Possible Fuel/Air mixture problem

Posted by: DonnieK

Possible Fuel/Air mixture problem - 09/10/20 09:02 AM

2005 CVPI here, 130k miles, mostly original... Kinda long story ahead, but trying to give full context.

So I searched through the topics and found a couple possible related, but ive got a combo of things happening.

I noticed a few months ago that the car would run slightly rough immediately after fill up. Many people report having problems STARTING, but mine would crank immediately, and then run rough for about 5 min before everything was fine. Didnt think much of it, ran some sea foam through for possibly some gunk in there. Also, I do 90% interstate driving in this car. 350 miles at a time.

So, about 3 weeks ago, I filled up in the city and was driving around and the thing started running VERY rough and died at several traffic lights. When I pushed down the accelerator, the engine would die, almost like it was choking out. Even got a backfire like there was a really bad misfire. Drove home and the the next day the car ran fine again, like nothing was the matter.

Yesterday, after the car had been sitting for about 4 days, I got in, and started down the interstate. After about 20 minutes, the engine just slowly choked out, and if I pushed the accelerator, it would actually lose RPM. So, after reading some of the forums, I checked a few things and nothing worked. Well, I ended up removing the gas cap and the car started right up. I put it in drive and proceeded to drive 180 miles without issue. Oh, I should also say the car had approx half a tank of fuel with the recent issue. So, I needed gas to get home, so I stopped and filled the tank, but didnt shut the engine down. It never even burped. Ran like a top all the way home.

So I deduced that I potentially had a bad gas cap. So, I drove to the gas station, filled up, then across the street to oriellys to get a new gas cap. Put the new cap on and not only ran rough this time, but threw a check engine light. 02 upstream sensor. ALso cyld5 misfire. So, took the cap off and was able to limp the car home.

Im at a loss here, without replacing basically all my air sensors, etc etc. Full blown tune up maybe, I guess its probably about time for that anyway. But does anyone have a guess on what might be going on here. Its like the engine is starving for air. But the fact that it starts right up is what is baffling me here.

Thanks for reading, if youve gotten this far.
Posted by: professorP7B

Re: Possible Fuel/Air mixture problem - 09/10/20 11:28 AM

Sounds like an EVAP vent valve or plumbing issue. As the engine runs and the fuel pump pumps fuel from the tank, air needs to enter through the EVAP vent to fill in the space left behind in the tank as the level drops. If it can't get in, a vacuum is pulled on the tank to the point that the pump can't pull fuel anymore.

An EVAP canister that is flooded with fuel will also cause this issue. "Topping off" (continuously clicking the gas nozzle after it clicks off) will easily cause this problem.

Removing the gas cap prevents a vacuum from being pulled on the system, hence "correcting" the issue. The upstream O2 code and Cyl.5 misfire are probably just a result of the engine going lean due to fuel starvation when the issue occurs.

I would start by checking the vent line from the canister. On my '11 anyways, the line comes off the right side of the canister (which is bolted to the trunk pan, under the car) and snakes up into the passenger side frame rail. Make sure this hose isn't blocked.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 09/10/20 03:10 PM

Good stuff! I read a similar issue with a similar fix. I'm gonna give it a shot and ill report back.
Posted by: Lance01

Re: Possible Fuel/Air mixture problem - 09/10/20 05:25 PM

Check all your rubber vacuum hoses. I had numerous cracks in various hoses so I went to the junkyard and got a handful of hoses off newer Fords. Went to the counter to pay and they let me have em all for free. My car now runs just a tad bit better now and no more hissing sounds from the PVC plumbing area.
Posted by: RF_Overlord

Re: Possible Fuel/Air mixture problem - 09/11/20 01:42 PM

I second everything professorP7B said.

In addition, check the CVS (Canister Vent Solenoid) in the same tray as the charcoal canister, It should be normally open to allow fuel to be pulled from the tank (as professor explained). If it's clogged or defective/stuck shut, you'll have that vacuum condition he described.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 09/15/20 04:40 PM

Ok, checked those lines, no apparent blockages. Put on a new fuel cap and once the car was cold, everything runs fine. But once the car gets warm, and then shut the engine off, re-start is fine, but runs rough and replicates issue. Took the cap off and still doesnt run very well. Took me about 20 minutes in the parking lot at lunch to get it where it would run good enough to drive.

Same problem, runs rough and when you push the accelerator pedal, it sounds like the engine is being choked out. So, under the hood, at the evap purge solenoid, I took on of the vacuum hoses off and it was sucking really good air. When I plugged it with my finger, the engine instantly died.

