99 Explorer 4.0 OHV stalling

[Kritikal]

I have a 99 Explorer 4.0 OHV that basically stalls upon starting
I'm getting lean codes for bank 1 and 2
I replaced the upper and lower intake gaskets
Before I replaced the gaskets it would start right up in the morning then have issues restarting throughout the day.
After replacing the gaskets it ran for a little bit then starting stalling at idle. Now it revs up upon starting then stalls.
I replaced the fuel injectors and fuel filter.
I unplugged the MAF, nothing changed and it didn't die as a result of plugging it back in like others have said it should.
I unplugged the AIT and it idled at below normal rpm still sounding like it wanted to stall.
Sometimes it idles for a bit then dies when I touch the gas pedal.
I don't know what's going on. I'd image at least a rough idle if there's a vacuum leak.
Any thoughts?

 

[EB4X]

When you removed the upper intake / plenum to replace gaskets....did you properly uninstall the EGR metal tube that goes into it (near front on drivers side) or take short cut and leave end going into EGR valve hooked up and just slid intake up and out of it? Leaks happen at that seal where EGR tube inserts into upper intake if not perfectly reinstalled....spray starting fluid around it while buddy revs to keep running and see if idle jumps up more...
High revving idle: Vacuum leak or possibly TPS...........

 

[C420sailor]

Fuel pressure?

 

[96eb96]

What are your fuel trims at idle, 1500 RPM, 2500 RPM?
Essentially high fuel trims cause those two codes. It means the engine is running lean and it is adding fuel. It is either getting excess air or can't provide enough fuel. Leaks could be anywhere, even the EGR could be worn and let air in.

High FT at idle = vacuum leak
High FT at high RPM = Possible Fueling problem.

Like other said, check your fuel pressure with a gauge. Turn the car off and see if pressure holds too.

Would be nice to see OBD freeze frame data as well. Codes with no other information are like saying you are cold. Are you stuck in a refrigerator or stuck in the North pole? See what I am getting at? Freeze frame data tells you the RPM band the problem happened at, if the car is warm etc. No one ever posts that along with their codes.

Would be nice to See BARO PID (forscan).

If you reassembled the upper engine and have more issues, likely there is some vac leak. May need propane or carb cleaner or smoke to find it.

 

[Kritikal]

I checked where the EGR connects to upper intake. Its sealed well.
Before the truck would not want to start and the coolant reservoir would be empty, the truck wouldn't overheat it just wouldn't want to start. I'd add coolant or water crank it a few times and then it would start. I replaced the ECT sensor. I'm noticing the fan comes right on when starting and the coolant doesn't seem to be pulling from reservoir. This stuff sounds unrelated but it seems like there working together against me!
Here are some live data photos I took this morning.

 

[C420sailor]

That’s a lot more STFT than I’m used to seeing at idle. The other day, I think mine were single digits.

 

[Kritikal]

I disassembled the upper intake and discovered the o ring on the EGR tube was damaged but also discovered spark plug wire #5 was not connected! I replaced the o-ring on the EGR tube and popped the spark wire back onto the plug. Took it for a drive and all seems well, no codes appeared. Previously they was rattling under the truck which seems to have diminished though I can still hear it faintly. I attached a photo of the live data while it was idling. Do these numbers appear right?

 

[EB4X]

I got one! yippee ! ...that was your revving idle/vacuum leak and dying .... 5 cylinder not great either
Rattling is probably a bent heat shield or poor exhaust hanger ....it was magnified by rough idling engine.

 

[96eb96]

23ST and 24LT is 47 positive total trim. A CEL is on the way. A repair would make the numbers trend down(e.g. STFT negative). Unless the scanner isn't reading right.
The truck will remember ltft when you start and stft will be negative if things get better.

Eventually ltft will "learn" stfts correction.

They should in a perfect world be zero, but 0-5 range is optimal too.

 

[Justinwht]

A lean code usually means insufficient fuel, but it could imply too much air. The computer monitors the incoming system air flow through the mass airflow sensor and adjusts fuel flow accordingly.

But if you have a vacuum leak then more unaccountable air is getting in the system.

I had lean fuel errors and found the line on driver's side leading down from top of engine to canister behind and below driver's side headlight had several inch split. Spraying ether around the engine discovered it. Wrapped with electrical tape for temporary fix until I replaced the hose.

 

[LJM's98Exploder]

I have a 99 Explorer 4.0 OHV that basically stalls upon starting
I'm getting lean codes for bank 1 and 2
I replaced the upper and lower intake gaskets
Before I replaced the gaskets it would start right up in the morning then have issues restarting throughout the day.
After replacing the gaskets it ran for a little bit then starting stalling at idle. Now it revs up upon starting then stalls.
I replaced the fuel injectors and fuel filter.
I unplugged the MAF, nothing changed and it didn't die as a result of plugging it back in like others have said it should.
I unplugged the AIT and it idled at below normal rpm still sounding like it wanted to stall.
Sometimes it idles for a bit then dies when I touch the gas pedal.
I don't know what's going on. I'd image at least a rough idle if there's a vacuum leak.
Any thoughts?

