P38A Key/Remote Handset Problem

tank93 said:

I am sure there is more to passive immobilisation than what I am going to quote here but I believe the feature will automatically immobilise the vehicle when the ignition has been turned off even if the vehicle has not been locked with the key or remote handset. As I said sure there is more to it than that but I think thats the basic operation of passive immobilisation.............................happy to be corrected of course.

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I can only speak for certain on the diesel, but as I said, immobilisation is automatic within the EDC when the ignition is turned off much as you state. It has nothing whatever at that stage to do with the BECM.
The BECM does not immobilise the engine, it remobilises it when the correct conditions are met.

tomcat59alan said:

You could always put a remote jog switch in the wire that runs from the r f receiver to the BECM. Any spurious signals received cannot be passed on to the BECM .when you want to lock or unlock you have to press both remotes. @brianp38dse and I have been using this for years, and it's cheap.

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Yes, that is one of three options (sorry if this is yet another repeat, but it is an important mod to the P38):
1. Replace the Mk1 or Mk2 RF receiver with a Mk3. You need to open the receiver to see which one it is: Mk1 has a plain PCB inside, Mk2 has a metal can over the PCB, Mk3 has a daughter board on the PCB.
2. Fit a Marty RF filter between the RF Receiver and the BeCM.
3. Fit a jog switch as above and have 2x fobs.
Any one of those solutions will stop spurious RF.

P38 Monkey said:

Yes, that is one of three options (sorry if this is yet another repeat, but it is an important mod to the P38):
1. Replace the Mk1 or Mk2 RF receiver with a Mk3. You need to open the receiver to see which one it is: Mk1 has a plain PCB inside, Mk2 has a metal can over the PCB, Mk3 has a daughter board on the PCB.
2. Fit a Marty RF filter between the RF Receiver and the BeCM.
3. Fit a jog switch as above and have 2x fobs.

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No need for the filter or the jog switch with the MK3 receiver as it contains a signal processor that only passes valid codes to the BECM, I suspect that is what you mean?

Datatek said:

No need for the filter or the jog switch with the MK3 receiver as it contains a signal processor that only passes valid codes to the BECM, I suspect that is what you mean?

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He was only listing the options.

Datatek said:

No need for the filter or the jog switch with the MK3 receiver as it contains a signal processor that only passes valid codes to the BECM, I suspect that is what you mean?

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Sorry, now edited.
The issue of parking in a high-RF zone is a bit of an unknown. If the RF Rx is being swamped by some local continuous source of RF then that might not enable a good fob signal to be read by the BeCM. But in any case all the above solutions will at least stop the BeCM from getting swamped by incoming spurious requests so it can slumber gently. It would be interesting to hear if someone has modified their receiver as above in some way and whether that helps the correct RF key fob signal to be read by the BeCM.

P38 Monkey said:

Sorry, now edited.
The issue of parking in a high-RF zone is a bit of an unknown. If the RF Rx is being swamped by some local continuous source of RF then that might not enable a good fob signal to be read by the BeCM. But in any case all the above solutions will at least stop the BeCM from getting swamped by incoming spurious requests so it can slumber gently. It would be interesting to hear if someone has modified their receiver as above in some way and whether that helps the correct RF key fob signal to be read by the BeCM.

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The the MK3 receiver can still be swamped by local sources if powerful enough, but the signals will not affect the BECM.
I think several people have fitted the filter from Marty with success but again it will not stop swamping. It's a problem not just on the P38, even on a Honda blackbird.

Datatek said:

The the MK3 receiver can still be swamped by local sources if powerful enough, but the signals will not affect the BECM.
I think several people have fitted the filter from Marty with success but again it will not stop swamping. It's a problem not just on the P38, even on a Honda blackbird.

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I just wondered if selective filtering would help, as the BeCM at least gets a few moments to think about an incoming signal and maybe decode it, rather than being continually swamped and never recovering.

P38 Monkey said:

I just wondered if selective filtering would help, as the BeCM at least gets a few moments to think about an incoming signal and maybe decode it, rather than being continually swamped and never recovering.

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The Mk3 receiver only passes valid signals to the BECM. The MK3 receiver includes an 8 bit micro processor programmed to recognise the unique code at the start of the P38 FOB data stream, Marty's filter does the same thing as I understand it.
I can tell you for sure that unlike the earlier receivers, the MK3 does not produce any output except in response to a P38 FOB, I have proved this during bench testing.

