garys 68

iTrader: (1)

I got the 05 LM7 with DBW TB running great in my 72 Olds. It's hooked to a Muncie trans with mechanical speedo output and a Dakota Digital VSS. It has 2 pulses per revolution vs the stock 17 or 40 pulses.
When I engage the cruise control the throttle seems to surge between wide open throttle and closed.
Anyone else run into this and can tell me what to look for before I get whiplash?

garys 68

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ttt this morning

Schwanke Engines

iTrader: (1)

You are going to have to run with the 40 pulse system. Do you see vehicle speed when you plug into the PCM with a scan tool? It better be close to the actual vehicle speed, or it is not goin gto work properly.

garys 68

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I'll check the speed from the ecu today.
Can hp tuners or efi live adjust the VSS input signal to get it registering a higher speed?

Schwanke Engines

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You can't go lower than 10 in the software, that is why you need either the 17 or 40

garys 68

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I checked the speed with a basic scan tool. It is reading correctly (mph) and is stable.
I also confirmed the throttle position is varying radically with the cruise control on.
Any other thoughts?

garys 68

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bump for today, hoping someone has some ideas

G-Body

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My brother has a 2003 DBW engine in his swap with cruise and back when he had a th400 and was using the 11 pulse per rev ABS sensor in the rear axle as a VSS it had a surge in the cruise sometimes......swapped to a 4l80e eventually and even with the 40 pulse per rev sensor the cruise still seems to surge sometimes. So I`m thinking it might not be your vss....but I don`t know why it surges either.

garys 68

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I could live with "sometimes" but mine does it all the time.
So the guy who did my ecu set the VSS correctly (apparently HP tuners has a lower range). It is reading the correct speed, and it's stable.
It's like the ecu only knows idle and WFO with CC on......
Is there any difference in the TB control between an auto vs manual car with cruise? My engine/ecu was from an auto, I'm running a manual.
Or is there any "sensitivity" control in the ecu like on old vacuum operated systems?

2xLS3

iTrader: (3)

You actually don't have 2 pulses per revolution, since you sensor is running off the speedometer output on the tranny, whose speed depends on the ratio of the gears in the tailshaft. You should try to find which gear set spins the output the fastest and reset the ratio in the PCM to match it. The more pulses per mile from the VSS the better the resolution, for the control

garys 68

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I realize the 2 ppr VSS turns into about 1.4 ppr of the driveshaft. It's running a 8 tooth shaft gear and 17 tooth (lowest number) driven gear AND a 38% overdrive adapter, so I cant get any more speed to the VSS.
The ironic thing is that it's more apparent at highway speed that 30 mph.
I even know of someone using the same setup with an auto (th400) trans and no problems.

Schwanke Engines

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How is your ETC Pedal Torque Limit Reduction Table setup?

garys 68

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You may be on to something there. It seems there is a fairly long delay and revving before rpm drop after I drop the accelerator and push in the clutch.
I was not sure if that would affect cruise control though.
I'll get back with that info, thanks again!!!!

garys 68

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Turns out the ETC Pedal Torque Limit Reduction was left in the auto trans settings.
Any chance this would result in over revving condition when off throttle, clutch depressed AND surging with cruise control on?

garys 68

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Any suggestions, can I just set the ecu for manual trans and repin the the brake switch CC disable?