Help Needed with a 1998 GMC Sonoma SLS with 4.3L 2WD Automatic

305 Views 13 Replies 4 Participants Last post by Racer-X, 7 d ago

rojolobonm

Discussion Starter · 19 d ago

I have a 98 GMC Sonoma with a 4.3L, 2WD Automatic . I have a 3 way valve under the hood that has a line missing off of it. It's causing the engine to idle rought and the computer to throw a P300 Random Misfire code. Does anyone know where all 3 of these air lines go. Photot is attached. The line from the engine is connected, the line that goes down into the fender is also connected, I just can not locate the 3rd ine or where it connected to. Thank You

Vehicle Motor vehicle Hood Car Automotive tire

Hood Bumper Automotive tire Vehicle door Gas

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Rhotpursuit

· #2 · 19 d ago

It goes to a hard plastic line that enters the cab by a bundle of wires. You've probably noticed that your HVAC doesn't work as it's supposed to.

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rojolobonm

Discussion Starter · #3 · 19 d ago

Rhotpursuit said:
It goes to a hard plastic line that enters the cab by a bundle of wires. You've probably noticed that your HVAC doesn't work as it's supposed

if it's a small diameter hard plastic line it's hooke up to that one, but thank you!

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rojolobonm

Discussion Starter · #4 · 19 d ago

Rhotpursuit said:
It goes to a hard plastic line that enters the cab by a bundle of wires. You've probably noticed that your HVAC doesn't work as it's supposed to.

Would you happen to know where the 2nd line goes to other than the hvac line? Thank You

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Racer-X

· #5 · 19 d ago

rojolobonm said:
Would you happen to know where the 2nd line goes to other than the hvac line? Thank You

The one line goes to intake manifold vacuum. One of the other lines goes into the cab, to the HVAC. The third goes to a vacuum reservoir ball. That could be hanging from the hood,or it could be inside the fender at the base of the A pillar.

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Rhotpursuit

· #6 · 19 d ago

Racer-X said:
The one line goes to intake manifold vacuum. One of the other lines goes into the cab, to the HVAC. The third goes to a vacuum reservoir ball. That could be hanging from the hood,or it could be inside the fender at the base of the A pillar.

His should be in the fender.

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hogster

· #7 · 19 d ago

just a "heads-up".....that "3 way conn" is also a check valve..if ya ever take the line off, remember the orientation

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rojolobonm

Discussion Starter · #8 · 19 d ago

hogster said:
just a "heads-up".....that "3 way conn" is also a check valve..if ya ever take the line off, remember the orientation

Thanks! I replaced the plugs, wires, cap and Rotor. I found that all 3 of the line had just disintegrated due to age. I found 2 out of 3,but the third willbe inside that fender. Could you throw me a bone and tell me which line goes to which leg correctly? Thank you

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hogster

· #9 · 19 d ago

rojolobonm said:
Thanks! I replaced the plugs, wires, cap and Rotor. I found that all 3 of the line had just disintegrated due to age. I found 2 out of 3,but the third willbe inside that fender. Could you throw me a bone and tell me which line goes to which leg correctly? Thank you

see Racer-x's post above

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Racer-X

· #10 · 19 d ago

rojolobonm said:
Could you throw me a bone and tell me which line goes to which leg correctly? Thank you

In your pic, the top connection on that has the check valve, and goes to the intake manifold vacuum port. The one pointed to the right and the one pointed down are interchangeable. Those hook up to the HVAC controls inside the truck and to the vacuum reservoir. Whichever way fits best will work.

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hogster

· #11 · 7 d ago

...dunno if this is of any value, but a while back I deleted this check valve n put an insert tee in its place, when I was tryin to narrow down a possible vac. leak....my AC system still works fine...However mine's a '00 S10 4.3, so dunno if there was a design/concept change btwn our years

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Racer-X

· #12 · 7 d ago

hogster said:
...dunno if this is of any value, but a while back I deleted this check valve n put an insert tee in its place, when I was tryin to narrow down a possible vac. leak....my AC system still works fine...However mine's a '00 S10 4.3, so dunno if there was a design/concept change btwn our years

The only issue you'll have with that is when you take off hard, with a lot of throttle opening, your HVAC vents will change to defrost, and when you let up on the throttle, it'll change back to whatever you hàve selected. Some folks find that annoying. The check valve prevents that.

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hogster

· #13 · 7 d ago

Racer-X said:
The only issue you'll have with that is when you take off hard, with a lot of throttle opening, your HVAC vents will change to defrost, and when you let up on the throttle, it'll change back to whatever you hàve selected. Some folks find that annoying. The check valve prevents that.

yep-that's the only thing I noticed that acted diff, like downshifts on hills and passing on an interstate, but I never bother'd to put the Ck. back in when I eventually found/fixed my vac. leak...never bother'd me as it was but a momentary thing...next time I'm @ the u-pick-it yard, I may grab one and replace, as I'm sure i didnt save the old one

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Racer-X

· #14 · 7 d ago

hogster said:
next time I'm @ the u-pick-it yard, I may grab one and replace, as I'm sure i didnt save the old one

There are inline (one in, one out) vacuum check valves available at reasonable prices at your local parts stores. Just sayin'. Stick that in the line going to the engine.

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