Fuel Pump Always On?

[woznaldo]

Ok, back story is I put reversed polarity power through my stim and MS1 V2.2 board. I wasn't getting fuel pump prime, so had a look in the trouble shooting section of the assembly guide which pointed to Q3 and Q5 transistors being blown. Subsequently the transistors were changed and the fuel pump now primes, but....

....it doesn't stop. What else might I have blown that might lead to this condition?

I have check for a short between Q3 and Q5 legs and have confirmed that I put them in with the correct orientation.

[DaveEFI]

The 5 volt rail is protected against reverse polarity connection, so the processor should be OK.
I've been caught out by some versions of the 2N2222 having a different pinout. Did your replacements look identical to the originals? And have exactly the same number?

Try measureing the volts from Pin2 on Q3 to ground. You should see the volts change with the priming pulse.

BTW, only Q3 controls the pump. Q5 is FIDL.

Did you have suitable fuse in your power supply? If not, it is possible there might be some PCB damage.

[woznaldo]

No, I didn't have a fused power supply. I've checked the transistors for pin out and they are correct, both having a central base pin.

When I did a search I found a thread that referred to a diode, but it was a V3 board and I'm not sure it exists on my V2.2? D4 from memory?

At the moment I'm not too worried as I can still tune the car, but it's not ideal from a safety point of view.

[DaveEFI]

You could also check by removing the processor chip then powering up. If the pump runs, you have a fault in the driver circuit.

[woznaldo]

Thanks Dave, I'll give that a whirl tomorrow.

[woznaldo]

I couldn't wait and just went out to the car and plugged in the MS without the processor fitted and the fuel pump whirled into life, so it looks like I have a driver circuit fault somewhere?

[jsmcortina]

Check for shorts on the transistors.

James

[DaveEFI]

I couldn't wait and just went out to the car and plugged in the MS without the processor fitted and the fuel pump whirled into life, so it looks like I have a driver circuit fault somewhere?

That driver circuit is about as simple as they come. So most likely a soldering fault or failed transistor. Examine the soldering carefully on both sides of the PCB using a strong light and magnifying glass. If you've mounted the transistor tight to the board, it may have shorted where you can't see.

[woznaldo]

When on the Stim, can I pull the mini timer to get 0 rpm to simulate the car before start?

[DaveEFI]

You should be able to set the stim to zero RPM? Can here. But you don't need to test with that. The fault has been established. With no volts to the base of Q3, it shouldn't be conducting. So that needs sorting first.

[woznaldo]

Ok, firstly I can't get my Stim to go to zero? 151 RPM is as low as it gets?

I've pulled the processor off and checked for 5V pins and I get 1, 12, 13, 15, 20, 31. If I jump any off these pins to the left side of R13 the fuel pump LED on the stim lights up nice and bright, with exception of pin 12. Pin 12 still lights up the Fuel Pump LED, but it's very dim?

I would say that the driver circuit is ok? It still doesn't work on the car, so maybe I need to check the loom plug on the car?

[DaveEFI]

I've taken you through the fault finding process and established your driver circuit is faulty. No real point in asking for help if you ignore it.

[woznaldo]

Sorry Dave, I'm not trying to ignore your advice, far from it. I appreciate all on this forum who offer assistance and would like the think that I may be able to do the same for others in the future.

I have cleaned the board several times with a cut down paint brush and isopropyl. I've removed flux where I've found it and I've tried to establish each component in the circuit is working as it supposed to.

I couldn't find anything that stood out as wrong, so tried to establish where the circuit got power from. In an attempt to eliminate any obvious issues.

I will continue to check over the circuit, but can you confirm that the driver circuit consists of the R13, Q3 and D7?

Thanks.

[DaveEFI]

Yes. You could have a fault outside MS with the pump relay circuit. Checked by unplugging MS entirely. If the pump doesn't run, but does with MS and no processor, there must be a short somewhere in the driver. Most commonly a blown transistor - even if it has been replaced.

I'd obtain a new 2n2222 or preferable a few of them. They are pretty cheap. 1.50 gpb for 10 from Ebay in the UK. Having spares to hand means something never fails. ;-)

Snip off the old one, and remove the legs one by one. This makes damage to the PCB less likely. Clean the solder pads with solder wick, and check for shorts with a DVM.

Mount the new transistor about 1/2" above the pcb, and solder quickly using just enough solder. Check each pad on both sides for solder bridges.

[billr]

While you have the transistor out for replacement, connect the MS (either whole, or mainboard only) to the car and confirm that the FP behaves normally. Turn the pump on-off using a jumper from the collector to emitter pads of the transistor.

[woznaldo]

Thanks again. Ok, I've removed Q3, took it to the car and used a jumper between collector and emitter and fuel pump came on each time I touched the emitter with the jumper.

I replaced all three components (D7, Q3 and R13) but the fault persists. I even changed Q3 again but no change?

I have noticed that it has been particularly difficult to get a clear hole through the solder pad on the emitter pad each time I've replaced it? Not sure if this indicates anything?

As that pin goes to a common ground, can I leave the emitter leg out and use a jumper to a different ground to see if there is a short on that part of the board? I did do a continuity check between the Q3 solder pads and they are all open circuit with each other?

[DaveEFI]

The pump relay gets its +12v from the battery, and the transistor supplies the ground when conducting. So its emitter is always connected to ground. It's the collector which switches on and off controlled by a small current fed to the base. Really, just like a relay.

[billr]

Do you have a extra of that transistor? Nip the base leg of the installed one and bend it slightly so it is open, see if the transistor is "off" like that. You can probably bend the leg back and solder the leg back together afterwards, or replace the transistor again. I assume you have installed it with a bit of gap between the transistor body and the PCB...

Post photos of that area of the PCB (both sides).

And, post a photo of the transistor, especially showing the manufacturer's logo and P/N. I have seen about every permutation possible with the leads of those TO-92 devices, let's try to confirm that it is being installed correctly

[woznaldo]

The transistor has the part number: CTP2N2222A.

There is a dimple in the center of the curved surface of the body. I'll get some pictures up this afternoon.

[billr]

I should back away from this thread, with apologies for any bum info/advice I have given. I overlooked that this is a V2.2 mainboard, and I have no knowledge of that circuit. I looked briefly for a schematic, but it didn't easily pop up, so I would just guessing on anything further. Sorry.