93 4.0L rough idle/stalls

[fearsome]

Considering the symptoms, could this be the sole problem? I will continue looking at what people suggest, but am just curious if this could be the only cause of my problems.

 

[MrShorty]

Faulty FPR could explain a lot of your symptoms. If it were me, I would replace the known bad FPR, clear the keep alive memory (disconnect battery while replacing the FPR), then test drive it to see what it does then. Check the codes again to see what codes (if any come back), and work from there.

 

[fearsome]

I'll give it a try, I just wanted to avoid replacing another $70 part if I didn't need to. I'll post results later. Thanks again to everyone contributing!

 

[liqhx2]

i understand what you mean bud i've been in the same boat your in now but what i have learned is fix the obvios first then move on but also usally when the FPR goes bad it will foul the plugs so either clean the plugs or replace them good luck

 

[fearsome]

I know, it's known to be bad, I'll have to fix it whether it is the cause or not. I'll also be replacing all "tune-up" items when I get to this. Only thing is, I'll have to put this on hold for 2 weeks until I get paid again. I appreciate everyone's help and will be back, likely begging for help!

 

[fearsome]

*URGENT* 93 rough idle/stalls

Well, I'm back again. It took longer than expected. Here is what is going on. I have replaced the IAC and FPR. The explorer is still running at @ 500 rpm and will usually die. I pulled codes and the KOER test is still throwing a 136 - O2 sensor code. I see the O2 sensor but have no idea how to get to it to replace it. Can someone please help me, I really have to have this running in the morning. Thanks for any suggestions!

 

[svande8952]

Usually, o2 sensors just unscrew from the pipe. I haven't replaced one on the ex yet though.

I replaced one in my chevy truck and it was pretty easy.

 

[Rhett]

I see the O2 sensor but have no idea how to get to it to replace it. Can someone please help me, I really have to have this running in the morning. Thanks for any suggestions!

I find replacing the O2s on our trucks to be difficult. Once you have done it a few times, you will invent new words to describe your delight for this task.

Your truck, if it's a later model 93, will have 2 O2s, one on each manifold pipe. You may possibly have just 1, but most 93's had 2. To do it right, you must replace BOTH O2 sensors.

The easiest (if I can use that word) (it's not easy by any means) method is to get an O2 sensor socket, lots of extensions, a tough breaker bar, and try to get the old O2's loose. Sometimes they are tough to break free. (You may be forced to start the truck and let the pipes heat up a bit to aid in removal...but be careful of hot exhaust pipes if you must do that.)

Then, once the sensors are unscrewed, you can pop the hood, and pull the sensors up through into the engine bay by their wires. Then it's a simple matter of unplugging the old O2 and pluggin a new one in, fish it down thru the bay, and more cussin' to screw it back into the pipe.

It may be necessary to cut the O2 wires before removal to enable you to unscrew to old sensors. Of course, once you do this, for all practical purposes you must replace the O2s then. If you must cut, be sure to cut the wires BEFORE the connector. (i.e. close to the O2 itself).

 

[fearsome]

At the suggestion of a user in an old post, I removed the front wheel and the splash guard. From there I could remove the o2 sensor. Rhett, I'm afraid that if I described my delight I'd get banned from the site. Well, I ran out of light so I will attempt the driver's side tomorrow. Thanks again for everyone's suggestions! This is definitely the best forum I belong to!

 

[fearsome]

Now I'm really puzzled. I have replaced the driver's side o2 sensor. Now, it will start fine and rev up a little, but when it kicks down to idle it dies. I will not even stutter at 500 rpm as it used to.

So far I have cleaned the MAF filaments and sparkplugs. I have replaced the IAC valve, FPR, TPS, and both o2 sensors.

I can hear the fuel pump run immediately before the engine starts and just after it dies. Fuel filter was replaced about 2 years ago.

Any ideas?

 

[johndavid]

just a quick note: if this is a 4.0l mfi engine....(not an sohc)....you really need to check the upper intake gasket to the fuel rail and the fuel rail to lower intake for vacuum leaks, sets lean codes and causes a rough, low idle and stall, 4.0L MFI engines with high miles are the worst, also cold weather will usually compound the concern, good luck.....johndavid

 

[MrShorty]

Any codes still being output? If you can't get it to run the KOER test, any CM codes?
What's your fuel pressure? I know you replaced the FPr, but there's more to getting the right fuel pressure than the FPR.

 

[Glacier991]

I am sitting here smiling. When I read the initial post I thought to myself... "Now HERE is a question begging for Mr. Shorty's expertise."

He's the first one I'd listen to on this type of Q.

This board has some "golden oldies" whose advice is always good. He is at the top of THAT list.

(sorry about the oldie thing Mr. Shorty <g>)

 

[fearsome]

I pulled the battery ground after replacing the last o2 sensor, I'm not sure if I can get it to output codes or not. What are CM codes? I don't know if I could get it to do a KOER test, but I would think it would not be accurate with my foot on the gas throughout the test.

 

[MrShorty]

CM= continuous memory. That's the set of codes output after the separator pulse during the KOEO test. If you can get the engine to run by holding your foot on the gas, run the engine for a bit until the engine warms up, then shut it off and run the KOEO test.

You're right, you wouldn't get a good KOER test if you have to hold your foot on the gas.

Out of curiosity, how well does it run when you hold your foot on the gas?

 

[fearsome]

I finally gathered a small amount of money and hope to get this thing running. Here is where I'm at:

Fuel pressure is at 40 psi
KOEO - 111
KOER - 136

I have replaced the IAC, FPR, TPS, and both O2 sensors. The fuel filter was replaced 2 yrs ago. I cleaned the MAF filaments and the spark plugs appear to be fine. I don't see or hear any obvious vacuum leaks, and am not sure how to check the gaskets for leaks other than visually.

The engine started and ran today after I gave it gas, but it has been sitting for a month. It shudders but continues to run. There is no CEL since I disconnected the battery back in January.

I greatly appreciate all suggestions to this point and hope that everyone continues to do so!!

 

[MrShorty]

Are those codes recently pulled, or are you simply reiterating them? Any CM codes?
There's more to diagnosing codes than replacing parts. Codes point to problems in circuits, not sensors. If you backprobe the offending O2 sensor circuit, what do you get? If you can get access to a full function scanner, and your '93 is capable of outputting live data to it (I think '93 is around where they started adding that functionality to EEC-IV systems), that could be a useful tool in diagnosing this.

 

[fearsome]

Those codes were just pulled today, no other codes were present. I'm basically contained to my driveway and will have a hard time pulling codes if it does not include a paper clip. I know that replacing sensors is not the best way to repair a problem, but I assume all parts were original with 250K miles on them.

 

[fearsome]

When you saw backprobe, I assume you want me to measure the voltage on the O2 circuit? Also, what is the fuel pressure supposed to be set at?

 

[MrShorty]

Yep, looking to see what the O2 sensor is outputting. One thing I neglected to mention, a KOER 136 is easily set by performing the KOER test on a cold engine. O2 sensors don't function at all until they reach something like 600 F, and the KOER test isn't long enough by itself to get the O2 sensor warmed up. Especially if there are no CM O2 sensor codes, and given the rough nature of the engine running, i would suspect the O2 sensor may not have been warmed up prior to the KOER test.

fuel pressure should be 40+/-5 psi.