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On my 98 Chevrolet K1500 truck with a 5.7 I noticed it

running rough one day in...
On my 98 Chevrolet K1500 truck with a 5.7 I noticed it running rough one day in December. It ran fine til last week and it ran rough again and kept getting worse but not consistent. I had just filled up and it had hard the past few days and I thought I had bad gas, when I stopped to get something to treat the fuel it would not start. I got it home and changed the fuel pump. It was late at night and it started right up. I shut it off and it would not start the next day. I changed the fuel filter because I was going to any way and it started and ran and I moved it. I waited a couple days to use it and it would not start again. Today I noticed that the fuel pump did not come on when I turned the key on. I trouble shot the fuel pump relay and when I jumped across the #30 and #87 plugs where the relay goes the throttle body and fuel pump came on. I bought a new relay and it would not start. Trouble shot the relay again, jumping everything worked. I am assuming the fuel relay good and it is not now. I checked the wiring harness under the alternator and found the harness was not in its holder but I found no damage on the outside. I pulled the wires out of the plastic conduit and no damage what so ever. Not sure what to do next.
I have had great success with Just Answer except my last question I got no answer, no help and I still got charged for it. Even after I complained. I do not want that to happen again.Thank you,
Marty
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Answered in 2 minutes by:
2/26/2018
Eddie
Eddie, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,769
Experience: I have 20 years professional experience in advanced engine controls and transmission rebuilding.
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Hello Marty, so if you jump 30 to 87 at the relay, does the fuel pump run then and the engine start?
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Customer reply replied 5 months ago
Never tried that. Let me check.

Alright, let me know what happens.

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Customer reply replied 5 months ago
Well I did all this hours ago and left my key on. I am charging now.. I will let u know.

Alright, sounds good.

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Do you know if it has the original spider fuel injection unit on it? or have you replaced it?

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Customer reply replied 5 months ago
Original

Alright, try to jump that relay and see if it will run and if it won't run then, make sure your PINK wire is hot at the spider injection unit with key on. If you have fuel pressure after hot wiring the fuel pump relay and it still won't start then I suspect the spider injection unit if it's original.

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Customer reply replied 5 months ago
I just jumped 87 and 30 and it started. Ran a little rich seemed like but it ran. I noticed that when I jumped 87 and 30 that the throttle body and pump both came on without the key. I am guessing that the relay connects between 87A and 87 when you turn the key?Thanks,
Marty

The Engine computer grounds the fuel pump relay, make sure you have two hot pins in the relay socket with the key on.

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Customer reply replied 5 months ago
Ok
Customer reply replied 5 months ago
I should have two hot "slots" in the fuse block when the key is on. Are these 87a and 87?
Customer reply replied 5 months ago
I have two slots hot. the upper right and lower right. Not sure of the number because the schematic is 90 to the actual relay.
Customer reply replied 5 months ago
OK, if I have that then what? Thanks.

If you have that ground on 85 when cranking, then there is no reason the fuel pump shouldn't run normally. I'm thinking you won't have a ground, because if you did and the relay was good then the fuel pump should run.

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Customer reply replied 5 months ago
Ok so if I don't have a ground......??
Then the wire from the RUM that grounds the relay could be broken or corroded, or the ECM itself could have failed.
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Customer reply replied 5 months ago
Ok how do I find that wire and is it just a ground. Any idea on the path. I agree its a ground issue. How could I check the ECM to make sure its working ?

Here is the wiring diagram, the wire is GREEN/WHITE out of C4 at the ECM, that grounds the fuel pump relay. ohm it out from the relay to the ECM connector, should be less than 3 ohms, if it's not 3 ohms or less, I would try running a new wire and see if that fixes it, if the wire is good from the relay to the ECM, check for a ground at pin C4 while cranking, if you don't have a ground there, then I'm leaning towards the ECM being bad.

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Customer reply replied 5 months ago
Ok thanks... I will check this out tomorrow. I suspect a wire but have looked a lot of places and found nothing. I will let u know

Alright, sounds good. Thank you.

