P0506 Code, out of ideas

[Drewstang]

I started getting a P0506 code every couple weeks or so, I did some research and diagnosing and found a couple vacuum lines were loose and adjusted the intake tube on the TB. Then it came back again so I replaced the IAC with a new Duralast 03-04 Cobra model. That seemed to help but not for long. Now the code is back and will come back on the second key cycle after clearing it. I've checked all the vacuum hoses inside and out with a pump and the starting fluid method. I'm out of ideas and looking for help. This car has been Eaton swapped and given me very little problems until this. Any ideas?

[sailsmen]

Check your popoff on the Eaton.

[Drewstang]

Tested the bypass valve. Arm moves as vacuum is applied and it will hold vacuum.

[Zack]

Post a picture of the IAC on the plenum please

[Drewstang]

http://i5.photobucket.com/albums/y185/Drewstang/03%20Marauder%20Ver%202/6F0B4104-1A9F-49A9-907F-8BA53446BCDC_zpsxfkvjkea.jpg (http://s5.photobucket.com/user/Drewstang/media/03%20Marauder%20Ver%202/6F0B4104-1A9F-49A9-907F-8BA53446BCDC_zpsxfkvjkea.jpg.h tml)

[Drewstang]

I also noticed the HVAC fan is not consistent on speed while driving and there is a hesitation in the throttle. Vac at idle is 19-20 in, part throttle 5-10 in. More testing with starting fluid and still nothing. I'm starting to lean towards a gasket leak on the blower / lower intake manifold.

[Drewstang]

Any suggestions? This is frustrating as hell.

[Paul]

Evap fuel solenoid and its lines? (on the firewall to left of tran dipstick). I dont know how its plumbed with the eaton, but the oem lines are hard plastic and sealed by oring. Maybe theyre leaking? It could also be temp or vibration related and not show when your testing.

And what about egr valve. Can they create vac leaks when theyre old/dirty?

[Drewstang]

Evap fuel solenoid and its lines? (on the firewall to left of tran dipstick). I dont know how its plumbed with the eaton, but the oem lines are hard plastic and sealed by oring. Maybe theyre leaking? It could also be temp or vibration related and not show when your testing.

And what about egr valve. Can they create vac leaks when theyre old/dirty?
I checked the lines going to the evap solenoid, but I did not test the solenoid itself. EGR is deleted on my car. This code comes on no matter temp or condition on the second or third key cycle after clearing.

[Drewstang]

I checked the EVAP and lines going to it with no luck. Out of frustration I checked the line going to the boost gauge. I could hear it leaking behind the booster. Unhooked the gauge and capped the line, then cleared the code and drove the car all weekend without it reappearing. I'll be getting a braided line from the local speed shop today and running through a different grommet.

[FordNut]

I checked the EVAP and lines going to it with no luck. Out of frustration I checked the line going to the boost gauge. I could hear it leaking behind the booster. Unhooked the gauge and capped the line, then cleared the code and drove the car all weekend without it reappearing. I'll be getting a braided line from the local speed shop today and running through a different grommet.

Good find. Thanks for posting the solution, we'll know what to look for if we have a similar problem.

[RF Overlord]

Good on ya' Drewstang! I know it sucked to troubleshoot, but I'm glad it wasn't a difficult or expensive fix.

Especially thanks for posting the fix. Many times we give info/advice and never hear the resolution.

[Drewstang]

Glad to help guys, thanks for the suggestions.

[Drewstang]

After tracking down a few vac leaks I thought I had this beat. The tuner suggested using a FoMoCo IAC instead of the aftermarket unit I was using. I've done this and the code is back again. I did notice it seems to be AC related. We had a week here that I did not use the AC at all and I did not get the MIL at all. The next week the temp and humidity soared and the MIL came on. When the summer started the AC compressor would not engage and turned out to be a faulty relay which was replaced. My gut tells me the AC compressor is to blame by "drawing down" the idle speed too much for the PCM to compensate for. Anyone else experienced this?

[ByronRACE]

After tracking down a few vac leaks I thought I had this beat. The tuner suggested using a FoMoCo IAC instead of the aftermarket unit I was using. I've done this and the code is back again. I did notice it seems to be AC related. We had a week here that I did not use the AC at all and I did not get the MIL at all. The next week the temp and humidity soared and the MIL came on. When the summer started the AC compressor would not engage and turned out to be a faulty relay which was replaced. My gut tells me the AC compressor is to blame by "drawing down" the idle speed too much for the PCM to compensate for. Anyone else experienced this?