Amateur assessment here, but could that mean the purge solenoid is fine and doing what its supposed to and perhaps my issue with the evap canister valve, or the canister itself?
Posted by: professorP7B

Re: Possible Fuel/Air mixture problem - 09/15/20 07:02 PM

If I'm understanding you correctly, you pulled the supply line to the purge solenoid and felt vacuum, plugged the end of the supply line with your finger and then the engine died? If you pulled the hose from the solenoid down to the canister and you felt vacuum it was either in a purge cycle when you checked it or the purge valve is bad.

With the purge solenoid completely disconnected from all hoses and wires, try blowing through it; you shouldn't be able to. If you can blow air through it while it is unplugged/disconnected, it's stuck open. This could certainly cause a lean condition, and if left long enough fuel trims might be so rich that once the vacuum leak was plugged up (via your finger blocking the purge supply line) it just choked out with fuel.

I'm spit-balling a bit here based on what I'm reading so far. But what I've described above might also explain why messing with the fuel cap seems to have some effect on the running condition.

I know these engines are also seriously prone to intake problems, but haven't dealt with one personally. I'm sure others could chime in on that possibility.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 09/15/20 09:29 PM

It wasnt the line from the tank, but rather the line from the solenoid to the intake manifold. I pulled it off and was unable to blow through it. It runs a purge when the car is cold, correct? The car was very warm when I plugged the hose and made it stall out. It doesnt seem like there is a vacuum leak, but is it possible that the leak is so subtle, its hard to detect?
Posted by: RF_Overlord

Re: Possible Fuel/Air mixture problem - 09/16/20 12:21 AM

Originally Posted By DonnieK
So, under the hood, at the evap purge solenoid, I took on of the vacuum hoses off and it was sucking really good air. When I plugged it with my finger, the engine instantly died.
That's the opposite of what should have happened. The Vacuum Management Valve (a.k.a. the purge valve) is normally closed, so removing the line going to the intake should have caused a massive vacuum leak. When you put your finger over the end, you were simply restoring it to normal.

Originally Posted By DonnieK
could that mean the purge solenoid is fine and doing what its supposed to and perhaps my issue with the evap canister valve, or the canister itself?
That's what it sounds like to me...
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 09/17/20 09:01 AM

Ok, update. I checked the purge solenoid and it "SEEMED" to be working fine. I couldnt blow any air through it. Also, I removed and cleaned the canister valve on the back of the car. It clicked, when my wife turned the car on, (I could feel it while I held it in my hand). So.. both seemed to be working. I know this isnt precise, so I still had my doubt.

Upon reading more on symptoms, I finally decided, I wasnt having problems fueling the car, and also when the car was cold. So, I decided to goto my local pull-a-part and I got a new purge solenoid. I thought maybe that dude is staying closed all the time, causing the engine to starve. So, I reset the check engine light, put the new solenoid on and it seems to be running fine now. I took it down the road and got it warm, then shut it down for about 30 minutes, and it fired right back up just fine. Still hasnt kicked a code back out. So, fingers crossed that may have fixed it. Im going to go and fill the tank again, because now, the gas needle has moved off FULL, so I want to see if that causes the problem again.

I'll report back. Thanks for the info so far.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 09/17/20 05:31 PM

Additionally, I filled the car tank up today after driving and had no issues.

Seems like I may have resolved the issue. Thanks for the info. The new purge solenoid fixed it up.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 10/24/20 10:20 AM

Ok, reviving this thread. The problem isnt as bad, but not when the car is run from cold, its fine, but after its up to operating temp, if I turn it off and back on, it runs real rough. Not kicking any codes and no problems fueling, so I dont think its my evap canister. Any other ideas?
Posted by: Site66

Re: Possible Fuel/Air mixture problem - 11/05/20 12:37 PM

May be the fuel pump only becasue at that age its such a high failure rate.
Replace the fuel filter by the passenger side tire first.

Been through a pump replacement on another CV myself it sucks. But I confirmed it by renting a fuel pressure meter and it has a shrader valve on the fuel rail to hook it too. It reveled low fuel pressure that changed over time.

At the time it was so common I could not find a pump anywhere locally. Dealers sold out auto stores sold out.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 12/22/20 06:35 PM

Im wondering about the fuel pump. Im hesitant because the pump seems to be working fine, since the car will run just fine when cold without a full tank of gas.

After I fill up the tank, and the car is hot, thats when I have this issue. Im going to swap the fuel filter though and see if that helps.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 01/15/21 05:53 PM

For continuity sake, I had the problem reoccur again, so this time I swapped the Evap Canister Vent Solenoid and it SEEMS to have fixed the problem. I tried to re-create the issue twice and it seems to be holding solid. We shall see.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 07/21/21 09:41 AM

Originally Posted By Site66
May be the fuel pump only becasue at that age its such a high failure rate.
Replace the fuel filter by the passenger side tire first.

Been through a pump replacement on another CV myself it sucks. But I confirmed it by renting a fuel pressure meter and it has a shrader valve on the fuel rail to hook it too. It reveled low fuel pressure that changed over time.

At the time it was so common I could not find a pump anywhere locally. Dealers sold out auto stores sold out.



So, I had this issue again, and you are correct. Im having a low fuel pressure issue. I took it to a professional mechanic this time, and he mentioned something about a Fuel Pump Control Module or something like that. He said its maybe located in the trunk. He was still trying to track down the part and all the exact info, but sounds like I might be in for a new fuel pump. That would explain my lean misfires when the problem occured. I googled and seems like 06+ only have the fuel pump control module. My 05 system diagram only shows the pump.
Posted by: RF_Overlord

Re: Possible Fuel/Air mixture problem - 07/21/21 01:04 PM

That control module is called the FPDM...Fuel Pump Driver Module. It's located in the front left corner of the trunk. FPDMs have existed since 2003, when Ford switched to a returnless fuel system.

Its purpose is to vary the duty cycle of the pump to maintain the desired fuel pressure.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 07/21/21 01:29 PM

Awesome. So my guy says that he has to go through Ford to get one. Every had any problems with that, and what I might be possibly looking at to get it replaced?
Posted by: RF_Overlord

Re: Possible Fuel/Air mixture problem - 07/21/21 02:43 PM

Replacing it is simple. I've never had to actually do it as they rarely fail, but it's plug-and-play with no programming needed.

You don't have to go through Ford to get a replacement. Dorman and other aftermarket companies have them.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 07/30/21 11:08 AM

So, turns out we replaced the Hi Pressure Sensor on the fuel rail and that cleared all codes and the car is running great now. The codes were all in the computer but tripping the Check Engine, which is why I never even considered replacing this sensor. I put a 21 dollar Amazon special on there and I should have known better. No more knock off electronics. Car is running like a champ now. But I may try to locate one of those modules now, before I get in a pinch. He said there is a specific Police Interceptor one that is not cataloged. So he was having a problem locating it. I'll check those you mentioned. I definitely appreciate everyone's advice.
Posted by: RF_Overlord

Re: Possible Fuel/Air mixture problem - 07/30/21 03:22 PM

Specific Police Interceptor FPDM? I've not heard of such.
Posted by: SocalSam

Re: Possible Fuel/Air mixture problem - 07/30/21 04:15 PM

I didn't catch the DTC that you found. It is a great idea to have a $10 code reader in the glove box to take some of the guess work and parts shotgunning out.
Posted by: STR

Re: Possible Fuel/Air mixture problem - 08/09/21 09:11 AM

Bringing a semi dead thread back, but adding to what SocalSam said, FORScan Lite for Android will let you view live fuel pressure.

I think the app itself is $5.99, and it'll work with most of the cheap Bluetooth OBD2 adapters. It's not very intuitive, but there's a TON of stuff you can view, from fuel pressure to engine fan duty cycle. You can also cycle each module on the car through a test procedure (and "burp" the ABS pump to get air out of it).
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 08/09/21 10:30 AM

Originally Posted By RF_Overlord
Specific Police Interceptor FPDM? I've not heard of such.


Yea, so, my guy is definitely trustworthy, but I dont think he has much experience with ex-police vehicles. He called Ford to get the part information and im sure thats something they must have told him. He mentioned that he owned a panther himself, but after test driving mine, he specifically mentioned how much more spunky mine was. So, this is why I dont think he has much interceptor experience. But overall he did a good job.
Posted by: DonnieK

Re: Possible Fuel/Air mixture problem - 08/09/21 10:32 AM

I was shopping for scanners, but there were a ton of options out there and I wasnt sure which one would be too little and which one would be too much. I will definitely look into this for the future. Had I scanned it, I would have known that fuel delivery was about 10psi too low. Also, it was throwing a few codes that werent activating the check engine light, but definitely making the car run like crap.
Posted by: Tenevic_P71

Re: Possible Fuel/Air mixture problem - 08/09/21 03:17 PM

ForSCAN has almost everything you would ever need to work on these cars and is free to download to PC.