savanna.seven

iTrader: (5)

Im hoping one of the gurus will pop in.


Im lost, 87 Tii. Running extremely bad.
Ive tried unplugging the TPS and no change. Car stutters thoughout power band and doesnt have enough power to drive under load. Sometimes.


Where im at now is ive tested the Ohm readings for my TPS BEFORE i plug it into the harness and its within spec. 1.0ohm closed 5.4ohms open, Now. As soo as i plug the connector in it reads 0.8ohm closed and some odd hundred ohms open.

ALSO, the range is no longer Linear. With it unplugged the range is very smooth 1 to 5.4 however with it connected the range goes .8 to 1.2 smooth then all hell breaks loose and skyrockets to hundreds throught the range then back to 1.5 right before the plunger fully extends. after its WOT its back in the hundreds.

I have gone to the ECU to test the TPS signal wire and its fine. Tested with multimeter and it beeps with a strong signal. I unplugged the Connector from the ECU and probed the pin and solid beep. Tested the ground wire for the TPS and its good, as well as the 5v power wire to it.

Ive swapped my AFM, Pressure Sensor, TPS several times, ECU 3 times. What is going on? I got the car to run perfect again re pinning the TPS signal wire then it crapped out again once i got on the freeway. Trailered it home and probed again, multimeter says everythings fine. except the TPS is erratic.

AGreen

iTrader: (11)

Let's start with a basic electricity lesson:

1) You CAN NOT check resistance on an energized circuit.
2) Connecting the TPS to the ECU will change its resistance, as you're now adding resistances in parallel, i.e. the ECU.
3) Checking voltage wins every time vs. checking resistance. The Mazda FSM will tell you a lot of resistance values, and those are ok, but for a true reading of what the ECU is reading, backprobe the connector and measure VOLTAGE.

Try to backprobe the wires at the ECU, and have a buddy wiggle the TPS wires if you think it's the culprit. Seriously, everyone's so scared of checking voltage at the ECU, but if you've already replaced it, you know how easy it is to get to it.

savanna.seven

iTrader: (5)

i didnt check it with power to it ever. I have my breaker for the battery off.

This is all with the car off. Im referring to WOT as the plunger being fully extended.
Ive tested with voltage before and i personally have not seen any difference in performance.

No breaks have been found other than the bad crimp job that was previously there lol. But its fixed and re-soldered,

AGreen

iTrader: (11)

Ok, cool. However, read #2. Resistance with it plugged in will change the circuit's total resistance. It has to be set with the engine fully warm, check voltage at the ECU. A reading of 1.000v is what you're looking for with the throttle plates shut. Watch the voltmeter while a friend wiggles the harness to see if it's a wiring issue. The voltage will fluctuate if it's got bad wiring or a bad connector.

satch

iTrader: (1)

Are you replacing the TPS with a used one or brand new? And have you gone through the ECU pinouts and measured their voltage and compared them to the values stated in the FSM?

savanna.seven

iTrader: (5)

Im currently outside double checking that now. I didnt know that it would change like that.

I do have one question though. before this issue when i set the tps couple months back i had it all plugged in and did it and there was no bad range like it is now. Does this indicate faulty wiring?

Im not too good with wires, would the age or condition of the wires change its resistance potential even if there is no break? Im not sure if thats even the correct way to say it, i hope you understand lol.

savanna.seven

iTrader: (5)

Used. But from good running cars. And i spec them each time. Last one i used tho made my car run REALLY rich. while mines made it lean.

I know this only that at the time i had to use my SAFC to dump fuel to get it to idle smooth. I have since removed the safc and wires to simplify my troubleshooting.

savanna.seven

iTrader: (5)

Ok i did the volt way. I got .875v idle and 4.740v wot with clean linear movent through throttle. now i adjusted it to as close to 1.0v and the cars running better BUT still have stutter in the powerband. ill post a vid of the readings and rpms in a moment.