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Customer reply replied 5 months ago
OK, sorry for the delay. I checked for a ground on pin socket 85, none at ignition or or cranking. I tried to get a reading through the wire but got none. I did verify I had the right one so I spliced it and still nothing. How can I make sure it is the ECM, everything I read online says it is almost never the ECM but a dirty or loose connection. I admit the vehicle is 2 years old and has 280,000 miles on it.
If I do verify it is where do I take it to get it "flashed". The issue is the truck died out in the middle of nowhere. We had to tow it with a tractor to higher ground with all the rain we are having.
Thanks for all the help and sorry for the delays but I have to go to it to check all this out.
Customer reply replied 5 months ago
OK, I am confused, the pin 85 should send a "ground" at cranking or the ignition first turned on but not all th the time? Is this til the relay closes and connects? What grounds it all the time? Sorry just trying to understand it all.
Customer reply replied 5 months ago
Any suggestions

The ECM sends a ground for the first 2 seconds the key is turned on to "prime" the fuel system, then when cranking, the ECM grounds the relay constantly. so if you sit with your key on the fuel pump doesn't and isn't supposed to run the whole time.

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If your not getting any ground on pin 85 at the relay, and your sure the wire from the ECM to pin 85 in the relay socket is good, (less than 3 ohms) then I would have to say it's the ECM because as soon as the ECM is powered up via the ignition switch it is supposed to ground pin 85 at the relay for a couple of seconds regardless of whether the engine is cranked or not.

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Customer reply replied 5 months ago
Ok any way to check the ECM for sure.
Customer reply replied 5 months ago
Ok

Check for a ground directly at the ECM when you turn the key ON, on GREEN/WHITE at the ECM, if you get no ground there when you turn the key on, pull all the connectors out and make sure everything looks good, and if it does, In my opinion I would say the ECM has failed.

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Customer reply replied 5 months ago
Ok spliced the wire all ready and cleaned all the pins so I guess it is

It sure sounds like it to me.

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Customer reply replied 5 months ago
There has to be a way to bypass that. Everything else works fine or did. I have to have it running to get a diagnostic done. I will work on that before I go through the pain of getting a new ECM and finding someone to "flash" it.

well, jumping the relay bypasses it, from 30 to 87, or you could put in a simple toggle a switch to ground the relay pin 85 and bypass it. You could wire a relay to provide a ground to the fuel pump relay via ign. power. There are ways to get around it. But the way GM designed it is via the ECM so the pump doesn't run the whole time the key is on.

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At least we do know now why the pump isn't running, and that is because the ECM isn't provided a ground for the relay. If your sure the wire is good, then I do know that as soon as you hit the key at power up the ECM it is supposed to ground that pin to prime the fuel system.

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Customer reply replied 5 months ago
I never checked the fuel fuse..
So all the relay, does besides disrupt power is to prevent the pump from running all the time?
Customer reply replied 5 months ago
you are saying, find a ground and connect the green and white wire and then add a toggle switch in between, I would add a fuse too. You switch the switch on while starting and after starting turn it off because the relay will be connected and that circuit is grounded.

The relay is there to prevent running larger gauge wires into the ignition switch as well. that's why there are so many relays these days. so you can control a large amperage circuit without running big wires everywhere.

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Customer reply replied 5 months ago
Oh, that makes since.

That is one way to get around it yes, but if you ever forget to shut the switch off, battery would be dead in a couple hours most likely.

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Customer reply replied 5 months ago
Not if the hot shuts off with the key.I am just getting the relay to connect. I finally found some circuit info and it is supposed to stay grounded for 10 seconds then it ungrounds.
Customer reply replied 5 months ago
sorry that was asking. I am headed to get it. I was afraid that by bypassing the relay and running the wire between 30 and 87 but it should be ok then I can work on another. First, I think I need to get a diagnostic to see if anything else is wrong. If so then a new ECM is in the future. I just had the compression tested and it is great. I really want to keep it just for going to deer/duck camp and back and a third vehicle. I know the value is basically 0 but it is handy to have and is in great shape.

I totally understand, those trucks are hard to kill with the vortec in them. It sounds like it's not the ECM as far as firing the injectors because it does run when you jump the relay though, so if that was the case and I wasn't planning on driving the truck cross country. I would probably set up a toggle switch to ground the relay before putting ECM type money in it. and 98 is the first year you did have to flash the PCM's. if it was 97 it was plug and play.

