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1989 Chevy Truck lack of power

Tiny
PLY48
  • MEMBER
  • 1989 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 280,000 MILES
I have an old body style 89 k3500. I hear a loud air sound coming out of the throttle body around the IAC. I've changed out the injectors, pressure reg., IAC, o2 sensor, ERG, ERG sensor. The engine idles up and down and when you give it gas it lack power. Engine has been rebuilt 2 years ago and has ran great until 3 months ago. It has good fuel pressure. I'm baffeled to what it could be. I put in a super chip a year ago and it ran good.
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Sunday, March 30th, 2008 AT 11:24 AM

11 Replies

Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Any check engine light? Could be a cat converter that is melting down, Try loosening the exhaust before the cat/cats to let the gasses out, drive it to see if it has power again
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Monday, March 31st, 2008 AT 7:24 AM
Tiny
PLY48
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  • 6 POSTS
I have no check engine light and the cat is removed.
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Monday, March 31st, 2008 AT 6:08 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Try spraying around the TBI with carb cleaner, you may have a vacuum leak that is leaning out the mixture. Those TBI's sucked the throttle body gasket right around where you are describing
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Tuesday, April 1st, 2008 AT 7:43 AM
Tiny
PLY48
  • MEMBER
  • 6 POSTS
I sprayed carb cleaner around tbi and got nothing. I hear a loud vaccum sound around the iac inside the throttle body. I've changed the iac and still the same thing. Idle goes up and down. Whats next? Greg
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Saturday, April 19th, 2008 AT 11:24 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
There should be a little whistling sound out of the TBI, that is normal. Makes me wonder if it has an internal vacuum leak. That truck has a TH400 trans, is the vacuum modulator good? (Looking for possible vacuum leaks). What is the exact fuel pressure? Should be 9-13 lbs with good volume as well
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Sunday, April 20th, 2008 AT 7:38 AM
Tiny
PLY48
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  • 6 POSTS
Yes it has a th400 and the modulator is ok. I see that the iac goes in and out. This whisltling sound is to loud. The fuel pressure is @12lbs.
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Monday, April 28th, 2008 AT 6:51 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Might want to remove the TBI just to see if it sucked the gasket internally. When was the last tune up? If you have a timing light, use it to see if the timing is advancing when throttle is applied
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Tuesday, April 29th, 2008 AT 7:20 AM
Tiny
PLY48
  • MEMBER
  • 6 POSTS
I changed the throttle body gasket and it was entact. I'll check the timing. It was tuned up about 6-8 months ago.
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Tuesday, April 29th, 2008 AT 6:40 PM
Tiny
PLY48
  • MEMBER
  • 6 POSTS
Checked the timing and it is good. Whats next? Greg
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Tuesday, May 13th, 2008 AT 9:48 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Take it to a shop with the ability to put it on a scanner and watch the sensors while driving it
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Wednesday, May 14th, 2008 AT 7:36 AM
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Make sure all the vaccume lines are hooked up to the TB -- if so -- then it may be a worn out throttle body shaft. Non-repairable -- Make sure there are no internal leaks inside of the TB -- If all checks out replace the throttle body ( TB ).
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Monday, May 19th, 2008 AT 4:17 AM

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