I have been trying to fix this problem for the last 4 months. My 93 351w shortbox has a problem starting when hot. It starts perfect first thing in the morning and when its hot if you shut the truck off wait a few seconds and start it again its fine but if it sits for more than 5 min or so all it cranks for a really long time and finally sputters and fires, very much so like it was flooded.

I have replaced all plugs, wires, cap, rotor, fuel filter, fuel pressure regulator, coolant temp sensor, air filter , cleaned IAC, set timing. checked fuel filter, scanned for codes, flushed injectors twice. I could be forgetting something that ive done but im absoultly stumped. Anybody could help please im running out of hair to pull!!!!

 

Hi 'Zilla,
If you have dual tanks, does it do this on both?

If you suspect flooded, the next time hold the accelerator to the floor and see if it starts quicker. This tells the computer to turn off the injectors btw.

Have you hooked up a fuel pressure tester and checked the bleed down rate? It could be a couple of slow leaking injectors or FDM checkvalves.

If your bleeddown rate is ok, I would suspect the PIP sensor next. Its in the Distributor. You might be able to pick up a whole dist from a parts store with a decent return policy that would let you bring it back if thats not it.

Tim

 

I got same problem 94 f150 5.0 automatic I change the spark plugs,wires pick up coil,coil,fuel pump, pressure regulator,ignition module,filters,distributor cap and rotor. still the same hard to star hot after sitting awhile start fine cold
I will post an answer if some day I can fixed

 

The same advice goes to you :-)

How does it start with the pedal to the floor when its doing this?

Check your fuel pressure. hook up a gauge and then turn the key on three times, but don't start. It should read around ~40psi. now start the truck and it should drop to about 30. Pull the vacuum line off the regulator and it should jump to 40's again. There should be no gas in the vacuum line or the port on the regulator, replace it if there is. Recoonect the vacuum line and the pressure should drop to 30's again.

Now shut the truck off. watch the pressure, it should not loose more than 5psi in 30 seconds. If it does suspect leaking injectore or a bad checkvalve.

Tim

 

revisiting this thread as i have been back to diagnosing the problem. Checked the fuel pressure today and found that it does jump to 40 when turning the
key on twice. then when i start it it drops to 30, then back up to 42 when the regulator vacuum line is pulled off. when i shut the truck off it will hold 34 psi for about 30min before it starts to drop. I also checked for spark and found coil is working fine got lots of spark at start up. I did notice that when i first hooked up the pressure gauge that the pressure only went to 20 psi, so i was gonna fail the pump. but after having the gauge on and it reading 42 psi it still did not want to start very good. I think its pretty safe to say it cant be a fuel problem, but at this point i dont want to rule anything out. anymore advice????

 

bad grounds. clean them. check the engine to frame ground.

 

when hot does it cranck just as well when cold?

how about changing the starter!

 

IT always cranks the same. one of the other mechanics at my shop says that when he hears me try and start it it sounds like after cranking for a few revoultions the truck starts firing on a few cylinders and then more and more until it fires up. Dont know if thats whats happening forsure. I did not check the grounds as i figured since it starts beautifully when cold that they should be fine but as i said ill try anything.

 

is coolant misteriously disappearing? i had a similiar problem with hot starting that turned out to be coolant leaking in the engine, but that doesnt sound like your problem.
how old is the battery? the starter might be fine when cold because it is easier to start cold, but a fresh new starter when hot might fix it.

 

remove the ignition control module off the distributor and have it checked at autozone

 

next time it will not start use one jumper cable from good ground on engine to good ground on frame. than try to start.

 

As a matter of fact coolant is disappearing. If that is the cause of the hard start i too will blow a gasket!

 

For the distributor module would that be the one found on the left fender. I tested the charging system and everything appeared ok. The engine turns over everytime with no problem.

 

I had the same problem. My truck would only start in the morning this summer when it was cool. If I drove it somewhere, and turned it off for a short time, it would start. But, if it sat for 5 or 10 minutes it wouldn't start. If it was warm from the sun, it wouldn't start. It always started like there was no problem in the early morning. I disconnected, sanded, and torqued all the grounds, replaced the TFI module on the distributor... spray a little gas in the intake manifold, and it would start and rev fine every time until the fuel was burned.

I THINK I found the problem last Monday - took the day off to work on the truck. I found the + wire to the frame mounted in-line fuel pump had a breach in the insulation. The wire inside was severely corroded. I've spliced the wire, and she seems to be running fine. It's getting cooler here in MA, so I guess I'll find out for sure next summer...? My best guess is with the corroded wire there was some function of temperature and/or humidity that allowed it start in the morning. After warming up (drying out??) the connection didn't pass enough current anymore.

If you say that you checked the fuel pressure, that it was on target, but still wouldn't start... then I'm concerned that my problem may not be fixed after all. Time will tell.

 

hmmm... i dont think that i have that problem. I believe this truck only has one pump in the tank. it doesnt have dual tanks either. I have not checked the grounds though. There was another thread on here from a guy who replaced some capacitors in his ecm when his truck wouldnt start. I have another 93 with a 302 and im wondering if the ecm would work to test if i switched them?