Bypassing CCM to Enable Starting
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From: Derry nh
Bypassing CCM to Enable Starting
My CCM is acting up and I don't want to get stuck somewhere with a "no start" situation while I'm trying to fix it. I've bypassed the Starter Enable relay but need to fake a "Fuel Enable" signal from CCM to the ECM. ECM's looking for a falling-edge signal some time around inserting or turning the ingition key.
I think a momentary switch with a resistor to ground on the Fuel Enable line should work. The resistor should protect the CCM output from being hard-tied to ground.
Any thoughts?
I think a momentary switch with a resistor to ground on the Fuel Enable line should work. The resistor should protect the CCM output from being hard-tied to ground.
Any thoughts?
Team Owner
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From: Park City Utah
No, that won't work. The ECM and the CCM communicate, and "agree" on the communication that takes place. I simple resistor won't replace the CCM and allow the engine to start.
You screen name implies that you have an '84 which doesn't have a CCM. What year car are we talking here?
-Tom
You screen name implies that you have an '84 which doesn't have a CCM. What year car are we talking here?
-Tom
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From: Summerland B.C. Canada
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From: Derry nh
I did have an '84 for a while... now have a '91. I know there is some serial communication between the ECM and CCM but didn't know if that included a Fuel Enable handshake.
The FSM for the Fuel Enable test mentions that the CCM generates a high-to-low level transition on the FE output to the ECM, which I can sort of see with a voltmeter when ignition turned to "ON". Was thinking I can duplicate that signal to enable the injectors.
This is just a temporary work-around. My CCM had been intermittent lately and is now working and I can't get it to fail. Since the problem is still lurking, I don't want to get stranded somewhere with a no-start condition so trying to find a way to start if (when) CCM goes down again.
The FSM for the Fuel Enable test mentions that the CCM generates a high-to-low level transition on the FE output to the ECM, which I can sort of see with a voltmeter when ignition turned to "ON". Was thinking I can duplicate that signal to enable the injectors.
This is just a temporary work-around. My CCM had been intermittent lately and is now working and I can't get it to fail. Since the problem is still lurking, I don't want to get stranded somewhere with a no-start condition so trying to find a way to start if (when) CCM goes down again.
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From: Park City Utah
As I understand it, the ECM and CCM do have a "hand shake" and it is different every time, so simulating itis "impossible".
If you have intermittent problems w/the CCM, I'd be inclined to double/triple check the connections at the ECM, CCM and grounds.
If you have intermittent problems w/the CCM, I'd be inclined to double/triple check the connections at the ECM, CCM and grounds.
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From: Derry nh
Turns out the "secret handshake" isn't all that special... just a 30Hz 5V squarewave. This fellow at www.bakerelectronix.com sells modules that provide this, but I found a schematic and built my own. Now with the CCM completely dead (LCD fuse pulled) I can start the car. Have to also bypass the Starter Enable relay but that's just a jumper wire.
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Team Owner
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From: Park City Utah
Turns out the "secret handshake" isn't all that special... just a 30Hz 5V squarewave. This fellow at www.bakerelectronix.com sells modules that provide this, but I found a schematic and built my own. Now with the CCM completely dead (LCD fuse pulled) I can start the car. Have to also bypass the Starter Enable relay but that's just a jumper wire.
What mseven asked....
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From: Derry nh
I don't understand the speedo and mileage questions. The VATS Bypass circuit just generates a Fuel Enable signal to the ECM, allowing it to enable the injectors. Doesn't have any effect on the dash display. I'm still having a CCM issue which intermittently disables the ignition but now I can switch in the bypass circuit so I'm not stranded.
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From: Derry nh
Yes, I know about the features of a bad CCM... I'm beginning to believe I have one. The dash display and interior lights started randomly cutting out and I can't find the problem. Today when it cut out I banged the top of the CCM and lights came back on. THis has happened once or twice before. I hate to jump to conclusions but I can't see any signals that are in the CCM connector wiring that would cause this kind of problem, so doubting it's anything in the wiring harnesses but rather a bad B+ or ground solder joint on the CCM circuit board.
Racer
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From: Muskogee OK
Do you show any CCM codes?
It looks like you have your fuel enable solved but just in case others have the same problem, I found this last year when I thought I had a faulty CCM.
http://www.fieroaddiction.com/passkey.html
If your CCM is reading the proper key code, but not enabling fuel, this should solve the problem.
It looks like you have your fuel enable solved but just in case others have the same problem, I found this last year when I thought I had a faulty CCM.
http://www.fieroaddiction.com/passkey.html
If your CCM is reading the proper key code, but not enabling fuel, this should solve the problem.
Le Mans Master
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From: The Motor City
to be controlled by the ccm (as well as a myriad of other entries).
