P0171/P0174 - '96 3.8L - suspect vacuum leak

[Winny_the_Pooh]

All,
The wife complained recently about the van idling rough. I checked it - it was there but it was slight, not horrible. A couple of weeks later, we get the CEL and Autozone checks the codes and we get P0171/P0174. In general, the engine performance is not all that bad though.

Based on my research on the forum, I suspect a vacuum leak (IRMC's, EGR, etc. etc). I have a vacuum gauge. Would I be able to measure a drop in vacuum? If so, where is the best place to insert the gauge?

I also have a vacuum pump. Can I pull vacuum and see if it bleeds off? If so, again, where to insert pump?

I ask because I want to properly diagnose it and not shotgun it.

I have about 100K miles on the van. I cleaned the EGR ports at about 70K when I did the lower intake gasket repair. Could these be gunked up again? I also replaced the vacuum line assembly at that time (broke it during disassembly). I also replaced one O2 sensor at that time during the initial stages of debugging (it was a shotgun). My OBD scanner is on the fritz so I am somewhat handicapped in monitoring the O2 sensors.

I also notice I am losing coolant again. The wife had reported some on the garage floor but I haven't noticed it. The oil looks good so I think my timing cover repair is holding. I worry that the pitting I saw in the intake and heads when I did the lower intake repair may be coming back to bite me. But, when I had that problem, I was getting a P1131, I believe. Plus, I had TONS of white smoke in the exhaust.

Got a long weekend and 70F to 80F, sunny weather in Dallas so it is a good time to work on the van .

Thanks in advance,
George

[busboy4]

Hi
from recent experience I will tell you it is a bit tough to narrow down any leak with the vacuum pump as the main "take-offs" for vacuum go a number of different directions. The main (larger) vacuum line off of the back of the manifold goes first (via the red line) to the vacuum reservoir on the right fender. You could check that reservoir for a leak. The black line off of the reservoir goes to the IMRC control solenoid on the back of the intake - You can check it by holding one end closed and pulling a vacuum. You can check the IMRC vacuum line (yellow/blue) by pulling a vacuum on the line at the solenoid and seeing if the IMRC'c close. You can check the A/C circuit by pulling the red line from the A/C vacuum check valve up under cowl, and pulling a vacuum there - it will tell the A/C side is o.k. - if you can change from defrost to vent to floor heat, that will tell you too.

In my case recently I believe the IMRC solenoid failed and allowed a vacuum leak. I tested the valve using my hand pump and it does not hold vacuum when open - power on. I have it removed and the "main" (red line) vacuum capped at the reservoir on the right fender thus isolating the IMRC circuit and the van runs/idles fine. I also have the IMRC actuators disconnected and the IMRC's open.

Keep in mind that you can use your pump as a guage too - connect it to the red line at the reservoir on the right fender . Start the car - mine shows 20" plus at that point. You should see a similar reading at the A/C check valve (red line), canister evap control - on firewall with yellow line, at IMRC solenoid - back of manifold black line, and at the EGR solenoid - back of manifold red line. Don't hesitate to suspect the solenoids as I mentioned I believe mine was the culprit. Also, as I shared in a different thread, the entire vacuum "manifold" ( all the semi-rigid lines) can come out as a unit for closer inspection. It takes a bit of finesse, and threading of the lines but it is possible and makes checking the individual lines easier.

Good luck. I'm sure it is frustrating.

[reekor]

The MAF (Mass Air Flow) Sensor might be dirty, clean it with brake cleaner.

Originally Posted by Winny_the_Pooh

All,
The wife complained recently about the van idling rough. I checked it - it was there but it was slight, not horrible. A couple of weeks later, we get the CEL and Autozone checks the codes and we get P0171/P0174. In general, the engine performance is not all that bad though.

Based on my research on the forum, I suspect a vacuum leak (IRMC's, EGR, etc. etc). I have a vacuum gauge. Would I be able to measure a drop in vacuum? If so, where is the best place to insert the gauge?

I also have a vacuum pump. Can I pull vacuum and see if it bleeds off? If so, again, where to insert pump?

