Just replaced the OEM fuel pump and strainer a week ago on my 97 F150 4.6l w/auto trans after 19 years (I bought it new) because on a cold start I was having to prime the fuel rails with the key on,key off 4 or 5 times to build the fuel pressure up before the truck would start right up. On a hot start there was no problem and would usually start right up without priming. I checked the fuel pressure on the new Bosch pump (OEM was also BOSCH by the way) and it is pressurizing to about 35 psi at idle and bleeds down slowly after a couple of hours to around 15 to 20 psi. I assume it will bleed down to almost zero after sitting all night but I had to return the fuel pressure tester last week. Also when disconnecting the fuel pressure regulator vacuum hose the pressure would jump up to around 42psi. The old OEM pump was running about 5psi lower pressure on idle (30psi) with the fuel pressure regulator jumping to 40 psi on vacuum hose disconnection.

I also replaced the fuel filter with a new Motorcraft one about a week before I replaced the fuel pump. I have switched the horn relay and the fuel pump relay and there is no difference in performance either way. The IAC was replaced bout a month ago with an aftermarket Duralast unit and I cleaned the MAFsensor with QD contact cleaner because I was also having some rough idling issues which have been resolved since then. The truck idles fine now after starting.

Yesterday I cleaned the throttle body butterfly and intake as best I could using TB cleaner without removing it. I also cleaned the crank position sensor with QD contact cleaner after reading multiple threads on this and other forums that oil and dirt from years of use might contaminate the Crank sensor contacts. The truck runs fine with no CEL light in the past week since the fuel pump was replaced and I have used it daily.

In any event I am still having cold start issues needing to prime the rails several (3 to 4) times to pressurize the rails so it will start. Today I had to give it a shot of starter fluid for a second or two and the truck fired right up. I have had to do that once during the week on another cold start because twice now even with multiple prime attempts the truck will not start without a quick shot of the starter fluid.

I am thinking that maybe the crank position sensor is going bad and not sending the signal on a cold start to inject fuel but why wouldn't it do that when thee ngine is hot on a hot start? Why would a quick shot of starter fluid cause the truck to run fine from that point forward until the next cold start? Is there anything else I should check or test? Should I just go ahead and replace the crank sensor now?

The truck has about 155,000 miles on it and still has the original plugs,wires, and twin coil packs but the gas mileage is the same as new and I have checked it religiously on every fill up since I bought the truck new. The truck runs great other than the cold start issues with no misfires of any kind and accelerates nicely without hesitation. It is a daily driver for me. Would old plugs and wires cause cold start issues?

Any advice on what else to check from the helpful pros on here would be greatly appreciated.

 

Had to use a quick shot of starter fluid this morning to get it started after cranking several times. The truck runs perfectly fine after starting, idles great, accelerates with no missing or hesitation and no Check engine light at all! I wish the light would turn on to at least point me in the right direction with a code. The light does illuminate when the ley is in the on position for a few seconds so it is working.


Any advice on diagnosing this starting problem would be greatly appreciated.
Thanks.

 

When it cranks and won't start, does the check engine light stay on, or does it go out while cranking?

 

The CEL goes out while cranking. It only turns on for a few seconds with the rest of the instrument lights while the key is in the ON position but goes off while cranking and stays off after the engine starts.

 

That indicates that the PCM is seeing the CKP signal.

 

So I guess I can assume the crank sensor is OK from your post but the mystery continues on why the priming is needed for a cold start condition and not on a hot start.
Thank you for your input.

 

What does the fuel pressure show WHEN it is cranking and not starting?

 

On a cold start it would barely register (from sitting overnight) but after priming several times it would come up to 35 psi. I never actually read the gauge during the actual cranking before priming. I may have to go rent the pressure gauge again. At idle it would maintain about 35 psi steady. It would take several key on/key off cycles on a cold start to get to 35 psi. Revving it slightly would raise the pressure to about 42 psi or thereabouts. Pressure Bbleed down was very slow after engine was off.

 

Just this morning again for the second day in a row I had to use a quick shot of starting fluid to start the truck even after priming with the key on/key off 4 times. I had several long (5 second or so) crank cycles and it would not even attempt to start. It seems I only need to use the starting fluid after a complete overnight cool down. The rest of the day the truck either starts immediately if I restart on a hot start or within an hour or two of being run. What is driving me crazy is that the truck runs perfectly after starting, like a frigging sewing machine. It seems to me that the injectors may not be receiving an adequate signal to turn on or not squirting enough gas to start but why only when it is dead cold? Also, why with just a very small 1 or 2 second shot of starting fluid does it fire right up? Do the injectors inject such a small amount? If the injectors are bad why no CEL codes, engine missing, or rough idle or running?

Would old plugs and wires cause this even with no apparent misfires of any kind and no decrease in gas mileage? I ma going to get them changed in the next few days but I am doubtful that is the root cause of the cold start problem.

Any insight or advice you guys could give me to point me in the right direction to solve this mystery would be greatly appreciated. Thank you.

 

Well I would say if you still own the truck ?, get rid of the auto zone IAC valve!! This truck is the same as mine and they DO NOT like those non motorcraft parts AT ALL!!"" Also try buying a obd scanner ", (?not just code reader) and do a quick youtube crash course on reading fuel trims and freeze frame data". It will save your wallet and stop all headachs guaranteed!

 

Was this problem ever solved? I am having the same exact problem in extreme cold (0f and below) If I have my block heater plugged in it fires up no issue. With the block heater unplugged I have to prime crank prime crank several times (4-6x) in order to get it to run. Fresh battery and fuel pressure is good. No other drivability issues to report.

 

https://www.ford-trucks.com/forums/1...g-problem.html Go around and play with voltmeter. When truck is starting. Continuity will not help at all.

 

Sure sounds like your fuel pump is getting weak
The intake valves may be carboned up too
Soaking up some fuel as well causing the long hard start
The FP should build to 35 psi right away when the key is turned on
It should also maintain its fuel pressure overnight within 5psi so the initial build to 35 or 40 psi happens instantly