Datatek said:

The Mk3 receiver only passes valid signals to the BECM. The MK3 receiver includes an 8 bit micro processor programmed to recognise the unique code at the start of the P38 FOB data stream, Marty's filter does the same thing as I understand it.
I can tell you for sure that unlike the earlier receivers, the MK3 does not produce any output except in response to a P38 FOB, I have proved this during bench testing.

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My point was that, in the presence of swamping RF being received by the RF Rx would the signal from the key fob get lost in the noise. So in cases where the range is much reduced at present, supermarkets etc, would the filter get rid of that problem or not. If the key fob signal carries a lot of junk RF noise with it, will the decoder at the front end of the BeCM have an adequate eye height on which to work. I am assuming that the (baseband) output of the RF Rx / filter would be in raised cosine format.

P38 Monkey said:

My point was that, in the presence of swamping RF being received by the RF Rx would the signal from the key fob get lost in the noise. So in cases where the range is much reduced at present, supermarkets etc, would the filter get rid of that problem or not. If the key fob signal carries a lot of junk RF noise with it, will the decoder at the front end of the BeCM have an adequate eye height on which to work. I am assuming that the (baseband) output of the RF Rx / filter would be in raised cosine format.

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No, neither the filter in the MK3 receiver nor Marty's filter will affect the condition where the FOB signal is swamped by other local RF. This is a problem that affect all RF FOB's to a degree. The filters are after the receiving stage. The RF receiver in the MK3 FOB is much better quality than the earlier receivers and is more selective. Channel spacing varies but 12.5Khz seems to be common, I cannot prove it at the moment but I suspect that the MK3 has a very tight control on channel frequency, the early receivers respond to any 433mhz signal and probably 432 & 434Mhz.

Datatek said:

No, neither the filter in the MK3 receiver nor Marty's filter will affect the condition where the FOB signal is swamped by other local RF. This is a problem that affect all RF FOB's to a degree. The filters are after the receiving stage. The RF receiver in the MK3 FOB is much better quality than the earlier receivers and is more selective. Channel spacing varies but 12.5Khz seems to be common, I cannot prove it at the moment but I suspect that the MK3 has a very tight control on channel frequency, the early receivers respond to any 433mhz signal and probably 432 & 434Mhz.

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So, if it has a tighter notch filter on the RF input, possibly a Mk3 receiver solution might help reduce swamping, compared with the Marty filter or the second switch-fob. Would be interesting to see if anyone has upgraded and noticed a difference. My solution: stay well away from supermarkets.

P38 Monkey said:

So, if it has a tighter notch filter on the RF input, possibly a Mk3 receiver solution might help reduce swamping, compared with the Marty filter or the second switch-fob. Would be interesting to see if anyone has upgraded and noticed a difference. My solution: stay well away from supermarkets.

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My solution as previously said is to turn off EKA and immobiliser and use the key, when I go into Poitiers I park on the top floor of the multi story whee there is an array of transmitter aerials, the FOB does not work but no problem with the key

Datatek said:

My solution as previously said is to turn off EKA and immobiliser and use the key, when I go into Poitiers I park on the top floor of the multi story whee there is an array of transmitter aerials, the FOB does not work but no problem with the key

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That is the plan, but as some people have stated previously I dont think its possible to completely switch off the immobilisation system (not on GEMS anyway, maybe different on EDC) but if I can get EKA/passive immobilisation switched off that will do for me.

Thanks for all the replies and guidance, greatly appreciated.

tank93 said:

That is the plan, but as some people have stated previously I dont think its possible to completely switch off the immobilisation system (not on GEMS anyway, maybe different on EDC) but if I can get EKA/passive immobilisation switched off that will do for me.

Thanks for all the replies and guidance, greatly appreciated.

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The petrol uses a rolling code for the immobiliser, I suspect but do not know that other than that the function will be the same as the EDC. Immobilisation automatic when ignition switched off. With EKA off and Immobiliser off, re-mobilisation will also be automatic. I must emphasise, that is just a guess as I have never seen a V8 P38 let alone been able check the functions but the BECM is the same between petrol and diesel.
Triggering the alarm will still prevent mobilisation, the alarm can be cleared by locking/unlocking with the FOB or the key.
The term "Immobiliser" in the BECM is a misnomer, it does not immobilise rather the opposite, it mobilises the ECU/EDC if all conditions are met.