Fuel pump diag

Is testing a fuel pump with a amp probe enough to condemn it?

Car in question is a Suzuki Grand Vitara 2.7. Customer complaint is CEL, runs bad, and stalls. Codes are bank 1 and bank 2 lean. Fuel trims are lean at idle and gets worse at higher RPMs. With the customer complaint and scandata I'm pretty confident it's the pump. Pull it in and put the amp probe on it, I think it was around 4 or 5 amps, it looks terrible, and rpm is less than 2800. Put a fuel gauge on it and has 26psi at idle and drops under load.

So my question is did I really have to raise it up and put my pressure gauge in line to verify pressure? It doesn't have a schrader or accessible connection up top to install gauge

Dropping pump presure under load can only have two causes, pump or filter and you have evidence for the pump --- I would change both pump and filter

Andy.MacFadyen wrote: Dropping pump pressure under load can only have two causes, pump or filter and you have evidence for the pump --- I would change both pump and filter

Yes, fuel pump fixed it. What I was asking is do yall think that with a complaint of stalling and running rough, scandata of lean codes and positive fuel trims that go more positive as you raise the rpm, and pump waveform that looks bad and shows that its under 3k rpm is enough to call the pump without taking a fuel pump pressure reading?

Not trying to nitpick, but how terrible was the current waveform? If it had dead segments? Absolutely, skip the gauge and go directly to pump replacement. If it was just kinda noisy? Then I'd get the pressure gauge out.

Sorry, not trying to answer a question with a question.

bruce.oliver wrote: Is testing a fuel pump with a amp probe enough to condemn it?

Most of the time I would think no, if it's showing low amps you would still need to rule out power and ground and if high amps a potential blockage

Unless like Tyler says you can see dead segments you would still need a gauge to confirm a fuel pressure fault

I remember a while ago working on a landrover with a lack of power, the fuel pump in the rear wheel arch sounded horrible and two mechanics said "well it's obviously the pump what are you doing under the bonnet?"
the trace was noisy as well but the pressure was in spec so even though it sounded terrible I had no reason to replace the pump , the fault ended up being the egr valve
when I asked the customer about the pump he said it had a aftermarket fitted two years ago and has always been noisy but runs fine

It's all about building evidence until your confident enough to make the call, there's a trainer here in the UK called James Dillon, one of the things he says when diagnosing try to imagine a situation when you've fitted a part and you still have the same problem, what test would you do next?
Now do that test before you fit the part and can potentially save yourself from fitting a unnecessary item

I think in your situation if you had replaced the pump just based off the amp trace and ended up with the same fault the next test would have been the gauge, so you were correct to confirm a pressure fault first and built good evidence to condemn the pump

I have a hard time condemning a pump without a pressure check. I think you had enough evidence to justify the job, I just always have that nagging little "what if..."
If I think there's a way for me to get my gauge in there, I go for it.

While we're on the subject, here's a situation I was in this week. Dodge truck, no fuel pressure, pump isn't spinning. I bypass the pump relay (so it's powered all the time), put my amp probe over the pump circuit, and beat on the tank. I get spikes of up to 18A when I hit the underside.

Is THAT enough to call a pump? :huh: Or are power/ground checks required?

In that case, I think you have all you need
I doubt you'd get close to 20 amps with a bad pump ground.
Unless you've got some trick up your sleeve.

It's never a bad thing to perform a fuel pressure test. I think the thing to remember with a situation like this, low current, low RPM, low pressure, is that a voltage drop anywhere in the circuit can cause these readings. I hate that the pumps are usually inaccessible because performing a voltage drop across a load is a standard, and very important, diagnostic test.

Noah wrote: In that case, I think you have all you need
I doubt you'd get close to 20 amps with a bad pump ground.
Unless you've got some trick up your sleeve.

Nope, no tricks this time. I loaded the pump wires with a headlight anyway, because paranoia.

Thanks guys. I should have saved a before and after on the fuel pump waveform but I didnt. I need to start making time to do stuff like that. Now that I have a pico I will try to do better.