I ask because I want to properly diagnose it and not shotgun it.

I have about 100K miles on the van. I cleaned the EGR ports at about 70K when I did the lower intake gasket repair. Could these be gunked up again? I also replaced the vacuum line assembly at that time (broke it during disassembly). I also replaced one O2 sensor at that time during the initial stages of debugging (it was a shotgun). My OBD scanner is on the fritz so I am somewhat handicapped in monitoring the O2 sensors.

I also notice I am losing coolant again. The wife had reported some on the garage floor but I haven't noticed it. The oil looks good so I think my timing cover repair is holding. I worry that the pitting I saw in the intake and heads when I did the lower intake repair may be coming back to bite me. But, when I had that problem, I was getting a P1131, I believe. Plus, I had TONS of white smoke in the exhaust.

Got a long weekend and 70F to 80F, sunny weather in Dallas so it is a good time to work on the van .

Thanks in advance,
George

[Winny_the_Pooh]

Thanks all. I did a little work over the holiday and I measure about 19" after the engine settles down into a "normal" idle. What is interesting is that, after shutting down the engine, I can hear "pressure" bleeding off for another 3 to 4 seconds. That is, I can hear a hiss that continues after all else is quiet. It appears to be coming from the area on the back of the upper intake where many of the vacuum lines attach - more on the PCV valve side. I will try to remove the cowl or get a mirror back there to see if I can isolate it further.

Does anyone think this "pressure bleed" sound after shutdown is a smoking gun?

I should mention that I sprayed carb cleaner toward as many places as I could to no avail. But, I was not able to get the can in the rear of the plenum where I am hearing the sound due to the cowl being on. So, jury is still out.

At idle, it seems as the engine is "loping" sloping - runs OK and then rough and then OK, etc.

[weedman]

Winny-Have you been able to isolate the hissing sound you mentioned in this thread. I have that as well on my 99' and was wondering if I have a vacuum leak as well. I've been getting terrible mileage( <10 in city; 17-18 Hwy) and can't seem to find the problem. I did the intake fix, as well as everything else associated with poor mileage and no results. Is the vacuum kept when the engine is turned off, or is it released?

[Winny_the_Pooh]

Weedman,
No luck yet although I have not invested alot of time due to wife needing the car. She is out of town this week so I have a window to take the cowl off and search in back of the plenum for any potential source of the leak. I would not expect vacuum to be held when engine is off due to path through throttle body and air cleaner. But, my hissing sound is coming from the back of the upper plenum.

I did get a new OBD tools and monitored several parameters on a 15 mile drive the other day. Basically, the long term fuel trim is maxed out at 25, especially at idle. The LTFT values drop to 14 or so at highway speeds. The freeze frame indicated that the P0171/P0174 was thrown at idle with the LTFT at 24.2. The MAF output looked good for the speeds we were driving. So, I am still suspecting vacuum leak. This is consistent with all of my research on the web.

Good luck and I will post further once I find the culprit.

[Ed_Strong]

What OBD II tool did you get if you don't mind me asking? ...and how much did it cost?
I'm on the market for one but don't know much about the basic ones or how reliable they are compared to the high end models...!

[wiswind]

Look at the PCV line......a number of connections just on that.
The flexible elbow for the PCV line that is on top of the upper intake manifold.....next to the throttle body....has been known to develop a crack on the inside of the elbow.
Follow the line all the way back to the PCV valve.....making sure that everything it in place.

Also....make sure that the crankcase breather tube......from the front valve cover (Pre '99 models) to the big flexible air hose (from MAF to Throttle body) is in place. It is easy for it to not be seated in the flex line....as it is on the back side, where you cannot easily see it.

VERY carefully....with the engine running, you can gently flex some of the vaccum lines....one at a time to see if you can track down a leak.

Hopefully one of the IMRC actuators is not developing a leak.

The location that holds a vaccum is on the passenger side fender.....near the fire wall.......a small black box is a resevoir to hold vaccum for the diverter door inside the passenger compartment......the door that selects which vents the air goes......Heat, Defrost, Vent.......
Not to be confused with the "blend door", which is electrically operated.....and selects how much air travels over the heater core.....for temperature select.

