OK, good testing & feedback. I agree it seems you have a continuity problem on the VPWR wire, could be open circuit, could be poor pin/socket crimp connection, or maybe a corrosion problem in the IAC, or computer firewall connector.

Maybe the reason you read B+ on the VPWR lead is because its open circuit back to the computer, so in effect the circuit has no load on it, ie infinite resistance, so no voltage drop from the IAC coil loading the circuit.
For sure the meters high impedance to ground when you probe the VPWR lead, doesn't load the circuit much at all.

So check the connectors for corrosion & flex them while doing the continuity test to see if you can cause contact, as that could indicate on which end of the wire run the problem is.

 

Ok well i went and looked at the connections and they're all clean. Both wires are nice and tight at both ends so i retested the VPWR wire but first i tested the IAC connector from the female side of the connector to about 1/2in down the wire (put a small hole in the insulation) and get an infinite reading and the same on the IAC wire. But out of nowhere when i tested from the IAC connector to the female side of the PCM block i'm suddenly getting 0.4 Ohms of resistance on the VPWR wire (back probed from the IAC connector to the female connection of the PCM firewall block) and nothing on the IAC wire.

I'm not sure what's going on here but i took a look at a wiring diagram and found out the VPWR wire splices off and goes to each of the fuel injectors and to the EVR solenoid. Could this be the reason why i'm not getting much of an Ohm reading back? Beacuse there's too many loads on the same wire for it to read much of anything?

I'm not sure why i'm suddenly not getting a reading on the IAC wire but i'll go back and recheck everything.

Thanks

EDIT: Ok well i decided to test my meter by putting the probes together when it was on the 200 Ohm scale (same scale i've bee testing on) and it gave me a reading of 0.3 Ohms which is the same i'm getting on the VPWR wire and also the same reading i get when i touch both probes to the intake manifold, compressor, and firewall. So i'm geussing this means my VPWR wire is suddenly good?


Here's the diagrams i was using. I've highlighted the VPWR wire and its route and labeled where it's going off-screen for you.

Figure1:


Figure2:

 

The red lead is B+, so what ever the battery voltage is, thats what should be on the Red IAC lead at KOEO, as its being fed off the same splice as the computer, fuel injectors, ect, that become hot when the ignition is switched to Run & this is as it should be..

The White/Blue wire is the IAC switched load VPWR lead, going back to the computer.

SO, the IAC Red lead is B+ DC & the W/B VPWR lead is the IAC computer switched ground lead/load & when the engine is running its pulse width will vary/lengthen at idle, depending on the engine load, like A/C, blower motor, lights ect being turned on.

When engine load increases, the computer ground switches the IAC for a longer time/pulse width, it'll be open longer & the idle speed will go up to handel the load/drag put on the engine, so idle speed remains in spec.

Not sure how your meter is wired to perform, but when we cross connect its leads on the Ohms setting, thats the same as a low resistance measurement, essentially its measuring the resistance of the meters test leads, in your case they're .3 ohms.

With the wiring harness Disconnected from the computers firewall connector & the IAC, you should be able to measure end to end continuity on the IAC Red & W/B leads & they should measure low resistance. I know you posted that the IAC Red lead measured 6 ohms & thats high IF the computer & IAC connectors were Disconnected. By disconnecting the computer firewall connector, you should be bypassing the B+ splice, so that your only measuring the individual wires end to end resistance of the Red & W/B leads going to the IAC & it should be a low ohms value, like the .3 ohms number you have for the meters test leads.

If you measured resistance from the IAC connector, with the computers firewall connector Attached/plugged in, then the Red IAC lead would be connected to the B+ splice & read through any resistive load attached to that splice, so if you got the 6 ohm reading doing the test that way, it'll explain that number.

Right now it sounds like the IAC Red B+ lead is ok, for voltage feed & for end to end continuity.

BUT right now it seems that the IAC W/B, VPWR lead continuity is in question. So keep plugging away at it, to try & get an answer you feel comfortable with.
You could try back probing the W/B VPWR lead with the engine at idle & your meter on the 20 volt AC scale & see if the meter can detect the computer switched VPWR ground pulse.

