1998 Dodge Cummins Vacuum Diagram
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I didn't read through all 12 pages of this topic but I had the same issue. I checked every vacuum line and replaced every check valve in the system. Couldn't find it. I then took it to the Dodge dealer and they couldn't find it either. While I had it in getting the tires rotated, the mechanic there found the problem. There's a vacuum line running from the transfer case to the front differential. Somehow, a pin-hole leak was rubbed into this line causing the problems. Replaced it and no more probs.
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Thanks for the check valve advice, unfortunately I had to chase a few vacuum lines.
Found the cruise control line was really broken, thanks for that I. I would love to talk to the engineer that thought putting a fragile line like that under the battery was a good idea.
Checked the reservoir, held vacuum very well.
Checked the front CAD lines, and lines to transfer case all good.
Question, is there one line that acts like a breather? looks like a check valve with the end broken off.
And is anyone else running the Hughes FI Airgap intake manifold? Because I think that and the 50mm throttle body uses the vacuum quickly, and it still moves the vents to defrost on the big hills.
Anyone get a CAD delete for the front axle to free up some vacuum?
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Sorry if I missed it but after reading the whole thread, no one has said where they get the hard plastic vacuum hoses. Is this a dealer item or auto parts store. Can someone please tell me where to get it. I know a few guys put a hose over it but then I don't know what size that is ether. Thanks for any help as I need to replace the line from the T to the cruse control.
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Discussion Starter · #246 ·
Sorry if I missed it but after reading the whole thread, no one has said where they get the hard plastic vacuum hoses. Is this a dealer item or auto parts store. Can someone please tell me where to get it. I know a few guys put a hose over it but then I don't know what size that is ether. Thanks for any help as I need to replace the line from the T to the cruse control.
I honestly think you can go to any auto parts store and get vacuum hose. If you happen to have a piece of it that has broke off, you can take that in with you.
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ok, i've replaced both of the check valves from the firewall to the intake manifold, my air still goes to defrost, the blend door rattles around whenever i shut my driver door, and the a/c blower makes a racket whenever i turn it on the higher two fan speeds. i know the blower racket means probably time to replace the blower motor and blend door, just wondered how hard it was. is it accessible from underneath the dash without having to pull the dash out? as far as it still going to defrost, am i missing a check valve somewhere or am i just gonna have to start chasing vacuum hose? thanks for the help.
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I have replaced all check valves and even got a larger vacuum tank from hughes and mine still does it. I have chased all lines and hold vacuum. I have decided to eliminate any possibility of my engine not producing enough vacuum to keep the vent from going to defrost by ordering a electric vacuum pump. I found one on ebay for about $130 less than comp and summit racing, and its the same pump. I even went to the extent of chipping off the old grease in the back of the directional controls which a few holes were pluged up.
When I get the CAD for my front axle I will be pleased to rip out all those useless vacuum lines going to that actuator as well. I have also put a 50mm TB on top and I think that has had something to do with the vacuum loss so fast.
Correction, I may in fact have a intake manifold leak causing bad vacuum. If this is the case I will post an update, but I feel that the electric vacuum pump will help take that much more off the engine.
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Update; the shop I took it to really "fixed" my intake manifold gaskets a while back! Not only did I buy a bigger vacuum canister from hughes that I did not need, I spent money for services I did not receive, and I ended up doing the work correctly myself for $30. The shop used my old gaskets from hughes and RTV the from and rear of the intake manifold. Great work guys!
So in conclusion, if you have replaced the check valves, chased vacuum lines for leaks it is probably your gaskets that have blown. I will still install the vacuum pump i got for the brake booster in time. But word to the wise, DO NOT trust a shop you have spent thousands of dollars with in the past. take a day, and $30 and do it right. oh and my two cent, torque the friggen intake manifold bolts the way it says to in the Chilton manual. dont just torque them to 12 ft/lbs you will blow a gasket and have your vents go ape on you.
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i had the problem when going up hills or giving the truck gas while having the heat or a/c on it would switch over to defrost until releasing the gas. well, alot of guys on here said to change the valve at the t on the passenger side of the motor up by the firewall. well, i changed it and did not help. well, i finally found that there is also ANOTHER check valve on gas engines located on the manifold. I changed that and problem solved. works like a new one. so if you have changed the t valve and it did not correct it, i suggest trying to change the valve at the manifold. hope this helps anyone out that has this problem. i know it sure made me happy
Part # 4549209
updated. here is a pic of the valves so everyone can find them. cost (at dealer for me) was $3.91 each
UPDATE: picture of actual valve added.(Ram lovr)
Also, I did have cruise control problems when this part was bad. Would lose speed up hills and it would not correct itself.
This my be a dumb question but are both valves the same part #?
The one that is pictured is near the firewall, the one at the manifold is it the same valve?
Thanks
smokejumper
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yes all check valves are the same, not a dumb question. wish people would question some of this information
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Hi
You might want to check the vacuum chamber behind the right headlight it is used for cruse control and I HAVE CHECKED all the vacuum lines! That's how I found my feed hose was OFF and I too had on off air.Give it a shot it might pay off ,it did for me!
Myles
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Okay I finally fixed my problem.
I own a 1997 Dodge Ram 1500 SS/T 5.9L 360
Symptoms:The vacuum supply to the Heater A/C System may drop when accelerating or when speed control engages. This may cause the mode vacuum motor to switch to the defrost position, in my case it switched to my heater vents.
I changed both check valves, the one near the firewall and the one at the intake manifold passenger side, problem persistent. Now there is a vacuum line that runs with the accelerator cable over to the speed control servo, (which controls your cruise control), which is located under the battery tray, I removed my battery tray to get access to the speed control servo and found that the vacuum line had broken off at the rubber (L) shaped elbow, pulled the hard plastic piece out and pushed in the end of the vacuum line where it had broke reinstalled everything, drove down the road and cruise control works and a/c stays on front vents (FIXED).
I hope this helps, here our some pictures.
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great
Glad My problem was your problem.
it took me forever to find the vavuun ball for the speed control but the many friends here helped me track it down too!
Know you know where to look as i did!Nice to have steady air,heat too!
Myles
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i just got my check valves yesterday. is their a certin way these have to go I didnt notice any arrows on them or anything. i know i can blow one way through them how do they mount????
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Just a FYI for anyone who doesnt have a Dodge dealer nearby. I found this at a local Pep Boys, but most "chain" parts stores carry a lot of Help brand products. It was $4.99 -
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Replaced checkvalve by manifold and still didnt cure it. Found leak on toothpick size line going into fire wall. Duct-taped it and all working fine now, even cruise control.
Also those "help" checkvalves from auto parts stores dont fit. One side is way to small to accept size line.
'
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I paid $6.85 including tax for the check valve at the Dodge dealer today (P/N = 4549209). Fixed my ac vent switching problem. My check valve was definitely leaking. Could this leaky check valve also cause problems with the transfer case on a 4wd truck? The vacuum diagram shows this vacuum line driving the ventilation system, cruise control and the transfer case switch.
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Old Bettsey,
Keep in mind your motor draws air into it. They only mount one way with air being able to be drawn into the engine.
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Posted by: donnieholckss.blogspot.com
Source: https://www.dodgetalk.com/threads/goes-to-defrost-fixed.189564/page-13
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