I've been having issues with both hard starting (30 seconds cranking) and intermittent stumbling/stalling for the past several months. This past weekend I replaced the fuel pump which solved the stumbling issue, but the hard to start was still there. I had an old ICM from when I was initially trying to solve the starting issue, so as a test I put that one back in...it started perfectly, no issues. It did this for the rest of the day, but this morning when I went out, it was again hard to start.

In the past year the opti, plugs, wires, fuel filter, and coil have all been replaced. The engine is a rebuilt that was changed Sept 2012. It has occasionally thrown codes 44 and 64 (right and left bank lean), but I believe this was due to the fuel pump, as when the engine was changed and the pump replaced, the mechanic didn't replace the in-tank filter sock, and it was clogged with debris from the tank.

Any ideas what could be left to check?

 

Have you checked the fuel pressure, including the rate at which the prime pressure bleeds off when the pump shuits off? There are things besides a weak fuel pump that can cause that problem.

 

I checked the pressure about 6 months ago, and didn't change anything since. But I haven't had any stumbling or stuttering problems since the fuel pump change either, so would the pressure be related to the hard starting?

 

Which pressure did you check - after prime (bleed off rate), at idle or under load? Rapid bleedoff of prime pressure will extend the starting time. And if you checkd the fuel pressure 6 months ago, and just replaced the pump, the test needs to be repeated.

Rapid loss of pressure (if it exists) can be due to a faulty fuel pressure regulator, leaking injector(s), leaking lines, incudling the internal line in the tank, and a bad check valve in the fuel pump. A new pump would seem to rule out the latter.

Never 100% sure, but it's worth checking.

 

When I checked it it was the prime bleed off...it was a borrowed gauge and I wasn't really comfortable with taping it to the window. I did test it by revving it also though. Both held pressure for quite a while, but I will definitely test it again as soon as I can.

In the meantime, is there anything else that might be useful to test as well?