Engine losing power

Tiny
VINCE LETTAU
  • MEMBER
  • 1990 CADILLAC FLEETWOOD
  • 5.7L
  • V8
  • FWD
  • AUTOMATIC
  • 106,000 MILES
After I drive the car for about a hour or sixty to eighty miles it starts losing power and when I step on it the gas it acts like it wants to stall. So I back off the gas and it runs but losing power going up hills. Goes down to twenty five or less miles an hour.
Saturday, September 23rd, 2017 AT 7:50 PM

8 Replies

Tiny
STEVE W.
  • MECHANIC
  • 14,529 POSTS
After it loses power how long does it take to come back? Do you have to shut off the engine or just let it idle a bit?

The description suggests it has a weak fuel pump that cannot keep up with the engine demands when under load. It could also be a bad regulator mimicking the same issue due to the lower vacuum at high rpm.

A fuel pressure and flow test would be a good place to start.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Sunday, September 24th, 2017 AT 6:14 AM
Tiny
VINCE LETTAU
  • MEMBER
  • 33 POSTS
No have to shut the car down once this happens. I shut the car down and after the car sits or cool off it will run again for fifty to eighty miles and starts the problem again.
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Sunday, September 24th, 2017 AT 7:02 AM
Tiny
STEVE W.
  • MECHANIC
  • 14,529 POSTS
Okay as a strange test. Run it until it shuts off, then remove the fuel cap. Listen to see if you hear a hiss. It is possible the tank vent is plugged, but it sounds fuel related.
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Sunday, September 24th, 2017 AT 10:03 AM
Tiny
VINCE LETTAU
  • MEMBER
  • 33 POSTS
The car does not completely shut off it will idle okay. And no check engine light comes on. I checked the battery and the battery is bad. Good enough to start, but when the car gets hot, not overheated could it be not enough spark. Had a new alternator and belt put on two weeks ago. Or could it be the gas cap?
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Sunday, September 24th, 2017 AT 1:43 PM
Tiny
STEVE W.
  • MECHANIC
  • 14,529 POSTS
Bad battery should not make it lose power if the alternator is working. I would check fuel pressure and flow. Plus check the cap.
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Sunday, September 24th, 2017 AT 2:46 PM
Tiny
VINCE LETTAU
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  • 33 POSTS
Okay thanks, I will check that tomorrow. Vince
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Sunday, September 24th, 2017 AT 6:19 PM
Tiny
STEVE W.
  • MECHANIC
  • 14,529 POSTS
Your description of shutting it off to cool down sounds like the pump is failing. It cannot keep up with the flow and the mix starts to get lean which generates enough heat that it actually starts to vapor lock because the flow is not enough to keep colder fuel running through the lines. I might also swap the fuel filter as that could reduce the flow as well.
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Monday, September 25th, 2017 AT 3:15 AM
Tiny
VINCE LETTAU
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  • 33 POSTS
Thanks I will change the filter than the pump. Vince
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Monday, September 25th, 2017 AT 9:54 AM

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