Friend of mine's car has a weird condition. When it sits for some time Idling, it will lean out (according to the AF gauge), and almost run and sound like the motor (which is running a fresh rebuild) has blown. The car will run, and once you pull off, maybe 5 minutes later has smoothed back out. Let idle for a while, and again it will do the same. He's having fuel pressure problems (which we believe is do to the wrong Filter (carb type) but I wonder if this could also be causing the lean at idle? Any ideas?

 

I would resolve the filter issue first since it's very important. But it doesn't make sense to me that the fuel pressure suffers at idle, where the fuel intake is at a minimum.

I'm not clear though - are you seeing the fuel pressure drop as the engine leans out? Or might these be separate issues?

Dave

 

We replaced the filter, well deleted it entirely for the time being. Fuel Pressure is fine now, and moves with boost. But it still has the same idle problem. We are actually thinking there might be a bad injector in there. (850's and 1600's) We are swapping in a new set of 850's soon, may even put the 550's back in to see if it does it for them.

 

Just a quick note... AF gauges reading "lean" and the engine running lean aren't necessarily the same thing. Incomplete combustion and misfires will allow excess oxygen in the exhaust, making the AF gauge think it's lean, but it isn't.

You might already realize this, I dunno, but I thought I'd throw it out there...

Take care,
Shad

 

good point, never thought of this.like I said, we are going to try the injectors and see what happens, thanks for the idea.