PCM experts come inside
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From: South Jersey
PCM experts come inside Is it possible to slightly over clock our PCM's so the IAC motor reacts faster for bigger cams? This way it might cut down on the surging and stalling if we can get the IAC circuit to react faster. Just a thought. I might try and bump up the clock speed on my spare PCM and just see what happens. I'll post my results after testing.
Den
Den
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From: Lake Zurich, IL
Re: PCM experts come inside I don't believe so, it's a Motorola 68K processor, so it's an older not all that fast processor to start.
You may be able to pull the 68K out and put a faster version of it in (I think it's a 68332 processor) I'm not sure of the exact speed , but I think the 68332 is a 20mhz processor (683xx were available in 16mhz, 20mhz, and 25mhz) ... if it is 20 it may be possible to put a different 683xx chip in that operates at 25mhz... but then again the speed the processor works at is limited by the hardware on the PCM (not autosensing like new PCs) so even w/a 25Mhz you'd be the same...
I believe the speed it operates at is controlled by an oscillator on the PCM board... so it may be possible to replace this with a different oscillator to increase the speed of the chip... but then you may run into problems access the Intel Flash Chip... I don't know how fast it operates at, but it may not be able to keep up with the requests of a faster processor...
You may be able to pull the 68K out and put a faster version of it in (I think it's a 68332 processor) I'm not sure of the exact speed , but I think the 68332 is a 20mhz processor (683xx were available in 16mhz, 20mhz, and 25mhz) ... if it is 20 it may be possible to put a different 683xx chip in that operates at 25mhz... but then again the speed the processor works at is limited by the hardware on the PCM (not autosensing like new PCs) so even w/a 25Mhz you'd be the same...
I believe the speed it operates at is controlled by an oscillator on the PCM board... so it may be possible to replace this with a different oscillator to increase the speed of the chip... but then you may run into problems access the Intel Flash Chip... I don't know how fast it operates at, but it may not be able to keep up with the requests of a faster processor...
Re: PCM experts come inside Something to think about before you try:
You want to make sure there is nothing in the code that calculates timings based on number of CPU instructions executed. If you change the CPU speed - you'll screw up timings.
Or maybe the PCM uses hardware timers that are driven by the same crystal.
Imagine if the injector pulse width or spark advance calculation was altered after you changed the crystal frequency.
I have no idea if changing the crystal would effect the timers and if it did affect the timers I have no idea if that would in turn effect timing based calculations that the PCM performs. Just something to think about.
Regards
Paul
You want to make sure there is nothing in the code that calculates timings based on number of CPU instructions executed. If you change the CPU speed - you'll screw up timings.
Or maybe the PCM uses hardware timers that are driven by the same crystal.
Imagine if the injector pulse width or spark advance calculation was altered after you changed the crystal frequency.
I have no idea if changing the crystal would effect the timers and if it did affect the timers I have no idea if that would in turn effect timing based calculations that the PCM performs. Just something to think about.
Regards
Paul
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From: South Jersey
Re: PCM experts come inside Horist,
That's what i was gonna do. I was gonna change the crystal to a slightly faster one and see what happens. But you brought up a good point, can the surrounding hardware support a faster chip/crystal install. I've worked alot with the Intel flash chip that's in our PCM's and my eprom/chip copier/burner re-flashes the chip 10 times faster than our PCM does. So I'm confident the flash chip will be ok. I looked at the crystal on the board and I need to see what size it is. If it's a 20mhz crystal I'll try something in the 23mhz to 25mhz range and see what happens.
That's what i was gonna do. I was gonna change the crystal to a slightly faster one and see what happens. But you brought up a good point, can the surrounding hardware support a faster chip/crystal install. I've worked alot with the Intel flash chip that's in our PCM's and my eprom/chip copier/burner re-flashes the chip 10 times faster than our PCM does. So I'm confident the flash chip will be ok. I looked at the crystal on the board and I need to see what size it is. If it's a 20mhz crystal I'll try something in the 23mhz to 25mhz range and see what happens.
10 Second Club
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From: Cloud Nine
Re: PCM experts come inside Far easier to disassemble the program in the ecu and work out how the ECU commands the idle motor , I am sure the calibration dampens the IAC so it doesnt react too fast . I have programmed earlier versions of delco code to control how the IAC reacts , just nneds to find these table locations so that it can be modified with edit.
You usually find you get a bad "hunt" if you get the IAC to react to quickly , best to get on top of the tune and you will find your idle will stabalize
You usually find you get a bad "hunt" if you get the IAC to react to quickly , best to get on top of the tune and you will find your idle will stabalize
Re: PCM experts come inside If you do get the logic end to work that fast , then you'll need to design a new iac motor that can move fast enough to take advantage of it. Ever tested one & see how fast they move? It's electromechanical actuator (iac) that needs the speed improvment! They move slow by design for "fine " idle adjustments. <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
