lagging or stalling when applying gas but only at certain speeds?

1987 GMC S15
137,000 MILES • 2.8L • 6 CYL • 4WD • AUTOMATIC
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BUNKHITZ
  • MEMBER
  • 2 POSTS
I am having issues with my truck listed above lagging or stalling when applying gas but only at certain speeds. Offline and at certain speeds or up the hill it will stall slightly but not always at the same speeds or acceleration. I want to know if I am better off just replacing both or starting with the filter to see if that fixes my issue.
Aug 19, 2022 at 7:16 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

I would recommend checking fuel pressure to see if it is within spec. However, replacing the fuel filter isn't a bad idea either.

If you want to check the pressure, I attached directions below for testing the fuel pressure specific to this vehicle. pic 1

Pic 2 is related to the filter.

If you are losing power when it's under a load, the idea that it is fuel related is a good one. Let me know if you try testing pressure and the results. Also, I suspect when you said to replace both, the second one was the fuel pump. Read the very bottom of pic 1. You may find it of interest and helpful.

Let me know.

Joe

See pics below.
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Aug 19, 2022 at 4:13 PM
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BUNKHITZ
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I don't have any type of pressure gauge to read the fuel pressure, would checking the throttle body for fuel spray be sufficient?
Aug 20, 2022 at 6:31 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

That would indicate if there is fuel present, but if the pressure is high or low, it would be difficult to tell.

Have you tried contacting a nationally recognized parts store to see if they will lend one to you? Most times that will.

Let me know.

Joe
Aug 20, 2022 at 2:35 PM
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