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Old 04-01-2024, 03:09 AM   #21
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I own a 1997 RT 170. My vent controls are not vacuum operated but the old style slide and cable controls that open and close gates.
Mike Bee
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Former 89 VW Westfalia
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Old 04-01-2024, 04:45 PM   #22
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Big leaks like those that would make you lose power up hill will probably show up all the time. A clogged catalytic converter makes you use more throttle to overpower the exhaust restriction and that will lower the vacuum. The backpressure in the exhaust will also bleed back into the intake manifold more than normal during the short period of time when the intake and exhaust valves are open, further dropping the vacuum available.
It sounds like you suspect a clogged catalytic converter rather than a leak at a vacuum hose -- is there any relatively easy way to check specifically for a clogged converter?
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Old 04-01-2024, 05:40 PM   #23
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It sounds like you suspect a clogged catalytic converter rather than a leak at a vacuum hose -- is there any relatively easy way to check specifically for a clogged converter?

AFAIK, the normal and best way is a pressure gauge on the exhaust between the engine and converter.


I think a less accurate way is with a vacuum gauge on the intake. It would be in the 18 inches range in neutral idling and when you rev the engine to moderately higher it should fall right away for a very short time and then recover to a bit more than the initial reading. Of course vacuum leaks could make it so you don't even get the initial 18 inches.


If the the vacuum is a little low or even OK isn't a really big deal but if it fall with engine speed it is likely the converter, I think.
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Old 04-01-2024, 07:08 PM   #24
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My cruise control works at level - when I go up hills it lags. And it might be that my AC vents swiitch on their own (from blowing forward to blowing through the defrost vents) especially when I am going up hill though I need to confirm that.

I would like to understand better, if anyone can explain it, what would be going on in the engine when going uphilll that causes these effects. That is, let's say that the cause is a break in a vacuum hose coming from the manifold -- what is happening in the engine when going uphill? I suppose it is trying to get more fuel, perhaps more air to burn it all? If so, how does that end up being a loss of power or switching vents. etc.?
Booster gave an excellent explanation for the vacuum issues. I have owned Mopar vehicles since I was a kid, and the A/C shifting vents was always an issue. I'm old enough to remember when the windshield wipers in my Ford ran off vacuum, and would do the same thing. Going uphill in a rain storm, the wipers would stop. Not just inconvenient, but dangerous.
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Old 04-02-2024, 03:08 PM   #25
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Hook up scanner, check for codes, check fuel trim for lean condition. Computer will attempt to richen a lean condition to compensate. It will not hold the setting and continuously adjusts fuel trim (fuel to air ratio). A bad Oxygen sensor will drive it crazy. As will vacuum leak (throttle body hoses/gasket). Disconnect one vacuum line at a time from throttle body until fuel trim stabilizes. Then proceed down the path of the one that made the difference. Y If computer is in default mode, it will reduce speed/power. Need to reset computer after fixing problem. Most cheepo readers can't do that. Troubleshoot.. Don't throw parts at it.
Bad guesses get expensive.
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Old 04-02-2024, 04:29 PM   #26
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Originally Posted by mik [email
mikgil@icloud.com[/email];153133]Hook up scanner, check for codes, check fuel trim for lean condition. Computer will attempt to richen a lean condition to compensate. It will not hold the setting and continuously adjusts fuel trim (fuel to air ratio). A bad Oxygen sensor will drive it crazy. As will vacuum leak (throttle body hoses/gasket). Disconnect one vacuum line at a time from throttle body until fuel trim stabilizes. Then proceed down the path of the one that made the difference. Y If computer is in default mode, it will reduce speed/power. Need to reset computer after fixing problem. Most cheepo readers can't do that. Troubleshoot.. Don't throw parts at it.
Bad guesses get expensive.

From the posts, I am assuming the OP doesn't have a good scanner and wouldn't know how to use anyway.


Your way is a good way, and how I would do it, but I have scanners and data loggers for our van and my Buick Roadmaster.


OP is kind of stuck with pulling and plugging vacuum lines, using ether or propane (not recommended) to find leaks, or buying a cheap vacuum gauge, it think.
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Old 04-05-2024, 07:36 PM   #27
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Thanks all for your very helpful suggestions! I think that this will take me a while to run down and diagnose, so now I am wondering how much damage I am likely to do to the engine if I drive the van in the meantime. I have an appointment that I can get to avoiding hills even though it is 100 miles or so, but perhaps I shouldn't drive at all until I get it fixed. What do you think?
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Old 04-05-2024, 08:07 PM   #28
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Thanks all for your very helpful suggestions! I think that this will take me a while to run down and diagnose, so now I am wondering how much damage I am likely to do to the engine if I drive the van in the meantime. I have an appointment that I can get to avoiding hills even though it is 100 miles or so, but perhaps I shouldn't drive at all until I get it fixed. What do you think?

it all depends on what the problem is. If it truly is a vacuum issue and it is hoses probably no damage, but if it a leaking intake manifold you can have only a few cylinders running lean and cause some heat issue and in the extreme maybe burn an exhaust valve.


If it is a clogged converter it may cause overheating to a degree and it is causing misses in the engine running you might get excess fuel washing down the cylinder walls, which causes extra wear.



If it is confirmed to be plugged before you go, you have nothing to lose by giving it a few hard raps with heavy hammer to try to break the grid inside it to clear a path. Not all have grid style, I think, but sometimes it will work and get you going.
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Old 04-08-2024, 06:12 PM   #29
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So, I took the doghouse off, changed the air filter, and had a look around. The air filter was very dirty so that definitely was very long overdue for a change, which I am sure will help.

From what I could see easily it looked to me that there is a relatively large diameter hose running from the side of the intake manifold (on the driver's side) to the brake master cylinder servo and a smaller diameter hose on the other side which splits off into two. Does that sound right for a 2000 Dodge van? Can I check the vacuum by, say, removing the hose running to the brake cylinder and attaching a gauge there?
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Old 04-08-2024, 07:06 PM   #30
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So, I took the doghouse off, changed the air filter, and had a look around. The air filter was very dirty so that definitely was very long overdue for a change, which I am sure will help.

From what I could see easily it looked to me that there is a relatively large diameter hose running from the side of the intake manifold (on the driver's side) to the brake master cylinder servo and a smaller diameter hose on the other side which splits off into two. Does that sound right for a 2000 Dodge van? Can I check the vacuum by, say, removing the hose running to the brake cylinder and attaching a gauge there?

The brake booster hose is pretty large and will be hard to get a good connection to many vacuum gauges which are made to hook up to the small lines.


If you want to check all the actually vacuum running things like the heater controls and accumulator, a handheld pump/tester works pretty well for most folks. You would hook it to the hose the goes to the engine after you pull it off the intake manifold. Pump it to pull vacuum and watch to see if it holds that vacuum or leaks down so pretty easy to see what is happening. If you put a tee in that line so you can put a short hose to intake manifold you would also be able to check the running vacuum to see if the intake or brake booster or the hose to it are leaking with the engine running. You won't be able to pump them to check however only a running engine vacuum reading.


Most every auto parts store will have something like this:



https://www.amazon.com/DURATECH-Auto...%2C152&sr=8-17
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