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strange issue

This is a discussion on strange issue within the General Help forums, part of the LSx Technical Help Section category; i have a 2002 silverado with a 5.3 vortec and 205xxx miles on it. the last 2 summers when it ...

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    strange issue

    i have a 2002 silverado with a 5.3 vortec and 205xxx miles on it. the last 2 summers when it was hotter than 95 degrees outside it starts spitting and back firing and busting up when i push the gas pedal down. the more i drive the worse it gets until i cant even touch the fuel. the truck idles fine always. if i cut it off and let it sit for a couple hrs it is fine. it has never acted up after dark when its cooler outside. i do not understand this nor does any mechanic i have talked to. i have no idea where to start and i dont want to just start pooring out money. does anybody have any ideas of what i might be looking at? it has run up to 260 one time bc i left it running for about 30 mins one summer while i loaded my trailer. i never had any other probs like that tho. i do not think it is an internal issue. also i noticed the last time that its smells really rich when it does this. it does not throw a light on unless it revs over 4500 rpms and that says oxygen sensor but that is only on high rpms and when its not busting up. the service engine light will flash a few times but the only thing it says after that is multiple misfire. any input will be helpful as i am at a loss. i know it is hard to describe without seeing in person. thank you in advance

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    Veteran 0rion's Avatar
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    the first thing I would look at is fuel pressure when it's doing it.......it could be that when your pump gets hot it starts to fail. The multiple misfire also would make me think it's running out of fuel. Just something to check.

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    Senior Member Too Fast's Avatar
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    +1 fuel pressure. Or contaminated MAF.

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    ok ill check those 2 things and see what i get. not sure how to check the fuel pressure or what it is supposed to be....

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    did a quick search to see what the fuel pressure should be and this is what I found


    If 8th didget in VIN# is a Z then it should be--48 to 54 PSI
    If it is not a Z code then it is 55 to 62 PSI


    here's a video I found on youtube showing how to test it on an 01. Not sure if the schrader valve location changed but it should give you and idea of what you're looking for. You can get a tester at any parts store for ~$20 and it's a good tool to have around. The guy in the video brings up another good point....fuel filter. How many miles on your current fuel filter? I'd say step one is to verify your pressure though and go from there.


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    Senior Member Too Fast's Avatar
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    Yeah if the fuel pressure is low, an easy possible fix is a clogged fuel filter. However, in my career, I've seen a fuel filter fix a low pressure problem one time, the other 100s have been a faulty pump, with a few restricted lines and electrical issues thrown in to keep me honest lol!

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    Ok guys I finally got it to act up today. Ran into advance auto and purchased a actron fuel pressure gauge. Looked in the haynes book and it calls for 60-66 psi key on engine off. Koeo the pressure would jump to about 34psi as soon as I hit the key then drop to about 15. Did this a few times and it finally built to about 44. Cranked it up and it holds 37-40. However when I rev it lightly it would drop to around 20 and slowly build back up. Dont know much about these guages. Could be faulty guage??? what would the chances be? Also they were recommending a pressure regulator not pump. They said the pump either works or doesnt.

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    Also not sure if this matters but when I bled the pressure off to remove the guage the bleeder valve on my guage and the hose got so hot it burnt me. Seems abnormal.

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    I'm not sure if the trucks are like the f-bodies where the regulator is part of the pump module or if it's out on the rail. I do know that a pump isn't always "work or don't work". That pressure going up and then dropping like that would maybe point me in the direction of the regulator and the fact that as you primed it up it took a few turns of the key to build pressure. Those kind of things would make me think it's a regulator problem BUT that doesn't necessarily mean it has to be a regulator problem. It could be a leak in the hose going from the sock to the pump or it could be a weak pump or it could be a clogged filter. The hot fuel could be from a pump going out or the pump having to work hard to get the pressure up. Fuel that hot isn't normal.
    I would probably do the filter just for shits and giggles if it has very many miles on it. If it has miles on it then it's due up anyhow so it wouldn't be wasted money. I looked at rock auto and that regulator is ~$50-60 and it looks like the kind that goes on the rail so that would probably be the next thing I would do just because it's the least amount of work. Last would be the pump.

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    ok so im having an issue with fueling then? i was waiting for it to cool of and i was going to check the pressure on cold start just to see if there is any difference since it only does this when it get above 95 the pressure regulator is on the driver side fuel rail. i will pick up a filter tomorrow. i dont think that is the problem but it wont hurt anything and they are cheap. it never acts like this in cooler temps. that is the part that i dont understand. the pressure regulator is 58 at advance auto here. just didnt know if that really could be the issue so didnt want to just blow that much money. the fuel pump also whines really bad but it has done that since i changed it and i havent had this issue that long

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    Senior Member Too Fast's Avatar
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    You found the problem, Jon. New fuel pump and filter, and you're done. You have to drop the tank to change the pump, if you didn't already know. If the fuel pressure regulator is on the fuel rail, it's exceedingly rare for that to fail for a GM.

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    If the pump has been having the audible noise since installation, that tells me it's faulty or incorrect. But that's just me.

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    so yall are pretty certain that the fuel pump is what i am facing? thats an expensive fix. lol it has always whined i installed it at 147xxx now at 206xxx this prob didnt start til roughly 185xxx. the temp thing still bugs me, why if it was the filter or pump, is it only acting up when hot outside? i dont have alot less power than my grandpa who has the exact same truck other than him having only 20172 miles on his. i thought it was just mine was worn out and his was still new. before i spend that kind of money and go through that hell again, how certain are you guys? and could it be anything cheaper and easier? thanks for yalls time and patients

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    Smiles for 9.5 Years cammed goat's Avatar
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    Well, the pump could be pumping air as well as fuel, thus aerating the fuel. Remember, the fuel in the tank acts as a coolant/lubricant. Mix that with air and you end up overheating the pump.

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    ok thats a new idea. when i bled the guage it didnt blow steady liquid it kind of looked like the water drain on a air compressor..... either way i should replace the pump?

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    I would.

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    Ok guys I hate to keep rambling on about this but I have an update. Its now 83 degrees outside and I ran another fuel pressure test. Koeo pressure goes to to 50 and holds. Crank it and it holds at 41-43 and this time when reving it goes up to 45 at first then drops to around 38 then levels off about 42. Unlike before when it was around 98-100 degrees. The only other difference is before it had a quarter tank of fuel versus now has a half tank. If yall still think.pump then I will change it. The parts house has airtex, ac delco, bosch, and denso brands. Is there a better brand? They all run between 300 and 330 in price

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    rock auto is your friend......they'll be half that or better. I buy a lot of parts through them......good company to deal with.

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    Never heard of them. Not one around here. What brand or is there a preference?

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    it's a website.......hard to beat their prices and they have their shit together. One of those few select internet companies that has the online sales thing figured out. I can't link them since they're not a sponsor but think rockauto (one word) and also what comes before and after that in their address and you'll find it
    Last edited by 0rion; 07-26-2012 at 09:31 PM.

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