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electrical short


Tom V's Avatar
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01-09-05, 09:42 AM   #1  
electrical short

I am working on a 92 chevy astro van, it has TBI, no crank trigger, does have oil psi switch, and relay (both new), but this is my problem. A month ago, I took on this repair to find that someone has installed an alarm system incorrectly, so I removed it, then heard the fuel pump running after the vehicle was shut off, I then traced the problem to the fuel pump relay. This solved the problems including the fues blowing every time you turn the key.
After 30 days of driving the van to work, the fues began the same thing again, so I towed it back to my garage, took the fuel tank out (thought it was the pump), checked the fuel pump (okay), then began tracing the wiring, and could not locate any shorted wires. Also, I unhooked the pcm, and the fues would not blow (most likely because the short is in or after the pcm), I also tried to see what would happen if the relay was removed, in this test the fues was fine until I tried to turn over the engine, but when the oil psi got up to a certain psi, the fues blew.
Now the van is all taken apart, the pcm is sitting on the floor, the relay is back on (everything is hooked up), I have installed a test light instead of the fues, and it comes on when the key is in the on position.>>The auto manual says that if you are looking for a short, and the fues keeps blowing to install a test light in the fues area, and if the light comes on, that means there is a short, so that is what I did, and the light does come on.

I do not want to give up on this, and I do not want to spend the 80.00 for the new pcm if I do not need to, but I am frusterated!!!

I am not the world best mechanic, but do have an understanding of the engine and electrical systems, and I do work on the weekends to help people out.

If you can give me any advise It would be greatly appreciated..

You can e-mail me at:
work**[email protected]
home**[email protected]

Thank you.


Last edited by toyotaman11769; 01-09-05 at 09:52 AM. Reason: e-mail addresses not allowed for your own protection
 
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Desy2820's Avatar
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01-09-05, 10:42 AM   #2  
Trying to help,

I've heard that these cars have 2 circuits that activate the fuel pump. The first one is the fuel pump relay/ PCM. There's a second parallel circuit activated by an oil pressure switch. (This was a few years ago and it was wired to seperate 2nd oil pressure switch other than the one dash light was.) I'm thinking that this may be where your short is.

As to the test light.....wouldn't it come on whenever you fuel pump was running normally??.....Make sure the pump is unplugged during these tests, otherwise the current flow through the pump may throw you off. If it's lighting up with the pump unplugged, then you've got a problem.

Hope this helps!

 
toyotaman11769's Avatar
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01-09-05, 12:10 PM   #3  
The test light method to replace the fuse is correct. The circuit will not work (because of the resistance of the bulb). Therefore the pump will not run.

If the circuit doesn't contain a short the test light will not lite. The resistance of the windings in the pump will prevent the test light from liting.

What happens if the wire is shorted to ground before the pump windings provides a path without resistance for the test light to lite.

 
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01-09-05, 12:22 PM   #4  
I had one like this a couple years ago. The problem turned out to be the oil pressure switch. Try unplugging it.

 
jeff67's Avatar
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01-09-05, 12:41 PM   #5  
There are 2 different types of test lights. One type runs on a battery inside of it and if you have a short, the bulb will light up. You can also touch both ends of this test light together to have it light up.

The other type, runs on the power from the vehicle. If you have 12 volts on one side and ground on the other it will light. If you have a short or no 12 volts, it won't light.

Which type are you using?

 
Tom V's Avatar
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01-09-05, 04:46 PM   #6  
short in astro

I have removed the fuel pump and unhooked the wiring at the connector under the van, I am using a 12 volt (no battery) test light, I tried testing the system with both the oil psi sending unit, and the fuel pump relay unhooked (separatly) and found the with the relay unhooked, the fuse will not blow untill the engine cranks over, and with the relay hooked up and the oil sending unit unhooked the fuse blows as soon as the key is turned.
If I have to I will remove every item involved from the van and replace them one by one, but that would get expensive.
I have traced all the wires that are in the wiring diagram in the haynes repair manual, and found no problems.

There is something else that I found while messing around and trying not to catch the thing on fire (just kidding).
I checked the blink codes and they are saying the EGR valve is shorting out, but it is not on the same circit, I will have to unhook this and see if it may be the problem.

