Fuel Pump Output Problem

[SPatrickB]

My 3.6 VEMS has developed a problem with the fuel pump output. It started as intermittently shutting of the fuel pump for a few seconds but now does not turn on the pump relay at all.
I removed the relay and tested continuity from VEMS to the relay socket. I find when cranking, I get closed continuity back to ground as expected (output is switching ground). However when I put a relay back in, the circuit remains open when cranking, i.e. VEMS is not switching the output.
What could cause this?

[SPatrickB]

I should add that I'm currently running 1.1.96 firmware.
I have also checked that the flyback is connected. I don't have a TS Diode, is this a potential cause of the problem?

[VEMS]

Hello SPatrickB,


The most likely cause for this would be that the output got overloaded (drawing more than max allowed current for p259 which is 250mA) and one of the output channels has failed inside the p259.
I would recommend switching your Fuel Pump relay wire to an output with higher current capacity perhaps you have some leftover Injector or Ignition outputs ?

Best regards, Dave

[SPatrickB]

Thanks Dave.

Can anyone advise on how to test if the p259 is in fact the issue?

Is the TS Diode essential? i.e. could not having it cause damage to components?

[mattias]

Do you have a TS diode across the relay? Can't see how it's related to your problem.

If you use a DMM to measure current (use in place of fuse for the ECU) the demand should not exceed 150 mA by much. If you have LCD display and memory card for logging it might consume more by default. Inductive/VR trigger will usually be broken when the P259 chip dies as the signal condition chip for the trigger (not used in case of Hall sensor) shares the same +5V regulator.

I never ever use P259 for anything but simple LEDs or other non-inductive loads. It's still written in the pinout as the suggested fuel pump relay output, which is unffortunate because I've seen at least a couple of times that it died using the universal harness and relays. Over the years I've probably seen at least 20-30 cases of burnt P259 chips, I usually desolder the chip or just cut the VCC pin.

[SPatrickB]

Thanks Mattias.

I do have also; a recent problem with erroneous VR triggering above 3000 RPM, and intermittent problems with the fans, so it looks more and more like the P259 is the issue. I will test as you've suggested this weekend.

However, as you can see, I use the p259 for pump, fans and tacho so I really need it. Do you have any suggestions for adding components to help it "live". My relays draw about 150 mA each. Should I add low current relays first in the path?

BTW, I was not suggesting putting the TS Diode in the relay circuit but I do not have it in the flyback circuit so I was concerned that its' absence might have caused the damage.

Cheers,
Patrick.

[mattias]

P259 ch 0 (EC36-pin4) has a pull-up to +12V to make it able to drive most tachometers. And it's a very light non-inductive load so keep it.

The relays can all be driven with the stepper outputs (A,B,C,D) on the EC18 connector, they can handla 1A inductive loads.
Didn't you run wasted spark on your V8? http://www.vemssupport.com/forum/index.php/topic,2221.msg21784.html
If so, you have four un-used ignition outputs that can easily ground control a few relays..

The "flyback" you're talking about is for the injector FETs and not the P259 low current driver chip. If the board is very old it might not have any internal diode, this is very rare. Normally, just connect +12V fused injector power.

[SPatrickB]

OK, adding the FETs worked well but I followed another post which said to just cut the power leg on the P259.....I broke the track on the PCB doing this
Another thing is after the modification I lost a injector driver, as one inj now has 12v to it all of the time. Filled my exhaust with fuel.