Im going to start from the beginning... its long but plz bare with me...

Mods... (All done by yours truly)
Fresh Rebuild w/Street Port (under 1500)
New Optimum Yellow Top
PFC (Just Tuned By Glenn)
750/1680
Supra TT FP
DP/HFC/CB
Apexi Intake
Running Premix
Stock Non-Seq Twins on 10lbs

Cruising with some buddies after running my car on a few hi rev passes... cooling down and on my way back I start backfiring... didn't think much of it because these cars tend to do that... I parked the car for the night... It starts up and I go get gas when I fill up the car wont start... I push start it and drive off. At this point im thinking starter is going bad... drive it home... Later that night i have to take the car to work... I try to start it started right up... so im like ok wtf???

Drive it a little ways and i start backfiring and i notice im knocking like crazy... but only at low rpm's and when im lightly on the gas... if im at WOT it backfires and hesitates till the rpms go up, then goes smooth and starts to boost without knock... doesn't hesitate or backfire when I up shift at WOT ...I let of the throttle, it decelerates fine and only when i try to give it gas again it backfires and hesitates..

Then I notice fuel pressure is tripping out, check my voltage on my commander and it freaking out... between 12 and 16 volts... im knocking at low rpms... and only when i give it gas.. and its doing all of this as it the voltate surges.... i pull over and check my grounds, my fuel pump wires, everything i can think of and its ok... i press on the breaks and the pedal is freaking out... its pushing back and then letting off... i press on it hard for about 10 sec and my abs light goes on and it stops... WTF??? It took a few tries but it stated up... I drive it to go home... and i notice when im on a smooth road... i give it gas and its ok, i hit a bump i start backfiring and there is knocking and hesitation...

I get it home, and im messing around with it... and when i turn the key to on, then turn it to start... i notice what usually shuts off when you turn to start it (ie stereo) and i try again it shuts off and starts up... but im still knocking and having issues... now i cant get it to start...

Please give me some idea where to start... im going to get the alternator tested and even tho the battery is new im going to test it as well but not till tomorrow.. but Id like to know if anyone else has had the crazy issue and wtf it could be... thankx

 

ground?

ask your tuner... usually get at least 1 free troubleshoot if you spend an assload in a shop

look for thread titled something like "i seen something freaky on a dyno today"

 

Ok... So to fallow up on this thread to make it somewhat useful in the future... Im going to run new 8 gauge wire from the batt with a 50 amp fuse to the alt bolt, Im also going to run new + wire to the starter.... and clean up all my grounding points and run new grounds as necessary... Hopefully that does it... If that doesn't work im going to pull the batt and the alt and get them tested, im sure the batt is fine... the alt may have regulator issues but Im hoping the rewiring helps it...

 

Ok so I went out of order.... I tried to start it to get it to move, batt was dead (unfortunately it didn't help me with a diagnosis because someone said the saw the light on fml)... I couldn't even push start it... I didn't have time work on it and switch the alt and start wires... I took the batt to autozone and had them charge it... It took a 5 hours to get it to 12.3 but we tested it and it was ok... put it in my car and started right up... problem seemed to be gone but I wanted to drive it a little to be sure... sure enough it started to come back slowing like when it first started... tomorrow or the day after ill be able to rewire for sure and pull the alt and get it tested... anyone got any other idea's

 

Did you wire in the resistors for the big injectors?

Kinda sounds like the PFC injector driver is going into failure.

 

I did... but they came prewired and im not sure what the resistance is on them... I just assumed that it was correct, I know people use different ones... what would be best for 750cc and 1680cc injectors... If im doing all this i might as well put new ones in and see if that helps...

 

12-16 volts off the commander and a dead battery that tests out fine? Alternator. Check to see that all the connections are good. I would take a wire brush to them and throwing on a little dielectric grease wouldn't hurt. If your alternator went it could cause all of your problems suddenly (just like it seemed to have happened) since the PFC will adjust things like spark advance, and injector on times with the voltage. If that is swinging wildly it'll mess things up real quick.

 

Ok thankx... Today is the day I check everything, Im going to pull the alt and get it tested... if it tests fine im going to run the new wires for it... also the resistors on the injectors are 9.1ohm-1 Watt which ive read multiple threads where people have used them successfully for years...

 

Ok so yesterday I checked my alternator... I tested for AC current on my batt and got .8 to .12 volts... so bad alternator diode's... I was going to replace them but of corse Mazda used an alt that has a rectifier so Im going to get another and hopefully that fixes all these issues...

 

good luck!

 

And if that still doesn't fix it, have your injectors flow tested, it almost sounds like an injector is getting stuck sometimes... Also in California with FTBE and whatnot in our fuel I used to get my Primaries, and my Pulsation Dampener Replaced every 60k miles, kind of like a timing belt, except on a rotary (Which doesn't have one)