Hey, I'm new to the forums, and I'm sorry if this has been addressed in another thread, but I'm seriously lost at this point. I have a 1996 f150 2wd 5speed with the 4.9. I come to start the truck in the mornings and I hear the fuel pump run, when I turn the key over the truck starts and shakes, pings and dances around until it dies, or I shut it off. I turn the key off, then crank it again and it fires right up, and idles down and runs halfway decent. I have installed new distributor cap, button, plugs, wires, new fuel pressure regulator, and fuel filter. When the truck fires up finally it sounds almost as if I have a very small vaccume leak somewhere, but takes fuel decent. I've cleaned the iac, maf, and all electrical plug-ins. The truck only dose this if it's sat, say overnight, any advice at all is greatly appreciated thanks so much in advance

 

Did you check the plugs for .44 when you put them in? They rarely come correctly gaped. If you did, check fuel pressure,50-60 PSI at idle is what you need. I would run codes before renting a pressure gauge. If your TPS throttle position sensor is bad, here is a test you can run before you rent a pressure gauge.

 

i also own a 1996 f150 with 4.9 and 2wd, but i Have an auto. You are describing an issue I know of too well, too. The engine turns over and starts, but its bogged down, it usually takes a couple seconds for it to get proper. two things to note 1) your truck CANNOT have the accelerator pressed in any way shape or form and that includes a decaying cable which slightly changes the closed voltage over time and starts, etc. it will start out with fuel cut off.
2) also, too much fuel from injectors that leak will do this, its too rich
3) the fuel pressure is off, or restriction changing flow, the computer has a set amount of fuel it puts in, and it has a calculated value for spark and has an idea of what kind of air density there is, and also calculates ambient temp and uses all that together to estimate how much air should be entering when the truck is asked to turn over and then on. if any of those factors are off, it could do this
4) sticking emissions valves could lean out or make rich, such as a vapor valve or a egr valve, but you said you checked things. check your gas tank by removing cap and see if its been holding a vacuum
5) if this is consistently a cold morning thing, not a even a few hours or 20 minutes etc, check fuel issue by cycling key twice. like, to on, then back, then try and start, this would put more fuel up in the system. if you had a leak to the tank or externally, it would prob mask that being an issue, if you had it worse, it tells me it might be the fuel injectors leaking into the engine when off and that just made it richer
6) IAC valves can have issues even if clean, i use my scan tool and notice it sticks sometimes, where it just hangs on a plateau for a weird amount of time and then jumps in and over compensates very quickly. unless its a pcm processor fault(which i dont think) it would indicate something about the valve since the its not really supposed to go to a spot and then stop, its meant to be varying constant, even if small
7) there is an issue with air diverter valves and check valves i saw with a TSB for 96 4.9, i believe it also contributes to the weird noise on warm up only and clicking. but i dont remember if it was start stall. you dont have an auto so that is out of picture, too.

 

I'll try to go in more depth. It's not so much of a "cold morning"thing, it's more of a "sets too long" thing I've scanned the truck and pulled a few lean codes, you're defiantly right its dumping fuel, I've replaced plugs, wires, cap, button, fuel filter, and fuel pressure regulator. I put the regulator on the day before yesterday and I thought I had the issue solved, and I started it yesterday morning and instead of thrashing for 45 seconds and dying it thrashed for just a few seconds and died, then fired up perfect and idled at 800. I took the iac valve off and it looked really clean so I cleaned it as much as I could and cleaned all the plug-ins I could get to and chased vaccume leaks going through 2 cans of ether. So I take the terminals off and let it reset itself and the issue seemed to get worse. I tried to start it after unhooking the battery and it thrashed like crazy so I cut the truck off and try to cycle it again and start it, and it dose it again. I eventually have to make it take fuel and clear out. I thought the ecm was just relearning everything but it started missing while driving it too. My front gas tank doesn't like to take fuel I don't know if pressure in the tank would do this im down to checking fuel pressure to see if the pump is weak, that or the injectors are shot. Thank you for the speedy replies, its greatly appreciated!!

 

I think I found the culprit. When I first started riding this truck again, around 4 years ago I flipped the tank to the rear one. The truck started shaking and I assumed the pump was bad in the rear tank, so I kept the switch on the front tank, and kept riding with the occasional miss and hard start/thrashing.
this morning I had a doctor's appointment, and decided maybe when I tried that years ago maybe the tank was dry so at the fuel station I decided to put some fuel in both tanks so before I started the truck back at the pump I flipped the fuel switch to the rear tank and cycled the pump, I heard the pump run and cycled it again, and she fired up and ran real smooth so on to the doctor I went. When I pulled in the doctors office I cut it off, and tried to start it again, and he started up beautifully, got my meds at walmart and he started beautifully again. Here's hoping my front pump is getting weak. I will update later in the week if the issue pops up again thanks for the help!!!!!

 

Glad it is working for you now. Thanks for keeping us informed as to your success. I try not to let my tanks go below 1/4 full.

 

i know you seemingly found the culprit. But for future tip, something that is able to find vac leaks easier safer and cheaper is a propane torch unlit. Have the truck running and send some propane toward where’s you want to check for vac leaks. The engine will pull in snd buen the propane Increase idle speed and it won’t degrade rubber snd isn’t likely to start a fire nearly as much as solvent And not so expensive compared to use a lot of

 

thanks! I had the ether laying around. I'll defiantly give that a try next occasion. ether definitely is expensive, and the propane probably would work better, and probably will last longer! Thanks a ton!!