1992 Explorer with error code 173

[simonda]

I have a 1992 Explorer that I purchased new in 1992. This truck has been excellent and it now has 113,000 miles on it. Recently my check engine light came on for the first time and I had the codes pulled and the only one was a 173 which was a rich condition on the passenger side of the engine. I was told the place to start was to replace the O2 sensor on the passenger side so I bought one. I needed a new muffler anyway so I had the muffler shop put on the sensor at the same time. The muffler shop told me that they only saw one O2 sensor just ahead of the Y pipe and not in the manifold bank for the passenger side. They put the O2 sensor there, but the check engine condition condition was not fixed and my mileage since the light came on is quite poor.

First question is...Does a 1992 with a V6 have one or two O2 sensors? I want to be sure the thing was correctly installed. The error code definately said passenger side bank, but if there is only one O2 sensor, how can that be correct? Second question is...What should my next step be? I have a new air filter and new plugs and other than the milage and the light, it continues to run very well. Any advice would be greatly appreciated as I cannot afford to put money into replacing the wrong parts. I really need to try and fix this myself.

 

[Opera House]

Nice to have a shiny new O2 sensor but it likely wasn't needed. You either have a leaking fuel injector or leaking fuel pressure regulator. There is a vacuum line that goes to the regulator you should pull off and check for the presence of gas. It is fairly common at this age for the diaphragm to leak and dump gas into the engine. Costs about $70 and only two bolts to install. Disconnect the battery after to reset computer. You only have two O2 sensors (before and after cat) Computer nomenclature is set up for up to four.

 

[MrShorty]

173 refers to passeger side O2 sensor in cases where there are more than one sensor. In cases like your '92 where there is only one O2 sensor ('92 doesn't have one post cat like EEC-V systems), then 173 refers to that lone sensor.
Was the 173 a KOER code or a continuous memory code? I don't know that it makes a whole lot of difference here. Lik Opera Hoiuse said, it's probab;y the FPR or an injector stuck open.

 

[simonda]

Thanks so much for the quick replies and on Thanksgiving! I am sorry for being a backyard mechanic, but could you please provide just a little more detail on where I can find the fuel pressure regulator? If there is gas in the vacum line, then I am assuming the FPR is shot (leaking) and I should replace it.

Thanks for the clarification. Happy Thanksgiving.

 

[Brain]

Alldata gives the trouble code diagnosis here:
http://www.alldatadiy.com/alldata/A...857663/34850217/104736396/104748012/104748159

It lists the possible causes as:
-fuel injectors
-HO2S (you replaced that)
-Secondary Air Injection (AIR) system (you don't have that, neither does my '92)
-PCV/Hose (easy and cheap to check and replace)
-Vacuum (check vacuum connections)
-CANP (not even sure what this one is)
-MAP sensor (manifold air pressure sensor)
-Electronic Ignition Coil Failure (easy enough to test with a multimeter, about $20 at Radioshack)

I assume after you had the O2 sensor replaced that the codes were cleared and that this isn't an old code?

It is indicating a rich condition, so it could be a stuck open injector, or a FPR with a shot diaphram letting gas into the intake, or a MAP sensor problem. THe others seem like they would indicate a lean mixture insted.

The FPR is on the passenger side, right in front of the front fuel injector. It connects to the fuel distribution rail (top of all injectors fit into this rail) and has a single vacuum line running to it. Be careful as the gas lines are under pressure.

A simple enough test for the FPR would be to remove the vacuum line and turn on the key (not starting the engine). That would turn on the fuel pump (you can hear that) and pressureize the line. If it is leaking through the valve and into the intake manifold, it should come out the vacuum connection nipple on the valve.

 

[Brain]

After re-reading what I posted, I don't think I was too clear on where the valve is and what is connected to it. If you follow the upper radiator hose back to the engine, look right behind where the hose clamp is and you will see a braided steel line. That is the fuel line leading to the FPR. Follow it to the left and you will see it (at least the top of the fuel line connection). This line is under pressure, so it isn't the one you want to disconnect and inspect.

