I've tuned the VE and seems to be dead on 128 across most of the lower rpm/map table, especially idle/cruise. Car runs..well, I guess a little shaky. Meaning the car vibrates some. This goes back to a post I had previously about the cam, I guess I don't really know what to expect from it. Ramjet 350, cam is .5/.5 lift, 270/270 dur., 110 lsa. Idles OK in idle mode, I've tried adjust timing from 20* to 30* on the idle SA table, without seeing too much of a difference (that I could tell).

When in gear, same thing in idle mode. When I pull up to a stop sign, it's jumpy, meaning it kinda jerks randomly while on the brakes, even at 750 rpm. Not that it wants to overcome the brakes or anything, just that you can feel it jerking and shake just a bit. Is this a consequence of running a stock converter with this type of cam? Any help on how to tame it down and get a smoother transition from driving to coming to a stop?

Any help appreciated.
Ben

 

I have a cam very similar to yours and I am assuming its a roller. Not an automatic so I don't have the issue while in neutral but it sounds like you have a surge. Try reducing the Idle Prop Gain a few percent at a time.

 

Well I've tried values from 150% to something like 15%, trying to reduce a stall when putting it in gear, so I wasn't sure that I was adjusting the correct thing for that. I'll work some more with it.

Right now I think I have it at the SAUJP value, I think 37%.

What about the drive idle speed deadband, could the IAC be trying to compensate for small changes in RPM causing an oscillation (or surge)?

 

I get that same phenomenon occuring with my setup. When I'm stopped at a light and allow the car to inch forward while keeping the brakes applied, I get some jerkiness that gets worse with temperature. I'm idling my engine at around 650 rpm (with about 15 IAC steps in drive). Don't want to idle it higher because it gets difficult to hold the brakes.

Not surprisingly, the Ramjet is a short runner manifold like the Miniram. I too have a cam similar to yours with factory converter. But I've never been able to eliminate the jerkiness. Damn thing runs like a bat out of hell anywhere off idle, but the idle is not quite where I want it.

 

I try to get my IAC count into the single digits. With a larger cam, the air intake velocity can be a problem. So you want as much air traveling through the throttle body and not bypassing it via the IAC. As for the Prop Gains, make the changes small in either direction until you can feel if its better or worse. And I keep my idle SA down around 23d.

 

I messed around with it some today, I got it mellowed a little by dropping the timing down to 18d in idle mode, still got a little bit of a surge, ran a little rougher. I'm gonna take SA back up, I'll try 23d with different IAC settings.

 

I had the same thing with my 350HO. With Fast's advice, I enabled open loop idle and set the AFR at 13.5 and it idles the the L05 did. I know it burns more fuel, but it idles so well that I don't want to go back to closed loop idle. Same here man,BLM/INT was 128 at idle but it shaked, even at 800 rpm for me. Now it's like butta at 650 rpm.
Before OL idle, I changed everything from injector terms to SA to prop gains, etc and nothing worked. Idle SA for me with the open loop idle is about 28 deg. Try it out!
Mike

 

How do you set up OL idling?... or what do you tables get changed in the $8d mask?

 

Did ya'll know that when applying and releasing the brakes a little, it's acts like a vacuum leak for a second as the booster fills and empties? Can even see it on a stock car. On a MAF car, that air is un-metered, which really can give it heck, because it would lean it out. The IAC counters this air, but it's always late. With non stock stuff, things quickly can get into a funk and oscillate/overshoot.

You should try to tame the IAC. More PROP gain would counter any sudden RPM changes from a steady idle, but can easily force an oscillation by itself. Reduce the Integrator gain, widen the deadband, reduce the PROP gain, turn off differential completely. But, learn what each thing does as you reduce it. No sense just randomly changing stuff...

 

so what would a bad brake booster do to a cars tune? wow guess that's kind of general, oh well give it a shot!

 

Bringing this one back from the dead. (i love searching!)

I have the same thing going on right now. Bit of a "mild cam", tuned my ve to get me 128 blm/int at idle, but still runs "rough". So all you did was adjusted the minimum closed loop values up and set the idle afr to 13.5 with 28* advance at idle? Is your base timing still set at 0* physically and at in the computer? If you dont mind me asking, what is your BPW and what is your ve table like on the idle cells?

 

91 Chev has not been active since 2008?

Not sure if your mask allowes OL idle? Threre may be a way to do so. Temp you can disable CL and witness idle condition.

Not sure if BPW will affect idle. set it accurately and forget it.

 

*****. In that case i guess we should stick to my original thread. I dont think mine specifically allows for idle open loop. As of right now it does idle better in closed then open. About the BPW, i have been told that the values in the ve table need to be between 45-95 for the injector to work properly and that you have to set your BPW to allow for that. Sense i have a couple of my values set at around 31 or so, i think i need to bump my BPW down so i can bring that number back up.

 

I fudged my BPC to get my VE under 100 in some cells. That was because my header collector to ext pipe had a leak. My learns kept adding fuel. With my BPC table set correctly I am now at 90 max for VE. Set it correctly and forget it. Unless something odd occurs in VE table. Then address that.

 

Could also reduce the RPM error SA and Retard at idle by lowering the values of the smaller error cells. (the zero, 50 and 100 RPM cells)
Spark can jump around allot at idle with a rough cam.
Look at these two tables.
L81F0-L81F4 Idle SA vs. RPM error
L81EB-L81EF Idle Retard vs. RPM error

There are also two table associated with this for MAP correction.
If MAP is jumpy at idle it will also cause changes to the spark.
These are all at 1.0 setting normally but you could reduce them to see if the spark stabilizes if it doesn't react to just lowering the RPM error response.

 

That's kind of another thing i had been thinkin about is making all the idle sa and ve tables the same.

 

Put a fresh spark plug or 2 in the motor and let it idle for a few minutes, yank the plug and post up a picture.

 

How long does it need to run to get a good "reading" on the plug?

 

Few minutes at operating tempature should be good.

 

what is idle spark advance and retard error? - is this the same on a 7727?