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I have a 1995 gmc 5.7 TBI. erratic idol and i lose power…

I have a 1995...

I have a 1995 gmc 5.7 TBI. erratic idol and i lose power when accelerating.

Mechanic's Assistant: How old is the transmission? Have you checked the fuel filters?

Rebuilt trans 2 months ago with updates and torque converter. changed fuel filter, plugs, wires, rotor and cap. checked timing all good

Mechanic's Assistant: What is the model of your '95 GMC?

Yukon 4wd

Mechanic's Assistant: Are you fixing your Yukon yourself? What have you tried so far?

Yes. fuel filter, plugs, wires,cap and rotor, cleaned throttle body, pcv. no vac leaks. does this model have a low oil pressure shut off for the fuel pump? it does burn oil but i check regularly and its a little low

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Thats all i have

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Answered in 1 minute by:
3/19/2018
JFN1
JFN1, ASE Certified Technician
Category: GMC
Satisfied Customers: 5,628
Experience: GM Master Technician
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No, it does not have a low oil pressure shut off, first of all. Common misconception because people see that the oil pressure switch is part of the fuel pump circuit, but it has nothing to do with low oil pressure.

All of that stuff didn't change the symptom at all? Is the check engine light ever on?

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Customer reply replied 1 month ago
thanks for clearing there misconception i didn't think it was an issue but I'm left scratching my head. light never comes on.

What is the idle like, does the engine run well and smooth, with an unstable idle, or is it misfiring and running rough at idle? Does it misfire when you're accelerating?

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Customer reply replied 1 month ago
for the most part idol is fine. it hiccups roughly every 30sec

What's it like when it loses power when accelerating, like the engine shut off, like a misfire, like it isn't getting enough fuel like it's just sluggish?

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Customer reply replied 1 month ago
i live in the hills of west Virginia when on a trip this weekend i traveled 160 miles one way no problems on the way home it struggled to take the hills and shook the truck like it was starving for fuel.
Customer reply replied 1 month ago
fuel pump whirls fine.. i have no way to check pressure though.
Customer reply replied 1 month ago
sluggish
Customer reply replied 1 month ago
it kept downshifting to make up for loss of speed through the hills. the same hills it took just fine days before
Customer reply replied 1 month ago
it revved fine but once up top the hill it lost power again

This is either going to be a catalytic converter or a fuel pressure issue. There are tests for both.

You can borrow these tools at Autozone, Advance, etc.

Exhaust back pressure is checked with a back pressure gauge, which attaches in place of the oxygen sensor. Put the gauge on it, put the gauge up near the windshield where you can see it, and go drive the vehicle until it acts up. When it does, make note of the gauge reading. Allowable back pressure is 1psi, if the gauge is going off the scale when it acts up, you need a new converter.

Fuel pressure is similar, you need a TBI fuel pressure gauge (it's different than a regular fuel pressure gauge). Fuel pressure should be 9-13 psi all the time. Put the gauge up where you can see it while you drive, go make it act up, and when it does, make note of what the fuel pressure is.

I'd start with these two tests.

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, just let me know, I am happy to follow up.

JFN1
JFN1, ASE Certified Technician
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Customer reply replied 1 month ago
thank you! will do.
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