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Customer reply replied 5 months ago
I realized that because I found plenty of 97 ECM's and they were cheap with no instructions. The 98 had all those extra instructions and warnings. I have not found anybody except the dealer than can flash it. I am sure I will but until then I am gonna test a toggle and use the fuel sender ground. Same size wire and pretty low power I am sure.Thanks

Absolutely, Thank you. Let us know if you have any further questions.

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Customer reply replied 5 months ago
OK, I am regressing. The wire I thought was the wire from the slot for pin 85 was the wrong green and white wire. There is another green and white wire and I have confirmed that it is connected through slot 85 but can not find it going into the ECM. I ran power into the slot and grounded it out on the OTHER green and white wire coming out of the relay/fuse block but when I try to ground the green and white wire at the Black slot on the ECM it does nothing. Does the green and white wire from slot 85 go into the ECM at the Black slot? I am just checking because there is only one and that proves that the wire is bad. I do have the Black bundle unplugged from the ECM. I would not power a circuit going into that. It is just super hard to get an Ohm reading on those small wires without stripping them.
Customer reply replied 5 months ago
The chart you sent me shows that C4 you mentioned is Black I am just checking.
Customer reply replied 5 months ago
Not sure which pin is #1 but I spliced that green and white wire and still no ground when the key is on in slot 85. So back to grounding it through a switch.
Customer reply replied 5 months ago
Ok, that would be hard to check anything. Except the wire. I will look at that. I noticed the connector is upside down from how it goes in the ECM.

Alright, let me know what happens.

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looking for two GREEN/WHITE wires in the connector almost together seperated by one hole. Then ohm it out from relay socket to pin 1. should be less than 3 ohms.

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The GREEN/WHITE closest to the end of the connector grounds the fuel pump relay.

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Customer reply replied 5 months ago
I grounded the wire going to slot 85, I double checked and the slot is grounded and put the relay in and I knew something was wrong because when I turned the key on no pump came on. It would not start. It is a new relay. Still starts jumping 30 and 87.
Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
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Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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OK. I read through it, and I'm confused a bit, so I just want to back up and start from scratch.

When you turn the key ON, does the pump run for two seconds, then shut off?

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Customer reply replied 5 months ago
Here is what I did. I took the Green and white wire connected to the slot pin 85 goes into and grounded it to the body, totally separate. I did vs ground to another grounded wire to alleviate any problems there. I ran that wire through the firewall and left it in tact. The plan was to get the ground to work and then install a switch. Turn the switch on when starting, turn off when started.
I checked slot 85 and it was grounded when power was applied to it. I re-installed the fuel relay and turned the key on.. nothing. The throttle body and fuel pump should have turned on. I tried to start but it did not start. Not sure but this makes total sense to work. It may be the relay but it is new. I cannot find the old one as it was probably good all along.Suggestions?? Still runs when jumped between pin slots 30 and 87.
Customer reply replied 5 months ago
Just saw your last response. When the key is on now nothing happens with the fuel pump. When I apply power by jumping the relay from 30-87 it starts and runs fine. Basically fuel pump does not come on. Does the throttle body come one when the fuel pump does?

I don't know what you mean by "throttle body comes on". The throttle body doesn't do anything electrically.

The fuel pump relay is different than every other relay in the truck. Pin 86 is permanently grounded, the PCM runs this pump by applying POWER to pin 85, thereby energizing the relay and making the pump run. You still have that wire run to pin 85? Attach it to B+, the pump should run.

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Customer reply replied 5 months ago
OK, sorry for the delay, I had a meeting. When I jump pin 30 and 87 I hear a noise at the throttle body, maybe that is just fuel pressure and I hear the fuel pump. I have a wire attached to the wire for 85 but I grounded it. I was told that and have seen online where when the key is turned on that ground is activated or during cranking. It then shuts off.Sounds like you have better information or at least different than I had before. The thought is that the ECM is not grounding.What is B+? I am just trying to bypass the relay and get the fuel pump to run during starting and when the ignition is on.I have one more thing to do then I will be able to check it out. So, you are suggesting I connect 85 to where?Thanks for the help.

That's the thing: all the info you've been told so far is wrong. You don't ground that pin to make the pump run. You put power to it. PCM applies power to that wire, NOT ground.

I propose that you put it back the way it belongs, and start from scratch, because you took it apart on the assumption that the PCM wasn't grounding it. Well, the PCM WASN'T grounding it, because it's not supposed to. You should have been checking for power on that pin all along. So let's go back to the beginning, and test this again, instead looking for POWER on that wire from the PCM.

