Chasing a short
05-14-12, 04:27 PM
#1
Chasing a short
I have been chasing down an issue with my FC since day one of owning her, and recent symptoms indicate that there is some type of ground or shorting issue.
Anyone know where or how to chase down a short aside from pulling the whole wiring harness and swapping in another one?
Symptoms:
Car has a sporadic idle. All symptoms point to bad TPS, BAC, OR AFM, swapping all theses sensors made no change.
If I turn the heater on full blast and turn the headlights on the car idle smooths out. So the electrical load is lessening the short somewhere and allowing the injectors to get proper voltage and fire correctly.
Lastly when the car is full throttle the stock coolant temp gauge on the dash acts like it's turning off. Just completely falls as if the engine is off, but once I'm not full throttle it bounces back to the normal temp reading.
Anyone know where or how to chase down a short aside from pulling the whole wiring harness and swapping in another one?
Symptoms:
Car has a sporadic idle. All symptoms point to bad TPS, BAC, OR AFM, swapping all theses sensors made no change.
If I turn the heater on full blast and turn the headlights on the car idle smooths out. So the electrical load is lessening the short somewhere and allowing the injectors to get proper voltage and fire correctly.
Lastly when the car is full throttle the stock coolant temp gauge on the dash acts like it's turning off. Just completely falls as if the engine is off, but once I'm not full throttle it bounces back to the normal temp reading.
05-14-12, 06:33 PM
#2
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rule #1 is to try to isolate the issue to a specific circuit in the car, if you can narrow it dow as much as possible the fix is usually really easy.
since there are two symptoms, we can look at them separately and see where they intersect.
the gauges are fed power from the meter fuse, so that fuse/circuit is worth checking. i don't know where else that circuit goes...
the others are a little non specific, but i'd be tempted to try a different main relay, or ignition switch (i think you could probably clean them).
the diaring wiregram is @www.foxed.ca if you don't have it. go to school, and find the biggest printer and print it out
since there are two symptoms, we can look at them separately and see where they intersect.
the gauges are fed power from the meter fuse, so that fuse/circuit is worth checking. i don't know where else that circuit goes...
the others are a little non specific, but i'd be tempted to try a different main relay, or ignition switch (i think you could probably clean them).
the diaring wiregram is @www.foxed.ca if you don't have it. go to school, and find the biggest printer and print it out
05-14-12, 06:52 PM
#3
I ended up giving up on the stock FC 20+ year old wiring and ecu and built my own full standalone and wiring harness. 1980's fuel injection is sketchy at best.
05-14-12, 07:58 PM
#4
Literally every single sensor under the hood has been replaced except the BAC.
See detailed thread here: https://www.rx7club.com/showthread.p...637&styleid=12
Hence my thinking now that it must be a grounding issue somewhere.
See detailed thread here: https://www.rx7club.com/showthread.p...637&styleid=12
Hence my thinking now that it must be a grounding issue somewhere.
05-14-12, 10:17 PM
#6
sporadic idles are usually vacuum leaks; assuming you don't have a vacuum leak, the next thing is to make sure you have a good battery with good battery cable connections
you will need wiring diagram from the FSM... i would print one out so you can write on it
than check all aftermarket wiring hacks.. radio, alarms, turbo timers, amps, gauges, lights, electric fans... etc... all that Chinese crap is a prime source for nightmares.
check the alternator, make sure it is operating correctly
one by one pull fuses from the fuse box to see if you can isolate the circuit
also, the rats nest is full of potential dried up and cracked wires just looking to short
you might think about investing in a power probe, its a test light on steroids
http://www.powerprobe.com/PP1.html
you will need wiring diagram from the FSM... i would print one out so you can write on it
than check all aftermarket wiring hacks.. radio, alarms, turbo timers, amps, gauges, lights, electric fans... etc... all that Chinese crap is a prime source for nightmares.
check the alternator, make sure it is operating correctly
one by one pull fuses from the fuse box to see if you can isolate the circuit
also, the rats nest is full of potential dried up and cracked wires just looking to short
you might think about investing in a power probe, its a test light on steroids
http://www.powerprobe.com/PP1.html
05-14-12, 10:53 PM
#7
I've already done all the grounding mods. There is no vacuum leak. It has to be a wiring issue somewhere. Brand new Optima. Main cables are fine. Alt is a reman FD alt that's only 2 years old. 11.8V on everything that should see 12v. I finally installed my SAFC NEO today hoping to crank up the fuel at idle to get it to idle correctly, but that didn't help at all. One thing I did notice was that with the throttle closed, TPS voltage at the ECU is .8v. I tried adjusting the screw and it stayed at .8V regardless of how I adjusted it. There are no aftermarket wiring hack jobs. Everything aftermarket in the car I have installed, and the problem has existed since I've owned the car. I spent the batter part of 6 hours today looking for wiring issues and they only thing I saw out of the ordinary was this:
All that nasty corrosion...
I think the wiring harness is shot. At this point I cant think of any other solution.
All that nasty corrosion...
I think the wiring harness is shot. At this point I cant think of any other solution.
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05-14-12, 11:17 PM
#8
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Call up your Mazda dealer. I work at a Chevy dealer and we can get connectors with pigtails for damn near anything. Its worth a shot. I have seen before corrosion to backfeed circuits which sounds like whats goin on. At minimum clean the corrosion and see if anything changes. I recommend changing that connector anyways.
05-21-12, 08:58 PM
#13
Miraculous fix. So I took a dame out for lunch the other day, and on my way home I was not very nice to my FC. When I was done on my drive, I stopped at a light and it was idling perfectly at 1200 RPM. So I turned down the idle to 750 RPMS, and the car has been absolutely perfect for 7 days now. I have no idea how, or what, happened, but somehow no lift shifts and clutch kicking fixed my issue. I'm guessing what ever was shorted, god knows where, pulled itself back into line and the car is driving great now... Typical Rx-7, if you treat it nice it won't run, but beat and abuse her and she's as happy as a clam. 
05-22-12, 10:37 AM
#16
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Miraculous fix. So I took a dame out for lunch the other day, and on my way home I was not very nice to my FC. When I was done on my drive, I stopped at a light and it was idling perfectly at 1200 RPM. So I turned down the idle to 750 RPMS, and the car has been absolutely perfect for 7 days now. I have no idea how, or what, happened, but somehow no lift shifts and clutch kicking fixed my issue. I'm guessing what ever was shorted, god knows where, pulled itself back into line and the car is driving great now... Typical Rx-7, if you treat it nice it won't run, but beat and abuse her and she's as happy as a clam.
the second idea is that maybe the clutch switch was bad... maybe all that clutch kicking fixed it?
05-22-12, 02:45 PM
#17
Either Rxy likes her, or she's jealous and decided to finally behave. Although 2 nights ago the cat decided to commit suicide... I don't think it was the clutch switch. I've never had starting issues -aside from a bad starter.
05-22-12, 03:15 PM
#18
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Another Idea: High resistance, like corrosion, at certain connectors. When you were testing, disconnecting, and reconnecting connectors, you got rid of the resistance.
05-22-12, 04:41 PM
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there are two clutch switches, one for Americans to start the car without hitting stuff, and one for the ECU, maybe it was the other one?
either way, i'm happy you're happy
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