A P259 spoiled my install

[rob@vems.co.uk]

I'm trying to garner an idea of numbers of people who've blown the P259 chip during an install.
Hopefully we can find a way of getting people the information regarding how to avoid it before it happens.

[tom70]

Mine worked for a good 12months before it decided to give up. It gave up on the return of a shopping trip, I didn't made any modification to the VEMs or car prior to the destruction of P259.

 

[Sprocket]

I have done it twice, first time I have no idea how, but second time I blatently disregarded the grounding rules and smoked it, no ones fault but mine

[lugnuts]

I haven't had a P259 fail yet, for an unknown reason.

But I have heard it is weak, so I only use it for the Tachometer now.
I use Stepper, Inj, or Ign to drive the fuel pump relay, so I don't get a call from
someone sitting on the the side of the road.

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I had one car that had a few channels of the P259 and Inj Fets fail. I did a full re-wire of the harness, re-did the grounds twice, went from low_z injectors with resistors to high_z injectors, still had problems.

The car ran properly for a few weeks..... then the owner replaced his coil wire, and the car started misfiring again.

I asked what kind of coil wire it was, and found that it was solid core (BIG No-No-).
It turns out - that the 4 idnition leads were solid core the entire time.

Got a new set of OEM wires, and all of the misfires and problems disappeared.
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I had an ECU that was in service for 6 months, blow out the Stepper Chip while bench testing it controlling a relay.  No reason was found. The ECU still works in a non-stepper application.
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My second ever VEMS Install,  the ecu would lock open the injectors and fuel pump randomly during start-up.
Once a day, once a week, no rhyme or reason.
I was using an FJO injector driver, and logging my Autronic WB 0-5v into the analog channel.
I removed both of those items, and the ecu has been in service ever since (2 years)

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I have had 3 cars, that have had injector fets fail for absolutely no reason. Flyback was connected, grounds were solid, EC26 was connected to GND5, etc. Two of them were with 12 ohm injectors, one was with 5 ohn injectors. I lost many potential customers over these failures.

[mattias]

I've spoiled a couple of installs from the P259 killing itself, but that was years ago. So it never spoils an install for me any longer because I never use it. I always change the v3 harness to use free IGBT outputs instead.

[Sprocket]

I still use the p259 to drive relays, but I made sure right from the very start that the relays are internally flyback protected, and as it happens, the Rover relay pack is, as are all the individual Siemens relays (yellow). Tyco manufacture an almost identical relay http://www.tycoelectronics.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7FV23134-X0000-A001%7FG%7Fpdf%7FEnglish%7FENG_DS_V23134-X0000-A001_G.pdf

It must be simple enough to introduce a flyback circuit for each channel onboard? I understand the reverse voltage thing is bad, but then that is down to the way the grounding is externaly connected. Could this not be done internally too? And while we are at it, many OEM ECUs have individual sensor grounds for each sensor, connecting to their own pins, which leads to the need for more pins. Some of you may have seen this before, but I'll show it again. I butchered my front plate and instead of fitting an EC18, I fitted another EC36. Spacing was tight and off center, with the original 18 pins in the middle, and the others around them. Used for internaly wired options. It would mean a redesign of the board layout, but it doesnt look a major problem to implement this. The only real issue is crossing over the loom connectors. I got round this by using a Red EC36 connector from Rover which has a different gender. I had to rob it from a loom. I wanted to use the matching EC36 ECU connector, but at the time I could not bring myself to buy an expencive OEM ECu just for the connector, so I just glued a piece of plastic onto the connector and cut the other one off, to change its gender. I dont suggest you try this on a built ECU, as I damaged one board trying this, so built the next one with this from the start.

[multiplex]

wow i like the idea of 2 36 pin connectors!

i blew my p259 but it was many many years ago  . i attempted to replace the chip, but still never regained functionality.

i've managed to survive on stepper, inj & ign.

[MWfire]

i use p259 for rpms(90% of instalation), relay for fuel pump (95% of instalation), relay for N20, relay for fan, relay for water injection.... So far i didn't fry any p259(instaled more than 20) and i use all types of relays ...
Maybee is problem in GND?

[GintsK]

I usually do same as MWfire. With three relays hooked + tacho it works.
Most often P259 becomes fried during incautious installation procedure.
Main P259 weakness is internal ground connection.

What can be wrong in solution when both grounds are connected inside ECU versus recommended solution to connect both grounds 15cm from ECU??

[rob@vems.co.uk]

The 15cm separation is to ensure that the voltage rise on the grounds is factored in to the A2D.  When the grounds are coping with several overlapping injector and coil events the voltage rise a few mV - this is likey to effect the sensor readings which are very discrete.

[GintsK]

Yes but question is what is difference if connection is in the ECU. Sensor readings will be smooth because by default sensors should be grounded at pin 26.

The only way to get bad/noisy sensor readings is by grounding sensors at different place with no connection to pin 26.

[mattias]

Needless to say, the P259 is in itself not at fault - the PCB simply lacks protection for this chip. In the cases I had trouble with the P259 I could never really find the cause of it, and I am always careful with how I ground everything.

[MWfire]

One important thing. When you connect internal in vems analog and power ground you need to check resistance between analog ground(pin 26 on harness) and car ground when vems is disconected. If that resistance is infinity then instlation is good, but if you have resistance like 100 or 1ohm then current will flow thro analog gnd wire and make noise.

I have internal connected ground on may cars(1.9ohm injector pwm) and other many cars and no spikes in sesnor readings if shilded cable is used for sensitive sensors.

[BigD]

Mine's alive but my config is based on multiplex' which assumes a dead P259 I only have the warning light running off of it.

[mr_g]

Why isn't analog ground and power ground internally connected with 2 diodes?

AG--K A--PG
AG--A K--PG

This way if you have loosy ground P259 wouldn't fry...