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chevy g30 motorhome issues

Old June 14th, 2012, 8:37 AM
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CAP
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Default chevy g30 motorhome issues

hello, I have a 1983 chevy motorhome ' the engine is spiratic goin up hills. the van lurches forward with failing power . It stalls easily when accelerating and decelerating . It is actual everytime you accelerate it acts like it is going to stall. I have done the basic change of spark plugs, octane booster ,and carb cleaner. I would like some help with what may be wrong. I am prob going to check fuel pump. The motorhome has a carburator and is a 350 cu in.
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Old June 14th, 2012, 9:26 AM
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if you do a brake torqe ,does it miss,under a load.im thinking plug wires.
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Old June 14th, 2012, 11:18 PM
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Check the obvious stuff first, like: making sure the air cleaner can breath (flapper valve stays open, filter isn't filthy), the choke is not stuck closed, plugs and wires are solid, distributor cap is tight, engine isn't consuming large quantities of oil, fuel isn't 8 years old, fuel filter isn't clogged, etc.


Then, check every vacuum connection and hose you can trace.

You'd be amazed at what a vacuum leak can do to kill performance on '79+ smogged-up small blocks.

Primary concerns / hit list:
(I know there's a lot here, but these engines had a lot of vacuum-dependent equipment. It's all part of the same system. Yours may differ slightly, but the basics are the same.)

Before digging into the list, just do a quick inspection of every port on the carb. Make sure the connections are good, and the hoses are not cracked, dry rotted, spongey, or otherwise deteriorated. If you find anything that is at all suspect, replace it. You'll need about 25-30 feet of 5/32" hose and a few feet of 7/32", if you replace everything. It wouldn't hurt to replace any 'T', 'Y', or straight connector that seems damaged, either.

1. There should be a vacuum line coming from an open (not switched) port on the back, top of the intake (with an automatic tranny, this is where your tranny modulator line should come off, too). It should be connected to the EGR valve and vacuum advance on the distributor, along with a 'T' fitting that should go to the air cleaner. If there is ANY problem with those hoses or the connections, you'll have issues. This one is double-edged. If you have a leak in anything on these ports, your distributor may not advance properly (timing issues), and you still have a vacuum leak causing other problems.

2. Make sure the EGR diaphragm is not torn or rotten. It creates a massive vacuum leak.

3. Make sure the evaporative emissions system is connected properly (including vapor hoses and vacuum hoses). OR, make sure the port on the front of the carb is plugged, so it doesn't create a vacuum leak. It should be the large port on top, at the front of the carb.
---Use the procedure described in #7 for replacing the rubber boots for the 'gang' connections on the charcoal canister, if they're deteriorated.

4. Go back to the air cleaner. Inspect the hoses on it and the Thermac switch (make sure it's not broken), to make sure you have no vacuum leaks. Then, disconnect the hose and see if you can pull a vacuum on the hose to the flapper valve in the snorkel (use your mouth, if you don't have a vacuum pump). It doesn't matter if the valve doesn't move. You just want to make sure the valve stays open (default position, unless it got stuck), and doesn't have a vacuum leak. If it leaks, just cut and plug the hose close to where it comes out of the Thermac switch.

5. Make sure the PCV system is connected to the large port on the front of the carb base plate (not the port on top), and that the PCV system doesn't have any bad connections, cracked hoses, or hoses that are not connected. (You may have to trace a few hoses farther than expected. The layout varied by year, so I can't be specific on equipment, connections, or locations.)

6. Make sure the choke pull off actuator on the carb does not have a bad hose running to it. This is a short little guy, from a port on the carb, that is often ignored by mechanics, because it's a pain to change without removing the actuator (which isn't actually very hard). Check the actuator for a damaged diaphragm by starting the engine, and watching for the arm to be pulled into the body of the actuator. All you need is about 3/8"-1/2". If it moves, it's good.

7. There will be somewhere between 4 and 12 vacuum connections on the front of the intake. These are should all be "gang" connections, where the vacuum hoses are molded into a single rubber boot that connects to the ports. The ports themselves are on thermal switches/valves. They don't actually have a vacuum source here. However, those rubber boots rot very quickly, and are a major cause of leaks. If yours appear to be deteriorated, they need to be removed. First, take pictures and make note of exactly where each line connects to the ports (they go straight through the boots, no crossovers or anything funky). Then, cut the boots off, and replace the lines one at a time, out to the next connection they make ('T's, 'Y's, check valves, switches, where ever they may go). Be sure to clean any connection, before sliding the new vacuum hose on. I know it's tight and dirty in this area, but it's worth the trouble.

