Piston slap or rod knock?????

My '96 GP with a 3.1 has a cold start knocking sound. I posted earlier this winter about it, but now that the weather is nice, it continues to knock on cold starts. Is this common?? Is this just the gm piston slap I hear about or is it a rod knock?? It increases with rpm's and seems to stay for quite a few minutes-like until the engine is up to temp. How can you determine between rod knock or piston slap and what can I do about it??

Bone yard,

My '89 Lincoln 5 liter Ford engine has had a start up knock the whole 12 years I have owned it. It varies at times--sometimes sounds loud enough to suggest pending engine failure--sounds like a main bearing. Failure never happened. This may be a comfort to you? You have described the condition similar to mine. Those who hear my start up probably figure--well he has an engine problem! I put 120,000 miles on this engine--no engine problems. Plugs always look OK. I figure it is low initial oil pressure to the back cylinder because after first acceleration, the knock is gone. Can't say for sure, but sounds logical for me. I dread doing any remedial stuff--I simply keep the oil changed and always have used the oil vicosity recommended for this engine (10/30). I am tempted to add an oil pressure read out gauge on this car--but do not have a real logical dash position for it. So--I pass.

John R