To replace fuel pump or not to replace fuel pump?
2005 Chevy Silverado customer complains about intermittent stalling. Scan of vehicle revealed no codes. Fuel system tests find a 55 psI pressure reading (spec 55-62... so as you can see it’s on the low side of the scale. Fuel amperage waveform reading is as shown below. Various parts replaced as Indicated by the customer. My shop could not duplicate the concern. Do you use a scope waveform capture of the fuel pump to make a Diagnosis? :)
I think it needs a fuel pump, but I think it also needs some more analysis. Is it a TAC engine? If so, what is the TPS% at a hot no-load idle? Also when it stalls does it restart right away? Does it remain a crank no start condition for more than a few minutes? This is the most I’ve ever enjoyed a beta test 😁
I want more information. Stall and no start? Stall and starts right up? Not enough info to have a path. Would I use a current capture to call a fuel pump, no. It could lead me to more testing.
The customer describes it as ... “slowly the truck starts chugging out then it stalls”. Then he says he has to wait about 5 minutes and it restarts. He has had the truck at another shop and the “other” shop says there is nothing wrong with the fuel pump. We had the truck all day and I had my techs test drive it on and off during the morning. With not being able to duplicate the problem. Bob
Volume testing for the pump. I would also check ignition with the symptoms. I've seen as i think most of us have, coils and modules fail, cool down and work again.
Of course I use current testing for diagnosis of a fuel delivery. I would assume you know your capture doesn’t look good. Being at the bottom end of pressure and seeing your capture, I wouldn’t like that pump. Would I call a new pump a fix to your issue, kinda hard to, not knowing any info on health of engine or seeing any type of data. Without seeing the issue happen, all you can do is inform
Hi Lane Yes I know the scope capture of this pump looks terrible ... matter at fact it probably one of the worst fuel pump pattern I’ve seen in awhile. I generally would never condem a fuel pump based on an amperage waveform capture... but with almost a 3 amp swing ? The customer has a brand new “carter” fuel pump in the back seat waiting for me if required.
Might not be doing the truck any better with “that” new pump he has 😂.
Hi Kevin, In addition to the test shown I like to do a few single-shot captures showing the stall current of the pump. This technique might be able to uncover resistance in the circuit since the stall current is usually far greater than nominal current. And like Bob mentioned, performing a pressure/volume test will uncover marginally operating system issues. I'm sure that you're aware…
What is stall current?
Hi Dustin, Stall current is the maximum current drawn through the motor at zero RPM. Setting up the scope for a single shot trigger will allow one to see this as shown in the examples below.
How about driving it while current ramping the pump? If you can duplicate the symptom you can analyze the waveform for any changes while the problem is present.
I have had luck watching data pids when a fuel pump intermittently fails. Watch for fuel trims and oxygen sensor activity. The times I have caught it the fuel trims go positive and o2's go lean equally on both banks. Other than that, need more info. I also suggest doing some spirited driving to duplicate the concern.
What about the battery cables/ends for poor connection/voltage drop. Also the ground @ the rear cylinder heads. If I am amp testing a FP I also look @ the relay on/off.
I had one yesterday,but with a 6.0,that was about 1000 RPM slower than yours at key on and 500RPM running amperage near the same measured at PCMB fuse. It looked very similar with similar symptoms. I did a capture of key on in rush and then start/run. I smacked the tank during capture to attempt to induce an issue. My volume fell a little flat at 50 PSI maintained pressure at full load during
I agree with other replies. Testing the pump at idle only yields inconclusive testing. Yes that waveform raises some serious concern about the pumps health. If it’s not your problem it will be soon. No doubt it’s failing. Is it the cause of your stall? Unknown due to lack of testing during a fail condition. I would absolutely recommend testing the pump under several operating conditions…
Hi Kevin. Yes, I've used pump wave forms and current ramping to back up suspicions of intermittently failing fuel pumps and the one you posted isn't at all healthy appearing. Working in a dealership for many years, these would arrive almost daily at the door and 99% of the time it was the pump and rarely was a waveform part of the diagnosis. We'd more often perform routine physical inspections
Well just a follow up on this pump discussion. With the fact we had this vehicle for a day and we could not replicate the symptoms of the customer, but with the fact it was meeting the bottom end of the pressure spec and almost a 3 amp swing in the captured waveform and the customer describing the symptoms of a failing pump, plus with the fact no codes were setting to point in a different