Random Misfire

06monera96 · Nov 16, 2016

damm pretty darn lean under boost for the first few seconds eh?
Looks like when you stab the gas, your car loses pressure.
Losing pressure prob dropping the psi in 1 of your injecto for a moment just enough to detect misfire

redfirepearlgt · Nov 16, 2016

Shouldn't the target AFR in closed loop be trying to maintain 14.0:1 vice 14.7:1 being most 93 octane pump gas has about 10-15% ethanol in it? Maybe its trying to and can't. Yet there seems to be no climb on the Duty cycle demand. 11.6 - 12.0 seems pretty lean as well at WOT.

I had that discussion with my tuner and he explained why 14.0 is the ratio to select because of that when setting up the datalogger. Maybe what the log displys in live link as I look at it is due to you selecting 14.7 vice 14.01:1. However that all said, I'm going on mine targeting 14.0 at closed loop and staying close to that and pulling down to 11.4-11.6 WOT in really dense cold air running 9.5 psi boost. My datalogs coincide with the wideband on the car.

I am assuming you are running a 93 octane tune as I look at it and not race fuel??? What kind of fuel system are you running? Return or Returnless? If stock you are running at least a Boost-a-pump?

Saleen304 · Nov 16, 2016

Running e85. Those values are just lambda corrected to show applicable AF for pump gas. Anyway target is the same.

Saleen304 · Nov 16, 2016

Also, during this datalog I did not notice any misfires, but my graph is just not right. Maybe it's an unrelated issue like spinning the supercharger too fast beyond it's efficiency or slipping clutch. I did not smell clutch during the pull, but I did a couple weekends ago when I went drag racing.

Saleen304 · Dec 9, 2016

Update: Replaced both vct solenoids and installed fore billet fuel rails. Still have the misfire.

bujeezus · Dec 9, 2016

Sonuvabitch. I was just wondering today if you had got it figured out.

redfirepearlgt · Dec 9, 2016

Saleen304 said:
Running e85. Those values are just lambda corrected to show applicable AF for pump gas. Anyway target is the same.

Okay....explains that as well.

So new VCT solenoids did nothing. With random misfires on both banks common sense says it has to be something in common with the whole system. So to review from memory, you've replaced the PCM with no change in symptom. You've verified the alternator is good and putting out proper voltage with no minimal AC ripple. Plus you just upgraded the fuel rails which had no effect. What I can't remember is if your fuel system is open or closed. If closed there is the possibility of a flaky FRP sensor. Otherwise since the PCM has been ruled out, the Alternator has (according to your voltage check readings) been ruled out, the only other thing I can think of in common with the system that could cause random misfires would be something in the fuel delivery system. Finally there is the fuel itself to question (but I assume you have tested it) or possibly the tune has gotten corrupted on the tuner (but I would assume you have reflashed the tune to the hand held and then reflashed the PCM several times. A failure on the PCM relay would cause the car to die as it provides 12vdc to the COP's. A failure of the Fuel Pump Relay would also cause the car to die (or not start) as it provides 12vdc to the FI's AND Fuel pump/FPDM. I would be curious to know if you have good 12vdc at the injectors with key on engine off however. PIN2 on any FI would be where you could back probe to see if you have solid 12vdc. It could be that the FUEL PUMP RELAY, though working has built up carbon on the face of the contacts which could cause a weak signal to the FI's which could cause the misfire.......BUT I AM REALLY REACHING HERE. I still believe there is something going on in the fuel delivery system. Vacuum leaks you would see on your vac/boost gauge and likely hear from a higher idle and lower boost.

Hope you get this thing figured out man. I know its a tough one. I don't envy you a bit.

BruceH · Dec 9, 2016

redfirepearlgt said:
Shouldn't the target AFR in closed loop be trying to maintain 14.0:1 vice 14.7:1 being most 93 octane pump gas has about 10-15% ethanol in it? Maybe its trying to and can't. Yet there seems to be no climb on the Duty cycle demand. 11.6 - 12.0 seems pretty lean as well at WOT.

I had that discussion with my tuner and he explained why 14.0 is the ratio to select because of that when setting up the datalogger. Maybe what the log displys in live link as I look at it is due to you selecting 14.7 vice 14.01:1. However that all said, I'm going on mine targeting 14.0 at closed loop and staying close to that and pulling down to 11.4-11.6 WOT in really dense cold air running 9.5 psi boost. My datalogs coincide with the wideband on the car.

I am assuming you are running a 93 octane tune as I look at it and not race fuel??? What kind of fuel system are you running? Return or Returnless? If stock you are running at least a Boost-a-pump?

FYI 14.7 (14.64 actually) is how American systems display 1 lambda. Closed loop should always target 1 lambda. Lambda will have a different afr depending on the fuel but 1 lambda is always the target for normal driving.

What I'm saying is that E10, E85, or pure gas should always show 1 lambda or 14.64 which equals 1 lambda on a wideband.

Saleen304 · Dec 9, 2016

redfirepearlgt said:
Okay....explains that as well.

So new VCT solenoids did nothing. With random misfires on both banks common sense says it has to be something in common with the whole system. So to review from memory, you've replaced the PCM with no change in symptom. You've verified the alternator is good and putting out proper voltage with no minimal AC ripple. Plus you just upgraded the fuel rails which had no effect. What I can't remember is if your fuel system is open or closed. If closed there is the possibility of a flaky FRP sensor. Otherwise since the PCM has been ruled out, the Alternator has (according to your voltage check readings) been ruled out, the only other thing I can think of in common with the system that could cause random misfires would be something in the fuel delivery system. Finally there is the fuel itself to question (but I assume you have tested it) or possibly the tune has gotten corrupted on the tuner (but I would assume you have reflashed the tune to the hand held and then reflashed the PCM several times. A failure on the PCM relay would cause the car to die as it provides 12vdc to the COP's. A failure of the Fuel Pump Relay would also cause the car to die (or not start) as it provides 12vdc to the FI's AND Fuel pump/FPDM. I would be curious to know if you have good 12vdc at the injectors with key on engine off however. PIN2 on any FI would be where you could back probe to see if you have solid 12vdc. It could be that the FUEL PUMP RELAY, though working has built up carbon on the face of the contacts which could cause a weak signal to the FI's which could cause the misfire.......BUT I AM REALLY REACHING HERE. I still believe there is something going on in the fuel delivery system. Vacuum leaks you would see on your vac/boost gauge and likely hear from a higher idle and lower boost.

