98 4.0 SOHC Hard Start Rough Idle/Rev

[terrychoppers1]

Hi

This has been a project that is still currently on-going but the old 4.0 SOHC would start and run just had low oil pressure so i swapped it out with a 4.0 SOHC with 76k miles on it. All the sensors are swapped over etc...

You have to spin it for 10seconds+ to get it to fire up and once it hits it will stumble and buck usually not pulling much more RPM's than the starter. Once it gets a steady fire it will hover around 700rpm bucking and puking then die. You can get it started by having someone hit the intake with some carb cleaner as your turning it over, once it gets started up and can rev the motor just a little bit it will idle on its own and purr like a kitten. Any type of drastic throttle change more than 1/4 throttle and quickly will result in some misfiring and bucking if you hold steady at the new throttle position it will pick up and rev smooth until throttle changes. A flat foot WOT will kill the engine.

It will idle fine i've let it run for 10-15 mins you can turn it off... try to start and its virtually impossible until you wait for a 10 or 15 minutes


Things i've tried so far:

New MAF
Fuel Pressure test
Cam sensor
Crank sensor
New Fuel Filter
O2 upstream sensors are brand new, rear ones are deleted via SCT
several treatments of "HEET" to the fuel tank (gas has sat for almost a year)
checked for vac leaks
installed a new set of coolant temp sensors (since the gauge inside the cabin doesn't seem to be responding... even with the new sensors)

I have an SCT3 programmer the only codes its throws are lean code bank 1 and 2 and O2 heater sensor code.



Tomorrow i'm throwing in new plugs, re-confirming the spark plug wires and firing order and doing a compression test just for poops and giggles. I'm wide open for some light on this problem, i may bring my camera with me tomorrow and video the "starting procedures" to help visualize the "bucking and puking" terminology haha.

Hi
I'm new here and I am wondering if you have gotten the problem figured out? As I am having the same thing with my 02 Explorer. It was running great until this last winter I tried getting up a very deep snow covered hill. When I got to the top it died and has not been able to get it started since. Your symptoms are very much like mine.

 

[Mike Cuers]

This has been a project that is still currently on-going but the old 4.0 SOHC would start and run just had low oil pressure so i swapped it out with a 4.0 SOHC with 76k miles on it. All the sensors are swapped over etc...

You have to spin it for 10seconds+ to get it to fire up and once it hits it will stumble and buck usually not pulling much more RPM's than the starter. Once it gets a steady fire it will hover around 700rpm bucking and puking then die. You can get it started by having someone hit the intake with some carb cleaner as your turning it over, once it gets started up and can rev the motor just a little bit it will idle on its own and purr like a kitten. Any type of drastic throttle change more than 1/4 throttle and quickly will result in some misfiring and bucking if you hold steady at the new throttle position it will pick up and rev smooth until throttle changes. A flat foot WOT will kill the engine.

It will idle fine i've let it run for 10-15 mins you can turn it off... try to start and its virtually impossible until you wait for a 10 or 15 minutes


Things i've tried so far:

New MAF
Fuel Pressure test
Cam sensor
Crank sensor
New Fuel Filter
O2 upstream sensors are brand new, rear ones are deleted via SCT
several treatments of "HEET" to the fuel tank (gas has sat for almost a year)
checked for vac leaks
installed a new set of coolant temp sensors (since the gauge inside the cabin doesn't seem to be responding... even with the new sensors)

I have an SCT3 programmer the only codes its throws are lean code bank 1 and 2 and O2 heater sensor code.



Tomorrow i'm throwing in new plugs, re-confirming the spark plug wires and firing order and doing a compression test just for poops and giggles. I'm wide open for some light on this problem, i may bring my camera with me tomorrow and video the "starting procedures" to help visualize the "bucking and puking" terminology haha.

Check the inlet manifold - made of two sections of plastic with "O" rings as joints - these O rings get hard / perish with age and heat cycling - leak in air and cause over fueling till engine hot and O rings seem to close up.

 

[terrychoppers1]

Check the inlet manifold - made of two sections of plastic with "O" rings as joints - these O rings get hard / perish with age and heat cycling - leak in air and cause over fueling till engine hot and O rings seem to close up.

I have had the air manifold off and replace the gaskets. Still the same problem. I found two vacuum line's that needs to be replaced and some frayed wiring behind the motor, injection wiring I think. The vacuum line's that are bad are the red plastic one that goes to the fuel regulator? And the green one that goes to I'm not sure what you call it. And a larger one that goes to the gas tank I think. I also replaced the coil pack as the other one is very rusty.