1999 Expy 5.4L v8 throwing multiple codes, help please!!

[Witchy_Libra_33]

Hi guys! I'll try to keep this post short, but I want to make sure I cover everything that's happening with my Expy.

Ok so I have a 1999 Expy 5.4L triton v8 with around 260,*** miles on it. Had it almost a year now, and everything has been smooth sailing until about a month or so ago. The start to everything was when my husband was under the hood trying to check the spark plugs. While in the process of doing this, one of the connectors from the heater core hose assembly broke as he was simply trying to move them aside so he could get to the spark plugs on the left side of the engine (plugs 1-4), which wasn't a hard fix, just bought new hoses and replaced broken parts, but he never got to check the spark plugs. Now here's where the nightmare begins. After fixing the hoses, the Expy started idling a lot rougher than usual and while driving, it would start shaking/vibrating pretty badly between 40-50mph but would stop at lower or higher speed than that. Along with that, the SES light came on (and has yet to go off) and the oil pressure gauge started going haywire. The low oil pressure light would come on and the gauge would drop to the low side of gauge for about a minute or so and then return to normal for a few minutes and then drop down past the low side and back to normal over and over, and now the light stays illuminated and it's reading below the low side of gauge. A friend suggested to get an oil & filter change, which was done with no problem. Thought that might have been the issue seeing as the Expy started running noticeably smoother with very little shaking/vibrating noticed, but still present. Borrowed an OBD II scan tool from a family member, hooked it up to our car and it gave these codes:

P1400 DPFE Circuit Low Input
P0308 Cylinder #8 Misfire

So naturally the first thing checked were the spark plugs. This was done about 2 days after the oil change. Bought all 8 new plugs and had them changed (#8 was absolutely horrific looking, so it's safe to say that was overdue!). Took it for a test drive only to find the vibration from before had returned, but much worse, along with loss of power on acceleration and revving up past 3000rmps before shifting. At this point we are getting frustrated as to what's going on, so we again plug in the OBD II scan tool and this time it spit out the following codes:

P1400 DPFE Circuit Low Input
P0171 System Too Lean (Bank 1)
P0174 System Too Lean (Bank 2)
P0303 Cylinder #3 Misfire
P0307 Cylinder #7 Misfire
P0308 Cylinder #8 Misfire
P0113 Intake Air Temperature Sensor 1 Circuit Low

Double checked all spark plugs and discovered the boot from coil pack for #7 was shot and needed to be replaced. Ok, no problem, bought and replaced. After which, the SES light went off for first time since it lit up. Did a test drive to town and back, maybe a total of 10 miles round trip. Expy was running smooth with very minimal vibrations, but by the time we got home, the SES light was lit up again so we went ahead and plugged in the OBD II scan tool for a third time and it's still spitting out P1400, P0171, P0303 and P0307. For reference, the plugs and oil change were all done within the last week and a half, so it's a current ongoing issue that we can't for the life of us figure out what the exact problem is or what needs to be done to actually fix said problem. Is anyone has ANY advice or can point me in the right direction or knows what the deal is and can tell me how to fix it, that would be awesome and I'd really really appreciate it because it's becoming such a headache, I'm ready to roll this thing off a cliff!! Please help!! Thank you so much in advance!!

 

[Hamfisted]

Look for vacuum leaks. That'll cause your P0172, P0174 codes, and misfires as well. Bad coil boots will also cause misfires. The easiest way to find vacuum leaks is with a smoke machine. If you don't have access to one of those you're just gonna have to do it by close inspection and listening for air hiss.

Mechanics Smoke Machine on Amazon






.

 

[Witchy_Libra_33]

Look for vacuum leaks. That'll cause your P0172, P0174 codes, and misfires as well. Bad coil boots will also cause misfires. The easiest way to find vacuum leaks is with a smoke machine. If you don't have access to one of those you're just gonna have to do it by close inspection and listening for air hiss.

Mechanics Smoke Machine on Amazon

My husband was just saying something yesterday about it possibly being a vacuum leak somewhere, so that will be the next thing we check, thank you for the advice!! I'll post an update after it's been checked (and fixed if needed) and let you know if that solved anything.

 

[VoxVeritatis]

Included in the vacuum leak check should be an intake manifold check at the crossover (low, in front of manifold on my 2002). After chasing down potential hose vacuum leaks in my 2002 Eddie Bauer 5.4L Triton at 100K miles less than you have on yours, I isolated a leak at that crossover. Replaced the plastic manifold. Also replaced coils, injectors, and plugs at the same time since I was deep into it. And no more issues since.


Footnote:

Sadly, my daughter was stopped at a light, and some guy in a minivan admitted he wasn't watching and rear-ended her. I'll be bidding my EB Expy a bittersweet farewell. It has the heat shield rattle, and exhaust running hot - no codes...but probably needs cats. Bought it new (2 miles on it), and after this week, it'll be gone. I still have the original price sticker.

Updated to add: Has 189K original, garaged, one-owner miles. Minivan driver's insurance has offered $5K. Holding out for closer to $6K minimum. Still drivable with no frame damage, but a 'wrinkle' on the rear driver-side quarter panel, and needs a new rear bumper. Repair estimate is more than 70% of the cash offer.

