Revving past 8000+ rpms

[robz]

We have a stock pcm from an 03 vette and are trying to buzz the motor past 8000rpm.
The car is tuned alpha-n (TPS vs. RPM) and this table ends at 8000rpm.
Initially we were getting a fuel cutoff right at 8000rpm so we decided to populate the main VE table with the thought that the PCM would default back to the main VE after the TPS vs. RPM table ended.
It seemed to work somewhat as we were able to now buzz the car to 8235rpm, 8350rpm, and 8475rpm on consecutive pulls BUT the car still experienced an abrupt fuel cutoff.
It seems that we are making progress but are not sure why the fuel is being cut and why at different rpms. The only thing we changed was a slight adjustment in AFR during the above pulls on the dyno.
The fuel pressure is rock solid up to the point where it cuts out and it acts like it's hitting a rev limiter. My tuner has mentioned that he has raised all 3 rev limiter options above this point(9000+).

-Could the injectors be maxing out? But why the abrupt fuel cutoff?

-Any suggestions on how to get around this?

-Do you think we have to manipulate the PCM or the software?

We want to buzz the motor to aproximately 9000 rpms.
Thanks.
Rob

[dlove]

A little off topic, but are you going to have the car at the lsx shootout?

[edcmat-l1]

A little off topic, but are you going to have the car at the lsx shootout?

I don't think he's bringing to the shootout, but he'll be at MIR for the smackdown.

[geoff]

Just for grins have you tried using a MAF??? The car we had when I was at Thunder Racing in 2004 was being shifted at 8400 pretty consistantly. It had a MAF on it. Might be interesting to try it to see if it gives you any extention.

FWIW I have been on certain people here for a LONG time to do a custom OS to go past 8000 RPM. :angel_innocent: Still wish it would get done...I have a 3.25" stroke crankshaft sitting in my closet needing some exercise at about 9500 RPM :devil_2:

[GMPX]

RobZ, I sent Paul an updated .calz file for you to test with. It has the TPS VE Swap over RPM limit raised.

Geoff, I understand you'd like that, but majority rules in development priorities.

[robz]

RobZ, I sent Paul an updated .calz file for you to test with. It has the TPS VE Swap over RPM limit raised.

Geoff, I understand you'd like that, but majority rules in development priorities.
Thanks. I'll try it.

[robz]

I don't think he's bringing to the shootout, but he'll be at MIR for the smackdown.

We're headed down to the sticks on the 5th!

[edcmat-l1]

We're headed down to the sticks on the 5th!

See yas there!!!

[vetteboy2k]

RobZ, I sent Paul an updated .calz file for you to test with. It has the TPS VE Swap over RPM limit raised.

Geoff, I understand you'd like that, but majority rules in development priorities.
Ross,

To clarify some... in the custom OS5 after the TPS VE table A0007 reaches 8000 RPM does the car use the last column 8000rpm 100% TPS for fueling for the entire rpm or does it start back at 400rpm 100% TPS (ie revert back to the top where as 400rpm actually is 8400rpm)

If not anyway to get control of fueling past 8000 RPM, as the cars fueling requirements are less as the rpms climb that high.

[GMPX]

It will just use the last value in the 8000 RPM column, it doesn't wrap back around. The problem we had with Robz (which I never thought of) was the upper RPM threshold to switch back to the normal VE map was limited to 8,000RPM, so once they got above that it was jumping out of the TPS VE table, we just extended that allowable RPM up to 10,000.

Cheers,
Ross

[ScarabEpic22]

Cool fix Ross, are you going to update the .calz files in the next release with this fix too?

[robz]

It will just use the last value in the 8000 RPM column, it doesn't wrap back around. The problem we had with Robz (which I never thought of) was the upper RPM threshold to switch back to the normal VE map was limited to 8,000RPM, so once they got above that it was jumping out of the TPS VE table, we just extended that allowable RPM up to 10,000.

Cheers,
Ross

We'll try it Ross( vetteboy2k is the tuner) and report back.
We will also try new injectors.

Ross,
Is there anyway to give us fueling control over 8000rpm whether its TPS vs. VE or PE vs. RPM?