I should have said the is only one vacuum line and one fuel line leading to this valve.

Hope that helps.

 

[simonda]

Yep. After I had the O2 sensor replaced, the codes were cleared. So the next step is to test the FPR. I'll do this on Monday after return from the holiday trip and will post results. Thanks for the detailed description on the FPR location and additional advise.

 

[simonda]

I have removed the vacum line on the FPR and turned the key, but I did not see any fuel coming out the vacum nipple on the FPR. So I guess this leaves the MAP sensor and a possible stuck open injector. But the original code was a 173. Would the MAP sensor show a different code? Do I need to have the codes pulled again? What might be the next best step to take here? Other than the check engine light and the crummy mileage (~11 MPG mostly highway), the truck is running fine. Any advise appreciated greatly.

 

[Runnin'OnEmpty]

Simonda, a bad MAP sensor will usually trigger a 126-129 code. Notice I said "usually"......

You might be able to listen to the injectors and see if one isn't clicking. A piece of garden hose will substitute for a mechanic's stethoscope. The one that is quiet will be the one that is stuck open.

The very poor mpg still points to a bad FPR. But, as was stated, the vacuum hose should be damp with fuel if it's indeed bad.....

 

[MrShorty]

All 4.0 engines are MAF based EFI, as opposed to a speed density system like the 2.9 uses which uses a MAP sensor. Some MAF systems will use a BAP (same as a MAP only for measuring atmospheric pressure rather than manifold pressure), but I don't think a '92 has a BAP.

Have you run the KOER test? If not, I would do so in the interest of getting as much information as possible.
Have you put a fuel pressure gauge on it? If not, then I suggest getting a fuel pressure guage on it.

 

[simonda]

Just a bit more info that might help zero in on this problem.

I had the codes pulled again and I still have the 173 rich condition. The O2 sensor voltage verys very little and it is hovering between .85 and .9 volts. The guy that pulled the codes tried to tell me that my new O2 sensor was bad out of the box (Bosch part). I find that kinda hard to beleive.

I have noticed that the check engine light does not come on right away. It usually waits until I have been driving at least a few minutes and reach speeds greater that 30 MPH. Once it is on, it pretty much stays on until I turn off and restart the engine.

I have not checked the fuel pressure as of yet. I don't own a gauge. I guess I will either have to buy one or get a shop to check it. I double checked for the presence of fuel on the FPR nipple and it is very dry. Could it still be a bad FPR even with no fuel on the FPR vacum nipple?

I have never replaced the FPR, Fuel filter or cleaned the MAP sensor. Could the problem be a dirty or bad MAP? I am not sure how to locate and clean.

Sorry I am continuing to learn and I enjoy that. Also trying to fix this with a limited budget.

If the above additional info helps with zeroing in, please post additional advise.

 

[MrShorty]

The CEL won't come on right away with an O2 sensor code, because there needs to be a delay built into it to allow the O2 sensor to warm up before the computer throws a fault.

DO you know yet if the 173 is both a KOER and CM code? Several electrical faults (including a bad sensor) could cause this code. Have you tried going through the pinpoint test that Brain linked us to?

 

[simonda]

Boy I am really green at troubleshooting engines with computers. I am not even sure what the difference is between KOER and CM. The person that pulled the codes did not tell me this. Wish I had asked. I did look at Brian's link, but was also confused a bit. Do you mean the part about the PVC valve? I did remove the valve for inspection and the plunger moved freely in the PVC valve. But I don't know what a KOEO test is. Sorry for my ignorance and thanks for your continuing assistance.

 

[Brain]

KOEO=Key On, Engine Off (before you twist it far enough to engage the starter)
KOER=Key On, Engine Running
CM or Cont=Continuous Memory (when a code is in memory but is not a "current" KOEO or KOER code)

If there was fuel in the vacuum line, that would be a sign of a bad FPR, but not having fuel there doesn't mean that the FPR is good.