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Customer reply replied 5 months ago
OK, when would we get power to that pin? ignition on, while cranking. Thanks... I have been chasing this thing for a while. Just for background. I have replaced the fuel pump, fuel filter and the fuel relay. It does run with being jumped from 30 to 87.Putting back to original now and checking for power. Just so we are clear, it is a 1998 Chevy 4X4 truck with a 5.7 Vortec.

Yes. All of the above is correct.

:-)

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Customer reply replied 5 months ago
OK, Jerry I really appreciate you looking into this and seeing all that is screwed up. I used to have two hot slots before and now I only have 1 the slot for pin #87.. #85 has no power either in any scenario. First, am I supposed to have 2 hot slots with it just sitting there?
I was told previously that Pin #1 on the Black (C-4) plug on the ECM was supposed to go to slot 85 of the fuel relay? Is that correct. My concern is that there are 2 green and white wires coming from the relay center and going into Black. I thought I had them right but was told about the #1 pin and I switched them. I need to be back to original before we start re-troubleshooting.

One one hot pin at pin 87. Pin 30 is the gray wire that goes to the pump. Pin 86 is ground at all times (check it by putting a test light between pins 86 and 87, test light should light up). Pin 85 is the dk grn/wht wire that goes back to the PCM, and the PCM applies POWER here to run the pump.

You get a two second prime with key on, so pin 85 will light up a test light to ground for two seconds. Then it should light up again as soon as you start cranking.

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Customer reply replied 5 months ago
Everything you said is correct, only 1 hot, #87 hot all the time, it grounds to 86. There is no power to 85 when cranking.

OK!

Now, we go back to the pin at the ECM, connector C4 pin 1, the dark green/white wire. Is there power on this wire as it comes out of the ECM?

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Customer reply replied 5 months ago
Thanks again, at least what you are saying and what I have are the same...
Customer reply replied 5 months ago
checking
Customer reply replied 5 months ago
Nothing. I would check the pin but I am buy myself and when I unplug C-4 from the ECM and run through the plug back to 85 it works. That wire is the one I replaced.
So I need to get power to that the wire connected to pin #1/ slot 85?

Yes, if you get power to it, the pump will run. It appears that your computer is no good, though I would check all fuses first. PCM gets that power from a fused source, and I don't know which one (manual doesn't tell me). Might be easier if you found a bad fuse and it suddenly worked.

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Customer reply replied 5 months ago
A bad fuse anywhere or just in the fuse/relay block? The only ones marked fuel on my vehicle are vacant so I am assuming those were for a diesel.
If I get a power source to 85 that is only on while cranking or ignition on the only thing I risk is having the pump on while the key is on. I could remedy that with a switch.
After I get I running I am going to get another diagnostic done. I have had a very hard time finding someone to "flash" my new ECM. 98 was the first year after "plug and play" I think.
Checking fuses.. Thanks

96 was the first year for trucks that had to be programmed, and every year since then. For the most part, only dealers do programming. I own a small repair shop and I do a fair amount of programming, because I own the equipment and pay for the subscription to GM's website so I can do it. Most small shops won't make this investment, but I did.

Yes, you can put a switched power source to this. Note that there is a safety hazard with this. The way the factory has it wired, the pump shuts off if the engine stops running. If you get into an accident and the engine stops running, the pump won't pump gasoline everywhere and kill you. The way you're talking about doing it, though, if the engine dies with the key on, the pump will keep running, and if there's a fire and a fuel leak, it will just be a non stop inferno until the power is removed from the pump. Serious stuff, so consider what you're talking about doing.

I would check all of the the fuses, it only takes a minute to run a test light across the top of each fuse and make sure it's hot on both sides.

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Customer reply replied 5 months ago
All the fuses are good, just checked them. I totally get the safety thing but I thought that slot 85 would only be hot for 2 seconds with the key on and then go off. Does it stay on after cranking and engine start? If it stays hot after start the only reason to put a switch in the circuit is to shut off if the engine died but unless incapacitated I would shut the key off.I know a lot of things go unpowered during cranking to maximize the power to the starter. Any suggestions on something that is on for crank and with the key on I can connect to? This is just a temp fix til I can find a place to get an ECM and get it flashed. It died in the middle of no where and I had to get a tractor to pull it to a friends duck club because we had some flooding. It is still out in the middle of no where. I really want to get it running and take it and get it diagnosed. I doubt this shows up but a few months ago the only thing wrong was the redundent 02 sensors and I went and replaced that.

