Offroad Trailblazers and Envoys

Gas tank Baffles...

Dumping ground for offroad Trailblazer or Envoy general discussion.

by HARDTRAILZ » Sat Sep 11, 2010 12:10 am

I have notices several times that on steep shit the truck seems to bog down and lack fuel, then after a few seconds will regain fuel and power up obstacles. Anyone else have this happen. It gets annoying and I think I will need a custom fuel tank with some baffles so it doesnt struggle for fuel. That or as I saw several times on the past rip...Propane LP gas systems are not affected as we are. I have not researched it since mine is still a DD for a year or so, but was told the conversion is around a grand.

Anyone have this issue on steep stuff? Or do I have something else wrong?
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by fishsticks » Sat Sep 11, 2010 12:12 am

I haven't had fuel issues, but I've had my oil pressure drop off a couple times before. That's a little unnerving. I've considered running a half quart extra to try and stave it off.
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by The Roadie » Sat Sep 11, 2010 12:26 am

I got the low oil pressure light in Moan a couple of times. No fuel issues though.
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by The Roadie » Sat Sep 11, 2010 12:28 am

MOAB, not moan, of course. Can't edit my own post with Tapatalk,rats.
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by HARDTRAILZ » Sat Sep 11, 2010 12:33 am

If not fuel then why a loss of rpm and power on steep stuff, Mike and I were talking and it seemed the only reasonable thing. It had to be real steep to...but not long, just the near vertical stuff that would dump the fuel to the rear and only later in the day where fuel would go to the back of tank.
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by fishsticks » Sat Sep 11, 2010 1:04 am

HARDTRAILZ wrote:If not fuel then why a loss of rpm and power on steep stuff, Mike and I were talking and it seemed the only reasonable thing. It had to be real steep to...but not long, just the near vertical stuff that would dump the fuel to the rear and only later in the day where fuel would go to the back of tank.



Assuming our fuel pumps have a cup built onto them like the other GM designs I've seen, it makes sense that would happen if your tank was low and the cup emptied. Propane is one way to go. A fuel cell mounted horizontally is another.
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by TangoBravo » Sat Sep 11, 2010 1:32 am

does anyone know where the pick up is on our tanks? I am also thinking and this may be thinkin way to much into it but if it is an isolated issue with one truck this maybe a possibility, Having a background as a firefighter/operator I have some understanding of pumps lines and the affects on these things on flat ground and inclines. But it could be something as simple as your fuel pump is ready to go, or stock lines are pluged. It takes way more work to move the same volume of fluid up a incline then it does on level ground. But if what your saying is that it only happens during a spacific level in your tank, this I would be of no help on, as in my mind if your truck is in perfect working order then we should all be having the same problem or atleast a good number of us.
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by HARDTRAILZ » Sat Sep 11, 2010 8:34 am

Makes sense. Maybe my fuel pump is weak. It happens when the tank is near full or closer to half. Maybe I am getting some sort of bubble or pressure thing. I dont know, but it is annoying.
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by Trail X » Sat Sep 11, 2010 9:52 am

Yeah, if your cup emptied, your engine would die immediately, it wouldn't struggle.

However, Tango does have a good point.... you're lifting the fuel an extra 4 or 5 feet when you're on a steep incline. It would reduce the pressure at the injectors if the pump pressure stays the same.
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by TangoBravo » Sun Sep 12, 2010 12:19 am

Yeah I don't think I have explored in the extreame's that Hardtrails has but I have had my TB on some angles with varied fuel amounts and have not had any issues.
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by HARDTRAILZ » Sun Sep 12, 2010 8:58 am

I guess I will look into replacing the fuel pump. I also have figure which bearing on one of the engine pulleys are dying. I can hear metal bearing noises, but temp and steering seem fine. Will try to figure it out today.
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by Trail X » Sun Sep 12, 2010 12:13 pm

The idler seems to be one of the first to go bad on these vehicles. Sounds almost like you've got a blower under the hood.
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by janesy86 » Sun Sep 12, 2010 12:52 pm

Mine just started make some noise as well, need to check it out soon.
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by HARDTRAILZ » Sun Sep 12, 2010 10:23 pm

Idler it prolly is. I hooked up Regulator with some of my offroad goodies today and he said the same thing when looking under the hood. I guess I hit the parts store on the way home from work tomorrow. I did notice a loss in mpg since the sound started, but everything esle was ok.
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by bartonmd » Mon Sep 13, 2010 8:48 am

JamesDowning wrote:Yeah, if your cup emptied, your engine would die immediately, it wouldn't struggle.

However, Tango does have a good point.... you're lifting the fuel an extra 4 or 5 feet when you're on a steep incline. It would reduce the pressure at the injectors if the pump pressure stays the same.


If the cup emptied, then got a little more sloshed into it, the pressure would just drop as the injectors used fuel, and it wouldn't die instantly... I've had it happen while towing in the mountains with my Caprice on less than 1/4 tank of gas...

That is a good point, with this vehicle, though... I forgot that especially the later ones are returnless fuel systems, where the regulator is in the tank, instead of at the engine like on older vehicles... You go up a steep incline and there is a pressure drop, which causes the bogging, then the computer sees the pressure drop and lean condition, and increases pulse width on the injectors to compensate...

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by HARDTRAILZ » Mon Sep 13, 2010 9:58 pm

JamesDowning wrote:The idler seems to be one of the first to go bad on these vehicles. Sounds almost like you've got a blower under the hood.



you were close...tensioner pulley. $15.40 was a nice cheap fix. Glad it was nothing worse.
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by Regulator1175 » Mon Sep 13, 2010 11:21 pm

:excited: I identified it correctly within 10 seconds of listening to it! :cheers:
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