Having an issue with my 350 TBI. The vehicle is actually not my bird, but happening to my 1995 G20 Van. I figured it was a similar platform to our 305/350 TBI cars so I was hoping you all could help.
What's happening: When I hit highway speeds (60+) I lose the air to my vents. It goes to the dash and floor. It happens weather or not I have AC on or just economy air. When I let up off the gas it returns, but does the same when I re-accelerate up to those speeds.
I've searched hard for this issue and most people are saying that it's a vacuum issue somewhere on the engine. I pulled the doghouse and used a carb cleaner around every hose I saw and no idle change or effect on the engine idle. I haven't tried anything else.
Is there something other than a vacuum leak that could cause this?
Probably a split vacuum hose somewhere. If it was far enough from the intake, the carb cleaner might never reach the intake in a quantity necessary to increase the idle. Or, the issue could be close to the switch side. But I do agree, it seems like a vacuum line issue.
I ordered a Vacuum check valve, be here tomorrow. Going to swap that and test. If the problem persists I'm going to increase my efforts to find any breaks, cracks, splits in vacuum lines. Appreciate the replies! I'll let you know!
So, I'm cracking the engine case open today, tomorrow I replace that vacuum valve, and I just want to be ready. I noticed that the valve I have has one port capped off. Pictures I have seen in other applications, such as this image here of a 94 G20, has a hose connected to the bottom of the "T" valve. Look below at my attached image to see that mine is capped (the small white valve). Is this for the brake booster? I know that some applications use a vacuum line to the BB..
Normally the thing goes to the engine, the ac vacuum system, and the "orb of power" aka the vacuum reserve canister.
Okay. Looks like mine just connects to the intake manifold and then to the almighty orb, and I guess the ac is capped for whatever reason. I am not original owner, bought the van months ago, so I don't know if this was changed by previous owners or if this is something that changed from 94 - 95. 1995 is the last year of production for the G series vans. 1996 is when the vortec change occurred, I believe...
I'll swap in the new valve tomorrow, keep this line capped, and see if I can get a fix in. Thanks for the help, I'll update tomorrow.
hmmm if theres no line going to the ac though... then the vacuum ac wouldn't operate? try look for the line that goes to the ac and see where that goes
According to the diagram below (1st pic), #45 is the AC vacuum hose that is splitting off from the Great Orb vacuum line, which btw is fed from the original picture I posted, the line coming off the valve.
Look at my application (the second pic) and you'll see a smaller white-ish line splitting off and disappearing behind the firewall/wiring harness. The line goes into the firewall toward the driver, which I assume is going to the AC controls. Is that correctly where you meant the vacum line should go to the AC?
So, replacing the small check valve in my first pic (OP) did not fix the issue. If anything, I feel like it's slightly getting worse. I consistently lose air from the vents down to my feet and dash as I approach 60 mph. At 65 mph I have almost no air to the vents, and it's all to the floor and windshield. I also feel like it is lacking power when it does this.
I tried the smoke method, but I am not sure I am doing it 100% correctly. I used a cigar, blew smoke into the hose that travels from the Ball, into the manifold. When I did this the smoke exited the intake manifold up where the injectors are through a small hole (that is supposed to be there).
I am unsure of where to attempt the smoke method and which other hoses I should check. Any behind the dash that could cause this issue? I hope not, because the dash is extremely tough to get out. >.<
Im a little confused...The picture of the actual engine bays is yours right?
So you have two areas of interest,,, the first pic with the check valve, and the second with the 'orb? So,,, the vacuum line goes from the manifold, to the 3 way valve with the cap, and from that valve, the line goes to the orb" in your second pic right?
Tru check first thing that al lyour connections are tight... I find the hose on the orb likes to work its way loose at times.
Im a little confused...The picture of the actual engine bays is yours right?
So you have two areas of interest,,, the first pic with the check valve, and the second with the 'orb? So,,, the vacuum line goes from the manifold, to the 3 way valve with the cap, and from that valve, the line goes to the orb" in your second pic right?
Tru check first thing that al lyour connections are tight... I find the hose on the orb likes to work its way loose at times.
Correct, the line goes from the back of the manifold near the dist, up into the 3-way (capped) valve (that I replaced). It then runs forward to the small engine bay and splits, one line going to the ball, the other (the thin, white line) going into the firewall (assuming that goes to to the AC head unit?).
Correct, the line goes from the back of the manifold near the dist, up into the 3-way (capped) valve (that I replaced). It then runs forward to the small engine bay and splits, one line going to the ball, the other (the thin, white line) going into the firewall (assuming that goes to to the AC head unit?).