PCM has tons of compensation capability; it opens the IAC; which can raise the idle well over 1200RPM on most Fords. In fact, I use the IAC as cruise control with a switch chip on my cobra replica. 1600rpm in 6th is about 65mph. So, I doubt load is causing the RPM drop to fall out of spec. The code will only be flagged if the strategy fails to compensate for the RPM drop; it's not immediate.

The IAC would have to open up and the RPM not increase; or the IAC itself doesn't open up (bad pcm driver FET or intermittent connection). What are your LTFT values at idle on a warmed up engine? What is the MAF reporting (in units of air mass). What does the ECT say the engine temp is? Does the system report it's in closed loop? These things may offer a clue. Most 4.6 Fords idle at about 24kg/hr of airflow at 750rpm. Fuel trim values should be under 10%; and hopefully under 5% at idle. The ECT is a major influence on air fuel ratio in open loop, and an in-bound failure that reported a too-warm temperature could lean the mixture excessively during warm up, cause low idle, and trip the code. A temperature being reported too cold could keep the strategy in open loop and cause other problems.

If the MAF reports much less than 24kg/hr, you're pulling in unmetered air from somewhere or the maf is bad or dirty. A 1/8" diameter hole somewhere will flow about 8kg/hr of air at idle and result in a 15-20kg/hr reading. That's the kind of thing you see if you have a small vacuum line off. Are you an oiled K&N filter user? If so, you may have a contaminated MAF. That oil plays hell on the sensor...see it all the time. Sometimes you can clean the element with sensor cleaner or starting fluid and get it back close enough; sometimes you can't. If enough oil gets baked into the element, it's done.

[Zack]

Just turn the code off

[Drewstang]

Just turn the code off
My OCD won't let this happen.

PCM has tons of compensation capability; it opens the IAC; which can raise the idle well over 1200RPM on most Fords. In fact, I use the IAC as cruise control with a switch chip on my cobra replica. 1600rpm in 6th is about 65mph. So, I doubt load is causing the RPM drop to fall out of spec. The code will only be flagged if the strategy fails to compensate for the RPM drop; it's not immediate.

The IAC would have to open up and the RPM not increase; or the IAC itself doesn't open up (bad pcm driver FET or intermittent connection). What are your LTFT values at idle on a warmed up engine? What is the MAF reporting (in units of air mass). What does the ECT say the engine temp is? Does the system report it's in closed loop? These things may offer a clue. Most 4.6 Fords idle at about 24kg/hr of airflow at 750rpm. Fuel trim values should be under 10%; and hopefully under 5% at idle. The ECT is a major influence on air fuel ratio in open loop, and an in-bound failure that reported a too-warm temperature could lean the mixture excessively during warm up, cause low idle, and trip the code. A temperature being reported too cold could keep the strategy in open loop and cause other problems.

If the MAF reports much less than 24kg/hr, you're pulling in unmetered air from somewhere or the maf is bad or dirty. A 1/8" diameter hole somewhere will flow about 8kg/hr of air at idle and result in a 15-20kg/hr reading. That's the kind of thing you see if you have a small vacuum line off. Are you an oiled K&N filter user? If so, you may have a contaminated MAF. That oil plays hell on the sensor...see it all the time. Sometimes you can clean the element with sensor cleaner or starting fluid and get it back close enough; sometimes you can't. If enough oil gets baked into the element, it's done.
ECT has been reading 180 at idle on warmed up engine. I'll have to look at MAF measurements and loop. LTFT was below 5% at idle, but I'll double check. MAF could be dirty or oily as it has a Spectre filter on it that hasn't been cleaned in a while.

[ByronRACE]

When the maf gets dirty, they read less air flow than what is actually entering the engine and the PCM delivers too little fuel, so the mixture runs lean and the idle will tend to be low during open loop. During closed loop, fuel trim will correct the issue and it will trim out with positive fuel trims and a correct air fuel ratio and idle speed.

If idle is low enough long enough at start up on a cold engine, that might set the code. Just an idea.

B

[Drewstang]

When the maf gets dirty, they read less air flow than what is actually entering the engine and the PCM delivers too little fuel, so the mixture runs lean and the idle will tend to be low during open loop. During closed loop, fuel trim will correct the issue and it will trim out with positive fuel trims and a correct air fuel ratio and idle speed.

If idle is low enough long enough at start up on a cold engine, that might set the code. Just an idea.

B
Thanks, I'll check into that. Its just weird how the AC seems to affect it as well.

[Zack]

Thanks, I'll check into that. Its just weird how the AC seems to affect it as well.

The IAC valve raises the engine rpm to compensate for the compressor clutch engaging