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Old 03-25-2024, 12:52 AM   #1
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Default losing power uphill

Apologies if this is not the right forum for this question, but my 1999 RT 170 all of a sudden today started losing power uphill. I couldn't get it above 10 or 15mph but it did keep creeping up the hills to get me home eventually. My first thought was problems with the transmission, but it is working on straightaways -- it seems to be shifting gears fine and I can turn off overdrive on downhills and hear it downshift. And it is starting up and running normally otherwise and no engine lights are on. Any thoughts on what else might cause such a thing?
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Old 03-25-2024, 03:36 PM   #2
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Clogged Fuel Filter, failing Fuel Pump, dirty Air Filter, faulty mass airflow sensor to name a few things to check out. Other things could be ignition related. Bad spark plugs and /or bad spark plug wires.
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Old 03-25-2024, 05:50 PM   #3
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Apologies if this is not the right forum for this question, but my 1999 RT 170 all of a sudden today started losing power uphill. I couldn't get it above 10 or 15mph but it did keep creeping up the hills to get me home eventually. My first thought was problems with the transmission, but it is working on straightaways -- it seems to be shifting gears fine and I can turn off overdrive on downhills and hear it downshift. And it is starting up and running normally otherwise and no engine lights are on. Any thoughts on what else might cause such a thing?
You don't say what altitude you are at when the van loses power. The mountains, of course, are always a problem above 7,000 feet or so. If it isn't that, I'd check your vacuum system hoses. A number of years ago, I had to replace most of the vacuum hoses on my 1997 Dodge when I had similar issues. The other symptom you might see is that your cruise control doesn't work, or the heater/AC controls don't work well.
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Old 03-25-2024, 07:23 PM   #4
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Clogged Fuel Filter, failing Fuel Pump, dirty Air Filter, faulty mass airflow sensor to name a few things to check out. Other things could be ignition related. Bad spark plugs and /or bad spark plug wires.
Thanks! It is true that the air filter hasn't been changed for a very (very!) long time, so that at least is easy enough to fix.

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You don't say what altitude you are at when the van loses power. The mountains, of course, are always a problem above 7,000 feet or so. If it isn't that, I'd check your vacuum system hoses. A number of years ago, I had to replace most of the vacuum hoses on my 1997 Dodge when I had similar issues. The other symptom you might see is that your cruise control doesn't work, or the heater/AC controls don't work well.
Thanks again! I am in upstate NY so its pretty hilly but we don't go nearly that high -- google maps lists the hill I was struggling up at 2200 feet. But my vacuum hoses have been leaking for years. My cruise control and heater/AC controls never worked great, the cruise controls lags going uphill (when I used to be able to go uphill easily, that is!) and the AC switches vents on its own somethimes. But I wonder how the vacuum hoses could effect my power going uphill without the cruise control?
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Old 03-26-2024, 07:35 PM   #5
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Thanks! It is true that the air filter hasn't been changed for a very (very!) long time, so that at least is easy enough to fix.



Thanks again! I am in upstate NY so its pretty hilly but we don't go nearly that high -- google maps lists the hill I was struggling up at 2200 feet. But my vacuum hoses have been leaking for years. My cruise control and heater/AC controls never worked great, the cruise controls lags going uphill (when I used to be able to go uphill easily, that is!) and the AC switches vents on its own somethimes. But I wonder how the vacuum hoses could effect my power going uphill without the cruise control?
You are losing vacuum at the engine intake manifold. Loss of vacuum means loss of power. The engine will idle ok, but won't perform correctly. The fuel/air ratio is never what it should be in this case.
On my Dodge, the vacuum accumulator is located in the right front fender. Don't overlook this item when replacing vacuum hoses.
The fact that the cruise control and A/C controls don't work are symptoms, not the cause of vacuum loss.
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Old 03-26-2024, 10:13 PM   #6
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The fact that the cruise control and A/C controls don't work are symptoms, not the cause of vacuum loss.
I would not make that assumption when dealing with 25 year old rubber and plastic bits.

25 year old rubber and plastic parts, what could go wrong?
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Old 03-27-2024, 02:46 PM   #7
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A number of years ago, I had to replace most of the vacuum hoses on my 1997 Dodge when I had similar issues. The other symptom you might see is that your cruise control doesn't work, or the heater/AC controls don't work well.
TomF - Do you have any tips on replacing these hoses for a Dodge 2500 van? I did a quick search for parts and nothing came up. Did you just purchase generic rubber hoses and run them to replace the existing ones (also, how many hoses are there and how do they run?). I guess the "vacuum accumulator" is a model-specific part I can find somewhere? Also, I remember hearing that there are small plastic "valves" of some sort in the vacuum system--did you have/replace these?
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Old 03-27-2024, 05:13 PM   #8
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If you do have a low vacuum issue (best to buy a cheapo vacuum gauge to find out for sure before wasting time) there is also a very good chance it is an intake manifold leak, usually on the rear for most V8 engines. Capping off vacuum lines one at a time can often determine which on is bad and if all get capped and it still shows low vacuum it would be time to check the intake for leaks.
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Old 03-27-2024, 06:05 PM   #9
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If you do have a low vacuum issue (best to buy a cheapo vacuum gauge to find out for sure before wasting time) there is also a very good chance it is an intake manifold leak, usually on the rear for most V8 engines. Capping off vacuum lines one at a time can often determine which on is bad and if all get capped and it still shows low vacuum it would be time to check the intake for leaks.
I am guessing that the two possible causes of an intake manifold leak are either a bad gasket or a cracked manifold?