8. Take a really close look at all of the plastic check valves in the mess of vacuum hoses that you just dealt with. Cracked, melted, or broken valves need to be replaced. One of the hoses coming from here connects to a hard line than runs down the left side on top of the intake. Be sure to check that connection.

9. Go back to the carb, and retrace every connection and every line. You missed a few. Be sure you make it all the way to the vacuum reservoir, the diverter valves (backfire valves) in the air injection system, the heater box (there's an actuator there), and anything else that looks to have a vacuum line attached.

10. Check the short pieces of vacuum line that connect to the hard lines for the transmission modulator, and valve under the left exhaust manifold. While you're there, make sure the valve moves freely. If it's stuck closed, or partially closed, performance will suffer. (And you'll be forcing excess exhaust into the intake, when you want it the least.)

11. If equipped, check the diverter/backfire valves for cracks. (Identified by: large hose from air pump, large hose to air injection manifolds, medium hose to air cleaner, one electrical connection, one vacuum hose.) Cracks in the plastic housing can cause vacuum leaks. If they're cracked, they need to be replaced or disabled (and the vacuum line plugged or removed by replacing the 'T' it comes off of with a straight connector).


I know that's a lot, but that's the vacuum system.

With all of that typed out, it's a little more obvious how dependent the engine is on vacuum, eh?

Last edited by Squigie; June 14th, 2012 at 11:39 PM. Reason: Forgot a couple things / edited for clarity.
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Old June 15th, 2012, 8:29 AM
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Originally Posted by hucks 66 View Post
if you do a brake torqe ,does it miss,under a load.im thinking plug wires.
well, i can get the tires to spin in the grass but I havent tried on the pavement yet
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Old June 15th, 2012, 8:31 AM
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thanks for this , info I will see what I can do
Originally Posted by Squigie View Post
Check the obvious stuff first, like: making sure the air cleaner can breath (flapper valve stays open, filter isn't filthy), the choke is not stuck closed, plugs and wires are solid, distributor cap is tight, engine isn't consuming large quantities of oil, fuel isn't 8 years old, fuel filter isn't clogged, etc.


Then, check every vacuum connection and hose you can trace.

You'd be amazed at what a vacuum leak can do to kill performance on '79+ smogged-up small blocks.

Primary concerns / hit list:
(I know there's a lot here, but these engines had a lot of vacuum-dependent equipment. It's all part of the same system. Yours may differ slightly, but the basics are the same.)

Before digging into the list, just do a quick inspection of every port on the carb. Make sure the connections are good, and the hoses are not cracked, dry rotted, spongey, or otherwise deteriorated. If you find anything that is at all suspect, replace it. You'll need about 25-30 feet of 5/32" hose and a few feet of 7/32", if you replace everything. It wouldn't hurt to replace any 'T', 'Y', or straight connector that seems damaged, either.

1. There should be a vacuum line coming from an open (not switched) port on the back, top of the intake (with an automatic tranny, this is where your tranny modulator line should come off, too). It should be connected to the EGR valve and vacuum advance on the distributor, along with a 'T' fitting that should go to the air cleaner. If there is ANY problem with those hoses or the connections, you'll have issues. This one is double-edged. If you have a leak in anything on these ports, your distributor may not advance properly (timing issues), and you still have a vacuum leak causing other problems.

2. Make sure the EGR diaphragm is not torn or rotten. It creates a massive vacuum leak.

3. Make sure the evaporative emissions system is connected properly (including vapor hoses and vacuum hoses). OR, make sure the port on the front of the carb is plugged, so it doesn't create a vacuum leak. It should be the large port on top, at the front of the carb.
---Use the procedure described in #7 for replacing the rubber boots for the 'gang' connections on the charcoal canister, if they're deteriorated.

4. Go back to the air cleaner. Inspect the hoses on it and the Thermac switch (make sure it's not broken), to make sure you have no vacuum leaks. Then, disconnect the hose and see if you can pull a vacuum on the hose to the flapper valve in the snorkel (use your mouth, if you don't have a vacuum pump). It doesn't matter if the valve doesn't move. You just want to make sure the valve stays open (default position, unless it got stuck), and doesn't have a vacuum leak. If it leaks, just cut and plug the hose close to where it comes out of the Thermac switch.

