change. check fuel pressure with new pump no change. new fuel filter installed (not one in tank but on driver side of car up front). i have a spare knock sensor ill try swap tomorrow. maby have to bug buddy for his ecu but i doubt it. any more ideas? also going to try compression test one more time tomorrow.

rx-7 obsessed

sry for double post is there a way to test my ECU without swapping no one will lend me a ecu to test

SecondGenPat

wait, you had 12.76v with the car running??? (generator output should be greater than that)

First, you need to rule out you FCD (didn't catch that before, sorry)
Swap it if you can, see if problem persist. If you can't swap it, remove it. Go for a drive (don't overboost!!) If you don't experience your problem you have found the culprit.

Also..
If I am correct the T2's use a fuel pump relay that has a resistor on the 30/87a path and a normal circuit on the 30/87 path.
if I remember correctly the resisted side is for idle and part load and should drop the pump to ~9v, then at medium to high load the relay switches to supply system voltage (generator output) to the fuel pump


You didn't specify if you retained this relay or not, if you did then you need to check pump voltage at idle and then again at load
you should get ~9v (check FSM spec) at idle, and system voltage at load

-Pat

HAILERS

86 non turbo body with a 87 turbo engine in it. No fuel pump resisor relay in that 86 non turbo car. Not needed. Been there done that with no problems noted. Fuel pump resistor relays purpose is imho to reduce wear on the pump. Could be another thing, but I think it's that.

Fuel pump pressure can be checked while driving by teeing into the pressure line off the fuel filter with a gauge and tying the gauge to the windshield wipers. PUll the plug off the wiper motor before driving the car. Prevents accidents.

All pins on the ECU can be checked out by backprobing the wires at the ECU with the key ON or idling. Fuel and Emissions section of the FSM, CONTROL UNIT pages lists the input/output of each wire on the ECU.

I've done this swap and have no problems. TPS wires had to be lengthened and the BAC wires lengthend and other minor changes to the wiring. Turbo boost sensor required and turbo afm required imho.

I'd just unplug that knock sensor box. You do have the Knock box, right? No box......remove the knock sensor wire from the harness.

At approx 1200 rpm the ECU self advances the timing and as a result the rpms make a sudden jump of a couple of hundred rpm at that point. Your at a idle of approx 900 rpms.......step on the pedal a touch and you reach 1200rpm...........timing advances and rpms go up to ??? 1500 rpm or so.

Do the windshield wiper job mentioned to get that thought out of the way.

TPS output on pin 2G should be approx 1vdc IF the engine is HOT. If not 1vdc, then adjust the screw til it reads approx 1vdc. A cold engine will read a higher number that is not relevant.

Pin 2I is the water thermo sensor reading and should read approx .4 to .5vdc with a HOT engine. A cold engine will read much higher......like 2-3vdc and is not relevant. If the hot engine voltage reads much higher than .5vdc.....the sensor has an open b/t it and the ECU. Pin 2I matters...although if the sensor has an open, it fails safe to approx 176*F and a hot engine should run just normal as can be. A cold engine will be hard to start and be messed up til it warms up if that sensor is disconnected/open.

IF your tach needle moves just fine the trail coil assy is just fine IF the two sparkplug wires are on the right plugs.

Boost sensor reading on pin 2B with the engine OFF key ON should match the figures in the CONTROL UNIT page.

FCD???? I'd disconnect it for now and put it on the shelf.

Any SAFC or equiv I'd disconnect and put on the shelf. I'd buy a RTEK 2.1 to replace those items and to help self diagnose the problems....to some degree.

I'd disconnect the 02 sensor wire at the 02 sensor and see if it makes a difference (only light driving related, not at idle etc).

Backprobing the ECU pins is made easier if you unbolt the ECU and tilt its plugs upwards for access.

Might try disconnecting the boost sensor electrical and go for a ride and see if the problem persists. Sounds boost sensor output related to some degree.

I'd watch MotoGp Sunday on the Speed Channel or whatever they call that channel these days. Watch the red Ducati and Stoner go zoom, zoom and win. Watch Rossi fall off his Yamahammer. Watch Pedrosa fall farther and farther and farther down the field as the race goes on. Watch Pedrosas team mate finish the races at least seven places further towards the front of the field. Watch Ben Spies finish third easily. Watch Lorenzo fall hard once more (high side, head first).

I've never been right about a race yet.....but there's always a first time.

rx-7 obsessed

alright well thanks HILERS u found the problem you have no idea how happy u made me. so with my fuel pressure line hooked up the pressure was right at FSM levels. unpluged my knock control box with no effect ( no fuel resistor fyi). got even more annoyed pulled the false floor and started back probing. after alittle bit of trouble trying to get in there while someone was workin the throttle it was the.....BOOST PRESSURE SENSOR...ya thats right after 1 year it of trying to figure it out it was that little black box RIGHT infront of my face. unplugged it made no difference at idle. got in the car touched the gas and OMG it went to 0 vac without feeling like its missing....plug it back in wont rev past 1500 rpm smoothly.... now the trick is to find one. i searched the for sale/wanted and found all s5 n370 sensors. found on on ebay for 40 bux american but im not a huge fan of trusting ppl. anyone know where to find a cheap one 344.50 from mazdatrix HAHAHA NO