Help! My fd is possessed!
#1
Senior Member
Thread Starter
Help! My fd is possessed!
The title is mostly a joke but only because I'm not superstitious enough to believe it so.
My car Is acting seriously weird.
To preface, my car is running stock twins on PFC + xavier borg's dl-340xb with the base map fully tweaked to the fc tweak recommended defaults.
Air pump deleted, acv deleted, fpd deleted, emissions solenoids deleted, double throttle and fast warm up deleted, catless midpipe, HKS v-mount, koyo n-flow, Antigravity atx-30 battery relocated to rear, walbro 450 with its own circuit & relay, aem 0300 x series wideband.
Onto the symptoms...
The car turns on and runs fine, idles (mostly) fine. I drive off and get going without any drama. After warming up the car to operating temperature (about 10 minutes of stop & go driving) the car's idle becomes audibly worse. After about 15 minutes, the car starts misfiring and having trouble staying on. At this point, with constant throttle on the highway, the car lurches over and over. My data logs on pfc-connect show the afr, iacv, and injx spiking to max values over and over. Basically a few sensors in conjunction go absolutely ballistic even as the battery voltage stays steady. Car is lurching on and off power with constant throttle.
The running quality quickly deteriorates until the car is sputtering, unresponsive to all throttle inputs, barely able to idle, and eventually stalls itself out. After i let the car sit for about half an hour, it starts back up and runs like nothing ever happened. But eventually it repeats the same behavior of sputtering out and stalling. (I limped it home this way)
Here's a list of things that are NOT the problem.
I compression tested the car after limping it home today and it tested >110psi on all faces and rotors (phew). It's a new mazda motor i swapped in 3 years ago with about 1k miles on it.
Ive smoke tested the car and it shows no vacuum leaks.
Idle air control valve is cleaned and works. Evident by the fact that my pfc's electronic dashpot is working.
My fuel pump is new, on its own circuit, and i hear it prime when i turn the ignition on.
The injectors have been cleaned and flow tested and are fully functional.
the water temperature showing on my aftermarket gauge stabilises at around 200f in traffic and 180-190 at speed so it's not overheating.
All signs point to some kind of electrical or fuel delivery issue, but i cant see how it could be a fuel system issue when ive been through the entire fuel system already. Could it be a bad ecu, or bad ground or something??
any thoughts?
My car Is acting seriously weird.
To preface, my car is running stock twins on PFC + xavier borg's dl-340xb with the base map fully tweaked to the fc tweak recommended defaults.
Air pump deleted, acv deleted, fpd deleted, emissions solenoids deleted, double throttle and fast warm up deleted, catless midpipe, HKS v-mount, koyo n-flow, Antigravity atx-30 battery relocated to rear, walbro 450 with its own circuit & relay, aem 0300 x series wideband.
Onto the symptoms...
The car turns on and runs fine, idles (mostly) fine. I drive off and get going without any drama. After warming up the car to operating temperature (about 10 minutes of stop & go driving) the car's idle becomes audibly worse. After about 15 minutes, the car starts misfiring and having trouble staying on. At this point, with constant throttle on the highway, the car lurches over and over. My data logs on pfc-connect show the afr, iacv, and injx spiking to max values over and over. Basically a few sensors in conjunction go absolutely ballistic even as the battery voltage stays steady. Car is lurching on and off power with constant throttle.
The running quality quickly deteriorates until the car is sputtering, unresponsive to all throttle inputs, barely able to idle, and eventually stalls itself out. After i let the car sit for about half an hour, it starts back up and runs like nothing ever happened. But eventually it repeats the same behavior of sputtering out and stalling. (I limped it home this way)
Here's a list of things that are NOT the problem.
I compression tested the car after limping it home today and it tested >110psi on all faces and rotors (phew). It's a new mazda motor i swapped in 3 years ago with about 1k miles on it.
Ive smoke tested the car and it shows no vacuum leaks.
Idle air control valve is cleaned and works. Evident by the fact that my pfc's electronic dashpot is working.
My fuel pump is new, on its own circuit, and i hear it prime when i turn the ignition on.
The injectors have been cleaned and flow tested and are fully functional.
the water temperature showing on my aftermarket gauge stabilises at around 200f in traffic and 180-190 at speed so it's not overheating.
