Idle Timing?

[trudynosports]

Got this truck dialed in nice, except it rumbles and shakes the truck about every 15 seconds of idle. When you monitor with the flashscan you can see that the timing is flaring up to around 30 degrees down to about 10 during the rumble then it clears up for another 15 seconds. Any ideas on this, is this the idle spark flare up that is causing it or is it just something that we have to live with.

Aaron.

[trudynosports]

Never mind I think. I enable the spark smoothing for 800rpms and below and put +or- 15 degrees in there for idle only, with no VSS and it seems to have cleaned it up nicely. I don't know if this is something that everyone does or not. The truck doesn't make any power though. The owner of the truck had the cam installed at the local dealer and they did not degree it. Based on what the mechanic told me as to how he placed it in the truck I think it's 2 degrees retarded. That would kill the bottom end and on a truck, that's what you want. It only makes 200 to the wheels on a Hot Cam? Stock on my dyno will make between 213 and 222 same truck. Darn thing sounds good and idles great now though.

Aaron.

[jfpilla]

Got this truck dialed in nice, except it rumbles and shakes the truck about every 15 seconds of idle. When you monitor with the flashscan you can see that the timing is flaring up to around 30 degrees down to about 10 during the rumble then it clears up for another 15 seconds. Any ideas on this, is this the idle spark flare up that is causing it or is it just something that we have to live with.

Aaron.

You can use the Bi-Directional controls to change your timing while idling and see if or how much added timing corrects it.

[Scoota]

It only makes 200 to the wheels on a Hot Cam? Stock on my dyno will make between 213 and 222 same truck. Darn thing sounds good and idles great now though.

Aaron.
Aaron, I think you would agree, it's no good sounding good if the thing doesn't go.

[trudynosports]

Exactly, the truck came to me with this cam already. I wouldn't have recommended this cam with no other mods, but that's beside the point. I was just wondering if anyone else has seen this same result.

Aaron

[dfe1]

I think you're looking at two problems relative to lack of power. The HOT cam really has too much duration for an engine with relatively low compression ratio and there's also a bit of incompatability between the cam's power range and air flow capacity of the heads, intake manifold and exhaust system. I've tuned a couple of vehicles with cams that weren't properly matched to the rest of the engine, and no matter what you do, you can't get any real power out of them. If you have the time and inclination, check the cranking compression and I'll bet you'll find it's a bunch lower than it should be. You may be able to help things a little by increase spark advance. Sometimes running "too much advance" in a situation like this will bring the power up, but that's an iffy deal- sometimes it helps, sometimes it doesn't.

[trudynosports]

Thanks,

I agree, just wanted to see what others had found in the similiar situations.

Aaron.