New 5.0L built, low compression and horrible MPG

[4pointslow]

Iac

IAC duty cycle should be 30-34% on a fully warmed up engine at Idle for your 1996 Explorer 5.0L
TPS Voltage should be .53-1.27 Key On Engine Off. That's just the range according to ford specs.
I believe most TPS readings are about .9-1 volt at warm Idle running.

 

[1997XLTRollover]

I get a feeling a new valve would read the same ohm reading. 54 isn't too far off from 38 and my f-150 works just fine and read the same identical reading.

If we assume the valve is good where would the next logical step be to look? Is there a ground that could be bad causing this circuit to not ground? I tried following the wire to be sure there are no breaks but it goes up into the body somewhere and I don't have a 96 wiring diagram.

On a side note my fuel gauge is getting worse by the day. Not sure if it's related but maybe they share a ground somewhere?

 

[4pointslow]

Ground wire

If we assume the valve is good where would the next logical step be to look? Is there a ground that could be bad causing this circuit to not ground? I tried following the wire to be sure there are no breaks but it goes up into the body somewhere and I don't have a 96 wiring diagram.

On a side note my fuel gauge is getting worse by the day. Not sure if it's related but maybe they share a ground somewhere?

1. If the power wire is good and the vent solenoid is assumed good the only thing left is the ground wire (control wire), stretched terminal on a connector, or bad PCM. If the problem is intermittent everything will test good unless you are lucky enough to have it act up while testing.
The PCM controls the ground so that wire goes from the vent solenoid all the way to the PCM. If it is the purple with white stripe it goes to pin 67 at the PCM. Do a resistance check from the solenoid to the PCM, it should be 5 ohms or less. We use guitar strings cut to short pieces on the end of our tests leads, they can not stretch a terminal open. Touch your two test leads together and see if it reads 0 ohms first, that will test the accuracy of your meter and leads.
Let us know the reading you get.

2. There is no other ground that could cause this code to set. No shared ground.

Have you checked the ignition switch in the steering column yet?

 

[4pointslow]

Canister Vent Solenoid Resistance

The specs I found on the Canister Vent Solenoid were out dated.
The new spec is 48-65

 

[1997XLTRollover]

1. If the power wire is good and the vent solenoid is assumed good the only thing left is the ground wire (control wire), stretched terminal on a connector, or bad PCM. If the problem is intermittent everything will test good unless you are lucky enough to have it act up while testing.
The PCM controls the ground so that wire goes from the vent solenoid all the way to the PCM. If it is the purple with white stripe it goes to pin 67 at the PCM. Do a resistance check from the solenoid to the PCM, it should be 5 ohms or less. We use guitar strings cut to short pieces on the end of our tests leads, they can not stretch a terminal open. Touch your two test leads together and see if it reads 0 ohms first, that will test the accuracy of your meter and leads.
Let us know the reading you get.

2. There is no other ground that could cause this code to set. No shared ground.

Have you checked the ignition switch in the steering column yet?

Ok thanks, I'll check that wire as soon as possible. I'll have to use an extension wire though obviously since my meter leads are not long enough. Think that will change my reading much?

Also no I have not looked at the ignition yet. It's my DD so I have to be careful with what and how much I pull apart each day. Could the ignition be the reason this evap is messed up or is that more for the fuel gauge?

 

[4pointslow]

1. no, hook the two test leads together and see if the ohms are 0, if not note what they are.
2.fuel gauge

 

[1997XLTRollover]

Well I tried adjusting the iac and if I lower the idle screw any more, the throttle plate binds and sticks to the throttle body.

 

[1997XLTRollover]

Well wiring seems fine. 0 ohms. I tested the extra wire I ran from the computer to the back of the truck and it read 2. So I measured across the whole circuit and got 2 ohms. So it seems like wiring is good. This makes no sense. I can predict when the light is going to come on so I don't think it's an intermittent issue.

 

[1997XLTRollover]

1. no, hook the two test leads together and see if the ohms are 0, if not note what they are.
2.fuel gauge

Could this P0446 code be caused by a leak in my EVAP system? My truck is pretty rotted in spots so I wouldn't be surprised. Everything else seems to check out. It may also account for my slightly lean condition depending where and how it's leaking.

 

[4pointslow]

Leak setting code

No.

 

[4pointslow]

Po443

The P0443 is an electrical fault code for the Canister Vent valve.
The problem can be intermittent or not.
It can be caused by
Open VPWR circuit
Open or shorted Canister Vent Valve
Control circuit open, shorted to ground or shorted to power
Or bad PCM
Stretched terminals in the connector or terminal fretting (corrosion) can also cause the code to set.
(The corrosion would have to be so bad that it caused an open circuit by interrupting the connection completely.)

 

[1997XLTRollover]

The P0443 is an electrical fault code for the Canister Vent valve.
The problem can be intermittent or not.
It can be caused by
Open VPWR circuit
Open or shorted Canister Vent Valve
Control circuit open, shorted to ground or shorted to power
Or bad PCM
Stretched terminals in the connector or terminal fretting (corrosion) can also cause the code to set.
(The corrosion would have to be so bad that it caused an open circuit by interrupting the connection completely.)