It would be interesting to see if those functions still worked using your bypass method. I do like your clever resolove to the problem at hand, though I'm not sure you will not have other issues.
As to vats, fuel enbable et. all, I do that all though the prom/chip. Those parameters are all availbable when tuning and are ana easy fix.
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From: Derry nh
Not showing any CCM codes... now. A few weeks ago I was constantly getting codes for systems that checked out fine.
As for speedo and odo, they work like they always used to. I only switch in the bypass signal if the CCM shuts down or goes to sleep and won't enable the injectors.
As for speedo and odo, they work like they always used to. I only switch in the bypass signal if the CCM shuts down or goes to sleep and won't enable the injectors.
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From: Derry nh
When the CCM is falls asleep though, the speedo and odo are blank, no backlight either or other interior lights. When the Fuel Enable signal is provided and the Starter Enable relay is bypassed the car starts and runs fine, but the dash display is still blank.
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From: Park City Utah
-Tom
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From: LA California
Check out engle1147's post here:
http://forums.corvetteforum.com/c4-t...or-bypass.html
Note the red, black, and blue leads. Most likely red goes to switched 12v, black goes to ground, and blue goes to the ECM.
But where on the ECM does the blue lead attach?
Maybe engle1147 will let us know and post a pic of the bypass installed on his '89.
.
http://forums.corvetteforum.com/c4-t...or-bypass.html
Note the red, black, and blue leads. Most likely red goes to switched 12v, black goes to ground, and blue goes to the ECM.
But where on the ECM does the blue lead attach?
Maybe engle1147 will let us know and post a pic of the bypass installed on his '89.
.
Heel & Toe
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From: N.Miami Beach Fl.
Vibrates at stops after replacing ignition lead wire
Hi Guys hope you don't mind me jumping in with a question?
My remote keyless entry was acting up with erratic locking unlocking turning security on and off a few months ago, Needed new battery I assumed so I used my 2nd remote and everything seemed fine until one morning the doors opened, lights, radio, air turned on but engine was locked down. Called an auto locksmith who said it was the relay switch line malfunction and just need to be replaced. he replaced it and everything went back to normal BUT! now I'm getting erratic jumps in oil pressure? and vibrations when I'm at a light or in slow traffic, but not in Neutral Took it to a dealer and had them run a complete diagnostic, No codes thrown, everything seems to be firing correctly, no explanations
Said it might be the alternator going bad? I don't think so as it only happened after the shutdown. I think it might be related to the computer signals on the security system needing to be reset, dealer said no. Anyone have any thoughts on it.
My remote keyless entry was acting up with erratic locking unlocking turning security on and off a few months ago, Needed new battery I assumed so I used my 2nd remote and everything seemed fine until one morning the doors opened, lights, radio, air turned on but engine was locked down. Called an auto locksmith who said it was the relay switch line malfunction and just need to be replaced. he replaced it and everything went back to normal BUT! now I'm getting erratic jumps in oil pressure? and vibrations when I'm at a light or in slow traffic, but not in Neutral Took it to a dealer and had them run a complete diagnostic, No codes thrown, everything seems to be firing correctly, no explanations
Said it might be the alternator going bad? I don't think so as it only happened after the shutdown. I think it might be related to the computer signals on the security system needing to be reset, dealer said no. Anyone have any thoughts on it.
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From: Derry nh
Don't recognize the odd behavior but sounds like that relay switch line needs to be replaced back to what it was. What exactly was it that the locksmith changed?
As for the "blue lead", it's pin B6 on the ECM (VIN 8) but probably easier to access under the passenger hush panel at circuit 229 pin C (one of the white 10 or 12 pin connectors). If you really need to know which connector I can do some disassembly and figure it out.
As for the nifty bypass circuit, there's one problem with it.... the output swings from 0V to 12V (it's a squarewave so that's why the voltmeter reads 6.2V 'cause it's 1/2 of 12V). Might be okay but in the FSM the ECM Fuel Enable input is 5V and I don't like the idea of hitting a 5V input with 12V, especially on the ECU. I used a 5V regulator to power my circuit (same as the one posted except for the diode and resistor across it) so it gives a 5V output.
As for the "blue lead", it's pin B6 on the ECM (VIN 8) but probably easier to access under the passenger hush panel at circuit 229 pin C (one of the white 10 or 12 pin connectors). If you really need to know which connector I can do some disassembly and figure it out.
As for the nifty bypass circuit, there's one problem with it.... the output swings from 0V to 12V (it's a squarewave so that's why the voltmeter reads 6.2V 'cause it's 1/2 of 12V). Might be okay but in the FSM the ECM Fuel Enable input is 5V and I don't like the idea of hitting a 5V input with 12V, especially on the ECU. I used a 5V regulator to power my circuit (same as the one posted except for the diode and resistor across it) so it gives a 5V output.