I fear I don't know very much about the vacuum system in my van: are the "vacuum lines" just rubber hoses that run from the intake manifold to various mechanical systems that use the engine's vacuum as kind of a power source? Or do they serve other purposes?
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Old 03-27-2024, 07:06 PM   #10
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I am guessing that the two possible causes of an intake manifold leak are either a bad gasket or a cracked manifold?

I fear I don't know very much about the vacuum system in my van: are the "vacuum lines" just rubber hoses that run from the intake manifold to various mechanical systems that use the engine's vacuum as kind of a power source? Or do they serve other purposes?
Yes, a bad gasket or cracked manifold are possible causes for a vacuum leak, but not likely. In my experience these Mopar engines are robust and reliable.
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Old 03-27-2024, 07:10 PM   #11
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I am guessing that the two possible causes of an intake manifold leak are either a bad gasket or a cracked manifold?

I fear I don't know very much about the vacuum system in my van: are the "vacuum lines" just rubber hoses that run from the intake manifold to various mechanical systems that use the engine's vacuum as kind of a power source? Or do they serve other purposes?
Yes, the vacuum lines are rubber hoses that use the engine's vacuum as a power source for the cruise control and heater/AC controls, along with engine timing, etc. They have thick walls that will not collapse under a vacuum, and can be purchased at any Auto Zone or other supply house. They have specific diameters, so bring a sample with you.
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Old 03-27-2024, 07:16 PM   #12
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There have been other good suggestions here. By all means, put a vacuum gage on the manifold, and change the air filter. My suggestion is based on many years of experience with Mopar engines. In any case, the deteriorated vacuum hoses need to be addressed. Good luck.
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Old 03-28-2024, 02:57 PM   #13
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There have been other good suggestions here. By all means, put a vacuum gage on the manifold, and change the air filter. My suggestion is based on many years of experience with Mopar engines. In any case, the deteriorated vacuum hoses need to be addressed. Good luck.
Thanks again Tom! Just one last question: I came across the attached image that was labeled as the vacuum system of a van of this era. Did you replace all of these various hoses, the check valve, and the resevoir/accumulator? It doesn't looks like it would be too difficult, but it would be a very aggravating job tracing all those hoses!
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File Type: png dodge-vacuum-lines-1.png (27.5 KB, 10 views)
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Old 03-28-2024, 07:12 PM   #14
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Thanks again Tom! Just one last question: I came across the attached image that was labeled as the vacuum system of a van of this era. Did you replace all of these various hoses, the check valve, and the resevoir/accumulator? It doesn't looks like it would be too difficult, but it would be a very aggravating job tracing all those hoses!
I didn't replace any components, just the hoses that needed to be replaced. I started at the engine and worked my way to the firewall where the hose goes into the cabin. The main hose from the manifold was broken, along with some of the smaller hoses at the firewall. Then I traced the hose along the firewall to the accumulator, and found that hose was broken at the accumulator. All in all, massive vacuum leaks. After replacing the hoses, the engine ran better, and the cruise control started working again.
When you buy the new hose, get a bag of the little plastic connectors to tie in all the new hoses.
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Old 03-30-2024, 01:41 PM   #15
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Hopefully, the hoses repairs should fix your problemes but if you still have power issues going uphill check you catalytic converter. A dying (clogged) converter will surely induce power loss going uphill , but would still allow you to cruise on flat ground.
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Old 03-30-2024, 06:23 PM   #16
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Hopefully, the hoses repairs should fix your problemes but if you still have power issues going uphill check you catalytic converter. A dying (clogged) converter will surely induce power loss going uphill , but would still allow you to cruise on flat ground.
Good point. My converter started making rattling noises quite a few years ago, indicating the innards were deteriorating. Eventually, the rattling stopped, and I never lost power, so I assume I now have a restriction free exhaust system.
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Old 03-30-2024, 09:46 PM   #17
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Good point. My converter started making rattling noises quite a few years ago, indicating the innards were deteriorating. Eventually, the rattling stopped, and I never lost power, so I assume I now have a restriction free exhaust system.

If the converter is plugged normally you might lose vacuum at full throttle but not at level cruise so I would think the cruise and heater would work.
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Old 03-31-2024, 04:27 PM   #18
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We have a 2000 RT 190, basically the same dodge van, find a good mechanic who likes Dodges, our experience has been that the ECM is a weak link between these vans and a dependable van, it has been replaced twice, once because it would not go into OD, went right in with a "new" ecm, second time it died on I91 near Brattleboro, a mechanic in Putney VT pulled the rabbit out of the hat, the ecm was not sending a 5v signal to the engine so it would not run.
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Old 03-31-2024, 07:17 PM   #19
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If the converter is plugged normally you might lose vacuum at full throttle but not at level cruise so I would think the cruise and heater would work.
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.?
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Old 03-31-2024, 10:23 PM   #20
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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.?

When you have low load and decent rpm, you get high vacuum in the intake manifold to feed the heater controls and cruise control.


When you go up hills and require more power, you open the throttle plates to let in more air to make the power and that lowers the intake manifold vacuum. Low vacuum makes those items quite working and spring back to their no vacuum positions. Small leaks might cause problems at full throttle but not and lower throttle positions. 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.
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