Fuel pressure question- 1996 4.0L Limited

[Themightyquinn]

I just bought a 96 explorer the other day (my third explorer). It seems it won't start in the cold. It started just fine when I brought it home Monday when it was well above freezing. But Tuesday night it dipped into the low 20's. I was able to start it with starter fluid but it would die when it burned all of the starter fluid. I suspected low fuel pressure from a faulty pump. Tonight I checked the pressure with a gauge and with the key on, it read 35 psi. After a couple of starting attempts it read closer to 40 psi. Now I can't even get it started with starter fluid. And it is 10 degrees warmer tonight (but still freezing). Now I am really scratching my head.

Now here is my main question. My Hanes manual gives specs for fuel pressure with the engine running. But obviously I can't check it that way. So what should the pressure read with the key on and engine off? Is it the same as when the engine is running or higher/lower? All I can find online is specs for engine running. I also think it is possible that moisture is present in the system and has frozen possibly constricting the fuel line This could possibly account for high pressure readings from a weak pump.

If anyone has any helpful input, please post it. Let me know what you think. It will warm up this weekend to temperatures like when the vehicle did start. I will post updates. Thanks!

 

[Runnin'OnEmpty]

If you've got 35-40 psi, that should be good enough
to run. I suspect, as you say, you now have ice in
the line constricting the fuel flow.

When I changed my fuel filter, there seemed to be
some water present, so that must be the low point
in the system. You could try putting a drop cord with
a light bulb under the fuel filter, and see if that thaws
it out....

I know you wouldn't do this, but under no circumstances
put any other type of heat source near the fuel system.
It can be very dangerous.

 

[RomeovilleIL]

If you show fuel pressure at the test port, that is already past the fuel filter. You did not list the engine for the 96. If its OHV my bet would be on leaking upper and lower intake gaskets. When it gets cold, the shrinking metal pulls apart enough to let in a lot of unmetered air so your engine starves. I believe the 96 was a return system so 35-40 psi is normal range.

 

[Themightyquinn]

***Update***
So tonight I finally got it started. It was 40 degrees outside. I found that having the intake duct disconnected from the throttle body was causing it to stall out after it had burned all the starting fluid. I have run plenty of vehicles with that disconnected and they ran fine. I sprayed about starter fluid in the tb for about 5 seconds and reconnected the intake duct and she started up quick. Also I added fuel to the tank thinking I might have a bad gas gauge, but the gauge did move after adding fuel. I also added Heet water remover. I ran the engine with the fuel pressure gauge attached and got pretty much the same psi as before, around 40psi. Also the fuel that came out from bleeding the pressure was pee yellow. I wonder if that was caused by the Heet? So still not sure why I had such trouble starting. Maybe there was water in the system since it seems like the fuel pump is providing proper pressure. Will try to start it later tonight as it is supposed to get in the mid 20s. I will keep post the results. Thanks.

Also, Romeo, I am not 100% sure which motor it is. The plastic cover that sits over the tb is not there. Is there a quick way of telling?

 

[masospaghetti]

By disconnecting the intake duct, you bypassed the mass airflow sensor that sits just behind the air filter. Computer had no idea what was going on since it was detecting zero airflow.

In 96 you had the OHV engine. It will say "4.0 EFI" in the upper plenum. Here is a typical 4.0 OHV:

Here is a typical 4.0 SOHC with the cover removed:

You may want to change your fuel filter if you are still having problems. It could flow enough to provide pressure in a static test (when the key on and engine off, no fuel is being injected) but be too restricted to sustain that pressure. Be careful though, those quick release clips can turn a 5 minute job into a royal headache if they break. Give them a good soaking with penetrating oil for a few days prior to removing them to help clean out any debris.

 

[Themightyquinn]

By disconnecting the intake duct, you bypassed the mass airflow sensor that sits just behind the air filter. Computer had no idea what was going on since it was detecting zero airflow.

In 96 you had the OHV engine. It will say "4.0 EFI" in the upper plenum. Here is a typical 4.0 OHV:

Here is a typical 4.0 SOHC with the cover removed:

You may want to change your fuel filter if you are still having problems. It could flow enough to provide pressure in a static test (when the key on and engine off, no fuel is being injected) but be too restricted to sustain that pressure. Be careful though, those quick release clips can turn a 5 minute job into a royal headache if they break. Give them a good soaking with penetrating oil for a few days prior to removing them to help clean out any debris.

Thanks masospagetti, it looks like I have the ohv but my air filter cover is conical. I will change the fuel filter this weekend. Since adding the Heet water remover and fresh fuel, it has been starting better.

 

[Themightyquinn]

Replaced the fuel filter today. Cut it open and revealed a nasty, filth soaked filter element. Before the engine idled over 1,000 rpm, now it idles around 600 rpm. Oddly, the filter change helped out the xmsn. It would not downshift into 1st from 2nd when stopping. Now it downshifts easily. I will post pictures of the filter later.