I'll check those connections.
Perhaps a line from the manifold straight to the check valve wiould be better? Eliminate the extra connection and that plastic Y by the orb... so just put the valve closer to the orb... it'll eliminate connections and potential breaks and porvide better vacuum I imagine? Id try that if you find no leaks.
Update: Still working on this. Not able to move fast on it. Pulled the AC control assembly in dash and checked the valve (it uses vacuum from engine to swap the modes) and it looked to be worked on by the previous owner with failed attempt at fixing. I'm not sure if this is what's causing the issue, but I'm going to just buy a new AC control assembly that'll come with the control valve.
this should be interesting.. .i wonder if at higher speeds you naturally lose some vacuum... and the valve by the engine keeps your ac working.. but if theres a leak by the controls, then that vacuum would also be lost
this should be interesting.. .i wonder if at higher speeds you naturally lose some vacuum... and the valve by the engine keeps your ac working.. but if theres a leak by the controls, then that vacuum would also be lost
The vacuum ball stores vacuum to keep the control servos in their position during periods of low engine vacuum. Check valve prevents air from entering from the manifold. Unless the engine is seriously under performing it should have plenty of vacuum at 65 or even 85 mph. Low fuel pressure, retarded ignition timing or a plugged cat could be causing the vacuum to fall off.
I have a 94 G30 van that has been converted to a camper that is doing the same thing. The vents worked great until 2 weeks ago. Mine started doing this exact thing and I just haven't had time to look into it, so I'm watching this closely.
The vacuum ball stores vacuum to keep the control servos in their position during periods of low engine vacuum. Check valve prevents air from entering from the manifold. Unless the engine is seriously under performing it should have plenty of vacuum at 65 or even 85 mph. Low fuel pressure, retarded ignition timing or a plugged cat could be causing the vacuum to fall off.
That's great information. Two of those (exhaust and fuel) I know are already problematic on the van. The exhaust pipe after the cat and before the muffler is extremely rusted and all the exhaust pretty much leaks out before the muffler, so it makes me think there might be a cat issue. Also, the fuel sending unit is out (gas gauge doesn't work and already tested the gauge), so that might also be an issue. I have both issues targeted in the near future.
I'll knock out one at a time and report back on any changes.
I have a 94 G30 van that has been converted to a camper that is doing the same thing. The vents worked great until 2 weeks ago. Mine started doing this exact thing and I just haven't had time to look into it, so I'm watching this closely.
Check Fast355's reply.. is any of these an issue on your van? Maybe we have an overlap that'll single something out.
The vacuum ball stores vacuum to keep the control servos in their position during periods of low engine vacuum. Check valve prevents air from entering from the manifold. Unless the engine is seriously under performing it should have plenty of vacuum at 65 or even 85 mph. Low fuel pressure, retarded ignition timing or a plugged cat could be causing the vacuum to fall off.
Second thought, the engine is actually underperforming at higher speeds. I feel like I have decent acceleration, if slightly sluggish pedal response, but at 55mph+ I have to press the gas to drop gears just to accelerate past 60 often times. I guess this could be clogged cat bogging down air flow?
Second thought, the engine is actually underperforming at higher speeds. I feel like I have decent acceleration, if slightly sluggish pedal response, but at 55mph+ I have to press the gas to drop gears just to accelerate past 60 often times. I guess this could be clogged cat bogging down air flow?
Mine had similar issues, where I had to go WOT to just get up hills without loosing 10+ mph. In the past 2 weeks I have pulled the TBI off a went to a carb. I have not drove it since in weather warm enough to need the AC. I will try to drive it this weekend to see it the issue is still there after removing the TBI.
UPDATE: I cut off the exhaust from the headers back (removing the cat) and ran straight 3" pipe from the Y-Pipe to the rear axle (this is temporary btw). This seems to have solved the issue almost completely. I drove about 50 miles, mostly highway. Air blows hard from vents no matter what speed or how hard I accelerate. Some power came back at higher speeds. No need to drop gears just to increase speed from 55mph+ up to whatever. I still feel like there should be more power from this old 350, but that might be a different issue.
The main point is, after removing the cat this solved the original issue I posted here. File this as solved for now. If I chase down the power loss I'll make a different thread with more details if necessary. Hope this helps others!
Added: Thanks to all those who replied and prompted me forward! Big shout-out to Fast355 for nailing the issue above!