[Winny_the_Pooh]

Thanks Wiswind, Reekor, and busboy4 for all of your excellent suggestions. Will post an update once I get a chance to follow through on your advice.

Ed_strong - I bought the one at http://obddiagnostics.com/. I had previously bought their kit and made my own pcb at work in trying to save a little money. But, I recently bought the complete unit due to my home-built one having problems. But, I have had good luck with their unit; my problems were due to my home-made pcb and some of the solder joints and my lack of robust packaging. I would recommend their product.

[Kashey]

http://www.leckemby.net/windstar/windstar01.html
It's for 2000 but may give some idea.

[Winny_the_Pooh]

I think I found the culprit. I pulled the cowl off today and started inpecting the vacuum lines in the back of the plenum. Within a couple of minutes, I found that the rubber hose that goes from the PCV valve to the hard plastic line that goes over to the top of the intake was deformed and split (good call wiswind). There is an obvious hole it it.

I have had trouble with the other rubber line that bends 90 degrees from the other end of this hard plastic line to the top of the intake plenum (near the throttle body). The rubber gets soft and moist. It's as if there is coolant or oil in the line. The rubber softens and eventually leaks due to not fitting tight to the nipple on the top of the upper plenum. I have been replacing this hose every 6 months to a year. But, this is the first time that the one on the PCV valve end has degraded so.

I wonder if I am getting a slight coolant leak due to the pitting in the aluminum lower intake and head surfaces that I saw when I did the lower intake gasket repair. Thus, this would explain the rubber lines degrading so. I had heard of some folks using an epoxy patch to fill these pits but I did not do this. I wish I had to eliminate the doubt that I have now. But, rather than tear it apart and redo these surfaces, I may go the Stop Leak route that wiswind has advocated.

What puzzles me is why I couldn't see this with the cowl on; it was so obvious. I had even run my hand along the line and looked at it with a light and mirror and didn't see this. But, with the cowl off, it was a no-brainer.

Thanks to everyone for all of the help and I'll try to get pictures and post back was the fix is confirmed.

[Edisto]

I found this link particularly helpful for 171 and 174

http://http://leckemby.net/windstar/windstar01.html

[wiswind]

The leckemby site is GREAT! and I have posted the link to it in a number of posts.
However, it ONLY applies to 1999 and newer windstars.

It is great that you have found the problem.
I am not suprised about original lines in the PCV path breaking down....as our '96's are pretty old now. If you are having to replace a rubber section over and over, I would suspect that the rubber in your replacement is not up to the application. I have only had to replace the one on top of the upper intake manifold 1 time...and it is still in great shape. I have 177K miles on the vehicle now.
There is oil inside these lines, so they have to be able to stand up to exposure to oil.

[cawind]

Hi, I got the same problem on my 2000 windstar and found the leckemby site that was real GREAT and came here.

I also found a loose vacuum line behind the plenum, it's one of the 2 splits on the other end of the red vacuum line (its the invisible end of the red vacuume line in leckemby's photo of "Vacuum Lines "). My problem is I COULDN'T see where it should be plugged in.

Can any of you help me on that?

[busboy4]

Originally Posted by cawind

Hi, I got the same problem on my 2000 windstar and found the leckemby site that was real GREAT and came here.

I also found a loose vacuum line behind the plenum, it's one of the 2 splits on the other end of the red vacuum line (its the invisible end of the red vacuume line in leckemby's photo of "Vacuum Lines "). My problem is I COULDN'T see where it should be plugged in.

Can any of you help me on that?

Hi
I have a '96 and am working based on that and brief observation of newer vehicles but........I would think the red one is "powering" your A/C system. Is your control of ducting working? i.e. can you switch between defrost, floor heat etc? If I am right about this line, I think not. Anyhow, I think you will find that the line in question goes up under the cowl towards the top of the right strut. I think you will find a vacuum reservoir up there where this line is headed. It may have come out of a "double" connection - red line into reservoir to provide vacuum, black or other colored line out to a check valve and then through the firewall to the A/C contols.

Hope that helps