 

Very nice description on everything but the initial 6 Ohm reading I you a few posts back was for the end-to-end IAC W/B wire when both the IAC connector and the PCM block we're disconnected which is now giving me no ohms reading at all.

At the start the current results were flipped with the W/B giving a resistance reading (6 Ohms) and the VPWR giving nothing at all. Now the W/B is giving no resistance feedback and the VPWR is giving .3 Ohms. Now sure what happened there.

I'll do the idle test you described and let you know what I get back.

Thanks

EDIT: Alright so i back probed the W/B wire and heres my results:

Battery Voltage: 12.50 volts

@ KOEO: 12.22 volts
@ Idle (cold): About 6.5 volts (2100 - 2500RPM)
@ Idle (hot): 12.22 volts (900 - 1100RPM)

After about 5 seconds of running from cold start the voltage went up steadily at about a tenth of a volt until it hit operating temp. Once the idle calmed down the truck was rocking pretty pretty good and sounded like it was going to die. It's done that before and a quick snap of the throttle sets t straight. It has died at idle but only once and that was with the old IAC on.

So it seems the signal is good and being regulated pretty well despite the absolute no resistance reading i had. What else could cause the P1504 code?

 

Well cable/internet is finally up, since last Friday evenings wind storm took it out, maybe long enough to answer your last voltage check.

Guess my answer would be the same as in post 48, to do a wiggle test on the VPWR lead on both ends, to see if you can cause an intermittent problem.

 

Well i went and did the what you suggested and even did it to the IAC signal wire and besides a slightly quicker drop down in RPMs it yielded no results.

I'm at a loss. The ECM is throwing a malfunction code but the circuit is completely fine. What else could it be?

Thanks

 

Well if you can't find or create a problem that matches the trouble code, have a shop with an o-scope have a look at the ground switching pulse that the computers IAC ground switching driver is doing, maybe the driver is acting out.

 

Would a Ford dealership be able to do that? I'm thinking of taking it to Ford anyway for new PCM parameters to be flashed and also seeing if they can do anything about the pesky fuel rails.

 

Probably depends on how large & well equipped the Dealership is. Call the Service Manager & ask, but be prepaired to part with a sizeable chunk of your gold for all you want done, as a large Dealership has plenty of overhead to feed!!!!! Don't you have a locally owned shop with a good reputation that you could try, or at least get quotes from on the work you want done????

So you never got those pesky fuel lines with the garter spring connections, apart???? Bet the local shop, or the Dealership SM could offer up a helpful clue or two on a tool, or technique to try.

Got to thinking some more about the end to end continuity tests you did & how you described your ohms scale meter reading, that I'm not sure about.
When you set your meter to ohms, with the test leads Not touching/open circuit, what does the display show/read???? Then when you touch the probes, how does it read/display????

 

Yes that's very true but i don't know of any shop that will replace lower intake gaskets but i'll look around more.

No i couldn't. No matter what i try those stupid things will not work for me but that's an idea. I'll see if i can get a hold of someone in the service department and see what they offer up in terms of techniques.

On the 200 Ohm scale (scale i used to test) when the leads aren't touching it reads a 1 at the far left with no numbers after it, just blank. But when i put the leads together it goes to 0.4 then a half second later it goes to 0.3 Ohms and stays there until i remove them. The 1 i am guessing means open circuit, or OL on a more expensive meter. I'll redo the test on the 2K scale tomorrow but besides for a lower reading it will (or should) result the same as on the 200 Ohm scale.

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EDIT: Ok well i did a little more digging in what can cause the P1504 and found a list someone had posted on another forum:

Ok going down that list:


So it seems it can still be one of two things if the intake leak can actually cause a P1504 to be thrown. The circuit is fine according to the tests i've done per your suggestions. The only other thing in question is the PCM/ECM which is a pretty pricey replacement

 

On what/how the multi-meter reads resistance with the leads touching & not touching. Here is a post that I'm not clear on, where you posted on page 3 that you were reading 0.00 ohms on your Disconnected IAC & Computer firewall connector, wiring harness short to ground test, on the IAC & VPWR leads, so 0.00 ohms usually means a low resistance, or a short to ground!!!!