 

[EngineerMike]

For the amount of labor to change all plugs, cost of new boots is minimal & they get old & misdirect the spark, so IIWMI'D change all boots when doing plugs. Coils are expensive & fairly reliable but they go bad also on occasion, so before changing coils U can swap existing coils to see if a miss follows the coil & only change bad coils.
Another help on finding vac leaks is a vac gauge, plug it inline with any vac hose, extension hose is good so you can put it where you can see it, & do wiggle test on all rubber & hard plastic vac parts while keeping an eye on the gauge for a drop in vacuum to indicate a problem seal or crack. I believe there is a hard plastic vacuum canister by the battery, the 4wd shift vac solenoids are on the firewall next to batt, then all the vac stuff on engine. Its easy to break old hard plastic lines due to brittleness when pushing stuff around.

I changed all plugs & boots on my 99 @ 170k and it drove radically smoother and I gained 6mpg (from 12-13 which I knew was wrong).

 

[JamaicaJoe]

One thing I learned apart from the many ways moisture can cause misfires in these engines, is that once a plug gets fouled you might as well go to lunch for a few hours because a fuel fouled plug is as bad as coil that got damp. Wait for it all to dry out and try again. It is rough on the engine to drive like that and I think the ECU will shut down fuel to that side (lean code) to protect the CAT. For me it has always been simple stuff. The COP or boot gets damp and it misfires. Also the plugs should be changed at 40K intervals.

 

[jr1under]

Re: the P030x codes, my Exp and F150 have thrown several of those over the years accompanied by running horribly. Maybe I've just been lucky but a new ignition coil has always fixed the problem. It did take a couple of repeats on the same cylinders to teach me never to use aftermarket coils.

 

[rjrodney]

Motorcraft plugs only for 1st Gen Expedition. I’ve used the off brand coils though without any troubles.
Also, check for coolant back there. The upper intake manifolds are known to crack and leak coolant down on the coils and plugs. This seems to happen to me every 10 or 12 years between the manifold and the heater return hose. Look for coolant in the engine valley and in the spark plug wells.

 

[VoxVeritatis]

Motorcraft plugs only for 1st Gen Expedition. I’ve used the off brand coils though without any troubles.
Also, check for coolant back there. The upper intake manifolds are known to crack and leak coolant down on the coils and plugs. This seems to happen to me every 10 or 12 years between the manifold and the heater return hose. Look for coolant in the engine valley and in the spark plug wells.

My experience precisely. In the 2002 5.4L it'll consistently be at the crossover in the front of the intake manifold.

 

[MesaGuy]

For your codes:
P1400 DPFE Circuit Low Input
P0174 System Too Lean (Bank 2)
P0303 Cylinder #3 Misfire
P0307 Cylinder #7 Misfire
P0308 Cylinder #8 Misfire
P0171 System To Lean (Bank 1) or
P0113 Intake Air Temperature Sensor 1 Circuit Low

For these codes:
P0303 Cylinder #3 Misfire
P0307 Cylinder #7 Misfire
P0308 Cylinder #8 Misfire
- For these three: replace the coil packs. But before replacing, go through and write the cylinder number on each coil you have with a Silver Permanent Market on the top. Then pull those three. Before pulling them, I would double check the seating of the wire-harness to coil plugs. These connectors often do not seat that well, and you have been in there changing plugs, so good chance you may not have gotten good seating. (The connector is not seated unless it clicks, and doesn't pull off when tugged (without pressing the release tabs). If it comes off with the tug, it wasn't seated. Assuming seating is good, you truck is old, and the coils could be failing together. Keep the old coils, you may end up putting back in later.

I'd buy genuine Motorcraft plugs, off a junker from a junk yard. (These are not a long term solution, because used coils are hit or miss for longevity, but usually better than aftermarket cheapy Made-in-China 10K-- coils.) Main reason is to give diagnostic capability at a low price. Replace the three failing coils. #7 is challenge, need a 7mm u-joint socket to get the bolt-head screw without pulling the fuel rail. #8 is a (non-)joy because it back under the ledge. #3 is not too bad.


P1400 DPFE Circuit Low Input
DPFE valve is Motocraft $60 new on Amazon (free Prime delivery), same at RockAuto, but not free delivery. I recommend the Motorcraft part. The Standard Motor Products is not a bad part, about $35 at either, the Motorcraft will last longer. This is an easy swap in. Right under the plastic cover on the engine. Remove cover. Mark (A,B) the two hoses and the two prongs on the old part, then remove the two hoses, unclip the connector on the back, unbolt, replace, reclip, rehose, in the same configuration (A,B) as original.

The other codes sound like a vacuum leak. So many places. On the '99 their is a right angle rubber hose "fitting" at the very back of the engine, on the back of the intake manifold. Exceptionally hard to get to. I usually have to lay on the engine manifold and reach back to the firewall, and reach down, down, down, and pull the rubber 90 degree rubber piece off the intake. Replace, put one end on the plastic vacuum tube that comes from the PCV valve, and lay on the engine, and plug it back into the intake. That piece often melts over time, and is frequently an issue on the '99. Otherwise, check the PCV valve grommet seal, and all of those vacuum lines on the passenger side, as you were messing with them when you replaced the plugs the first time. Another "often fails" '99 is the hoses between throttle body, and the air intake:


The front hose here, and the second one back at the rear both crack and often get leaks.