I will be sure to let you know what I find out, please respond if you think of anything, and I sure appreciate all of you responding.

Tom V

 
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01-09-05, 06:01 PM   #7  
how did you go about testing the fuel pump just because it runs doesn't mean its not the problem?
what fuse is blowing exactly and do you have a wiring schematic for that circuit so you know what this fuse is providing power to?

 
jeff67's Avatar
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01-09-05, 09:38 PM   #8  
Wiring diagram for
1992 CHEVROLET TRUCK ASTRO VAN 2WD 6 Cylinders 262 Z 4.3L TBI
(figure 9)
http://www.autozone.com/servlet/UiBr...3d80119101.jsp

If disconnecting EGR solenoid or sensor wire doesn't solve it, you could check if a wire from the alarm system that was installed has come lose somewhere such as at the ignition switch and is causing the short or if any bare wire is present from the alarm installation. Not sure if you have already checked those or if you removed all the alarm wires. Unplug the oil pressure switch and the fuel pump relay at the same time and see if the fuse blows.

 
toyotaman11769's Avatar
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01-10-05, 02:36 AM   #9  
Which fuse is it?

 
jeff67's Avatar
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01-10-05, 02:05 PM   #10  
Good question toyotaman, I was wondering the same thing but assumed it was the fuel pump fuse.

 
davo's Avatar
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01-10-05, 03:26 PM   #11  
My thoughts on this

I would back the terminal out of b2 and see if the fuse still blows that would take the pcm out of the picture.With everything disconnected relay,oil switch,pump and pcm check to see if the gray wire is showing a short to ground,I'm betting it will. If it does follow the gray wire to find the short.

 
Desi501's Avatar
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01-10-05, 04:38 PM   #12  
Just from your testing description you have isolated the short to the feed to the pump or the pump itself, the gray wire as Davo said. It appears the fuse only blows when that wire is energized.

 
Tom V's Avatar
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01-10-05, 08:51 PM   #13  
Found It!!!!!!

After 4 hours of testing, probing, and asking questions, I found the problem, it was the EGR valve solinoid, it was shorting out, but would work fine at other times which made it difficult to find.
I did not state that it was the fuel pump fuse that was blowing, since I was testing the fuel pump, also, I made sure the fuel pump was working when I tested it, but I had no reason to inspect the fuel pump further since the wires were unhooked and the fuse still blew. The Haynes manual has a wiring diagram in the back that I used to trace the wiring.

The Van is finished, and will be sent back to the owner soon.
Thanks for all your help.
Tom V.

 
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01-11-05, 04:17 AM   #14  
If the vehicle is fixed you gave incorrect information in your posts.Please try to be accurate in the future.

 
toyotaman11769's Avatar
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01-11-05, 09:50 AM   #15  
We never did find exactly which fuse it was?

 
davo's Avatar
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01-11-05, 01:42 PM   #16  
Posted By: Tom V I also tried to see what would happen if the relay was removed, in this test the fues was fine until I tried to turn over the engine, but when the oil psi got up to a certain psi, the fues blew.
.

.
This would indicate the fuel pump circuit was being tested.ECM/BATT fuse 15 amp orange wire hot all the time.The fuel pump relay would have no effect on the ECM/IGN 1 fuse which is hot in run for the EGR and other components.

 
Tom V's Avatar
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01-12-05, 07:42 PM   #17  
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I was unaware that this is a testing site, we have experts who are helping people troubleshoot problems, while others are only here to criticise!

I could look at this and understand that the fuel pump fuse was the one in question, and although only one person thought to ask me which fuse was blowing, I thought it was very clear.

Not being a certified auto repair mechanic, I visited this site to get help, which is what I thought it was for.

Could there be a posibility that some people are upset that I repaired the problem before they could figure it out? And if so, no one should be, I'm sure that many people who visit this site are much more skilled in auto repair than myself.

I was told to try to be more clear next time, when I thought I was being very clear this time.

I appoligise for wasting your time.

I thank all the people who tried to help me, and was glad when I figured out the problem, but for the ego driven EXPERTS, thanks for nothing.

 
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