12-27-10, 10:32 AM
Engine is hard to start when cold, cranks fine, occassional cough, catch, back fire; this increases until it finally catches and starts, then runs fine. Cloud of smoke out the tailpipe. Shut it off,and it'll start instantly.
Havn't checked fuel pressure, but leaning in that direction.
12-27-10, 11:10 AM
Northstar engine ?
Remove the beauty cover and pull the vacuum hose off the Fuel Pressure Regulator (FPR) - right rear of the fuel rail. Any raw gas in the line or FPR nipple ? If there is, the inner diaphragm is leaking and supplying a rich mixture - but this usually shows up more during a hot start. Change the FPR by removing the hairpin clip and pull it out of the fuel rail. Make sure the lower O-ring comes out with the FPR. Place a smear of oil on the new unit O-rings and slip it in.
Otherwise you may be in the Idle Speed Control and/or throttlebody cleaning business. While you're checking the FPR, check all the PCV clean and dirty air piping for cracks or loose grommets - vacuum leak.
May as well start by checking the fuel pressure as well as the things Sub mentioned.
12-31-10, 02:06 AM
The above is good to start with, what ultimately fixed mine (97 deville) with the same cough, hard start only cold, and back fire through the trap door, was the leaky FPR, new intake gaskets (rubber), and a fuel pump and filter mine has 176K. Don't forget about vac lines. Hear any hissing?