Anyway we can change the fueling parameters to read every 500 rpms instead of 400rpms which would allow for higher rpm fueling control?

[robz]

We'll try it Ross( vetteboy2k is the tuner) and report back.
We will also try new injectors.

Ross,
Is there anyway to give us fueling control over 8000rpm whether its TPS vs. VE or PE vs. RPM?

Anyway we can change the fueling parameters to read every 500 rpms instead of 400rpms which would allow for higher rpm fueling control?

We tried all and still are getting a fuel cutoff around 8000 rpms and sometimes slightly higher.

[GMPX]

There is the possibility that the PCM is at it's processing limit and cannot keep up beyond 8,000RPM. Or the 24x sensor is not capable of producing a nice clean signal at those RPM's.
With the fueling, once you hit the end of the table that value just carries through, it's not like it just stops or wraps back around to the start of the table.

[joecar]

robz,

Is there any way you have access to someone with an automotive oscilloscope that can probe the crank sensor signal to see what it looks like when you try to go above 8000 rpm...?

[Sparky8370]

Well Robz they are telling you to probe your crank, I think that's Austrailian for go f yourlself. :hihi:

[joecar]

Look at post #183: showthread.php?p=105501 (http://forum.efilive.com/showthread.php?p=105501&highlight=oscilloscope#post105501)

Probing your crank (!) will allow you to see if the CKP crank position signal is correct in amplitude/shape, and possibly see if the reluctor is slipping/walking (you will also need the CMP cam position signal to compare against).

Without a scope waveform you can't really tell... it's all very dynamic.

Also, probing your injectors (!) will show if they are being driven correctly.



Sparky, I wrote that with a straight face, but am now cracking up... :hihi:

[Sparky8370]

Look at post #183: showthread.php?p=105501 (http://forum.efilive.com/showthread.php?p=105501&highlight=oscilloscope#post105501)

Probing your crank (!) will allow you to see if the CKP crank position signal is correct in amplitude/shape, and possibly see if the reluctor is slipping/walking (you will also need the CMP cam position signal to compare against).

Without a scope waveform you can't really tell... it's all very dynamic.

Also, probing your injectors (!) will show if they are being driven correctly.



Sparky, I wrote that with a straight face, but am now cracking up... :hihi:
Until I saw that last line, I thought you didn't realize I was joking. I thought I was going to have to explain the joke, which I hate doing because that means it's not very funny.

[robz]

There is the possibility that the PCM is at it's processing limit and cannot keep up beyond 8,000RPM. Or the 24x sensor is not capable of producing a nice clean signal at those RPM's.
With the fueling, once you hit the end of the table that value just carries through, it's not like it just stops or wraps back around to the start of the table.

Something is going on similar to what you mentioned above.
We can take 10 consecutive dyno pulls and the fuel cutoff will occur at 10 different rpms.

--I wonder if a 58 tooth reluctor wheel would work better or repositioning the sensor?

--Someone also mentioned trying the blue/green pcm that came out in 04 for the corvettes which is a newer/upgraded version over the one I have in my car.

I'm confident this can be done, just need to figure it out or contact the right person.

[robz]

Look at post #183: showthread.php?p=105501 (http://forum.efilive.com/showthread.php?p=105501&highlight=oscilloscope#post105501)

Probing your crank (!) will allow you to see if the CKP crank position signal is correct in amplitude/shape, and possibly see if the reluctor is slipping/walking (you will also need the CMP cam position signal to compare against).

Without a scope waveform you can't really tell... it's all very dynamic.

Also, probing your injectors (!) will show if they are being driven correctly.



Sparky, I wrote that with a straight face, but am now cracking up... :hihi:

Thanks for that info, Joe.

[Bruce Melton]

Rob,

Not to raise your anxiety, but when you lose fuel abruptly at those rpms under load it is putting a helluva load on the mechanical parts such as timing chain and rotating parts. All those high buzzing parts are trying to go to zero almost instantaneously.
Gives me the chills.

[robz]

Rob,

Not to raise your anxiety, but when you lose fuel abruptly at those rpms under load it is putting a helluva load on the mechanical parts such as timing chain and rotating parts. All those high buzzing parts are trying to go to zero almost instantaneously.
Gives me the chills.