Hope you get this thing figured out man. I know its a tough one. I don't envy you a bit.

Returnless system. I forgot to mention that I also installed a new fuel pressure sensor when I installed the new rails. I have checked voltage at each injector and coil and they are good and consistent with each other.

redfirepearlgt · Dec 9, 2016

Saleen304 said:
Returnless system. I forgot to mention that I also installed a new fuel pressure sensor when I installed the new rails. I have checked voltage at each injector and coil and they are good and consistent with each other.

I can't do you any more good. I'm spent. I'll be checking in to see if there is a resolve. I'm curious. I keep thinking now to fuel delivery as in pumps or driver modules but I don;t see how based on the original symptoms as you have described them. I guess a guy could pop the fuel line, grab a five gallon can and with some help jumper the Fuel Pump relay on to drive the pumps and time how long it would take to fill a five gallon gas can and then do the math from that to see if fuel flow is correct. Likely a youtube video on how to do it safely. I'd be inclined to at least pull the pumps and inspect them if that has not already been done as well.

Good luck man. Sorry you are still fighting the problem.

Saleen304 · Feb 20, 2017

I don’t want to get too excited here, but I think it’s fixed!!! We had good weather yesterday so I decided to take the car out. I removed the fuse from one of my FPDMs to see what it would do (thinking maybe fuel pump issue) and it seemed to idle fine so I thought I would take it out. Once I got a mile or so away it went into fail safe mode. I put the fuse back in and it seemed fine and then it went back into fail safe mode. RPMs were hanging and it gave me P2104 and P2112 codes for throttle actuator control (forced idle) and (stuck closed). I reflashed the PCM and it didn’t seem to fix it. Everything on throttle body looked good, but I decided to take the throttle position sensor off my old throttle body and put it on my FRPP throttle body to see if that was the issue. It not only fixed that issue, but I drove it 60 miles with varied driving styles and no misfires! Part throttle, WOT, sustained high rpms, etc. Not sure why this would make this thing misfire like it did, but seems to be fixed….finally!!!

redfirepearlgt · Feb 20, 2017

Knock on wood man. Hope you got it. If the problem goes away I would love to know what the resistance on the bad TPS looks like when you sweep it. If that is the problem one would think there to be some jump in the resistance on one or both potentiometers in the TPS feedback unit. Would love to know what you find resistance wise as it sweeps (IE smooth and out of range or jumpy as it moves, etc.). Would be great 411 for future issues like this.

Hope to hear back.

bujeezus · Feb 20, 2017

I was wondering if you ever figured this out.

06monera96 · Feb 20, 2017

Same!

Saleen304 · Mar 4, 2017

Well, I spoke too soon. Misfire is back. Tried a new TPS and didn't work. Took off 62mm FRPP throttle body and put on a stock TB and still misfired. The P2104 and P2112 codes popped back up and car went into failsafe mode after the new TPS was installed. Went away when I put the old throttle body back on. Also, another weird issue. I have my data center show Average Fuel Economy and miles driven, but sometimes after I turn off the car and turn it back on it switches screens to just miles driven. Weird.

redfirepearlgt · Mar 4, 2017

Those two codes are specific to the TB. Have you replaced the foot peddle assembly which is responsible for providing the output to the PCM which determines TB position? There are two signals produced by the foot pedal as well as two positions produced by the TPS on the TB that provides redundancy or the drive by wire system to detect failures that would produce these two codes.

Oh and there is another thing I just thought of thinking back on my Saleen SC days. If using the stock intake tube with a CAI like the STEEDA or FRPP CAI, it has been known to collapse cutting off air when the throttle body opens. Don;t know what CAI you are running, but just thought of this.

I am just trying to think of anything at this point that may have been overlooked or out of the ordinary. Problems like this suck. I fight with intermittent problems on ancient CNC machine tools at work all of the time. About the time I think its been resolved after replacing something, it runs a week or so then the problem flairs up again. eventually it gets figured out, but sometimes it takes several revisits and some severe thinking outside the box. I feel your pain.

Saleen304 · Mar 4, 2017

Haven't changed the pedal. Car only has 24k miles and I've replaced about every goddamn sensor on it already. Think those codes are fixed though. Misfire is the nagging one. Oh, and I have a Techco intake with a hard tube so it isn't collapsing.

Saleen304 · Mar 6, 2017

So I have some hope I may have found the issue. I monitored the TP1 and TP2 voltage through the PCM to make sure it was a smooth ramp. Just sitting in the car with KOEO I could go though the sweep and listen to the throttle body open and close. I then had my wife start messing with the wires at the TPS and motor to see if it changed. Well it did. Specifically just wiggling the wires right at the TPS connector. You could hear the throttle plates open sporadically even though the throttle pedal was not moving. Got a new connector on order from Rockauto and hopefully that fixes it.

bcb06gt · Mar 6, 2017

Hopefully that is it. Good find.

05stroker · Mar 6, 2017

When you install the new connector, be sure you cut the wires back a good 1/2" or so , the wires are horrible about breaking close to the connector inside the isolation.

Random Misfire

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