Troubleshooting 0171 & 0174 Code Help

[fymbscu]

Just had my fuel pump replaced earlier in the week on Tuesday. Now today, Friday, I get a check engine light and the codes 0171 and 0174. A look under the hood reveals this part with a line freely dangling from it.

I thought the line looked broken, but maybe not, and I don't see an obvious point to connect it to. Could you identify the part for me and where the line should connect to. Been looking through the Haynes manual without success. I am stumped. I expect reconnecting the line will resolve this issue for me. Any guidance greatly appreciated.

 

[ThreeJs]

That's a heater control valve..

 

[rasouth]

ThreeJs called it. That is your heater control valve that connects somewhere underneath all those hoses and black canister to your blower unit. Looks like the hose broke. You might need to splice it together.

 

[1998Exp]

That's a heater control valve..

Indeed, it's the heater control valve. The broken (or more likely, disconnected) line is its vacuum control, which is shared with the vacuum motor that operates the fresh air inlet door. There should be a "T" somewhere near that motor -- which is under the glove box. Vacuum is applied to that motor (and the heater valve) in two positions of the climate control only: "MAX AC" and "OFF". If one of those is selected, there will be a vacuum leak, but I doubt it will be significant enough to trigger the lean codes. The disconnected line should have no effect if any other climate control position is selected. If moving the climate control to any other position does not resolve the lean codes, you have a vacuum leak elsewhere, or perhaps the new pump is not working properly.

 

[IronCurtain]

I got the same 2 codes a couple days after installing a new fuel pump in my 95 EB last year. Ended up being a faulty pump.

 

[rasouth]

Could be a dirty Mass Air Flow sensor. Could also be a leak around intake manifold. I had the same problem a few years back and sprayed starting fluid around intake while engine was running and when I sprayed around the leaking area the engine revved up.

 

[fymbscu]

Thanks all for the identification of the heater control valve. Took another look this morning and see the other end of the break, identified by red circle in photo.

It is present in the 2nd photo above also, but hidden under a shadow from the upper piece of the line. Its a tiny line. Not sure how to go about splicing it, rasouth. Is it your opinion that the line is not a replaceable part?

1998Exp brings up an interesting point about the "MAX AC" climate control setting. Lately, selecting this has sent the airflow to the defrosters until I play with the control to get the expected flow.

I've cleared the codes for now. Have a short trip this morning. Will see if they return.

 

[1998Exp]

...
1998Exp brings up an interesting point about the "MAX AC" climate control setting. Lately, selecting this has sent the airflow to the defrosters until I play with the control to get the expected flow.
...

When you select "MAX" (or "OFF"), the vacuum leak through that broken tube effectively disables the control, and it reverts to the default position, which is "DEFROST".

Hope someone has a magic solution to splice that broken tube. If memory serves, Ford has (or had) a repair kit for those, which includes some sort of special cement. I would try a short section of tight-fitting rubber tube first.

 

[rasouth]

I've spliced a couple of these small vacuum lines before because they become brittle over time. An ol' timer showed me. He used a piece of tubing that would just fit over old tubing, maybe two-three inches long, and tape both ends. I have used thick wire and stripped the sheathing off and used that. Maybe small water line like from an ice maker or air line from fish tank. A little big but as long as both ends are tape tight it should work.

 

[fymbscu]

I stopped by an AutoZone and picked up Dorman kit 47430 which contains four miscellaneous size "vacuum connectors," each 2 inches long. The closest fit is a bit loose. Will try to find a better match to the existing line. Any chances of finding the actual replacement part?

I have an old Power PC Mac and Ford has revised their parts site so that I can no longer get information from them in the TenFourFox browser. Have to use a public library computer now, but Ford also seems to have lost/deprecated info on the '99 Explorer. My VIN draws a blank on their site. Did not find any repair kits listed either.

The codes haven't yet returned. Will take some more time and get the repair right. Thanks again for all of the input.

 

[roscoe 0202]

I had a 99 that would throw that code when it first got cold I reset them and they would stay off for a year
roscoe

 

[fymbscu]

Hey guys,
Sorry for my absence. The power supply on my PowerPC computer went out shortly after my last post. Anyway, I fixed the vacuum line leak with a 5" section of medical-grade vacuum line that fit very snugly over the Ford line, using the friction between the two to keep it in place, although I did add electrical tape to the upper end.

Looking at the image above, it looks like a series of three alternately facing clips that might have held the line at one point. I tried using them, but decided against it as I thought it put too much stress on the line.

I'm not out of the woods yet. Had the 0171 code return on 11/21, and again on 11/26. Then the 0174 code returned on 12/3. Been delayed in replacing my fuel filter because of the computer problems, but wanted to do that before concluding I needed to do something more.