AGreen

iTrader: (11)

Yes, keep in mind that the wiring harness will likely have a few crimp connections and old corroded connectors. Run the car at idle and shake the wiring harness to see if it's a wiring issue. It's likely not a TPS problem. TPS is mostly used for idle; it doesn't read past 1/4 throttle anyways. How about the coil packs? Do you have access to a running car you can swap them out real quick?

savanna.seven

iTrader: (5)

Yea my friends car.
I have swapped coils before but for another reason. Ill do it again though.

So after i did all the adjustments i took it out for a run. It ran perfect and normal for about 3 min. i did a pull. Then put it in 5th at 30mph and wot to put it under load, no stutter still perfect. I pull into the Driveway have my wife take it and she said it was fine for her too, then it started acting up again. When she got back the car was idling rough again and would stutter all over again when revved.

TPS volt readings are still the same. Where else should i look now besides the TPS. Im feeling that theres multiple culprits.

AGreen

iTrader: (11)

That sounds like ignition breakup. I'd definitely try swapping the coils.

savanna.seven

iTrader: (5)

alright. Is there a way i can test ignition break up?

AGreen

iTrader: (11)

Replace the coils with good units and drive it. If it works, get some coils.

Out of curiosity, have you tried to clean up the grounds?

savanna.seven

iTrader: (5)

Alright. One question. When it does run rough if i press the gas all the way down its chokes and doesnt rev. Still ignition related?

savanna.seven

iTrader: (5)

yessir. new ecu crimp on the rotor housing and new wire replacing the one on the bellhousing. wirebrushed both surfaces

AGreen

iTrader: (11)

Well, I'm not going to sit on the other side of the internet and give you a definite yes/no answer. I'd have to have the car in front of me. But I have had similar issues before that have turned out to be ignition related, and this definitely fits the bill. In my experience, the FC CAS is VERY robust, and I can't see a reason for it to ever go bad. The ECU controls the ignitors, which are built in to the coil packs. The ignitors are essentially a pack of transistors that take a small signal from the ECU and in turn ramps its voltage up and sends it to the primary side of the coil. The coil then ramps that voltage way up to use for spark. The ignitor, being under the hood of the car, being solid state, are very prone to not working, or working intermittently.
Once again, it's hard to say if it is or is not your issue without seeing the car, but I'd just swap the coils (1 at a time) to see if the issue goes away. If not, oh well. At least you can eliminate one more thing

savanna.seven

iTrader: (5)

I hear you. I just have a hard time imagining the coilpack poopin out only under wot conditions but you are right. Im going to be swapping them out and doing some more probing after work. Ill keep the thread posted

AGreen

iTrader: (11)

Really the only way to check ignition operation properly is with an oscilloscope with an inductive lead attachment. Coil packs can act weird, especially in this situation. The reason is, under more load, there is actually a higher reflected impedance felt on the coil, which will be felt on the igniter. At higher rpms, the transistors inside the igniter can go into transistor burnout, which effectively makes them useless. There's more technical crap I could go on about, but just give them a try and see what happens.

And I like the way you're thinking about the TPS being the issue. 90% of the time, WOT problems can be traced to TPS problems. However, this is one of those 10% times. The TPS is only narrow range, and only indicates less than about 25% throttle.

A wideband would be really helpful here in diagnostics. If it's reading really rich I'd lean towards a coil pack, or ignition related, since it wouldn't be completely burning the extra fuel needed for WOT. If it goes really lean, I'd say check injector operation, or see if there's a clogged fuel filter or fuel pump sock.

AGreen

iTrader: (11)

I'm sorry, I used the wrong terminology. I meant "thermal runaway", not "transistor burnout". It's more prone to happen when they get old, and the more heat that gets to them, the less effective they get. Thermal runaway happens when transistor get hot and then essentially go into freakout mode and try to conduct like crazy. That makes them even hotter, and the vicious cycle continues. Once you let off the gas, the reflected impedance goes down, and the circuit doesn't draw as much current. This will cool the transistors off some as less current passes through, and it'll work fine for a little bit again.

