Is Cruise Control MPH loss normal?

[Zorlock]

Good evening gentlemen,

I think this may be another vacuum isssue of some type, but I'm not sure where to check for it. My ride is a 2002 B1500 Elkie conversion with a 318/5.2l.

You guys helped me out a few weeks back with the check valve issue that was allowing my climate control vents to randomly switch on their own. I went to my Dodge dealer and ordered that check valve today, should be here Wednesday...if they got the right part that is. So, I'm on the road to fixing that glitch.

Now, next annoying glitch I need assistance with:

I turn the cruise control on while on the freeway, I can set it at a chosen MPH and the 'cruise' light goes on on the dash. It works pretty good, until there is a hill of any type. Then it begins losing MPH's, slowly. The cruise stays on, but the MPH keeps decreasing as the hill continues. It does not ever compensate for the drag by adding more gas pedal or shifting into a lower gear, it just lets itself lose ground slowly. If the road levels out again, it will catch back up to itself eventually.

But the cruise control in my 96 Dakota (318/5.2l) always kept that truck spot onto the speed I chose. This van seems to think it's some arbitrary performance I am looing for.

Is this being cause by another vacuum issue? Can you guys help shed some light on where I need to look to address this problem at the same time that I have everything apart to replace that check valve?

thanks,
Dominick

[Dodgevanman]

On my '94 it will lose up to about 5mph on a hill, but the transmission will downshift to compensate.

Gotta remember that a conversion van is much heavier than a Dakota, so the drivetrain has to work harder to keep the speed up...you will lose speed on a hill.

How much speed do you lose?

[Zorlock]

How much speed do you lose?

Well, if I let the slide continue without intervening with my foot pushing down the gas pedal manually, 10, 15, 20 MPH will be lost. It depends how long a hill or rise it is trying to get over, I'm sure that if I didn't manually intervene on the pedal, it would slide back 30 mph or so.

I just assumed if the van started losing MPH from what the original speed setting was, that the C.C. sensor would get a read on it and add throttle as needed to compensate for the loss of speed, despite whatever the vehicle might weigh.

[alloro]

The CC vacuum actuator might not be pulling hard enough on the throttle. This could be due to insufficient vacuum and could also be related to the bad check valve issue. First replace that check valve and then see if the CC problem goes away or gets better.

[Zorlock]

The CC vacuum actuator might not be pulling hard enough on the throttle. This could be due to insufficient vacuum and could also be related to the bad check valve issue. First replace that check valve and then see if the CC problem goes away or gets better.

Ok, I will take it one step at a time. This idea that the two might be related to the same check valve/vacuum issue was actually in the back of my mind as well. I just wanted to bounce it off of the masters of Mopar van knowledge who frequent here to make sure there wasn't somewhere else to look in addition.

I'll see what happens when I get that check valve in and give an update later this week.

thanks for the input guys,

Dominick

[alloro]

If that doesn't solve the problem, then you might want to confirm that the vacuum feed for the CC comes off of that extra fitting on the brake booster check valve. If it does, that check valve could be the one leaking.