Bambam7

Ok, my car has never really run great- horrible mileage, running rich, whatever...
I always suspected electrical probs... I did the entire ECU harness test as on the FC3S.ORG website. Here's the results that were's to spec.

Pin 1K- Fuel Pump Resistor Relay- 12v while ignition on, and below 2v while idling.
My car- 0v while ignition on!! (.62 at idle- OK)

Pin 1V-Trailing ignition Coil- Ignition on, below 2V, Idle- 12V
My car-Ignition on- .94V. but at Idle-1.02V!!

Pin 2L-Intake air Thermosensor- supposed to be 1-2V When engine warm

My Car-3.18V when warm.

Pin 2F- Narrow range TPS- Full throttle supposed to be 5 V, mine only goes up to 4.59 V at WOT.

Ohms vary between different ground pins considerably! Will be correcting that tomorrow.

Also- injectors are supposed to be 12V at idle (or whatever system volatge is)
My primaries are 13.2, and my secondaries are 13.6- almost half a volt difference.....
Any opinions??

niner

that is strange
i dont know what to tell you but im going through the same troubles w/ my car right now
i need to do a lot more work on it when i get the time. -my car is 5hrs away from me at home(im at school)
keep us posted though b/c this might help me out

good luck w/ it though

Scott 89t2

do you have any codes? do you have spark on the trailing coil?

and I don't think N/A's have fuel pump resistor relays. I'm pretty sure only TII's do... do N/A pumps only run 9v at idle like the TII?

Bambam7

Yup, N/A's have fuel pump resistors. I was under the impression it is some sort of safety precaution- in case the car flips or something, if the engine shuts off for a reason other then the ignition key, it shuts the fuel pump off so it doesn't keep pumping fuel out.. I dunno. Could deal with idle, I'm not sure.
I do get an intermitant code for the resistor, only once in a while though.
Funny, it only shows up when I CHECK for codes, but the check engine light won't come one to signify there is a code in memory... curiouser and curiouser....
Also- never a code for the trailing coil- I'll check tomorrow to see if I have a trailing spark.

Oh one more thing- I couldn't get my 02 sensor signal to get over .03 volts...when giving it throttle....(revving hard in neutral) is this normal? I'll check it tomorrow while driving to see if it goes up higher.
I'm kindof intrigued about the difference in voltage between the priamry and secondary injectors though..... suprised the secondary voltage is higher, becuase they tend to have the worse grounds.

Scott 89t2

it sounds like your 02 harness wire is grounding somewhere if if never goes over that. that happened to me and I had to run a new wire. unplug the harness and measure straight out of the 02 sensor with the car running and see if it's normal (around .5v while reving). that would be a good cause of richness and bad milleage if it's grounding. It should have set a code though. and only some codes will light the light up. you always have to check the codes to see if you have any.

all cars have a fuel pump relays to turn them on and off. but I didn't think the N/A's had "resistor relays", which drops the pump voltage down to 9v at idle and light cruise. but maybe I'm wrong.

pp13bnos

iTrader: (1)

If you need a ecu, let me know. I'll sell a n/a 89+ for dirt cheep. CJ

Bambam7

Well, there is a code for the resistor relay, (#50 I think), And It's in the manual- It's the silver-finned object on the passenger side right under/behind the headlight. It's definately there... maybe only on 89+?

My O2 sensor was replace with a generic one.... could it be burnt out after a few months?

mazdaspeed7

Bambam, this might not be related, but here it is anyways. I got my 90 GTU with a blown engine, and enough other problems to keep me busy for a month after I had a good engine in it. I had an 89 GTU, which I totaled just after putting a rebuilt engine(3K miles) in it. So I bought the 90 to put my still good engine into it. Once I get the engine in, I had 15 different error codes on the ecu after the first time I started and ran it. Among those codes were 4 or 5 engine sensors, and the others were emmisions stuff, which i had removed. After doing some testing of the harness itself, I came to the conclusing that the harness was fucked. There were more than a few shorted/broken/otherwise messed up wires. I put the harness from my totaled 89 in it, and everything was fine.

Moral of the story, I think there was a quality problem with the 90 harnesses. I looked at it a lot, and some things seem to have changed from 89 to 90 on the harness. Some of the wires are different colors, and some are different types of wire. All factory, no "mechanic special" repaired wires. Look for the wiring harness out of a parts car before you go start replacing sensors/ECU. At worst, it wont cause any harm, and at best, it will fix your problems. You might want to look for 89 specifically.

Bambam7

Well, the harness doesn't seem to be suspect, except in the case of the 02 sensor signal. The other probs (trailing coil signal, and fuel pump esistor signal) are problems with the signal only under a certain condition- (ignition on/off whatever), if wiring was bad I wouldn't be getting any signals.

The voltage from the TPS seems to be lower than spec in idle and WOT positions though.... (narrow and full range, about .2 volts below spec, idle and WOT)
I'll be running some more grounds and positive feeds tomorrow.

mazdaspeed7

Not necessarily. Wire can be bad and still have continuity, but its resistance will be higher than it should. Wires could also be shorting each other if they touch, which could lead to really messed up sensor signals.

Heres something you need to do tomorrow. Reground the ECU. Theres 4 black wires on the right side of the middle plug, splice into those, and run a new wire to a good ground. Regrounding the engine/chassis couldnt hurt either.