Here's a picture of the incredible hulk:

savanna.seven

iTrader: (5)

Alright. well Swapped coils tonight. Took it for a drive. Ran fairly ok. Randomly hit a wall around 4400RPM on one of my pulls. other than that it ran decent. still had slight stutter. after driving around for about 20min it started running rough again. got to a point i could not accelerate again. same issue that left me stranded on the highway.

when i say stutters im referring to a similar sound to a harley motorcycle. Like Rx7s sound smooth harleys have a putta putta putta putta kinda sound and thats how it runs when its rough.

anyways it would be rough till the secondaries kicked in then pull hard. But then it was just rough all the time. it was stuttering regardless of what i would try. Clutch in would kill the car.
i limped it home and immediately went with tthe multimeter to check the TPS voltage at the ECU. No change. So i guess the TPS is not the culprit and you were right.

but now what? Im starting to feel that its always happening after i drive a bit..maybe temp sensative? I know that if my Thermo sensor is unhooked it will not start at all.

could a bad but working thermosensor produce symptoms of running rough like this? My wife drove behind me all the way and said it smelled extremely richer than normal. more so that my son in her car said ew stinky.

AGreen

iTrader: (11)

Usually the exact opposite of what happens on these damn things...

Hmm... that's good information. At least we know now that it's not burning lean and melting your engine down

Let me go look through some wiring diagrams. We're going to check the MAP sensor (I forget what Mazda calls it... like boost sensor, pressure sensor... something like that)

Do this first. At the vacuum line going to the MAP sensor (or whatever they call the damn thing... it measures manifold vacuum anyways, so nobody get butt-sore) unplug it with the engine running. Is there vacuum going to it? Can you put your finger over it and it gets vacuumed down hard? Now, shut the engine off. Trace the vacuum line back to its source. Where does it tap in to the intake manifold?

I'll get back to you on what wires to probe where.

satch

iTrader: (1)

Brown/Red wire at the Pressure Sensor reads 2.3 to 2.7 volts w/key to on. FSM suggests disconnecting the vacuum hose to do this test, but it probably doesn't matter much. B/W wire has 12 volts w/key to on. Of the other two wires, one is ground the other has 5 volts w/key to on.

savanna.seven

iTrader: (5)

Its getting vac. It runs to the nipple on the uim near the bac valve.

AGreen

iTrader: (11)

Yep, and the brown/white is +5vdc with key on, black is ground. Multimeter goes between the black wire and brown/red wire on the pressure sensor. Ideally, you would use a vacuum pump on the pressure sensor vacuum line to apply pressure/vacuum to it while you watch the voltage changing on the multimeter. You should probably check it when the car's having its fits.

Anything blocking the map line? Can you pull the vacuum line off at the MAP sensor and blow into the manifold without restriction?

What are the condition of the spark plugs? How about the spark plug wires? Do the plug wire ends show any signs of arcing around the spark plug? Do the plug wires fit tight and snug against both the spark plug and coil pack, and make a good seal? How about the CAS? Pop off the top of the CAS with a phillips head screwdriver and see how it looks inside. Is it corroded and rusted? How about the CAS connector plug? Does it show any signs of corrosion or the like?

savanna.seven

iTrader: (5)

NGK Spark Plugs are Brand New. Less than 20 miles.
NGK Wires are new aswell. Very Snug fit. Gotta use a flat head to pop the seal lol.

CAS looks perfect. No corrosion as far as i can tell inside of it. The black box looking thing, the pickup i think its called is good aswell.
Connector plug is probable the best looking plug on my whole harness lol. Only touched it twice. 1 to pull the motor, 2 after rebuilding and installing.


I just got done swapping the Thermosensor. The old one looked pretty nasty. I probed the old one for the hell of it just now and got a reading of 3.3ohms. dunno what it means havent looked up the FSM yet.

Im gonna check again right after i finish dinner.