If it reads like an open circuit/high resistance/test leads not touching, thats good, it means a high resistance/no short to ground.

I suppose if you had a bad intake vacuum leak, it could cause the computer to get confused about the IAC ground pulse duty cycle range.

With a vacuum leak that raises idle speed, the computer would want the IAC open pulse width command to be very short, in order to keep it closed more often, to try & compensate for the vacuum leak, in order to lower the vehicles idle rpm to get it in range. So if its monitoring the IAC duty cycle/pulse width & finds it below the expected value to cause idle speed to be in spec, it'll set a trouble code & the P1504 code is kinda ambiguous.

I agree the IAC resistance looks to be in spec, as well as the KOEO B+ feed to it.

Right now in my mind, with the extensive testing you've done, just the VPWR lead short to ground test/reading, or the computers VPWR lead ground switching driver pulse are in question & you need an o-scope to have a good look at it.
The switched ground pulse width should be a square wave form, whos pulse width changes with engine idle load, like when we switch the A/C on, ect.

Your meters AC voltage back probe reading sorta suggests things are ok with the VPWR end of the circuit. So if the VPWR short to ground test was ok, that would sorta leave you looking at the lower intake manafold gasket leak.

You don't have any evap system trouble codes set, so a vacuum leak in that system isn't likely, but the lower intake gasket coolant leak you've reported could be figuring in on things, so right now I'd focus on getting that put right & Then see if that also puts the fix on the P1504 code.

Keep plugging way & you'll likely find the problem. Keep us posted.

 

Well i wasn't able to find enough time to remove the upper intake manifold and inspect the VPWR wire (runs from the IAC and underneath the manifold causing it to be removed to be inspected) but i FINALLY received my order from autozone today that includes the 2 new O2 sensors, a door jam switch for the passenger door, and a new Duralast TPS.

I went and ordered a new TPS because the BWD sensor i put in 2 weeks ago was reading 13.2% throttle when the TB plate was completely closed leading me to suspect that is was poorly made so i ordered a new one. But now the Duralast TPS is having the same problem. It's reading 16.1% throttle when the TB plate is fully closed and only 86.7% throttle at WOT. I even backed the idle screw all the way off (no change) then started re-adjusting it and could see the percentage climb the more i turned it. Is there a way to fix this? It's causing the idle to be higher because of this when i'm trying to fix the stupid idle speed! I know it's causing idle problems because when i unplug it the idle drops. When not bolted to the throttle body i line the TPS slot up with the "blade" that fits into it and if i don't turn it to line it up with the bolt holes the throttle % is at 2 (way better than 16) but as soon i turn it to line it up with the bolt holes it starts incresing until it reaches 16.1% which at that time im lined up perfectly with the bolt holes.

I aske again, is there a way to fix this? It's very annoying in the fact that it's screwing up the idle and also i never what what my exact throttle position is.

Thank you

Oh also i'm currently in the process of contacting various local shops as well as my local Ford dealership to see what they can provide in suggestions and techniques to remove the fuel rail connectors.

 

The TPS mounting isn't adjustable. When its mounted, the electrical connector Disconnected, throttle closed, it'll typically measure 3K-4K ohms between the VREF & TP terminals & approx 350 ohms at the WOT position. With the TPS connector Disconnected, at KOEO, with the meters + test lead on the TPS connectors VREF contact, you should measure a 5 volt ref from the computer to a good clean ground

 

Then I need to order an adjustable one from edlebrock to get the correct reading. This TPS is perfectly fine. When not hooked to the throttle body it reads 0.0 like it should its when I hook it up to the TB and move it to line up the bolt holes that it goes to 16.1. It's either the pin that goes through the TB to the slot in the TPS not being positioned right or the TPS just isn't calibrated correctly

 

Are you sure you have the right part number????