Recently got rid of the ses light banks 1 & 2 lean codes by replacing The MAF sensor. I have no codes now and no ses. This is a 99 expidition 5.4 with 126,000 miles. The truck has become increasingly hard starting on cold mornings. I checked fuel pressure and noticed it would not hold unless the key was on. I replaced the fuel pump, pressure seemed to be holding but the truck is still hard starting. Does anyone think this could be a pressure regulator problem? If so where is at at? Ive looked all over the fuel rails and can't find it. If not the regulator any other ideas?

 

Your truck may be a closed loop fuel rail, that is the fuel pressure regulator is in the tank as part of the fuel pump assembly and there is no fuel return line. Until recently, the tables the PCM used to determine how long to hold an injector open to get a certain amount of fuel were simplistic and relied on a constant pressure drop across the nozzle. Since the pressure (or vacuum) varies in the intake manifold, a constant pressure in the fuel rail would provide different pressure drops across the nozzle. The FPR had a vacuum line so it could control the flow across the nozzles by varying the fuel rail pressure as the manifold pressure changes. The tables are more sophisticated now, they use a MAP (or throttle position) to adjust for the pressure drop differences.

Lots of fuel pumps don't hold pressure, the check valve gets gummy. It usually doesn't hurt anything. I'm at a loss for your hard start.

 

The next time you are having yhe hard starting problem slightly depress the acclerater while it is cranking, if it starts you are probly having a nn idle air bypass valve problem, may need cleaned or replaced also check throttle body for dirt.

 

Its about 6 degres this morning and again no start just a little pre ignition. ttried slightly depressing accelerator but makes no difference. Really stumped. I think I'll try plugs.

 

mine has same problem as 02roush, 7 degrees outside, last night it was like 5 or less, and the truck just dosent start. i've had the problem before where it starts weakly, and wants to stall out so i give it gas, then it seems to be ok and runs normal. last night was the first time it just didnt ever turn over, or even click. after a bunch of tries, the truck will then very weakly turn on so i gave it gas and it starts, but i'm worried that i'm doing something bad while continuoly reapeating to try and start the truck.

anybody with previous experience in fixing this problem, or 02roush if you come up with a fix, let me know!!

thanks very much for the help!
John

 

The only fix I know of is moving to a more temperate climate. I have 3 of these trucks and the two with the 5.4 are cold natured. They do not start well in the cold and will cough and sputter for about 2 minutes in sub-freezing weather. Once they have been cranked for the day they do not act that way again unless they have been shut down for over 8 hours.

The Lariat is the only one I purchased new and when I took it back for this problem the IAC was replaced and the throttle body was cleaned. This helped for about a month - the same length of time it took for spring to hit. Same problem the next year - dealer performed the same fix and it warmed up the following week...

 

Finally that was it. Plugs were shot. The truck has no trouble turning over never did. This my 3rd set of plugs at 126,000.
Thanks for the replies