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s-10 Blazer 1991 4x4 Runs rough, stalls, revs up by itself
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jackalope686
New User
Sep 11, 2008, 9:34 AM
Post #1 of 4
(1692 views)
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s-10 Blazer 1991 4x4 Runs rough, stalls, revs up by itself
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Hey everyone. Got an old 1991 model s blazer. its in really good shape, the body and interior. im in college and don't have much money atm. so im trying to figure out what ails my blazer, but ive run into a brick wall here. I thought it was the oxygen sensor confusing the fuel injection system, causing it to either mix too little gas or too much [causing it to either stall, or give about 50% power by itself]. Got it replaced, but it still does the same thing.
Symptoms:
-It will hesitate when i press the gas, a sudden increase in throttle makes it sputter before it takes off, almost like it floods it a bit. Once I get up to speed it runs fine, as long as I'm holding the gas down.
-If i suddenly have to let off the gas to stop, etc.. It sputters worse, and occasionally dies. It starts right back up though.
-It takes a while to start when its sat overnight.
-It has went up to about 5,000 rpms by itself twice, and wouldnt idle back down, so i turned it off and restarted it.
-The check engine light is on. It will sometimes flicker on and off, and the engine sputters while it does so.
-I'll occasionally feel a vibration under the brake pedal, and a noise. It isn't loud, but sounds more like something on the belt system rubbing.
Specifications:
1991
4.3L V6, Throttle Body Injection
4 Wheel Drive
4 Door
Rear ABS
Any help or insight you could give would be greatly appreciated, and I can provide you more information if needed. Thaks for your time.
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DanD
Veteran
/ Moderator
Sep 12, 2008, 6:47 AM
Post #2 of 4
(1677 views)
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Re: s-10 Blazer 1991 4x4 Runs rough, stalls, revs up by itself
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There are a couple of things that come to mind that might be causing this.
The gasket below the TBI unit had a tendency of failing and allowing false air to enter the engine, from below the throttle plates. Easy fix replace the gasket.
This usually caused a constant higher then normal idle rpm, along with a hesitation.
The next thing and because of some of the strange things you say that this truck is doing, is possibly the ECM (computer).
Back in the late 80’s to the mid ninety’s the ECMs were failing, due to the circuit boards cracking; causing poor or intermittent connection(s) internally.
GM’s test for this was to “simulate road shock” at the ECM. In other words, hit the computer with the palm of your hand.
The description of the test was to start the engine; lay the computer in the palm of one hand; then with the other hand, held 6 inches above the computer, give the computer a firm slap. It the engine runnings changed in the slightest or if the SES light flickered; replace the ECM, after checking that the ECM wiring connectors are not the cause of the bad connection.
Dan.
Canadian "EH"
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jackalope686
New User
Sep 12, 2008, 7:10 AM
Post #3 of 4
(1673 views)
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Re: s-10 Blazer 1991 4x4 Runs rough, stalls, revs up by itself
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Ok! Thanks for the reply. I'll be able to test the wireing and other things this weekend when I get back home. I'll tell you how it goes!
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jackalope686
New User
Sep 15, 2008, 7:23 PM
Post #4 of 4
(1655 views)
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Re: s-10 Blazer 1991 4x4 Runs rough, stalls, revs up by itself
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Wow. Thank goodness for my neighbor. He has 2 vehicles with the exact same engine in it, and he brought nothing but a free piece of wire and a code book and got the error code himself. He shorted two pins in the connector for the diagnostic computer, and it turns out it was the throttle position sensor. My dad replaced the idle air sensor as well before he found this out. But its much more responsive than its ever been, and has a lot more power. It actually has some bite again =D
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