73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: xjames14x on April 19, 2011, 05:50:00 pm
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My truck is a 79 Chevy K-10 with a 350, and turbo 400 transmission. i am having an issue with a major rpm drop when i put my truck into gear. when it is warm the idle is fine, i just replaced the modulator on transmission today, the vacuum hoses seem to be working fine. Is this a transmission issue? my carb is an edelbrock 1405 model, but it seems to be working fine also. if someone can point me into the right direction that would be great.
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I'd say you have a vacuum leak causing too much air to enter your engine and when you put it in gear, the rpms go down anyway.
take some WD40 and spray around all vacuum hoses in engine while it is idling. If the rpms shoot up more, you found a vacuum leak.
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Check your timing, make sure the vacuum advance is working
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Check your timing, make sure the vacuum advance is working
can you give me a example of the vacuum advance, because i believe my dad says that is working
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I'd pull the distributor cap off, then suck in on the vacuum advance hose and see if it moves the distributor parts inside (advances it).
Suck in on it and put your finger over the hose to prevent air from escaping, see if the advance stays advanced---doesnt move. If it moves, i"d say you may have a leaking diaphram in the vacuum advance (silver round thing the hose hooks to on distributor).
Make sure the hose is hooked to proper place fro vacuum. Mine, if you can follow, is from a 79 and hooked to carb port.
(http://www.delbridge.net/vacadv11c.jpg)
(http://www.delbridge.net/vacadv11b.jpg)
(http://www.delbridge.net/vacadv11.jpg)
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How do you have it hooked up? Where is the vacuum hose running from the vacuum advance? Is there suction present at the hose going to it with the engine idling?
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How do you have it hooked up? Where is the vacuum hose running from the vacuum advance? Is there suction present at the hose going to it with the engine idling?
from the vacuum advance to the carb, when the truck is in idle and you take the hose off from the carb that goes to the vac advance the truck will almost die
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the advance shouldnt be hooked up to a port that has vacuum at idle.
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you take the hose off from the carb that goes to the vac advance the truck will almost die
it will die because when you take a vacuum hose off the carb, you then have a major vacuum leak.
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Thats what I meant... ;D
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Keep the vacuum advance hooked up to manifold vacuum. Sounds like the timing is retarded. Try advancing it. Do you have a timing light?
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Keep the vacuum advance hooked up to manifold vacuum. Sounds like the timing is retarded. Try advancing it. Do you have a timing light?
yes we tried timing it, and on top of the manifold it looks like they plugged one hole for a vacuum i think, i will show you a picture of what im talking about
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Sorry for the blue star but below it is what i think is blocked off for some reason, is that the manifold vacuum? so that is supposed to go to the vacuum advance?
(http://i15.photobucket.com/albums/a398/whiteluda14/IMG_20110423_191956-1.gif)
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is your heater hooked up? if so, to what? That should be a heater hose to your heater core going into the firewall.
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no we need to get a new heater core, where is the manifold vacuum located
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The port on the front of the carburetor on the driver side.
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see my pic i posted. That's the stock place for a '79.
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ok yes i see it, that is going to my vac advance while the passengers side vac is going down to my transmission modulator, in the picture i posted you can see them...my father says that its my carb so im probably going to try to rebuild or buy a new one
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In your picture, to the left of your blue star, there are 3 hoses, 1 big and 2 smaller ones. 1 of the smaller ones should be hooked to your vacuum advance on your distributor. I have the same set up and that is where my vacuum advance is hooked up.
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I do not know if this is the same as you. When I would drive mine and as long as I stayed barely into the gas pedal it ran fine, when I pushed into gas more than say 1 " my truck would "chug, chug" then level out.
I ended up replacing my pcv valve and corrected the problem. In your picture, the big hose in between the 2 little ones should go to your pcv valve on one of your valve covers, mine is on my passenger side.
The pcv valve has to do with crankcase vacuum, that helps control the vacuum advance on your distributor as I recall.
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ok yes i see it, that is going to my vac advance while the passengers side vac is going down to my transmission modulator, in the picture i posted you can see them...my father says that its my carb so im probably going to try to rebuild or buy a new one
You should have manifold vacuum going to your modulator not ported vacuum.
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yeah, what Vile said. The manifold vacuum for the modulator is usually right behind the carb in the intake manifold. Near the distributor. It goes down to the transmission modulator.
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yeah, what Vile said. The manifold vacuum for the modulator is usually right behind the carb in the intake manifold. Near the distributor. It goes down to the transmission modulator.
ok im going to have to fix that then, this thing is just hillbillied together, im just trying to figure out stuff and knocking out things and narrowing them down, also talking to my father i need a new rotor for the distributer....going to go buy spark plug wires tomorrow and maybe even a new distributor cap, i appreciate all the help and i will keep you posted, you guys have been a lot of help
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ok so let me get this straight here.....i should have one vacuum hose going from the modulator on my transmission to a port on the manifold (passengers side near distributor?)? And then i would need a vacuum hose from the vacuum advance to my carb that is on the drivers side port next to the idle adjuster?
also if anyone knows the ins and outs of an edelbrock 1405 carb that would be great too
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you can download the tuning manual and rebuild manual for that carb on edelbrocks site.
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In your picture, to the left of your blue star, there are 3 hoses, 1 big and 2 smaller ones. 1 of the smaller ones should be hooked to your vacuum advance on your distributor. I have the same set up and that is where my vacuum advance is hooked up.
yes the smaller hose on the drivers side of the carb is going to my vac advance
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you can download the tuning manual and rebuild manual for that carb on edelbrocks site.
ok thank you, about to go to the parts store to buy a vacuum plug for the manifold, so i can hookup the modulator hose to that instead of it running to the carb