Fuel pump circuit

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Matt Cramer
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Re: Fuel pump circuit

Post by Matt Cramer »

If you desolder R19, does the PMP light go off?
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ur2slo
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Re: Fuel pump circuit

Post by ur2slo »

Here are some pics. I will take out R19 and see what happens
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Re: Fuel pump circuit

Post by ur2slo »

I removed one side of R19 and PMP is still lit up. Whats next?
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Re: Fuel pump circuit

Post by jsmcortina »

Sounds like you have a short-circuit on the transistors.

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ur2slo
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Re: Fuel pump circuit

Post by ur2slo »

Q14, Q15, Q20 are showing continuity between 2 legs. All other transistors test ok.
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Re: Fuel pump circuit

Post by SymTech Laboratories »

ur2slo wrote:Q14, Q15, Q20 are showing continuity between 2 legs. All other transistors test ok.
The "continuity" (actually an ohm or less) is normal. What about Q2? A short between pins 1 and 3 would cause the symptom you're describing.
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ur2slo
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Re: Fuel pump circuit

Post by ur2slo »

Matt Cramer wrote:Ok, here's the relevant schematic:

Image

First, put it on the Stim and check if there's 5 volts coming into R16 (that's the turn on signal).
Okay, Im getting 5V coming into R16 when injectors are firing from stim. What should I be getting at FP1? What are the specs of D4?
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Re: Fuel pump circuit

Post by SymTech Laboratories »

ur2slo wrote:Okay, Im getting 5V coming into R16 when injectors are firing from stim. What should I be getting at FP1? What are the specs of D4?
Q2 is switching the connection to ground, so you won't measure any voltage at FP1. D4 is 22V/1W Zener diode. It shouldn't be damaged, but if it is, the fuel pump will remain on indefinitely.
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ur2slo
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Re: Fuel pump circuit

Post by ur2slo »

Im getting 5V at FP1
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Re: Fuel pump circuit

Post by SymTech Laboratories »

ur2slo wrote:Im getting 5V at FP1
With the fuel pump relay connected?
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ur2slo
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Re: Fuel pump circuit

Post by ur2slo »

No, that is just with the stim connected.
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Re: Fuel pump circuit

Post by SymTech Laboratories »

ur2slo wrote:I removed one side of R19 and PMP is still lit up. Whats next?
Could you repeat this test, but with R16? R19 is for the FIDLE circuit, not the fuel pump relay circuit.
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Red_bull
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Re: Fuel pump circuit

Post by Red_bull »

Hello guys,

I have the same problem with my fuel pump circuit. I measured the voltage at R16 which is 4.85 volt on both sides. I checked R40 which is 1 ohm.

I have no sim and ECU is in a running car. Problem is that for now fuel pump is always on when car is on ignition and i would love to fix it.

Any more checks i can do?
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Re: Fuel pump circuit

Post by dontz125 »

Red_bull wrote:I have the same problem with my fuel pump circuit.

I have no sim and ECU is in a running car. Problem is that for now fuel pump is always on when car is on ignition and i would love to fix it.
I believe the original poster's issue was that his FP wouldn't turn ON; you say yours won't turn OFF. From one of the posts above:
SymTech Laboratories wrote:D4 is 22V/1W Zener diode. It shouldn't be damaged, but if it is, the fuel pump will remain on indefinitely.
Remove your D4. If that solves the problem, you need a new one. If it doesn't, check your wiring; make sure the pump is fed from the relay OUT pins, not the IN pin(s).
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DaveEFI
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Re: Fuel pump circuit

Post by DaveEFI »

Red_bull wrote:Hello guys,

I have the same problem with my fuel pump circuit. I measured the voltage at R16 which is 4.85 volt on both sides. I checked R40 which is 1 ohm.

I have no sim and ECU is in a running car. Problem is that for now fuel pump is always on when car is on ignition and i would love to fix it.

Any more checks i can do?
Remove the daughter card and check again. If the pump still runs continually, likely a problem in the wiring or driver circuit. If not, a problem with software or the daughter card.
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Red_bull
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Re: Fuel pump circuit

Post by Red_bull »

Ok now i see my post was a bit messy (sorry i was mega hangover yesterday)

- Pin 37 does not go to ground, but has 5 volt on it when the engine is running (like the first post of the original topic)
- Pin 37 stays as zero when i put ignition on and only comes up when engine is started. No short periode of voltage
- Currently i have the relay switched on ignition and not connected to the megasquirt


Thanks for the reply guys. Do the tips stay the same?
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Re: Fuel pump circuit

Post by dontz125 »

Yes; do Dave's check first.
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Red_bull
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Re: Fuel pump circuit

Post by Red_bull »

But i get the 5 volt when the engine runs. So if i remove the daughterboard i won't be able to start the car.

Is removing D4 the way to go?
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Re: Fuel pump circuit

Post by dontz125 »

Pull the daughtercard; do you still have the same malfunction?

THEN pull D4.
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