I vote for fuel pump pressure not sufficient . or a TPS problem myself and quite possibly the T.P.S. I always look at the mechanical stuff before getting into the electronics it's probably because the electronic stuff didn't exist for half my career as a professional mechanic but nowadays it's usually an electronic issue and the strange ones almost always turn out to be a bad ground someplace in the system . good luck

 

[EB4X]

OP >>> "I disassembled the upper intake and discovered the o ring on the EGR tube was damaged but also discovered spark plug wire #5 was not connected! I replaced the o-ring on the EGR tube and popped the spark wire back onto the plug. Took it for a drive and all seems well, no codes appeared"

 

[LJM's98Exploder]

OP >>> "I disassembled the upper intake and discovered the o ring on the EGR tube was damaged but also discovered spark plug wire #5 was not connected! I replaced the o-ring on the EGR tube and popped the spark wire back onto the plug. Took it for a drive and all seems well, no codes appeared"

Great glad to hear that . I really like this form and I'm hoping it helps me solve my persistent problem

 

[Kritikal]

OK. Here we are 2.5 half months later. Lean codes still persist. It'll run, but I'm still getting intermittent hard starts and rough running at high speeds. I decided to check my fuel pressure. I'm getting about 28psi at idle which decreases when I open the throttle. I removed vacuum line from fuel dampener and there was no change in pressure. Pressure will hold for quite a bit when turning vehicle off. I can hear the pump turn on when I turn the key. Relay seems to be working as it should; I removed it to relieve fuel pressure before connecting gauge to valve on fuel rail.
Here are the related repairs I've done within the past few months : new upper and lower manifold gaskets, new fuel injectors, new fuel filter.
As stated, fuel pump delivers pressure and holds, but it seems quite low. I say seems because I'm not 100% sure of the fuel pressure specs for a 4.0 OHV return-less fuel line. Live data reads are about the same from before. Should I replace the fuel pump assembly?

 

[EB4X]

"I'm not 100% sure of the fuel pressure specs for a 4.0 OHV return-less fuel line" In a return-less you should be getting a reading from 60 to 70 psi...your "regulator" you see on fuel rail is really a dampner...they look alike...only "return" systems have a regulator there...yours is in the tank....and therefore I'm assuming you shouldn't see much of a change disconnecting that during a test (I could be WRONG on this part)
How old is your fuel filter? If unknown replace that and then re-do fuel test if problem persists....

 

[Kritikal]

"I'm not 100% sure of the fuel pressure specs for a 4.0 OHV return-less fuel line" In a return-less you should be getting a reading from 60 to 70 psi...your "regulator" you see on fuel rail is really a dampner...they look alike...only "return" systems have a regulator there...yours is in the tank....and therefore I'm assuming you shouldn't see much of a change disconnecting that during a test (I could be WRONG on this part)
How old is your fuel filter? If unknown replace that and then re-do fuel test if problem persists....

Fuel filter replaced less then 3 months ago.

 

[EB4X]

Oops....just noticed you listed that prior... yep...sounds like fuel pump then.....28 psi for your setup is waayy too low.

 

[Kritikal]

Oops....just noticed you listed that prior... yep...sounds like fuel pump then.....28 psi for your setup is waayy too low.

It holds fuel pressure although it's low. Could it be a voltage issue? I purchased a meter but not exactly sure how to connect it to check the fuel pumps voltage.

 

[Justinwht]

I'm getting lean codes for bank 1 and 2 ... I unplugged the MAF, nothing changed and it didn't die ... I'd image at least a rough idle if there's a vacuum leak.

A lean engine code can be misleading. It means not enough fuel in the chamber for the amount of air, but if reworded you can say there is too much air in the chamber. The MAF sensor tells the computer how much air is being delivered to the engine and the computer adjusts for the right amount of fuel. If the computer is unaware of any additional air from a vacuum leak, it will give you a lean code.

I'd go ahead and clean the MAF sensor for good measure using a MAF compatible spray, anything else like brake cleaner or other solvents will contaminate the wire sensor. Its easy to get at after you pull out the air filter, its a thin wire stretched across the duct after the filter.

I was getting a lean code from a split vacuum line. Check for vacuum leaks using ether. My problem was a split hose that was intermittently sucking in air. It was the hose from the top of the engine on the driver's side going into evap emissions can just below the left headlight.

 

[Kritikal]

I tested voltage at inertia switch and where harness connects to fuel pump. Started at 12v jumped to 7v, upon turning key; does this rule out a wiring issue? Still getting under 30psi fuel pressure. Pressure is at or below 30psi when priming pump and idling and decreases when opening throttle plate. Truck will run, but of course struggles with low fuel pressure. I ordered a fuel pump, will be replacing in the next couple days. Will post results.