Anyone else experience boost fluctuation with a smarty catcher level software tune while using cruise control? Saturday I was cruisin at 72mph and the boost gauge would bounce between 2 and 10psi. It was more gradual, like it would catch a gust of wind every 5 or 10 seconds. Made driving with the cruise annoying.

that's the nature of vacuum cruise control and a higher than stock power level.  The stock cruise programming isn't calibrated for anything over 245 hp....

Not to sound like an idiot, but what does horsepower have to do with how the cruise works?

Truck truck thinks it needs x power to move the truck at x mph.  It may need 100 hp to do 75 so the cruise is programmed to try and get engine to the 100 hp calculation. 

 

So some example numbers, ]

 

So %30 TPS = 100 hp typically in stock form.

 

Well add a fueling box to mix, what hp you used to make at %30 tps is now equal to the hp you now make at %20 TPS.  

 

so %20 TPS  = 100 hp with a smarty.

 

 

So when the cruise control is trying to regulate speed it is thinking it will need a higher TPS input than it will actually need.  thus it will overshoot the target speed, and then pull out of the throttle to try and bring the speed down.  However you end up in a slingshot effect back and forth.

 

Now mix into it all the fact that in stock form our trucks need %10 increase in throttle to hold speed at a given grade.  so the cruise is programmed for that.  Increasing your power via a fueling box means you now only need %5 tps increase to hold speed. 

 

It is more complex than that, but you get the idea.  

Edited April 19, 20168 yr by Me78569

Sounds like the work of an engineer.... guess I'll just learn to live with it.

Crazy idea is to install a needle valve in the valve in the vacuum line. That way it would slow down the vacuum source so the PCM can't over shoot the acceleration process.

Might be worth trying.  Another Mopar1973man product?

4 hours ago, 440Rat said:

Sounds like the work of an engineer.... guess I'll just learn to live with it.

actually it is the work of trying to get the system to work in the easiest/cheapest/and most reliable method haha.  It is significantly easier to program pedals position vs speed then add + or - for hill increases, vs trying to program a predictive system to adapt pedal input based upon acceleration.

 

 

Cruise control works fine on a stock truck, can't blame an engineer for designing a working system haha.  That's like saying the engineers that built the 47re are lazy.  The 47re is fine when the truck is pushing 235 hp.  We can't be mad if it fails when we bump power levels.  Even a smarty / edge ez etc bump power by~ %25 over stock.

Edited April 19, 20168 yr by Me78569

9 minutes ago, Me78569 said:

That's like saying the engineers that built the 47re are lazy.

 

Depends when you look at the transmission is just the same old 727 from back in the 1960s and 1970s and just added 4th gear to it.

 

https://en.wikipedia.org/wiki/TorqueFlite

And it works fine.  How many 200k stock trucks do we still see on the road?  

 

When Ed tore my trans apart for his build he said it looked perfect inside.  Never replaced / rebuild and pulled at 200,xxx miles.  

 

Can't blame engineers for not designing the trans to hold that much power over stock.....  

27 minutes ago, Mopar1973Man said:

 

Depends when you look at the transmission is just the same old 727 from back in the 1960s and 1970s and just added 4th gear to it.

 

https://en.wikipedia.org/wiki/TorqueFlite

 

The 727 is a great transmission.  It provides great service and is pretty simple.  There is a reason that the classic design has lasted so long.  The guys that built it had some real sharp pencils.  

 

I like the new stuff, but I'm a big fan of old tried and true technology. 

Edited April 19, 20168 yr by CSM

8 hours ago, Mopar1973Man said:

Crazy idea is to install a needle valve in the valve in the vacuum line. That way it would slow down the vacuum source so the PCM can't over shoot the acceleration process.

 I run a horizontal boring mill that sends signals between 2 different controls to control axis position. When it works its awesome, but if one control gets lazy its a mess.

 

  How does an increase in pony power have an effect on vacuum?

because your truck thinks it needs X% TPS to accelerate from 55 to 60.  BUT that TPS % is based upon stock power levels.  

 

 

If you bump your power by %25 then in theory you need less TPS to increase speed.    

 

 

So if you set your cruise to hold 55 mph your truck holds TPS at that position until the truck slows down.  It will then increase throttle position to make up for the loss in speed.  However it will increase throttle more than needed as the truck now makes more power than stock and thus needs less tps input to accelerate in the manner as before.  

 

Your truck isn't smart enough to see the bump in power, all the programming is based upon stock power levels.  and the programming is basic, if speed is 3 mph slower than needed increase tps by %5 if it is 6mph slower than need increase TPS by %10.    

 

So it will increase by that amount but the truck will accelerate faster than stock, because it had more power, and thus it will overshoot the target speed.  

 

So the truck will then pull TPS input because it is going faster than the required speed.  It will then pull too much throttle because it overshot the target speed by a good bit.  And then you end up slower than the target speed.

 

 

 

 

Now if you were to put a needle valve in place it would effectively slow down the response of the cruise control. 

I think a restriction in the system might help, but it would not be ideal.  I am willing to try it though. 

 

 Ideally, we would increase the resolution of the cruise control brain while slowing down the rate of throttle movement.  I'd like to have an adjustable cruise throttle application rate in cab, to slow it down when I'm light but speed it back up when I'm heavy or going uphill.

 

Another thought would be if we could have a moving average of the input speed signal.  

 

Is the cruise servo driven by the pcm or is there an analog brain?

 

Edited April 19, 20168 yr by CSM

driven by the PCM via 2 wires........ might be PWM I dunno.    

 

Maybe worth messing with.  

 

:edit looks like the ECM also plays a role, yuck haha.

Edited April 19, 20168 yr by Me78569

Hmmm.... then mabe treat it like an analog control system and put a resistor in line with the servo.

humm.....  I don't know, I think the needle valve or similar would work best for higher HP trucks.  If you would numb the reaction time by %50 I think it would work pretty well.  

 

 

Interestingly enough I have found that if I am on boost with the cruise set it actually works pretty ok.  I have to be at 10+psi.   I don't like using cruising control in that situation though.  

1 hour ago, Me78569 said:

Interestingly enough I have found that if I am on boost with the cruise set it actually works pretty ok.  I have to be at 10+psi.   I don't like using cruising control in that situation though.  

 

pulling a hill or coasting down a hill it was fine, but flat stretches its like it couldnt make up its mind. I'll just learn to live with it.

 

 

yea I just dont use cruise haha.