All signs point to some kind of electrical or fuel delivery issue, but i cant see how it could be a fuel system issue when ive been through the entire fuel system already. Could it be a bad ecu, or bad ground or something??
any thoughts?
Last edited by Oppai; 08-26-24 at 08:24 AM.
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scotty305 (08-29-24)
#4
Senior Member
Thread Starter
The coolant temp sensor was replaced with a mazda OEM sensor about 2 years ago. I have a hard time believing it would go bad so quickly. Other culprits possible? Do these things going haywire all have a shared ground or something? Injectors, coolant temp sensor, idle air control valve...
Nonetheless i have ordered a new sensor to see if it will fix the coolant temp issue specifically...
(By the way, the actual coolant temp GAUGE inside my car which should be wired to that coolant sensor was displaying normal temps... could it just be a software glitch?)
Nonetheless i have ordered a new sensor to see if it will fix the coolant temp issue specifically...
(By the way, the actual coolant temp GAUGE inside my car which should be wired to that coolant sensor was displaying normal temps... could it just be a software glitch?)
Last edited by Oppai; 08-25-24 at 09:10 PM.
#5
Eats, Sleeps, Dreams Rotary
Resistance goes down as the temperature increases, and the resistance curve probably bottoms out at something like -38 F when resistance goes to infinity.
The resistance curve of the stock IAT (which is basically just a water temperature sensor) bottoms out at around -30 C at ~13,000 Ohms.
Coincidentally, -38 degrees is around where the Fahrenheit and Celsius scales cross over...
Last edited by Valkyrie; 08-26-24 at 12:21 AM.
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#8
Your PFC uses the OEM wiring harness, correct? And is your OEM harness still the original one that came with the car from the factory some ~30 years ago now? If so, it's been thru enough years of aging + heat cycles and wear & tear to most likely have at least a few poor/intermittent opens and possibly some intermittent shorts that will wreak havoc on normal operations. When my S5T2 was still on the OEM ECU, and around 20+ years old, I had lots of intermittent electrical gremlins - OMP would sometimes fault into limp home mode; could never keep the TPS set for long, wonky idel, etc... Replacing my OEM wiring harness killed all the gremlins and everything just WORKED after that.
#9
Senior Member
Thread Starter
#10
Senior Member
Thread Starter
Your PFC uses the OEM wiring harness, correct? And is your OEM harness still the original one that came with the car from the factory some ~30 years ago now? If so, it's been thru enough years of aging + heat cycles and wear & tear to most likely have at least a few poor/intermittent opens and possibly some intermittent shorts that will wreak havoc on normal operations. When my S5T2 was still on the OEM ECU, and around 20+ years old, I had lots of intermittent electrical gremlins - OMP would sometimes fault into limp home mode; could never keep the TPS set for long, wonky idel, etc... Replacing my OEM wiring harness killed all the gremlins and everything just WORKED after that.
#11
Senior Member
Thread Starter
92 rhd and coils are hooked up correctly. Otherwise the car probably wouldnt run fine initially
#12
Senior Member
Thread Starter
I suspect an intermittently bad connection (e.g., a broken wire).
Resistance goes down as the temperature increases, and the resistance curve probably bottoms out at something like -38 F when resistance goes to infinity.
The resistance curve of the stock IAT (which is basically just a water temperature sensor) bottoms out at around -30 C at ~13,000 Ohms.
Coincidentally, -38 degrees is around where the Fahrenheit and Celsius scales cross over...
Resistance goes down as the temperature increases, and the resistance curve probably bottoms out at something like -38 F when resistance goes to infinity.
The resistance curve of the stock IAT (which is basically just a water temperature sensor) bottoms out at around -30 C at ~13,000 Ohms.
Coincidentally, -38 degrees is around where the Fahrenheit and Celsius scales cross over...
#13
Racecar - Formula 2000
If it's not an electrical issue...
Have you logged fuel pressure when this happens? I'm suspecting fuel pressure drops off with heat. Not that this applies directly to you, but on carbureted cars this is usually vapor-lock. I'm wondering if the there is a leak or restriction in the hoses/filter in fuel tank before the pump which would cause it to not pump properly when it and/or the fuel gets warm.
