Never ending P0174 and P0171.

[glockman]

Warning: Long post.
Bought my 98 Explorer Sport with 4.0 SOHC from original owner with 119,000 miles on it. As soon as I got it home I changed the oil, flushed the coolant and rotated the tires. I checked the ATF and it was nice and red, no burnt smell so I figured I’d wait a while on that. Now we have a good base to start vehicle ownership with. About 10 days after this, CEL comes on. I pulled codes P0174 and P0171. I came here, read up for a few hours and designed a plan of attack. Start with easy/cheap parts and work my way up.
Cleaned MAF and checked with a DMM. MAF is good.
Checked TPS, also good.
Replaced the fuel filter ($8 and 20 minutes)
Still have CEL.
Replaced upper and lower intake manifold gaskets ($29 and two hours)
Still have CEL.
Checked my fuel pressure, mine is a return style fuel system, pump was putting out 30psi at the rail test port. Should be 35 to 45 so I replaced the fuel pump ($130 and 2.5 hours). At this point I made a mistake and didn’t check the fuel pressure after the pump was replaced.
Drove the car for about 7 days with no CEL (same as previous) and then on the 8th day, CEL comes on.
At this point I figure I have a random vacuum leak somewhere so I start spraying carb cleaner at all the vacuum connections under the hood. No leaks found. I did notice some coolant had been running down the block on the front of the passenger side. Took a closer look and found it was the head gasket was leaking. Apparently the PO found this and just put some stop leak in it. When I flushed the coolant it removed that and the thing started to eat coolant like it was oil in a two stroke.
Checked with a local shop, they told me it would be about $2500 to just fix the head gasket. I decided I would do it myself. I removed the engine, stripped it to a short block and was just about to send the heads in when I found a 2006 Mustang SOHC 4.0 with 13,000 miles on it on CL for $500. Bought the Stang motor and commenced to stripping it and swapping parts. Basically (like has been very well documented) I used the Mustang long block, and the following parts from the Explorer
valve covers, upper and lower intake manifold, fuel injectors, fuel rail with regulator, throttle body and all accessories.
While I had the motor out, I replaced the spark plugs, wires, coil and PCV valve. I also noticed a broken gray vacuum line coming from the intake to the passenger side under the coolant reservoir. I again came to the forum and found out it went to the vacuum reservoir under the inner fender. I repaired this line and finished installing the new motor.
Motor fired up and runs great. Drove it for about a week and CEL comes back on. P0174 and P0171. Pull out hair!!!!!
I should mention that it is now winter and I have noticed the explorer doesn’t blow any air out the floor vents. I also noticed that under hard acceleration it changes air flow from the vents to defrost. I have diagnosed this as a vacuum leak still present.
Again, I spray carb cleaner at every hose and find nothing. Decided to check fuel pressure just in case. Found it is still 30 psi at all RPM. I then unplugged the vacuum line from the pressure regulator and it jumps to 40 psi. I capped the regulator and the vacuum line for the time being and will see if the CEL comes back on. I also put a vacuum gauge on the line coming through the firewall under the glove box that feeds the climate control selector. I only have 5 inches of HG at that hose. I traced the line back and connected the gauge to the ling that feeds the vacuum reservoir and it has 40 inches of HG. Looks like I have a leak at the reservoir.
So, is it my fuel pressure regulator causing the CEL or the vacuum leak at the reservoir, or both? I will know shortly and will post my conclusion.
Hope this helps someone with similar issues. What a wild goose chase it has been.

 

[2000StreetRod]

leaking FPR?

You may have a vacuum leak in the fuel pressure regulator (FPR) due to a split diaphragm. It can easily be tested with a hand vacuum pump.

 

[glockman]

Thanks Dale. I plan on tearing into it after Christmas. I'm sure the FPR is leaking. I think the vac res is also leaking or the check valve isn't functioning since I had the FPR vac line capped when I read low vac on the firewall bulkhead vac fitting. I feeling I owe you a huge thanks as at least 70% of what I know about this car I learned from your posts. I really appreciate you sharing your knowledge.

 

[Scout3]

I'm no expert but I don't think you are pulling 40 in hg. Normal is around 20in hg.

Ed

 

[psmith240]

Check the egr tube where it enters the upper intake.
The green O ring. I was very careful when doing the OOm12 kit, but that o ring ended up being the problem, replacing it cleared my lean codes. Good luck!

 

[glockman]

Scout, you are probably correct. I didn't pay close attention to the gauge, just that it was way higher than when I was measuring inside the cab. I'll take another measurement. As for the EGR O ring, I replaced it when I replaced the motor.

 

[glockman]

Put the gauge on it today. Only had 20 mm of Hg. Put the vacuum pump on the FPR and found it wasn't leaking. Pulled the passenger inner fender and found the black vacuum supply from the vac res to the firewall was broken. Repaired the line and now I have good vac in the cab and at the FPR.

 

[dayday359]

I have the same codes plus P1150 AND P1151 I will be checking vacuum lines have put on 2 new O2 sensors thanks

 

[l1k2gadd]

Thanks for this thread. I bought my 2000 XLS and wanted to fix it and give it to my mom to get her out of her Club Wagon XLT van. I drove the thing about two weeks whilei was fixing it and then it started dying on me. I bought an OBD II scanner, found out the CEL was burned out from being on too much, plugged the scanner in, and found P0174/P0171 and started troubleshooting it (without coming here to research the problem). Now I have some things to check on the Explorer (after two years) to finally get it running right and maybe put it back on the road.

 

[glockman]

Update. About 7 days after repairing the last vacuum line and plugging the FPR vacuum in the CEL came on again. Checked fuel pressure and it was low. It appears that my FPR is causing low fuel pressure when vacuum is applied. I checked several parts stores and the dealer, none of them carry my year FPR. I capped the vac line until I can pull a FPR from the JY. All has been good for a couple weeks now( no CEL).

 

[glockman]

Update: CEL came back on with FPR vac line capped. I bought a code scanner that is supposed to read fuel trims. My thinking is that I can read fuel trims and determine if it is a vacuum leak or something else. Well, the fuel trims are static. They don't change after the car is started. I wanted to see if they changed from idle to mid throttle. So, next I was looking at reading voltages on my O2 sensors. Doing research I found that antifreeze will kill O2 sensors. I had a bad head gasket so I figured I might have killed all the sensors. I replaced both pre and post cat sensors on bank 1 to see if the 171 code would clear. Reset the code and drove it for 2 days. CEL is now back on with both 171 and 174. So it wasn't O2 sensors. I think I am done. I am taking it to someone with autoenginuity software/scanner. My plates are now expired, I have replaced the engine, fuel pump, checked fuel pressure, checked for and not found any vacuum leaks, checked MAF voltage. Everything is pointing to a bad ECM or a vacuum leak that I can't find.

 

[dayday359]

Mine ended up being a vacuum house right above the thermostat on the left side of the engine an elbow hose.

 

[glockman]

FINALLY it's fixed. Turned out to be the Vapor Management valve. This valve is located under the battery tray. In all their wisdom, Ford designed a spout of sorts for battery acid in the tray to drain. The spout drains directly onto the valve which is plastic and eats a large hole in the back of it causing a large vacuum leak. If you have these codes I suggest you check this first. It is $28 shipped from Rockauto. Took about 15 minutes to replace.

 

[dayday359]

Glade you got it fixed, will keep that in mind if that happens to me again thanks for sharing