Fuel pump testing help needed

[sbebenelli]

I'm learning to use the low amps probe and have spent hours finding as much info as I can about the settings and looking at different waveforms.

I'm working on a 2005 Ford E350 5.4,

Everything I read says to set to 20 ms and when I do that the 1st pic is what I get. When I set it to 50 ms I get more of a waveform like I should. What is the reason for me needing to set it at 50 ms and does this mean there is something wrong?

My 2nd question is why does it say waiting for trigger when it appears to be picking up a signal?

[crackerclicker]

if you like how it looks using 50ms then go with that. you can use the cursors to figure out pump speed. image below.

as for the "waiting for trigger", it is in auto trigger mode. you have a couple of choices. you can manually set the trigger to "position" the waveform or simply turn it off.

[Crusty]

In both your screen shots, the plus symbol is below the signal the machine is seeing.
The lower right group of 3 boxes, just to the right of your ms selection box, highlight the trigger in the very right box, press "Y" and then thumb pad up or down, left or right, and move it up a little bit so the + symbol is in the waveform voltage amplitude. Press the "N" button.
You can also go left another box so you can select the rising slope voltage or the dropping slope voltage.

[Rich Shepherd]

I'm working on a 2005 Ford E350 5.4,

Everything I read says to set to 20 ms and when I do that the 1st pic is what I get. When I set it to 50 ms I get more of a waveform like I should. What is the reason for me needing to set it at 50 ms and does this mean there is something wrong?
Try lowering the sweep to 10ms or 5 ms and see what happens.
Its possible the scope is not sampling fast enough at 20 ms to draw the actual waveform from the sample points. That is often what is happening if you set the sweep lower (longer) and the waveform looks better.
You can see an example here with a sine wave:

http://zone.ni.com/reference/en-XX/help/370051T-01/cvi/libref/analysisconcepts/aliasing/

If you search for waveform aliasing you will find other examples and even live demos such as on you tube.
Turning on Peak Detect will avoid this in most cases, but may provide a signal that is too noisy so just selecting a shorter time sweep is often the best solution. Peak Detect sets the sampling to a high rate.
In general if you turn on Peak Detect and see a solid band instead of a waveform, its a good indication the sweep selected is too long to display the waveform.
If you would like to see this effect for yourself, connect to a sine or square wave (Peak Detect off) and walk up and down thru the sweeps and observe what happens to the waveform displayed. Then Turn on Peak Detect and do the same thing.

My 2nd question is why does it say waiting for trigger when it appears to be picking up a signal?
To add to what has already been said:
The trigger is in the auto mode. That means if the waveform does not cross the trigger point (the location of the yellow +), the scope will automatically display a waveform untriggered. When this happens, the scope displays "waiting for trigger" on the screen and the waveform may roll across the screen. If the trigger were set to manual and the waveform did not cross the trigger point, the scope would not update the screen. It would only display a waveform if the waveform crossed the trigger point. The advantage of using the auto mode is that it allows you to see the waveform regardless of whether or not the scope is being triggered. Then if you need to set the trigger to stabilize the display of the waveform and keep it from rolling, you can see where to set it. If it was set to manual, you would have to keep moving the trigger blindly until you found a level that triggered the scope to display a waveform.
In this case you don't necessarily have to trigger on the waveform, just capture it, pause the scope, and then make a cursor measurement.

[sbebenelli]

I want to thank everyone for the comments. I'm listening and taking everything in on what is being said.

I'm working on a 2005 Ford E350 5.4,

Everything I read says to set to 20 ms and when I do that the 1st pic is what I get. When I set it to 50 ms I get more of a waveform like I should. What is the reason for me needing to set it at 50 ms and does this mean there is something wrong?
Try lowering the sweep to 10ms or 5 ms and see what happens.
Its possible the scope is not sampling fast enough at 20 ms to draw the actual waveform from the sample points. That is often what is happening if you set the sweep lower (longer) and the waveform looks better.

I tried lowering the sweep and all that did was make it look more bunched together. The best pattern I got was from the 50ms. When I went bigger than 50 it didn't look good either.

[greasybob]

Here is a video I made a while back on testing a fuel pump with low amp probe, it shows both total amp draw test and using AC couple http://www.youtube.com/watch?v=BbK8Gt-rvBo

[jake63vw]

Give it a shot by raising the trigger level until it intersects the fuel pump waveform. That will get you a much more clear waveform.

[Nickb]

Your screen shot is showing a tired pump. That is why you have to go to a 50ms screen shot. You are showing a RPM of around 3000. That pump is tired. Rule of thumb for me, is if I can't count out 8 segments over 20ms it is time for a pump. Remember 60,000 divided by one revolution of the pump represents RPM, in which represents volume.

[sbebenelli]

Your screen shot is showing a tired pump. That is why you have to go to a 50ms screen shot. You are showing a RPM of around 3000. That pump is tired. Rule of thumb for me, is if I can't count out 8 segments over 20ms it is time for a pump. Remember 60,000 divided by one revolution of the pump represents RPM, in which represents volume.

Thanks for your reply. I already knew it was bad and was exsprimenting with the amps probe to see what it looked like. After installing a new pump I still had to set it at 50ms to get the same pattern. The new pump also showed it running at 3000 RPM. This is a returnless fuel system and I assumed the 3000 RPM was the fuel pump module slowing the pump down. Truthfully the new pump looked about the same as the old.

I have hooked the amps probe up on many since just to get a look at known good pumps and I have not had to set it to 50ms on any of them accept this van.

[protraxrptr17]

Maybe this is a dumb question, but how do you know how many segments a pump has? Do they all have eight? Im assuming that is how you calculate rpm?

[fueltrim01]

most have 8 some have 10, most of the time you can see a repeat of a pattern.

[Timo]

on the way it looks on the screen / the armatures on the pump are worn. the chances it will work for a while but it is an indication that the pump will need to be replaced in the future

[lickitysplit]

fuel pump testing help needed

thats the reason for bringing the time base lower, they don't all have 8 segments. at 50ms you can watch pattern repetitions. more or less segments.