5. Make sure the PCV system is connected to the large port on the front of the carb base plate (not the port on top), and that the PCV system doesn't have any bad connections, cracked hoses, or hoses that are not connected. (You may have to trace a few hoses farther than expected. The layout varied by year, so I can't be specific on equipment, connections, or locations.)

6. Make sure the choke pull off actuator on the carb does not have a bad hose running to it. This is a short little guy, from a port on the carb, that is often ignored by mechanics, because it's a pain to change without removing the actuator (which isn't actually very hard). Check the actuator for a damaged diaphragm by starting the engine, and watching for the arm to be pulled into the body of the actuator. All you need is about 3/8"-1/2". If it moves, it's good.

7. There will be somewhere between 4 and 12 vacuum connections on the front of the intake. These are should all be "gang" connections, where the vacuum hoses are molded into a single rubber boot that connects to the ports. The ports themselves are on thermal switches/valves. They don't actually have a vacuum source here. However, those rubber boots rot very quickly, and are a major cause of leaks. If yours appear to be deteriorated, they need to be removed. First, take pictures and make note of exactly where each line connects to the ports (they go straight through the boots, no crossovers or anything funky). Then, cut the boots off, and replace the lines one at a time, out to the next connection they make ('T's, 'Y's, check valves, switches, where ever they may go). Be sure to clean any connection, before sliding the new vacuum hose on. I know it's tight and dirty in this area, but it's worth the trouble.

8. Take a really close look at all of the plastic check valves in the mess of vacuum hoses that you just dealt with. Cracked, melted, or broken valves need to be replaced. One of the hoses coming from here connects to a hard line than runs down the left side on top of the intake. Be sure to check that connection.

9. Go back to the carb, and retrace every connection and every line. You missed a few. Be sure you make it all the way to the vacuum reservoir, the diverter valves (backfire valves) in the air injection system, the heater box (there's an actuator there), and anything else that looks to have a vacuum line attached.

10. Check the short pieces of vacuum line that connect to the hard lines for the transmission modulator, and valve under the left exhaust manifold. While you're there, make sure the valve moves freely. If it's stuck closed, or partially closed, performance will suffer. (And you'll be forcing excess exhaust into the intake, when you want it the least.)

11. If equipped, check the diverter/backfire valves for cracks. (Identified by: large hose from air pump, large hose to air injection manifolds, medium hose to air cleaner, one electrical connection, one vacuum hose.) Cracks in the plastic housing can cause vacuum leaks. If they're cracked, they need to be replaced or disabled (and the vacuum line plugged or removed by replacing the 'T' it comes off of with a straight connector).


I know that's a lot, but that's the vacuum system.

With all of that typed out, it's a little more obvious how dependent the engine is on vacuum, eh?
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Old June 15th, 2012, 8:36 AM
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also theres no problem idleing,just moving. I did have to drive it to the gas station when I first got it. so I may have been running on old gas for 10-15 minutes on the highway, what damage could that have done
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Old June 15th, 2012, 5:02 PM
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Originally Posted by CAP View Post
also theres no problem idleing,just moving. I did have to drive it to the gas station when I first got it. so I may have been running on old gas for 10-15 minutes on the highway, what damage could that have done
If it sat for several years with a bad fuel cap, it can let quite a bit of moisture into the tank. Not only is it hard to make an engine run on water, but it can cause a lot of rust scale to build up in the fuel tank.

When you drive it again (and/or fill it up) fuel sloshes around and stirs up the scale, which can clog filters and fuel lines. In extreme cases (especially if you have a damaged screen on the pickup in the tank), it can damage the fuel pump.

Don't change the pump, unless you verify that it actually has a problem, though. The fuel pump isn't exactly easily accessible on these vans. If the fuel pump piston slides out of position when the old pump is removed, it can be difficult to get it back where it belongs, without removing the accessories in front of it, at a minimum.

Is there smoke coming out of the exhaust at all?
Idle, cruising, accelerating, or decelerating?
Black, blue, or white?
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Old June 16th, 2012, 5:21 AM
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Originally Posted by CAP View Post
well, i can get the tires to spin in the grass but I havent tried on the pavement yet
im not talking about spinning the tires,just foot on brake and give it a little gas and see if its missing under a load,if so most likely wires
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Old June 21st, 2012, 8:33 AM
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still no luck, do you think it could be a EGR carbon build up,i willl check it today,not sue where it is though, I have some new ignition cables coming today, so maybe that will do it
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Old July 28th, 2012, 9:12 AM
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Fuel filter was the problem on my 90 GMC pickup. Same symptoms.
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