Tuning in a long duration cam

[ngaio75]

I've recently installed long duration cams after sucessfully running MS fuel-only for a number of years, and am now having trouble getting the car to idle. The only change to the engine is the new cams (SOHC V6), and with the previous map and settings the engine will catch but will not idle, backfires (not sure if in intake or exhaust) and the best I can do is get it to "idle" at about 400rpm with the throttle open. Plugs are sooty, and I have tried blended Alpha-N (MAP readings in the low 90s at idle) without success. When the car is warmed up (a result of many tuning attempts rather than successful idle) it performs better, and if I can coax it up to about 3000rpm it comes right, which presumably is when it comes on cam.

I have a WBO sensor but the AFR is all over the place so I can't tell whether I am lean or rich. I originally assumed that I was lean, but have tried all sorts of numbers in the VE table around the idle area without success. Engine seems to need the throttle open to do anything so I'm wondering if I don't have enough air with the low vacuum.

Should I leave the original VE table alone and play with the Afterstart Enrichment and Warmup settings? Since the injectors are the same and the engine fires I assume that no changes to the injector parameters or cranking pulse is required?

Cam duration is 257 @ 0.05, 295 @ 0.01

Any suggestions on where to focus ?

[.boB]

That's a pretty big cam, sounds like the rpm range would be around 2,500 and up. But, that shouldn't be a big problem for the computer. One of the great things about EFI is that it allows you to run huge cams with poor vacuum signals, and still be easy to drive on the street.

Tuning for a cam like that is pretty much the same as any other cam. You might need to add a smidgen more fuel, but not much. It should run fairly well on initial start up, and should idle pretty well. It's usually the upper rpm ranges that need adjusting for the bigger fuel/air charge.

The problem you're having doesn't sound like a tuning/computer problem.

First, I would go back and check all my work. Look for the simple stuff first: vacuum leaks, loose plug wire, bad plug, ignition timing, etc. If all that checks out, look at the more involved stuff: cam timing, intake gasket. Go back and look at every step of the cam swap and make sure everything is exactly as it should be.

Then, review the entire EFI system. Look for sensors not plugged in, wires damaged, etc. Use your tuning software to review all the sensor inputs. Make sure the computer is getting the proper info.

What else did you do to the engine to take advantage of the cam? If you took a stock engine and put that cam in it, it's not ever going to run well. What's your calculated dynamic compression ratio?

[.boB]

Another thought.

Huge cams create a very poor vacuum signal. If you've set your fuel tables up to run on vacuum instead of or in addition to TPS, the computer will think you're under a big load, and add more fuel. Change it to run on TPS and RPM only.

[jcarruthers]

I am running a 300 degree cam, 2l straight six engine with a single throttle body.

Not an issue with my MAP signal at all.