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Curious on diagnostic procedure in this video

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02 Sep 2019 19:42 #33374 by tonybushmin
Just got done watching this video of a Hyundai Sante Fe fuel pump diagnosis and tests went as follows: amperage check at fuse, amperage check at relay (no amperage), test light at the pump on ground and load lights the test light, concluding a bad fuel pump. My question is how come a voltage drop test wasn't preformed because couldn't there still be a bad wire that will light the test light but still not allow enough current flow to power the fuel pump? Also how come an open you cannot get a amperage reading off of open circuit?

While writing the question I kind of realized that if you have zero amperage on the load side which would suggest an open anywhere past the relay and you check continuity with a test light that would only leave the fuel pump winding. Just looking for an explanation I guess.

https://www.youtube.com/watch?v=sq0HLREinNU

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03 Sep 2019 16:07 - 05 Sep 2019 11:47 #33396 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Curious on diagnostic procedure in this video
Okay good question about halfway through the video testing at the relay socket finds the fault is identified as an open somewhere betweeen the relay socket and the pump ground. As you already spotted the resistance of the test light is much higher than ( edit) a good pump.

Keeping this in mind normally with the relay unpluged using a test light connected to B+ we would expect to find a good enough ground from the fuel pump terminnal on the realay socket, through the wiring to the pump then through the pump to ground,

As we don't find a (good enough) ground with test light we know we are dealing with a complete open.

Now going to the back at the fuel pump we can get sufficient power and ground at the fuel pump (edit) connectors to light the test light.

Because of this we know the open or very high resistence is in the pump not the wiring or ground.

Back probing key on with the pump connected looking for voltage drop on the power and a few mv ground would also have worked.

As this pump was internally completely open this is one of the few cases a ressistance check on the pump would also have been a valid confirmation but in other cases not 100% definite test as a bad pump might not have a complete open.

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Last edit: 05 Sep 2019 11:47 by Andy.MacFadyen.
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05 Sep 2019 11:43 #33431 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Curious on diagnostic procedure in this video
This video is another variation on the same

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06 Sep 2019 20:59 - 06 Sep 2019 21:01 #33450 by tonybushmin
Replied by tonybushmin on topic Curious on diagnostic procedure in this video

Andy.MacFadyen wrote: This video is another variation on the same


Okay question #2 how does he do a ground to ground circuit test? Is it because if there was a bad ground he would ground out the pump on the opposite side of the circuit and light the test light? Because when there is a ground and 12v flowing to it the test light won't light because 12v is being pulled straight to ground? Sorry for trying to answer my own question again but I am just trying to get my words across.
Last edit: 06 Sep 2019 21:01 by tonybushmin.

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07 Sep 2019 07:58 #33453 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Curious on diagnostic procedure in this video
It is really a case of drawing a schematic block diagram and working out what voltage you should see at each connection but be prepared for curved balls for example completely water logged connectors. ISTR Paul has a good video in which the cause of a crank no start was found to be a new fuel pump that was wired in reverse polarity.
On the non-electrical side on some European cars it is no unkown for in-tank fuel filters to become disassembled resulting in a working pump but zero fuel pressure.
Paul also has great video on fuel pumps and fuel filters based on one of his own jeeps.

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09 Sep 2019 00:06 #33497 by ScannerDanner
Replied by ScannerDanner on topic Curious on diagnostic procedure in this video
I have a playlist on YouTube I want you to watch a few videos from. These all have some type of ground problem and when you see a bad one you will understand what I did in this video. Technically, if that pump was open (no current) and I did that ground to ground test with my test light, I'm really not checking anything, unless the open was on the ground wire.
www.youtube.com/playlist?list=PLAFYVCyen...2wgsCqa1Zj4335YlBF5p

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