FP output puts out +5v

[S.Bretz]

I got to the point of trying to get the fuel pressure set and was supprised to find the fuel pump is not working.
Some diagnostic showed that when the fuel pump output is activated there is 4.98v on the wire that is supposed to pull the relay to ground.

I have used this MS unit for years but never had to use the FP output since the stock pcm (now gone completely) controlled the FP circuit so this could be something that has been that way for the past 10years or so since I built the unit.

Does any one have any ideas of what might be crossed on the PCB that I should look for?


v3PCB with MS3 and 3x hardware.

1.3 is the firmware.

[DaveEFI]

To test the fuel pump relay driver on a V3, connect a relay to it. Remove the processor daughter card and with the board powered up apply 5v to pin33. The relay should make.

[billr]

That is pin 33 on the 40-pin processor/daughter socket of the mainboard, correct?

[S.Bretz]

Looking at the schems, that probably pin 33 on the processor.

bill I can turn the relay on/off with the output test screen and it will go from 0 at the "off" position to +5v in the "on."
I'm starting to think I may have possible wired a transistor in backwards or maybe the D4 diode is bad.

I will pull the squirts out tonight and see if I can find anything obvious sticking out at me....If anyone has any suggestions please post up soon no matter how silly it may be. I would like to cover all of my bases once I get it out and apart. The 3x isn't as simple to access the PCB as previous versions and its not the best position for my back to get the thing in and out of the vehicle (was a lot easier before the dash was back in LOL).

[S.Bretz]

I did not find anything that stuck out. The diode tests good, the resistors are what they should be (the 1.0ohm resistor did test 1.5, but that is probably from my test leads), the transistors both have something like 7.5mohm between the top two posts and the bottom post and the top two posts have very little resistance between the top tow posts (the top being closest to the heat sink). and I have continuity back to the processor.

I'm at a loss.

[billr]

Did you try removing the daughter board and jumpering 5V to that pin 33 socket?

Edit: I realize that will probably give the same results as using the FP test in TS, but it wouldn't hurt to confirm the problem is on the mainboard. Plus, as you trouble-shoot the mainboard you might as well do it with the processor removed and not subject to any harm.

[S.Bretz]

I did not remove the daughter card to test.

I'm getting some weird results now.

The voltage will jump up to "22v" when its really around 13.5 and the will come back down a few minutes later. I had a similar issue years ago with a diode going bad but in that case the voltage reading would slowly increase an the diode that was faulty would get really hot and the voltage would not come back down. At first I was thinking maybe it had something to do with the 1.3.0 code that's in it, but that doesn't make sense from what I'm seeing. I'm suspecting its a hardware issue since all of the sensors that hook up to 5v ref also change their values...for instance, the TPS will go from 0% to 6% and the temp sensor jump when the voltage read jumps.

I'm not quite sure what I could have messed up, but I guess I will need to pull it back out again and have a look around.

[S.Bretz]

I have not clue what happened... It works now and I did not make any modifications to it.

The only thing I did was install the windows updates for vista... I highly doubt that would have anything to do with the voltage reading all funky.

[S.Bretz]

The issue has come back a couple of times. It goes away after I touch the harness about 2-3in out of the connector on the 3.0 main connector.
So their a bad connection between a wire and connector pin, a bad connection at the pin to MS unit or I have a partially broken or crossed wire in that area.
The harness is pretty old, I'm thinking it may just be better to order up a new unit from DIY and start fresh if I can't find anything after pulling some tape/loom.

[Matt Cramer]

This sounds like the fuel pump drive transistor is damaged; I'd try swapping that out before changing PCBs.

[S.Bretz]

Thanks Matt, I will give that a try.

I also have a new issue. I'm not sure if its related. I pulled the connector apart today and inspected things. I found a ground return that looked like it could use another hit of solder to I took care of that....plugged every thing in and the voltage is staying stable... BUT the coolant temp that was changing with the voltage swings is at a steady 180F until I wiggled the harness (the coolant temp should have been closer to ambient..maybe 100F max).

I ended up pulling the CLT connector to see if it was the sensor and it stayed at 180. I then snipped the wire with about 5inches of lead to see if the issue was in the harness...and it was not. I pulled the connector apart again and made sure the CLT wire was not touching anything and it was not. It should be reading -40.

I tried a sensor recal and upgraded from 1.3.0 to 1.3.3 both with it still reading 180.

Pulled the MS out of the car and tore it down (broke the map off the map daddy and had to do some surgery). I have 0.01 from pin 25 at on top of the daughter card to r8 and from the other side of r8 to the db36 the meter reads the same. I have 4.98v from vref to ground and both of my resistor are metering out correctly too. With the reading bouncing around when I apply the CLT wire to and from ground leads me to think that one of the CAPS might be bad but I can' get a consistent reading them installed.

Does this problem sound typical for a bad cap?

[gurov]

i recently had a runin with the fuel pump drive transistor pair. i think it killed my MS3. i replaced that circuit with what's recommended to drive a boost solenoid, with a much beefier mosfet with some protection.

the circuit is the same for boost control and idle air - in the manuals.