I hear ya Bruce.
If I'm quick enough, I'm into the shift already and it doesn't rock the car much at all.
Once we know the point of cutoff we can set the limiter 50 rpms before it and also I can adjust my shiftlight to avoid activating any cut off.
With the knowlegde I will be prepared and be able to protect the car.
That's why I'm so determined to figure out how to get past the hurdle or work around it.
I really don't want to go to an aftermarket computer.

[joecar]

Update on the other thread, see post #204: showthread.php?t=11706 (http://forum.efilive.com/showthread.php?t=11706&highlight=oscilloscope&page=6)

[robz]

Update on the other thread, see post #204: showthread.php?t=11706 (http://forum.efilive.com/showthread.php?t=11706&highlight=oscilloscope&page=6)

Joe I have no issues/symptoms similar to his, so I don't believe anything is mechanically broken.
I do however feel that maybe the signal is not being picked up clearly @ high rpms.

That doesn't explain the fuel cutoff to me but maybe why it cuts off at different rpms.

[joecar]

If you can get access to an oscilloscope and get waveforms for CKP and CMP at various RPM's 2000, 4000, 6000, 7000, 8000, 8000+...

then we could compare the sets of waveforms... this will show if the signal integrity is failing at high RPM...

without an oscilloscope there's no other way to know.

[eficalibrator]

If you can get access to an oscilloscope and get waveforms for CKP and CMP at various RPM's 2000, 4000, 6000, 7000, 8000, 8000+...

then we could compare the sets of waveforms... this will show if the signal integrity is failing at high RPM...

without an oscilloscope there's no other way to know.

Be careful because the presence of the O-scope in the PCM harness' circuit may be enough to change the behavior. You may actually artificially decrease the signal integrity by adding some other device to the loop.

If you could put the CAM/CKP sensors on a separate rig with their target wheels and verify the waveforms outside of the vehicle, it would be a more scientific test. Cumbersome, but more reliable.

So, the real issue remains that somewhere between the CAM, CKP, and PCM there's just not a reliable enough signal beyond 8000rpm. I saw this on another PCM at a previous employer, and the only solution was to create an ENTIRELY NEW PCM that was capable of working with speeds that high.

[joecar]

Using a x20 (typically 20+MΩ impedance) attenuator probe and keeping the ground isolated should be ok, that won't modify the signal.

But, just using a x1 probe (~1MΩ) will modify the signal.

[robz]

ENTIRELY NEW PCM[/I] that was capable of working with speeds that high.

Hi Greg. If there is any way it can be done, or anyone you can refer me to to do this I would go for it, as I am officially "PCM limited" on the drag strip.

I cannot shift higher than ~8000 rpms and now I'm hitting this HARD limit before the stripe in 4th. A double wammy.

Who can reprogram a completely new PCM?

I've been told it has been done but have never seen any evidence and apparently everyones's too busy to do the job. Not sure if someone's just blowing smoke up my a$$.

[ScarabEpic22]

Hi Greg. If there is any way it can be done, or anyone you can refer me to to do this I would go for it, as I am officially "PCM limited" on the drag strip.

I cannot shift higher than ~8000 rpms and now I'm hitting this HARD limit before the stripe in 4th. A double wammy.

Who can reprogram a completely new PCM?

I've been told it has been done but have never seen any evidence and apparently everyones's too busy to do the job. Not sure if someone's just blowing smoke up my a$$.

Greg doesnt mean simply reprogramming a new PCM, anyone can do that with a Tech II or if EFILive supports full flashing of said PCM. I believe Greg's solution was to go back to the drawing board and actually make a brand new physically PCM that would have better control over 8000rpms. Basically, its impossible to do without the resources of a major automaker.

Have you thought about switching to a standalone to control fueling/spark above 8000rpms?

[robz]

Greg doesnt mean simply reprogramming a new PCM, anyone can do that with a Tech II or if EFILive supports full flashing of said PCM. I believe Greg's solution was to go back to the drawing board and actually make a brand new physically PCM that would have better control over 8000rpms. Basically, its impossible to do without the resources of a major automaker.