Have you logged fuel pressure when this happens? I'm suspecting fuel pressure drops off with heat. Not that this applies directly to you, but on carbureted cars this is usually vapor-lock. I'm wondering if the there is a leak or restriction in the hoses/filter in fuel tank before the pump which would cause it to not pump properly when it and/or the fuel gets warm.
Last edited by DaveW; 08-26-24 at 11:19 AM.
#14
Senior Member
Thread Starter
If it's not an electrical issue...
Have you logged fuel pressure when this happens? I'm suspecting fuel pressure drops off with heat. On carbureted cars this is usually vapor-lock. I'm wondering if the there is a leak or restriction in the hoses/filter in fuel tank before the pump which would cause it to not pump properly when it or the fuel gets warm.
Have you logged fuel pressure when this happens? I'm suspecting fuel pressure drops off with heat. On carbureted cars this is usually vapor-lock. I'm wondering if the there is a leak or restriction in the hoses/filter in fuel tank before the pump which would cause it to not pump properly when it or the fuel gets warm.
Maybe its worthwhile for me to try installing a temporary inline fuel pressure gauge to confirm this, but inducing these symptoms on the street is also really sketchy and not something i want to repeat...
Last edited by Oppai; 08-26-24 at 09:52 AM.
#15
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its not vapor lock, but a clogged canister will cause problems, when the engine pulls fuel out of the tank, it needs to be able to let air in to take up the space, if it can't, then the pump can't pump.
it gets worse as the fuel level drops, so if you have a full tank its usually fine, but if its near empty its bad.
you can diagnose by taking the gas cap off
i also had a car where the fuel filter rusted out internally, it would start and run ok, but the more you drove it the less power you had.
it gets worse as the fuel level drops, so if you have a full tank its usually fine, but if its near empty its bad.
you can diagnose by taking the gas cap off
i also had a car where the fuel filter rusted out internally, it would start and run ok, but the more you drove it the less power you had.
#16
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#17
Rotor or no motor
iTrader: (24)
i would zero out the coolant temp fuel enrichment so this variation in temperature does not contribute to any fuel adjustments. write down your numbers before you zero everything out and see the behavior
The following users liked this post:
Oppai (08-26-24)
#18
Senior Member
Thread Starter
its not vapor lock, but a clogged canister will cause problems, when the engine pulls fuel out of the tank, it needs to be able to let air in to take up the space, if it can't, then the pump can't pump.
it gets worse as the fuel level drops, so if you have a full tank its usually fine, but if its near empty its bad.
you can diagnose by taking the gas cap off
i also had a car where the fuel filter rusted out internally, it would start and run ok, but the more you drove it the less power you had.
it gets worse as the fuel level drops, so if you have a full tank its usually fine, but if its near empty its bad.
you can diagnose by taking the gas cap off
i also had a car where the fuel filter rusted out internally, it would start and run ok, but the more you drove it the less power you had.
#19
Senior Member
Thread Starter
#20
Rotary Enthusiast
The coolant temp sensor was replaced with a mazda OEM sensor about 2 years ago. I have a hard time believing it would go bad so quickly. Other culprits possible? Do these things going haywire all have a shared ground or something? Injectors, coolant temp sensor, idle air control valve...
Nonetheless i have ordered a new sensor to see if it will fix the coolant temp issue specifically...
(By the way, the actual coolant temp GAUGE inside my car which should be wired to that coolant sensor was displaying normal temps... could it just be a software glitch?)
Nonetheless i have ordered a new sensor to see if it will fix the coolant temp issue specifically...
(By the way, the actual coolant temp GAUGE inside my car which should be wired to that coolant sensor was displaying normal temps... could it just be a software glitch?)
#21
Ban Peak
iTrader: (49)
Your PFC uses the OEM wiring harness, correct? And is your OEM harness still the original one that came with the car from the factory some ~30 years ago now? If so, it's been thru enough years of aging + heat cycles and wear & tear to most likely have at least a few poor/intermittent opens and possibly some intermittent shorts that will wreak havoc on normal operations. When my S5T2 was still on the OEM ECU, and around 20+ years old, I had lots of intermittent electrical gremlins - OMP would sometimes fault into limp home mode; could never keep the TPS set for long, wonky idel, etc... Replacing my OEM wiring harness killed all the gremlins and everything just WORKED after that.