The different diagnosis tests that output codes (KOEO, KOER, CM) are done with a code reader in place (on a harness at the passenger side firewall). The code reader for the Ford (through '95) is pretty cheap at about $20-$30...works on Ford, Lincoln, Mercury cars and trucks from '81-'95. The people with later modes ('96+) have to pony up over $100 for a code reader (so consider yourself lucky that such a great tool is so cheap). It reads ECM, PCM, and ABS codes (if your truck has rear ABS like my '92).

Let us know if you have any other questions. We were all green at one time ; )

 

[MrShorty]

Read tests at www.dalidesign.com/hbook/eectest.html for information on running the tests and distinguishing between KOEO, KOER, and CM codes. Heck, you might even decide to go try it yourself

 

[Opera House]

Just another thing you can try. The FPR is controlled by vacuum and acts much like th acceleratop pump on an older carb. You step on the gas, the throttle body opens, the manifold vacuum drops,the fuel pressure increases, and the injectors dump more gas untill the O2 sensors can catch up with what is happening and take over. This can increase the pressure from 33 to 39#. If there is a leak in the vacuum line going to the regulator, the nominal fuel pressure will be higher. The computer may or may not be able to compensate for this. Either way, the computer will know something is wrong. You can run the engine at idle with the vacuum line removed. Check it with your finger for a good strong vacuum if you dont have a gauge.

 

[simonda]

Boy you guys are great. I can't tell you how much I appreciate your advise. I know I'll get to the bottom of this eventually...with your help.

Prior to seeing your above posts today, I was able to get a friend with a fuel pressure gauge help me measure the fuel pressure at idle. The value was right at 40 PSI. I think that is on the upper end, but within spec. Also, I just ran outside and attempted to feel for vacum on the FPR at idle per Opra house's recommendation and there is a nice vacum there. So...have I eliminated the FPR or could it still be bad?What about the fuel pump? Is this also eliminated?

My friend told me I should change the fuel filter. I have never done this on this truck and it has 112K miles on it (all my miles)....Probably a little slow on changing this! However could a clogged filter really cause a rich condition? I would think just the opposite since a clogged filter would mean less gas and thus lean. Is the fuel filter tough to change? I think it is under the truck.

Thanks Mr. Shorty for the link to the tests. I will study this carefully and perhaps make an attempt on the weekend.

And Brian, thanks for the explaination on the KOEO stuff. I can say that both times I had the code pulled, the key was on and the engine was NOT running. Both times the code was 173. I need to get one of the code puller tools. I thought they would be far more expensive.

Guess I am still a bit unclear on what my next step will be, but I will keep you posted.

One last note, my friend suggested that I get a bottle of Lucus fuel additive and run it through a couple of tanks. to clean the valves. I seriously doubt this would help my problem, but I guess I don't have a whole lot to lose, since that is a cheap step.

 

[simonda]

Small update.

I have noticed that I can smell the richness of the engine sometimes when I am at a stoplight. Also, I measured my mileage and I got 12 MPG with substancial highway content in the mileage.

I was still hoping that someone could comment on my questions in my previous post and in particular whether of not the measured fuel pressure value eliminates the FPR, fuel pump and /or filter. Thanks.

 

[Runnin'OnEmpty]

Simonda, your fuel pump, FPR, and filter are probably OK. The only part that would cause a rich condition is the FPR, and as you say, 40# is within spec (although high). If the problem was the FPR, I'd think you would get a rich condition on both banks.

The more I read this entire thread, the more I think you have an injector on the passenger side sticking open. This would explain the raw fuel smell when idleing. I would try listening to all three, to see if they are all "clicking".

 

[Opera House]

Your pressure shouldn't be at 40# unless the vacuum line was removed at the time. Presure is reduced by the the amount of vacuum you have 6-7#. With vacuum on the hose, it was likely normal. Gauges can also be off by 5#. If you can see the drop in pressure it is ok. If not, that vacuum line isn't as good as you think. You should have performed a fuel pressure leak down test at that time. It should have maintained presure for 30 minutes if an injector isn't leaking. Of coures, the pump check valve and regulator could also be a leak source, but that would be back to the tank.