NVMYRX7

on the middle plug.......do you ground one of the black plugs ao ground all of them refer to post above for more INFO^^^^^^^^

Thank You
Josh

Bambam7

Go to the website fc3s.org and print out the ECU checking section. It'll tell you what wires are grounds.
Here's what I recommend:
8 gauge from batt neg to chassis
8 gauge from alt to batt pos
8 gauge from engine block to gang ground under intake manifold, to firewall
12 gauge from ECU harness grounds to chassis

Some people with 3800 rpm hesitation may want to ground the seconday injector fuel rail as well, but it should be needed with these others.
I'll be finishing this crap tomorrow......

mazdaspeed7

https://www.rx7club.com/forum/showth...threadid=17974

Read that, and this next link is from there...its direct to the ECU regrounding how-to

http://home.earthlink.net/~burntoast/3700.html

tesla042

My 87 se has this, but my 88 gxl does not.. I always wondered what it was..

-Tesla

HAILERS

There's absolutly nothing wrong with the injector voltages. I've been monitoring my primary and secondary injectors for some time. At idle the primary injector will read 13.30v and the secondary 13.90. Very normal. The primaries being under a load and the secondaries sitting on their butts. With a cold car at 2L I get 4.32v. At 2J I get 2. 61 with a cold car. At 2I I get 1.36 with a cold car(0.50 with a fully warm car w/180 degree thermostat. 2Q, the bac varies, but with a/c on about 7-8v at idle. If you want to compare voltages just say so and we'll see what we can do. Oh yes. The o2 sensor. That needs heat to work. If you have your air pump, acv etc on the car, then you WILL get an low read like .070 or -.012 God only knows what. Depress the throttle and you will see the reading rise, especially while driving. If you do not have the air pump etc, then you should be getting a reading of .80 at idle after the car is warmed up. There's hedges to that last statement but its true on the whole.

Shamrock1054

Hey Hailers,

You have a test plug at the ECU, right? What injector impedance should the ECU see, on an '87 TII? Checked continuity on redone injector wiring, but not impedance. Thanx, man.

Gregg

Shamrock1054

I say impedance meaning resistance. Just got home from 24 hour on call "train wreck" at work, just a little punchy.
Gregg

HAILERS

SHAMMROCK....I took off the plug at the ECU and the plug at the solenoid resistor under the afm and ohm'd the wires from one end to the other. I got (2.9)(3.5)(2.7) and (2.8). I have no idea how much of each of those figues is the injectors themselves. Best of memory is they ran something like 2.0 or a touch over by themselves. Also this harness is made from two seperate harness. Took the good parts and spliced them together using Molex connectors(think thats the name). The 3.5 figure bothers me just a touch but not enough to make me do anything. Car runs just fine as far as I am concerned. The above can only applies to 86 thru 88 models. I used the above method to find out the splices in my 87N/A were bad to the secondary injectors. Put a meter on each end and wiggled the butt splices(previous owner) at the secondary injectors. Reading would come and go etc. EDIT; Just had something to say thats a little off the subject. In another post the fellow said the turb's ran a little rich with air flow opened up, and I can't help but think there is a misconception there. What makes a 02 sensor read high at idle is usually the person has disabled the air pump and acv. With airpump and acv working, then you have PORT air mixing with the air from the exaust ports whereas if you have no airpump and acv then there is no fresh air mixing and hence a rich mixture. Could be stepping on my dick when I write that, but probably not.

Shamrock1054

Thanx HAILERS,

In your opinion, best wire splice for underhood conditions; solder/heatshrink or crimp/heatshrink?

Thanx, Gregg

Bambam7

Ok, finsished all grounding, and did a few other things...
I spiliced off a few wires so I can test the o2 voltage, AND I can set the TPS from the reading at the ECU.
I reset the computer, and I beleive the car runs smoother all around.

I know I am running rich though, because I don't have the hose for the boost sensor hooked up (but it's hooked up electrically)- so It's always reading no engine vacuum, (havn't tried hooking it up again since re-grounding though...) and my O2 sensor is F*cked....

I took a reading directly from my 02 sensor- and at idle it reads about .2 volts.... If I rev it, I can get it to change around by .05 V + or -.
But get this, if I take it for a drive, and floor it in third or something, the voltage will DROP to about .07!!! What??? It seems to be doing the REVERSE of what it should be.....
Any have a clue?


Oh, also- I do have perfectly good trailing spark, so I don't know what the hell that other mis-reading is (0v when supposed to be 12V for the trailing coil) I'm gonna ignore it.

HAILERS

Might check the wiring on the o2 sensor. See if the center conductor is touching the shield or ground. If using a digital meter set on the lowest scale you should read .7 to .8v , at least thats what I get.

RETed

This is normal.&nbsp You'll only see the full 12V at the first 50 seconds of cold-start.


This is odd...


Looks like out of spec, but it should be okay.


Might want to check resistance at WOT - it could be beyond the 6k-ohm Mazda spec.


This is normal - the fuel injectors "see full voltage", so the readings are dependent on what you're alternator is churning out...



-Ted

Scott 89t2

was this with it pluged into the harness or not?

HAILERS

Common sense thing on the air temp sensors. One thing in summer, altogether different in January. IF you put two meters on the injectors as in one on a primary and one on a secondary you'll see that when you drive the car and stomp the throttle the primary voltage will disapate to about 3v while the secondary voltage stays around 13 and as soon as the secondaries do come on line both voltages go to the same around 8volts and drop downwards.. Does not prove a whole lot but you can see where you can get a hesitation if the secondaries don't open like they should and the primaries don't go from approx 3v to 8v at the same time the secondaries come on line.