Hey all, I have a 93 f150 with the 4.9L, 280k km (about 174k mi) that I've owned for about a year now and have slowly been going through top to bottom making repairs and dealing with issues by order of importance. All maintenance/tune-up etc. up to date (including ignition and fuel filter).
I apologize in advance for the long post but this problem is driving me crazy and I want to give as much info as possible.

Anyways on to my issue. The truck has had what I consider to be a long crank time for a while now, chocking it up to a weak fuel pump(I was only using the rear tank as the front had a leak) I didn't spend too much time on it. About a month ago when the weather started to get colder, a new but related problem started. On the first start of the day (or if it sits for more than 8 hours or so) it will now crank excessively long (at least 5 seconds) before starting and then will die soon after. Turn the key a second time and it'll start instantly and do it's usual Rev to 1500 for 30 seconds. If on the first start I give it even just a little shot of gas it'll keep running no problem, but skip the 30 second 1500 Rev.

I'm sure this problem is fuel related. I've hunted and hunted for vacuum leaks in this truck to no avail, but replaced all lines to be sure and checked each and every vacuum activated device with a pump. I've tested and cleaned the iacv and removed it from the equation and it will still do it.

Using a fuel pressure gauge when I put the key on to pressurize the system it'll usually only go to 25-30 psi (less if it's cold out (I think)). Do it again it'll be about 45 and a third gets me to 55. It'll do this with either pump (I've since replaced the front tank). Some sources tell me one KOEO should get me to at least 45psi, but i've read elsewhere this is ok. Can anyone give me an official verdict on this?

Now you would think it should start right up once it's been properly pressurized, nope. Exact same long crank, starts and dies symptoms. To add to the confusion, the truck sat once for 6 hours, I turned the key on, had 30 psi, and for the heck of it I tried it like that and it started and ran no problem. If after sitting overnight I crank the motor for 5 or 6 seconds with the distributor unplugged then plug it back and just bump the key it'll fire instantly and start better than ever. If I manually run the pump with the self test connector for 8 seconds or so it'll also start and not die. I was thinking maybe leaky injectors or leaky check valve somewhere but according to some threads on this site the pressurized system should lose no more than 5 psi a minute with key off. That seems excessive to me but anyway my truck is far from that, maybe 5psi an hour. In fact the other day I was flabbergasted to see after sitting 12 hours the truck still had a solid 50 psi.

I am at a total loss here, I wanted to try isolating just the fuel pressure gauge and the injectors, then the fpr, fuel pumps etc. And observe fuel pressure loss with key off but that other day of 50psi after 12hours made me rethink the whole fuel system issue. My gut still tells me it's fuel related but my brain is now going crazy. I have torn my hair out looking for vacuum leaks and have done everything short of smoking them out, however I think i'll try that too just to give me piece of mind.

Anybody have any suggestions? I'm in dire need of a second opinion. Thanks

 

Welcome to the forum, el chingadero!

I know little about the later [after 1986] engine control systems and it sounds like you are systematically working through this, but have you checked the stored codes and seen what the computer has detected? Based on your name and the fact that you mentioned kilometers, I'm guessing you are outside the US. That may affect things, but here in the US, one can simply go to most any automotive parts business and they will use their scanner to retrieve the codes. Normally, there is no charge. This might reveal something that has been missed.

Good luck!

 

Thank you 1986F150six,

My name is actually taken from a line from an old Eagles song, I liked the sound of it so i've used it for years online, I don't actually know much Spanish However you are right, i'm not from the US but actually up north in Canada.

Anywho, I meant to include it in my first post but I have indeed checked for codes and there are none (111) both KOEO and KOER. I also forgot to mention I have tested the fpr by checking that it holds vacuum as well as unplugging it while running and the fuel pressure rises by somewhere between 5 and 10 psi.

Thanks

 

Update:
So the truck hasn't done the excessively long cranking and dying problem for about the past week. I haven't done anything different at all. It still does however crank for longer than what I would say is normal, especially when the truck has been sitting for awhile. Not sure how I should proceed.

 

If it's intermittent, might be a faulty wire or computer.

Give the harness a wiggle test! grab a suspected section and wiggle it and see if you can reproduce some kinda error. Might be un-orthodox but with wiring, it helps diagnosis to uhm, manhandle them.