Have you thought about switching to a standalone to control fueling/spark above 8000rpms?

Yes. I have thought about it. I want to maintain factory gauges, however.
I'm surprised no one has figure out a way around this, but I'm sure ther'e just not enough people interested.

[mr.prick]

Send Ross a PM.
I bet if it's possible he would drop everything he's doing to re-map all LS1 OS' for this. :laugh:

The highest RPMs columns/rows reach is 8000,
increasing/decreasing in increments of 400.
8400 RPM would seems to be the hard limit of the OS if not the PCM itself.

[ScarabEpic22]

Yes. I have thought about it. I want to maintain factory gauges, however.
I'm surprised no one has figure out a way around this, but I'm sure ther'e just not enough people interested.

Sorry should have clarified, I meant piggyback an aftermarket like MegaSquirt to take over fueling and spark at say 7000ish rpms and go higher.

[eficalibrator]

Who can reprogram a completely new PCM?

Rob, it was a HARDWARE issue, not programming that was our limit. It took a complete redesign of the PCM's input devices to rectify. Expensive and impractical is an understatement unless you've got the same development budget as Porsche.

[robz]

I guess I've been so persistent because I've been told several times it has been done(Revving the stock PCM to 10,000 rpms) by a reliable source. I haven't actually seen proof of this but figured one of you fellas might be able to make it happen.

[robz]

Send Ross a PM.
I bet if it's possible he would drop everything he's doing to re-map all LS1 OS' for this. :laugh:

The highest RPMs columns/rows reach is 8000,
increasing/decreasing in increments of 400.
8400 RPM would seems to be the hard limit of the OS if not the PCM itself.

Now I'm not going to buy your hardware.

[joecar]

Hmmm... either way, I still say you need an oscilloscope for several things:
- to see CKP signal (in relation to CMP signal) at high revs,
- to see if plugs are firing correctly at high revs,
- to see if injectors are firing correctly at high revs;
are you able to say with certainty that any one of those is working correctly...?

Without it you'll never know...

What if you see the same problem with an aftermarket/custom system...?

[mr.prick]

I guess I've been so persistent because I've been told several times it has been done(Revving the stock PCM to 10,000 rpms) by a reliable source. I haven't actually seen proof of this but figured one of you fellas might be able to make it happen.

The only controller I know of that is used w/LS1 and
goes higher than 8000 RPM is the BS3.
I think it only goes up to 9500 RPM.
Ask your "reliable source" how they got the stock PCM to 10,000 RPM.

[robz]

The only controller I know of that is used w/LS1 and
goes higher than 8000 RPM is the BS3.
I think it only goes up to 9500 RPM.
Ask your "reliable source" how they got the stock PCM to 10,000 RPM.

I did but he speaks over my head, maybe he will chime in.

I spoke to another guy with a trans am who said he was able to rev to 8600.
I'll talk with him tonight and see if he's doing something different. It appears he has my same pcm with a 24 tooth reluctor wheel.

Both people who sucessfully rev over 8500 consistently said they were using the main VE table for tuning. Not sure if us using the tps table is restricting us.

[robz]

Hmmm... either way, I still say you need an oscilloscope for several things:
- to see CKP signal (in relation to CMP signal) at high revs,
- to see if plugs are firing correctly at high revs,
- to see if injectors are firing correctly at high revs;
are you able to say with certainty that any one of those is working correctly...?

Without it you'll never know...

What if you see the same problem with an aftermarket/custom system...?

Understood. I'm not sure i have access to that type of equipment.
I'm taking everyones suggestions and trying things as I can make them available.
As of now nothing has worked.

[joecar]

Understood. I'm not sure i have access to that type of equipment.
I'm taking everyones suggestions and trying things as I can make them available.
As of now nothing has worked.I understand it's not easy to access...

some repair shops are using oscilloscopes (they call them "lab scopes"), it's a matter of locating such a shop... ask which particular scope they use and if they have looked at crank/cam signals with it...

if they use a Picoscope then I know they will be able to easily capture a very high resolution waveform (and they are usually well trained on how to use it).

I also understand how frustrating it is when the answer is not found...:bad: