I am experience the infamous PO300. In speaking with John Sheppard, he has found a mechanical failure in 5th gear that the knock sensor detects, which it sensors as a knock event. In doing so the ECU triggers the PO300 code.

The code will only trigger while cruising in 5th gear. Once it is triggered I literally can feel the engine misfire.

Currently I am running a Jestr Tuning ROM with the PO300 fix but, I am still experiencing the problem. I am wondering if I adjust the knock values further more than the PO300 fix ROM values in the knock adj. table in order to desensitize, so to speak, the knock sensor further until I am able to get the transmission to Shep to be repaired.

Any thoughts?

 

Unfortunately, unless you are logging the audio the knock sensor picks up when it happens, and look at it with a spectrum analyzer, you won't have an easy time finding what it will take to fix it.

Which means by arbitrarily making changes, you can potentially make things worse, or less able to proactively react to real knock.

We're still not exactly sure how those filters work, the best speculation I have made was that each map represents a frequency range, and the values represent an intensity under different loads..

 

At what RPM are you looking at when the code trips? Adjusting the knock tables at pre boost rpm's is fairly safe as long as your sure your adjusting the correct rpm ranges and you have an idea how to tune.

 

The area I am experiencing the false knock due to the mechanical failure in 5th gear is typically between 4 and 5k rpm and between 70 and 80 mph and under cruising load.

 

ur only at 70-80 @ 4-5k in 5th ? is it a 6 speed?

 

If you are experiening misfire then there may be something wrong, when I get a faulty p0300 my car feels the save as before the code came on no misfire, luckily I have not got the code in a while ""knock on wood""

 

The car is a 5 speed.

As far as the PO300 code, as I am sure you are aware, there are countless factors and several potential reasons for that lovely code in our car. In my case I only expereince it in 5th between those rpms and speed. I've spoke with John Sheppard of Shep Trans regarding a mechanical failure that he has found in our transmissions (at least '03s) that at those rpms and speed will case a false PO300 as the knock sensor detects the failure through vibrations and thinks it is the engine when in fact it is the transmission.

Apparently the failure is rarely felt by the driver, as I do not feel it although I have noticed shifts hae become lightly harder due to the synchos failuring most likely.

He has a fix for the 5th gear failure as well as upgraded internal parts for the tranny.

 

I think I am having this exact same thing happen. It all started about 2 months ago after installing a 6-puck race clutch. In 5th gear, between 4-5k, out of the blue the car starts misfiring and CEL comes on. The misfiring is serious enough that you can feel the car shake. Only way to stop the shaking is to lift off the gas for a few seconds. Staying on the gas results in progressively worse shaking.

I was so freaked out by this because I couldn't figure it out. I did consider the "vibration from tranny (clutch) tricking knock sensor theory" but I thought it was a little far-fetched since I thought the frequency had to be pretty specific to trigger the knock sensor to act.

Any ideas on how to fix this? I am thinking the clutch is the problem in my case. Also, I'm wondering how this affects the car and if it can result in premature failure of other parts. Any thoughts?

 

I should mentiony problem occurrs between 3 and 4k not 4 and 5k, sorry.

Secondly m2 your problem sounds identical to mine. According to John Sheppard of Shep Racing fame, he has documented a 5th gear mechanical failure that falsely triggers the PO300 code. Apparently there is a vibration in 5th gear caused by the failure but, the driver can not feel it oddly. He also said there is not many other symptoms other than the false code.

Your description is spot on to the symptoms he described to me.

The only other thing I have experienced is that it is very difficult to shift quickly from 2nd to 3rd although I think it is a seperate issue, possibly synchro on its last leg.

I would give Shep a call and see what he says. He has a fix for the problem that I think he said was aroudn $325 or so. Depending or your mileage and use of your car you may want to opt for his rebuild service as well, which is what I will be doing shortly.

Adam
CLT Racing

 

If you can always reproduce the P0300 at a specific load and RPM range, then its important to log as much data as you can while its happening.

Specifically the snapshot info from OBD-II, and the MUT logs. In order to adjust the filters though, you need to understand what those tables mean, which means if I were to try to document this on a car known to have a problem, I'd use a recording digital 3d spectrum analyzer hooked up to the knock sensor, and record the data, while its happening, I'd then match up the logs from the MUT, to the Snapshot info, and then match the timestamp to the data in the analyzer to find the sound signature that causes it.. What you'll find is that the signature of the noise is different than the ECU's filters, but the intensity is greater and therefore it exceeds the thresholds of all the filters and therefore is triggered as severe knock, which in turn probably results in pulling a lot of timing, triggering the P0300 random misfire..

Until we have all this data, its not really possible to correctly alter the knock filters, therefore you have to look at it from a mechanical perspective, what can you do to reduce noise transferred from the driveline into the crank. Well first, you need to dampen the engine vibration and reduce the engine shifting as much as possible, second, you have to use a SPRUNG HUB CLUTCH DISK as it will reduce the amount of noise transferred from the spline shaft to the disk hub which would be directly transferred to the clutch cover, flywheel, and ultimately the crank..

There are some experiencing this due to resonance in the transmission, that is a little more difficult as it will get transferred to the crank regardless of the clutch type whether its stock/aftermarket sprung or unsprung. The only way to fix that is to have the transmission looked over and correctly shimmed so it no longer resonates. And then you can approach it from an ECU standpoint with the right tools.

As you can see, the critical tools are not something anyone but a high-end audio guy might have and their not cheap.. Even software and a high quality sound capture device for a PC isn't cheap.

Alot of time and effort went into determining what makes those filters do what it does, and I doubt changing anything in them will help the situation more than the harm it can cause by altering it.

 

Oh, and the reason I say it can only be resolved by knowing the signature is because you have to find a frequency range you picked up while logging that is never hit by true knock, and set the threshold higher in that range than the drivetrain noise your picking up..\

*** Agh, edit, my thought process is flawed as its likely additive how the filters work, so if your driveline noise signature is greater across the board, it'll always get triggered as knock as the knock signature is a subset of the thresholds required, and you may never be able to work around it without reducing the safety net that the filters offer. ***

 

A not-so-great option is to attenuate the signal before it gets to the ECU, I know the XEDE offered this feature as it was considered by them, that the ECU was too sensitive to knock.. I don't really like this option as it reduces the effectiveness of the knock protection the ECU offers, but if you don't have a choice, and you can't "fix" the problem, then you might have to do that, as its the least intrusive method to the ECU As we still don't know exactly how the knock filters work. But you will then need to log the signal before its attenuated using an ECU+ as it may be your only way to tell if your getting knock.

 

Wow, your true expertise is shining through on this one. As mentioned before it appears as though my problem lies in the tranny.

I'll obviosly post up some comments once Shep rebuilds the tranny and adds te specific components that he has found to correct the problem in the tranny.

 

It funny you post this Adam. I have put 50k on my car and just started getting the P0300 code now. Only on the highway at the cruising speed you expierience it too.

Im sure it has somthing to do with the tranny/ imput shaft since nothing else has changed as far as my flash and Ive changed the plugs twice now since I have started getting it.

I really dont care it doesnt bother me much. It only pops up every couple hundred miles and only in 5th gear on the highway. I just find it a PITA to have to pull the code to make sure its not somthing else.

I guess its off to Shep with the tranny after we do the head brother.

 

Seen this twice, highway cruise speed, part throttle, P0300 comes on, accompanied by sudden jerkiness. 2 different, 2003 Evos.