keithlucas

I have a 1986 f150 5.0 efi automatic that is hard to crank. When the truck is cranked for the first time in the morning it cranks right up but the rpm goes high for a short while. After I drive the truck and turn it off and start it up again it spins for a pretty long time before it cranks. When it cranks it runs the rpm up high for about 10 seconds and then levels off. It had a small battery in it and sometimes would not crank without a lot of trouble I put a big battery in it and now I can spin it until it cranks. I just bought this truck and trying to get it straightned out. Does anyone have any ideas as to what could cause this? Thanks
Keith

Chris_1

iTrader: (1)

If the engine is turning, that's cranking. When it starts running that's firing.
Sounds like you're wanting to say it'll crank but not fire ?
You'll want to check fuel pressure with a gauge - both cold and hot. Also check the vacuum hose to the fuel pressure regulator for a fuel smell - fpr could be leaking fuel into the intake through that hose.

nrivera04

Coolant temp sensor may also be bad. If it's bottomed out, it's telling your ECM to dump fuel to bring the engine temp up. Loaded cylinders are hard to crank on a warm engine.

CEL light on? Have you retrieved codes?

klricks

How high does the RPM go?
It is normal on a cold start for RPM to begin at about 1500 then drop down to about 800-900 after about a minute.

burnthelight88

Yeah the RPM thing upon startup sounds like normal warm-up for the truck. The long cranking could be various issues, but a lot of these starters have trouble cranking when warm...is it cranking at a normal speed and just not firing?

keithlucas

Yes it is cranking at a normal speed just does not want to fire. After a short time it will fire and seems ok revs up and the goes back to a fast idle I am going to try and get the idle a little slower. I have new sensors, dist cap, wires, rotor button ordered. Hoping that will help. Put in a new bigger battery just to be on the safe side.
Thanks for the help.

burnthelight88

Yeah do the tuneup first so we know it's not the easy stuff, could very well be a plug or wire issue. Get back to us after doing that stuff.

keithlucas

Thanks for the help been real busy with health issues but finally got some of the work completed.
Replaced Plug wires, plugs, dist cap rotor button, coil, both temp senders and while I was at it replaced all water hoses.

still when cold fires right up, after I drive it awhile and turn it off for some time and then crank on it again it does not want to fire just cranks for a long time with no firing at all. yesterday and today I tried pumping the gas pedal hard and fast and it fired up. any suggestions as to what could cause this? Once it fires up it runs just fine.

burnthelight88

I can't really imagine how the gas pedal would change much in an EFI... If it was slow cranking I'd blame the starter. I'm not really familiar with the EFI in 86. Do you have a check engine light? I'd check for codes if you do. Then you can disconnect negative terminal for a while and reset the computer and see if the problem persists.

DrinkinGasoline

Depending on the truck's mileage and maintenance history, timing comes to mind. A stretched chain, under heat/expansion conditions will cause valve timing issues, a starter to overwork itself, as well as tax the battery, naturally. At rest/cold the chain is contracted, but at operating temp or above, the chain is expanded. Keep in mind that if You do "re-boot" the computer, you will have to allow for key cycle code storage if You have emissions testing otherwise the station will reject the vehicle and not test it..(if smog applies).
When I rebuilt My 302, I used an '87 dual chain set-up with steel gears to avoid future stretching issues. I also use a gear reduction/high torque starter.