Probably half the fuses in that underhood fuse box are hot with key on/crank, and dead with key off. A test light is your friend here, just probe those fuses and find one that suits your needs, then tap into it. They make little fuse taps just for this purpose, you local parts store should have them.

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Customer reply replied 5 months ago
Ok, the ECM 1 is only on with the key. Plus some others. How do I make sure you get the credit for the rating vs the first person I spoke to. You have explained and fixed in a few hours what I have been messing with for over a week and I want you to get the credit.

The other guy bailed out, so I get the credit. I appreciate that you want to make sure I get it, so do I. :-)

Good luck with it!

Please take a moment to rate my answers by clicking on the stars at the top of the page, that's how I get compensated. If you need more help, I am happy to follow up with you.

Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
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Customer reply replied 5 months ago
Worked great, tapped into IGN fuse because there was room for the fuse tap and it works great. Thanks so much for looking into this. I was pulling my hair out for over a week and then you had the right info and finished in a day.
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01 ASTRO 65000 AT TIMES WITH PATTEREN WONT RUN SMOTH JUMP BACK FIRE TRIES TO QUITE HAD NOT BEEN RUN BUT VERY LITTLE FOR 1 YEAR BEFOR TROUBLE STARTED MOST TROUBLE IDLEING BUT HAS STARTED THISROUGH EVEN… read more
eauto
eauto
self employed
High School or GED
74 satisfied customers
2000 chevy: ive replaced 3 fuel pumps...1st a delco..aftermarket
Ive got a 2000 chevy blazer..4.3l Ive replaced 3 fuel pumps. The 1st a delco and the other 2 aftermarket. THe last time it went out I bought a replacement motor only. Installed it and my blazer ran ro… read more
zzdaryl
zzdaryl
Lead Auto Tech
Some college and advanced training
4 satisfied customers
97 CHEVY: 4X4..FUEL SYSTEM..THE FUEL FILTER, GUY DROVE IT
(3/97 CHEVY 1500 Z71 4X4 5.7 AUTO) FUEL SYSTEM TROUBLE? BE FOR I GOT STUCK WITH IT A SHOP HAD JUST CHANGED THE FUEL FILTER, GUY DROVE IT FOR A FEW DAYS AND BROKE DOWN 3 TIMES. HAD TOLD ME BEFOR THE FI… read more
Joecamel90
Joecamel90
Technician
Associate Degree
24 satisfied customers
2000 silverado Z71: ran..parts store..off and wouldnt start back up
2000 silverado Z71: ran like a champ until I pulled into a parts store for oil, came out and it started up but ran really rough. Tried giving it a little gas to clear it out but acted like it was gett… read more
Gary
Gary
Chevy Technician
Vocational, Technical or Trade Scho
9,642 satisfied customers
chev..mini van..When Im driving all is fine... then it starts bucking
Hi, I have a 1999 chev ventrua mini van. When I'm driving all is fine... then it starts bucking like no fuel.. or a mis fire on ignition. Not when it is cold. ususally has to heat up a bit. Then it wi… read more
michael
michael
High School or GED
582 satisfied customers
1990 corsica: few min..stalls and will not strat again untill it cools
My 1990 corsica starts when cold, runs for a few min. stalls and will not strat again untill it cools off. what could cause this? (no trouble codes are indicated)… read more
supermechanic
supermechanic
Service consultant
Vocational, Technical or Trade Scho
10 satisfied customers
runs well..replaced coil, cap and rotor and no luck. if it sits
starts & runs well for days and they will not start. replaced coil, cap and rotor and no luck. if it sits for a time... like overnight... it usually starts. started it today, ran it for 5 minutes, tur… read more
Mcgruder73
Mcgruder73
Auto Technician
Associate Degree
93 Suburban: Fuel pump..getting power..the diagnostic connector
93 Suburban k1500. Fuel pump is not getting power. If I power the diagnostic connector the pump will run but it will not get power when the key is turned. Fuse and Relay are new, fuel pump is new. It … read more
Carhelp4u
Carhelp4u
GM Service Training
2,560 satisfied customers
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Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

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