Replace the harness, free yourself of the headaches.
What you're describing sounds like a connection or signal ground loss issue due to a poor connection which is causing several things to go haywire at once. Replacing the harness is considerably easy, don't trip yourself up due to intimidation.
The following 2 users liked this post by Molotovman:
JP3 Motorsports (08-26-24),
rx7_nyc (08-26-24)
#22
With his modifications, I wonder how much of the original harness is actually there, or whether it was already re-wired?
There is a NIB emissions harness on Buyee for about $800 atm.
My point on the TPS was that owner found his TPS would appear in spec when cold and when warmed up, but would go out of spec when the engine got hot.
I am not sure if that would be a readable condition.
But it sort of fits your described problem, so might be worth a try, to try a different TPS.
(See recent posts by Tom Smith on this issue for his car.)
Also read up on the Fuel Pressure regulator. The FD FPR has a solenoid controlling it which the ecu activates under certain engine temperature conditions. Often on "reliability " mods" that solenoid is deleted. Be aware that if the FPR lacks a vacuum it will close, raising your fuel pressure. My vacuum hose to the FPR had turned to dust, likely contributing to flooding sensitivity issues I was having.
There is a NIB emissions harness on Buyee for about $800 atm.
My point on the TPS was that owner found his TPS would appear in spec when cold and when warmed up, but would go out of spec when the engine got hot.
I am not sure if that would be a readable condition.
But it sort of fits your described problem, so might be worth a try, to try a different TPS.
(See recent posts by Tom Smith on this issue for his car.)
Also read up on the Fuel Pressure regulator. The FD FPR has a solenoid controlling it which the ecu activates under certain engine temperature conditions. Often on "reliability " mods" that solenoid is deleted. Be aware that if the FPR lacks a vacuum it will close, raising your fuel pressure. My vacuum hose to the FPR had turned to dust, likely contributing to flooding sensitivity issues I was having.
Last edited by Redbul; 08-26-24 at 03:52 PM.
#23
Senior Member
Thread Starter
With his modifications, I wonder how much of the original harness is actually there, or whether it was already re-wired?
There is a NIB emissions harness on Buyee for about $800 atm.
My point on the TPS was that owner found his TPS would appear in spec when cold and when warmed up, but would go out of spec when the engine got hot.
I am not sure if that would be a readable condition.
But it sort of fits your described problem, so might be worth a try, to try a different TPS.
(See recent posts by Tom Smith on this issue for his car.)
There is a NIB emissions harness on Buyee for about $800 atm.
My point on the TPS was that owner found his TPS would appear in spec when cold and when warmed up, but would go out of spec when the engine got hot.
I am not sure if that would be a readable condition.
But it sort of fits your described problem, so might be worth a try, to try a different TPS.
(See recent posts by Tom Smith on this issue for his car.)
My harness has had the IAT sensor and rad fan thermoswitch connectors rewired for aftermarket sensors. There may also be a couple of other things I'm forgetting about.
#24
With a emission delete (and possibly a change to parralled turbos) a good deal of the "Emission Harness" (often referred to as the "Engine Harness') would likely have been deleted as well. So replacing the harness with a custom harness may be a more cost effective route than buying an entirely new EM harness and chopping it up.
I am assuming your Power FC is the proper spec one for your year and model.
There is a remote chance someone swapped in a newer set of coils. Even with the plugs hooked up wrong the motor will run, but as you get into higher revs (above 6000) trouble appears....in a big way.
I am assuming your Power FC is the proper spec one for your year and model.
There is a remote chance someone swapped in a newer set of coils. Even with the plugs hooked up wrong the motor will run, but as you get into higher revs (above 6000) trouble appears....in a big way.
#25
+1
Replace the harness, free yourself of the headaches.
What you're describing sounds like a connection or signal ground loss issue due to a poor connection which is causing several things to go haywire at once. Replacing the harness is considerably easy, don't trip yourself up due to intimidation.
Replace the harness, free yourself of the headaches.
What you're describing sounds like a connection or signal ground loss issue due to a poor connection which is causing several things to go haywire at once. Replacing the harness is considerably easy, don't trip yourself up due to intimidation.
The following users liked this post:
JP3 Motorsports (08-28-24)