Your thoughts?

 

[Turdle]

Unmetered air ( not measured by the MAF) is getting to the combustion chamber. Vacuum leak somewhere downstream of maf. Check the large intake air tube, brake booster and egr for vacuum leaks. replace intake manifold gaskets.

 

[fymbscu]

I finally got my answer and resolution to this case back in February of this year. Similar to what roscoe 0202 had said, the codes disappeared with warmer weather soon after my last post and didn't return until about a year later with the cooler weather. I was due for a SMOG check with my renewal in February and the codes were preventing the test. I settled for a smoke test from the shop that replaced the fuel pump and it revealed a leak at the base of the IAC Valve. I recognized that I had replaced the valve in May of 2017, but had not replaced the figure-8 shaped gasket at the time. Replacing the gasket cleared my codes and I was able to pass the SMOG check in time to renew. Problem solved.

 

[fymbscu]

Famous last words... both codes have returned in December. I have cleared them twice, but they have returned again. Since the previous leak was at the base of the IAC Valve, I decided to install the fiber gasket that came with the Valve when I bought it new in 2017. I didn't install it back then because there was no such gasket installed with the old Valve. Figuring the figure-8 replacement gasket wasn't up to the task, I thought I had nothing to lose if I gave it a try and added the fiber gasket.

My problem now is that I snapped the head off of one of the bolts when reinstalling the Valve. I am looking for advice about replacing the bolt. The local Ford parts is closed until Monday morning.

 

[Lee's Automotive]

Famous last words... both codes have returned in December. I have cleared them twice, but they have returned again. Since the previous leak was at the base of the IAC Valve, I decided to install the fiber gasket that came with the Valve when I bought it new in 2017. I didn't install it back then because there was no such gasket installed with the old Valve. Figuring the figure-8 replacement gasket wasn't up to the task, I thought I had nothing to lose if I gave it a try and added the fiber gasket.

My problem now is that I snapped the head off of one of the bolts when reinstalling the Valve. I am looking for advice about replacing the bolt. The local Ford parts is closed until Monday morning.

At this point it would probably be cheaper to go to a junkyard and get a new upper intake if you have the 4.0 SOHC I've done this several times and trust me its not fun getting the broken bolt out but at least its not the lower manifold bolt broken off in the head like I did the other day

 

[fymbscu]

Thanks for your feedback. I recovered the head of the broken bolt and I tried to match it up at the local Auto Parts stores as well as Home Depot on Sunday. I honed in on 1/4-20 from the thread guides and got several different lengths to cover all of my bases. Finally, removed the IAC Valve again today to find that I could unscrew the stub up by hand. That was a relief. Next problem was that the 1/4-20 thread bolts I picked up were not correct. A call to the Ford parts department to find out that the bolt is classified as "obsolete" and they couldn't/wouldn't help me with a replacement either.

This is what the bolts look like. It is a hair over 3/4" long with the hex flange head. I ended up bumming one from the mechanic who did my smoke test back in February. It was a thread or two shorter than the one that needed replacing. Do you know what the true spec for this bolt would be?

Thanks again for the advice. I guess I was more panicked than I needed to be.

 

[C420sailor]

Metric metric metric.

I don’t think there are any SAE threads on these trucks?

1/4” is prob 6mm

 

[fymbscu]

I had the head piece from the photo above with me on Sunday. Honestly, it only screwed well into the 1/4-20 blocks that I tried. It would bind in the 6mm-1.0 blocks, which was the only metric option available at 6mm. The tech at O'Reilly's, my first stop, suggested that I needed the 6mm-1.25 spec, which was not available at any of my stops. 1.25 was only available at 8mm, which was too large. Home Depot was my second stop and that is where I concluded that the 1/4-20 was the best fit. I only found the 3/4" length at Autozone. Anyway, I will take the stem piece with me on my return trips and check again.

 

[410Fortune]

why not take the other bolt with you for thread checking?

Ace hardware has thread checkers, Im not sure about home depot


With the codes 171 and 174 and a newer fuel pump I would:
check fuel pressure, should be 68 psi. Cheaper fuel pumps has really gone down hill in recent years, we usually recommend OEM replacement with Bosch pumps. If you only replaced the pump and not the whole in tank unit then that is another suspect (the pressure regulator)
In any case a fuel pressure test is a MUST for these codes.

Check the intake after the airbox for any loose clamps or leaks

inspect the base of your upper intake plenum, My guess is that it is leaking air, there is not a 99 Explorer SOHC on this planet that does not need new upper and lower plenum intake O ring gaskets.