Thought i would start new thread( i started with the fuel filter question).... i dont have a fuel pressure gauge cheapest would cost 50 bucks, so trying to trouble shoot without it... 2003 ranger 3.0 flex 162k.... so overnight 12 hours cool down morning cold start stumble for 5 seconds then clears out to 1500 rpm....... i do the same thing next day after priming with the key four times then start ..2 second stumble ...let it sit for 4 hours, re start same 5 second stumble........and 2 hrs... turning engine off and re starting no problems.... With 162k wouldn't the pumps life be almost over, i did try the injector leak test flooring the pedal turning key to start,,..nothing ...as far as fuel pump i found a Delphi FG0872 at Rock Auto $145.. any thoughts/opinions thanks.... getting back to the stumble this started two months ago it would happen say three times a week morning starts....... in the morning i will push down the rail valve using rag, it should be about 25psi right..... if 0 then i will know for sure

 

1998 and up Rangers use 55psi fuel pressure, 1997 and earlier were 30psi

Yes, push on the Fuel Test port, after it sits for 8 hours or so

But...............I am not sure what the concern is, stumble on start up is, well, not that big of a deal.
If you were losing power at higher speed/high load then I would be concerned and change fuel pump.

I have 400k on my 1994 factory pump, and still going, so mileage is not a factor

Since Priming cold engine doesn't seem to matter I would suspect ECT sensor more than fuel pump, even dirty IAC Valve.
If Extra Priming worked EVERY TIME then I would suspect loss of pressure when sitting, which could be Check Valve in fuel pump, but its not a sign the pump is failing, just the flap that holds pressure when pump is off is failing

Get a Motorcraft replacement pump, 3 times the price but will last 10+ times as long, fuel pump is not an easy part to change

 

This morning i had 0 pressure at test port............. my main concern is the pump failing out of town... but like you say Ron its not a sign of pump failure ..also i have pinging when the ac is on .. i remember i had this problem few years back.... carbon yes, after a high rpm blast it stops for a while .....87oct....... i put a octane booster in the tank yesterday, see if it stops ping, could also be pumping lower than 60psi... gas prices rising here in C/A ..87 oct $3-50 per gall...

 

Yea theres 2 others of us that are trying to diagnose the identical problem as well. Ive replaced the ECT and idle air control valve with no change. Runs drives fine after its 5 sec of stumbling. Does the ranger system monitor incomming air temp via IAT? Is that part of the MAF?

Looked up signs of a failing MAF and they do say rough idle, stumbling hard to start or wont start are all symptoms along with running rich at idle and lean while driving. I have cleaned the MAF using 3/4 a can of the special cleaner and may have helped some? Not sure. I imagine they have a finite life that cleaning alone cant cure right?

 

Well i know i have a bad valve in the pump body, as the fuel rail is 0 pressure overnight, or one hour... the truck runs perfect on the highway under full throttle, you may have the same problem, how many miles on your pump..

 

Well it got replaced last year due to the factory one sometimes not running till you cycled the key a bunch of times or smacked the tank. New one has maybe a few thousand on it.

 

I started this morning a couple of hours after checking the 0 rail fuel pressure, during the stumble i got a check engine light ...PO 303 misfire #3 cylinder i bet due to the low fuel pressure until it reached the injectors. I cleared that code and all was well..... i still had pinging under load with A/C on, so its either carbon build up or lower fuel pressure. I am going to order Dlephi fuel pump they have good reviews i dont want to keep getting the code PO303... i know the Motorcraft is best but i cant justify paying that much. ...... not a big job bed removal

 

Alright so I checked the fuel rail dampener for fuel in the vacuum line. Was bone dry. I noticed when i pushed the vacuum line back on it was kinda hard to push then it kinda "popped" on once it got far enough in... Decided to back it off about 1/4" and start it. Walla! no stumbling, felt like it ran smoother with more power and idled smoother. Only other thing is today it barely reached 55*F outside so maybe some temp sensor not reading correctly???

 

Two days ago i replaced the fuel pump, pulling the bed i used 2x4 x 24 on top of the frame, sliding the bed back three feet myself, a friend helped me slide it back. So no more cold start stumbles or check engine light...i still have pinging using 87 oct with A/C on.... high rpm freeway run clears that up....