Cranking Comp Chev LS engines

[maddog]

I have an LS7 running that I am trying to improve the initial startup on. It runs a cable throttle body and a medium to large sized camshaft and it was hard to hold the throttle open enough when starting it to allow enough air to assist in firing. I have since added an external idle control valve and with the ECU controlling this we have had great results such that as soon as it fires we have be able to achieve a good smooth idle. Previously it just hunted up and down the rev range.

The problem is just getting the initial firing. I have been playing over a number of days so that eaach time the engine is dead cold. I have tried low and high amounts of "Crank Comp" and phased it out over various time periods but the results are a bit inconsistent such that I can get a real read on what its wanting. As soon as it has started once and run for say 10 secs I can restart it straight away so that makes me think everything else is about right. I do also have a first injection trim of 90% set.

If anyone had any ideas or direct experience and settings you have used for one of these engines I would appreciate the help.

[Girch]

Is this on Ethanol?

[Scott@FP]

This may be a fuel supply issue and not comp related.

Put a fuel pressure gauge on the rail and make sure you have pressure before cranking. If the system leaks down to 0 pressure quickly after shut down, work on getting the regulator and pump check valves to seal better. After verifying your fuel supply during cranking, then work on the comps.