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1991 4.3 problems

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Old 08-29-2011, 08:41 PM   #1
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1991 4.3 problems

hello everybody I'm new on here and have a quick question. I just bought a 1991 s10 4.3 liter, and when i take off sometimes and on top end it wants to lose all power for a second or two and then go back to normal. it doesnt go dead or nothing. just annoying to be going down the road or taking off and you lose all power. any idea's? im thinking fuel pump
Old 08-29-2011, 08:56 PM   #2
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Re: 1991 4.3 problems

Quote: Originally Posted by blues102011
hello everybody I'm new on here and have a quick question. I just bought a 1991 s10 4.3 liter, and when i take off sometimes and on top end it wants to lose all power for a second or two and then go back to normal. it doesnt go dead or nothing. just annoying to be going down the road or taking off and you lose all power. any idea's? im thinking fuel pump
sorry i just thought of a better phrase what i meant to say (its cutting out)
Old 08-30-2011, 04:55 PM   #3
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Re: 1991 4.3 problems

Quote: Originally Posted by blues102011
sorry i just thought of a better phrase what i meant to say (its cutting out)
it only does it when the engine is warm. and its getting very low fuel milage. any ideas?
Old 08-31-2011, 12:20 AM   #4
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Re: 1991 4.3 problems

Give yourself a break. First make sure the MAP vacuum hose is
NOT clogged coming out of the TBI in the rear. Replace ALL the
vacuum lines you can see. Check the elbow under the TBI from
the PCV going to it to make sure it's not cracked. They fail
underneath. These 1Gens need input from the sensors that
GM came up with. If you know how to read a vacuum gauge
connect it to the port off the right side by the TBI on the manifold
to get a decent supply then read the vacuum gauge as you
increase off of idle.. It will tell you the story about your engine.

You state it goes to hell once warm. Replace the 02 sensor because
they burn out after 60,000 or so. Make sure you have NO exhaust
leaks nor vacuum leaks. Start from there. Make sure you have
good fuel pressure going to to the injectors, make sure timing is
set right and that everything you can see is right. THEN start
considering the CTS. the primary sensor to get it from open
loop to closed loop and go from there. If you need a voltages for
the CTS in it's proper function, post.
Old 08-31-2011, 11:58 PM   #5
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Re: 1991 4.3 problems

try simple stuff like the air and fuel filters
Old 09-02-2011, 03:30 PM   #6
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Re: 1991 4.3 problems

sounds good ill try that to. i put new plug and wires on it and the plugs must have been on there for many years they looked bad. it runs more smoother now but the same problem on the cutting out. so i took a jumper wire and checked my trouble codes and it flashed 34. i looked it up and it said map sensor signal low volgate(high vacuum). so does this mean i need a new map sensor or is something else is wrong with the vacuum causing it to send a bad signal to the map sensor? and again thank you in advance for any response
Old 09-03-2011, 01:09 PM   #7
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Re: 1991 4.3 problems

It may mean all you have is a clog in the port on the rear of the
TBI where the vacuum line goes to the MAP sensor. Even a tiny
bit of carbon or dirt will not allow the proper amount of vacuum
sent to the MAP. Clean out the port using carb cleaner and I've
used pipe cleaners to get junk out. Also check the vacuum line
itself for any tiny splits or cracks. One way to test it is plug one
end and blow a small amount of air into the other end while
emerged in a bowl of water. If bubbles show up, then you know
there is a prob with the vacuum line. Again check for vacuum
leaks with the motor running and spraying soapy water around
the base of the TBI and other vacuum port areas.

A split in the MAP vacuum line from the TBI to the MAP may or
may not show up as high vacuum sig. MAP's are not
that cheap, so simple tests might save you some money.
However sometimes the MAP itself can go bad via a bad
sensor inside.

Here's an idea of what they run.

http://www.rockauto.com/catalog/x,ca...parttype,11207

Here is a really good article on MAPS.

www.aa1car.com/library/map_sensors.htm
Old 09-03-2011, 06:40 PM   #8
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Re: 1991 4.3 problems

Quote: Originally Posted by bg's
It may mean all you have is a clog in the port on the rear of the
TBI where the vacuum line goes to the MAP sensor. Even a tiny
bit of carbon or dirt will not allow the proper amount of vacuum
sent to the MAP. Clean out the port using carb cleaner and I've
used pipe cleaners to get junk out. Also check the vacuum line
itself for any tiny splits or cracks. One way to test it is plug one
end and blow a small amount of air into the other end while
emerged in a bowl of water. If bubbles show up, then you know
there is a prob with the vacuum line. Again check for vacuum
leaks with the motor running and spraying soapy water around
the base of the TBI and other vacuum port areas.

A split in the MAP vacuum line from the TBI to the MAP may or
may not show up as high vacuum sig. MAP's are not
that cheap, so simple tests might save you some money.
However sometimes the MAP itself can go bad via a bad
sensor inside.

Here's an idea of what they run.

http://www.rockauto.com/catalog/x,ca...parttype,11207

Here is a really good article on MAPS.

www.aa1car.com/library/map_sensors.htm
thanks bg's i'll do it. while looking for vacuum lines i found a vacuum line in the front of the throttle body going to the air canister cut into, went and bought a new one and replaced it. I drove it for about 5 miles and it didnt cut out and the service engine light went out. but ill go over the rest of the lines and map sensor with a fine tooth comb. ill post when i get it all done and maybe someone will read this post and itll help them.
Old 09-03-2011, 08:06 PM   #9
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Re: 1991 4.3 problems

There you go. That vacuum line was probably going to the evap canister
down in the left side corner by the rad. If not a manifold vacuum line, then
it's right above the plates, close to being manifold vacuum.Something
like this. Maybe port A ?

Old 09-03-2011, 09:34 PM   #10
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Re: 1991 4.3 problems

Quote: Originally Posted by bg's
There you go. That vacuum line was probably going to the evap canister
down in the left side corner by the rad. If not a manifold vacuum line, then
it's right above the plates, close to being manifold vacuum.Something
like this. Maybe port A ?

yes it was the port A vacuum line. but after moving my map sensor around and the motor was going crazy so im going to buy a new map sensor to make sure, and i did another trouble code reading on it and now its showing codes 32 33 and 34. all linked to the map sensor.
Old 09-03-2011, 10:00 PM   #11
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Re: 1991 4.3 problems

Thats pretty wild. I hope you replace the MAP line as well, You can use
vacuum line, Whatever size the line is. Maybe 1/4", maybe 5/32 ?

Looks like you're almost there.
Old 09-04-2011, 02:42 PM   #12
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Re: 1991 4.3 problems

well i put the new map sensor on it. and so far so good but my check engine light is coming on and off at times and when i checked it, Its still showing trouble codes 32,33 and 34. if i disconnect the negative battery cable for 20 seconds and reboot the computer will that clear the trouble codes?
Old 09-09-2011, 08:41 PM   #13
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Re: 1991 4.3 problems

my truck is running great and isnt cutting out no more. thank you bg's for all your help, turned out it was the map sensor and i replaced the vacuum line and cleaned out the port where the hose goes into the tbi, heres a pic of here
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