I'm assuming you mean P0446. But assuming so I'm at a loss then. My circuit has no resistance, vent valve measures out perfect and when power is applied to it, it operates. I have no ground shorts and I've replaced the PCM and the same code comes back. I've cleaned the ever living hell out of what already looked to be clean connectors.

I can tell you when the problem will come back so I do not feel it's intermittent. I will reset it on Sunday, drive all week and Friday night it will pop on. It will pop on earlier if I take a highway trip during the week. My normal commute is around 50-60 MPH max and less than a 10 minute drive.

Could be be a clogged charcoal canister?

 

[1997XLTRollover]

http://www.obd-codes.com/p0446

If I'm reading that right it looks like if I had a major vacuum leak it would set the code too because it cannot get enough vacuum for the computer to test the valve. Maybe that big leak tricks the PCM to thinking it's not purging the valve?

 

[4pointslow]

Code

Looking at the Ford PC/ED for engine diagnostics I see some typos. So I must have looked at the description given by your scan tool that says open or shorted circuit and thought the code was P0443 which can only be set by circuit problems. I must be getting old. lol.

The code you say you really have P0446 links to a pinpint test that says it is for P1450. I then looked at the same code for a 1997 and found that the pin point test is for P1450 and P0446. Sorry for the confusion.
Here is the first Pin Point test for P0446, it can be caused by vacuum leaks, bad vent valve, purge valve, fuel tank pressure sensor, or cap loose/off etc.

 

[4pointslow]

Evap monitor test

The evap monitor test runs when the fuel is between 15-85% fuel in the tank.
The PCM closes the vent valve and then opens the purge valve and tries to pull a vacuum on the fuel tank. There is a fuel tank pressure sensor that measures the vacuum and reports back to the PCM. If the system can pull a vacuum then there is no large leak, then it closes the purge valve and keeps the vent valve closed to hold the vacuum in the tank. If it holds it long enough there is no small leak.

 

[1997XLTRollover]

The evap monitor test runs when the fuel is between 15-85% fuel in the tank.
The PCM closes the vent valve and then opens the purge valve and tries to pull a vacuum on the fuel tank. There is a fuel tank pressure sensor that measures the vacuum and reports back to the PCM. If the system can pull a vacuum then there is no large leak, then it closes the purge valve and keeps the vent valve closed to hold the vacuum in the tank. If it holds it long enough there is no small leak.

So basically odds are I have a leak somewhere. Everything on the purge circuit seems fine. Now here's the next question. Since my fuel gauge is FUBAR could that be screwing up the EVAP test? I would say 90% of the time the gauge is reading right so at some point it must run the test but sometimes the gauge just drops to E or jumps around.

Guess I have to find somewhere to get Nitrogen and run a smoke test on my EVAP system.

 

[4pointslow]

gauge

If the gauge alone is messed up then the evap system may not be affected.
If the sending unit or wiring is messed up it could affect the Evap system since the PCM is supposed to know how much fuel is in the tank when running tests.

 

[1997XLTRollover]

If the gauge alone is messed up then the evap system may not be affected.
If the sending unit or wiring is messed up it could affect the Evap system since the PCM is supposed to know how much fuel is in the tank when running tests.

Based on what I see I'd put my money on the sending unit. I could be wrong but that would be where I'd make my bet. Like I said my truck is fairly rusted and my EVAP lines look like hell so I wouldn't be surprised if I had huge leaks somewhere. I'm going to find some nitrogen and smoke it to see if I can find anything.

 

[1997XLTRollover]

If the gauge alone is messed up then the evap system may not be affected.
If the sending unit or wiring is messed up it could affect the Evap system since the PCM is supposed to know how much fuel is in the tank when running tests.

Ok well I know it's been a bit here but I'm fairly confident my EVAP system is now fixed and I have no check engine light for the first time in 2 years (light at the end of the tunnel... sort of). It was funny, I was smoking the EVAP system after finally finding Nitrogen and ran 2 full cycles and found no leaks, which actually surprised me based on how my lines look. Then I ran a third cycle and bam, something exploded (read: smoke all over the place) probably from the reverse pressure I was putting through the system. Long story short it was blowing out my purge valve.

This seemed odd to me so I took my charcoal canisters down and sure enough there was a fair amount of dirt clogging the intake side. I cleaned it out best I could and put it back on. So far I've run 2 tanks through and the light has not come back, usually it comes back after 1 tank. So I would say I accidentally fixed my issue with my EVAP system.

Now here's the disappointing part, my fuel economy has not changed. It's the same horrid fuel mileage I always get. Around 10 city and 13 highway. Even if we assumed my speedometer was off 10% that's still only 11/14 and we all know I should be getting better than that even with 32's, at least I would think. My 99 got 9mpg with 10 ply 35's, I would think with 6 ply 32's I would do a fair amount better than that.

Could small leaks in my y pipe on my cats effect this? There are some really really small pin holes on the bottoms of my cats (so it would only effect my downstream o2's) and I mean small.

 

[4pointslow]

Explorer

In theory any leaks after the front O2 sensors, wont effect the way the vehicle runs. That's because the rear O2 sensors are only for setting catalyst efficiency codes, they don't even effect fuel trims.

The front O2's, they are a different story. Any leaks before them will cause air to be drawn into the exhaust system and those O2's will report a lean condition. The PCM will then add fuel and there goes your fuel mileage down the toilet.