low speed surge with TPS at 0.4%

[The Alchemist]

Hi people. a rather urgent query mainly to put me out of my misery.
This cammed VY Clubsport we did last week has almost caused a divorce with a niggly low speed divibility issue in around town traffic.
Logged it today its caused by timing oscilating between 34 deg and 12 to 14deg at low speeds say up to 14km/h with the TPS almost closed at 0.4% and 800 to 1100rpm.
I have ruled out idle spark swing pid, all the torq control pids, EGR & AFR spark pids, DFCO is "zeroed" out at 140 deg C and it still does it. At a TPS over 1% it goes away and the spark follows the main spark map and stays steady and the car smooths out and just ticks along nicely.
Also checked the main map transition into the base map and back again and thats all OK
Any ideas?

Mike

[johnv]

welcome to the world of cam idle tuneing

you may need to look at the under and over shoot correction tables B5935 & B5936 and lower the amount of timeing the pcm can pull or add in its attempt to smooth out the lumpy cam idle .

[The Alchemist]

hahaha, thanks a lot John
Update: managed to smooth out most of the shudder at light throttle by adding airflow with the throttle cracker and follower. A combination of the 2 at various TPS, Speed and rpms got it sorted in the end. Almost like a standard car again
The spark still fluctuates wildly under about 1% TPS but doesn't seem to affect the low speed drivability > Interesting.

Any comment on why the spark would be jumping around, have logged idle spark pid and its flatlined during the oscillations so its not that..........

[SSpdDmon]

Post up the tune if you don't mind and I'll take a look...

[macca_779]

what size cam is it?
my suggestion would be to set timing in B5933 to at least high 20's below 1600rpm/0.32Gcyl.

[johnv]

Another thing to try is to set up timeing tables, high & low octane and Idle ingear & neutral to the same values in the low load and rpm areas (up to 1600rpm) use the Bi Directional conrol to find what the car likes

This way when PCM transitions from one table to next ie idle in gear to high octane the timing won't jump around and transition smoothly.
john

[The Alchemist]

Hi guys, still need to post up the tune , sorry SspdDmon, thought I had it beat.
Customer came back 2 1/2 weeks later > today.
All was fine but now its "come back "........was the complaint.
Funny how the extra 12% torque and 20kw are quickly forgotten if the damn thing doesn't lift off idle smoothly > lesson number "1"

Whats happened is that it hasn't "comeback" infact I drove it and it was fine but the customer has got used to the car over time and was back to lifting off the clutch with 0% throttle in slow traffic which causes a slight bucking until the car is over 5km/hr or so OR the throttle is open over 1%.

I logged the idle transition and the timing is still dropping from 23 degrees (base and main spark map setting) down to 15 to 18 degrees as you lift off the clutch and the rpm drops out to about 400-500rpm, MAP lifts up to almost 80-90kpa, TPS is 0% and speed is 2-4km/hr > Why does it do that when both spark maps clearly say 23 degrees? I mean even if it thought is was still at idle (tps=0%) the low RPM would cause the idle spark to swing upward given the desired idle rpm is set at 900rpm, not downward.

I am going to try adding at the 400rpm row in throttle cracker at 0,3 and 6km/hr a much higher figure like 0.8g/s and see if this prevents the hesitation we're getting.

Mike

[johnv]

Another thing to try, is to add more timeing in the map cells bellow were it idle is set , so when revs drop off from normal idle timeing is increased to help compensate and pull revs back up to target idle speed.

[SSpdDmon]

Hi guys, still need to post up the tune , sorry SspdDmon, thought I had it beat.
Customer came back 2 1/2 weeks later > today.
All was fine but now its "come back "........was the complaint.
Funny how the extra 12% torque and 20kw are quickly forgotten if the damn thing doesn't lift off idle smoothly > lesson number "1"

Whats happened is that it hasn't "comeback" infact I drove it and it was fine but the customer has got used to the car over time and was back to lifting off the clutch with 0% throttle in slow traffic which causes a slight bucking until the car is over 5km/hr or so OR the throttle is open over 1%.

I logged the idle transition and the timing is still dropping from 23 degrees (base and main spark map setting) down to 15 to 18 degrees as you lift off the clutch and the rpm drops out to about 400-500rpm, MAP lifts up to almost 80-90kpa, TPS is 0% and speed is 2-4km/hr > Why does it do that when both spark maps clearly say 23 degrees? I mean even if it thought is was still at idle (tps=0%) the low RPM would cause the idle spark to swing upward given the desired idle rpm is set at 900rpm, not downward.

I am going to try adding at the 400rpm row in throttle cracker at 0,3 and 6km/hr a much higher figure like 0.8g/s and see if this prevents the hesitation we're getting.

Mike

I'm a little confused. Are you saying you don't get why the engine starts to stall out when you let out the clutch in first gear, without giving it gas, and you're barely moving (1~3mph)?

When dealing with aftermarket cams, it's important to remember that their powerband is shifted up and they're not as efficient down low. Slipping the clutch without giving it gas when the car is almost stationary is going to stall out the engine.

If you want to try and tackle timing, make sure you're logging the correct grams/cylinder pid so you can see where you need to make your changes to the base timing table. Once you apply 1.19% throttle, it should switch over to the main spark table assuming his car is setup like the M6 cars I've seen.

To use the throttle cracker like a stall saver, I added in 6 grams/second to my entire 400rpm row since I idle close to 1,000rpm (850 to be exact). So, when I'm driving and my throttle cracker is active, it'll add IAC progressively if rpms fall below 1,000.

[The Alchemist]

I'm a little confused. Are you saying you don't get why the engine starts to stall out when you let out the clutch in first gear, without giving it gas, and you're barely moving (1~3mph)?
Hi there, yes I get why, the customer does not ....
When dealing with aftermarket cams, it's important to remember that their powerband is shifted up and they're not as efficient down low. Slipping the clutch without giving it gas when the car is almost stationary is going to stall out the engine.
Thats what I try to explain to him...
If you want to try and tackle timing, make sure you're logging the correct grams/cylinder pid so you can see where you need to make your changes to the base timing table. Once you apply 1.19% throttle, it should switch over to the main spark table assuming his car is setup like the M6 cars I've seen.
Will double check that.....thanks
To use the throttle cracker like a stall saver, I added in 6 grams/second to my entire 400rpm row since I idle close to 1,000rpm (850 to be exact). So, when I'm driving and my throttle cracker is active, it'll add IAC progressively if rpms fall below 1,000.

As much as that > wow! Will try that today.

Thanks for your suggestions.

Mike