Fuel Pump Relay Behavior

[Blazer79]

I have a MS2 with 2.90 firmware. Bought it assembled from DIYAutoTune a few years ago.

I had to connect the fuel pump relay to the car's ignition switch in order to start testing it because I never got it to turn on from the MS controller. I thought it was me who had wired it incorrectly.

Now I'm restarting this project and used a MegaStim to test it, and I have the following behavior:

As soon as I connect power to the megastim (with the RPM pot all the way down), the FP LED turns on. As I slowly turn the RPM pot I see the IG, I2 and I1 LED flashing, but the PMP LED turns off.

Shouldn't the correct behavior be that the PMP led stay on as long as the car is running?

I'm using TunerStudio 2.6.01 lite and couldn't find any parameter to change this behavior. Is it something hardware related?

Any help greatly appreciated.

[Bernard Fife]

Blazer79,

This sort of 'inverted' behavior is usually cause by damaged transistors in the drive circuit. You don't say what main board you have, so I can't tell you exactly which those are, but it will be in the schematics (for example it is Q19 and Q2 on a V3 board).

We used to see this issue occasionally in the old days. Replacing the transistor(s) normally fixes it.

The transistors might have been damaged by static, overheating (either during operation or during soldering), or they may have been defective from the start.

Lance.

[trakkies]

What I normally do with fuel pump relay driver possible faults is to remove the processor board and jumper 5v to pin 33 . The should active the relay - it needs to be the relay rather than just an LED, which draws less current. If it doesn't, the fault is in the driver circuit. Usually the ZTX 450.

[Blazer79]

Thanks for your replies.

Sorry I forgot to mention it's a v3.0 MB.

I'll replace those transistors and see if it works. However, I'm thinking about leaving the fuel pump relay connected to the ignition switch instead, since another transistor failure could leave me stranded in the middle of nowhere. Are there any disadvantages of doing this?

Thanks again

[trakkies]

Problem with running the pump with the ignition is if an injector starts weeping. You could get an engine full of petrol, if it can run with the engine stopped.
I tend to prefer a 2N2222 to the ZTX450. Can't supply as much current, but is more reliable, and more than adequate for a normal relay, which only takes about 0.1 amp.