93 4.0L rough idle/stalls

[fearsome]

*URGENT* 93 4.0L rough idle/stalls

I have replaced the IAC and cleaned the MAF filaments. The engine vibrates alot and will idle at about 500 rpm before dying. I barely got it home the other day by using one foot on the gas and one on the brake. Spark plugs look good also. This suddenly started a few days ago, it didn't slowly develop or give me an indication that something was wrong. Any ideas?

 

[MrShorty]

Might run the self-tests and see if the computer can see a fault.
fuel pressure where it should be?
All cylinders firing? Try a cylinder balance test to see.

 

[fearsome]

I took it to the autoparts store and they let me borrow the code reader but were unable to help me. I cannot find the test connectors anywhere. I did find a red ABS test connector that looks just like the STO, but I can't find anything that looks like the STI connector. Can anyone help? Again, this is a 93 explorer sport 4.0L automatic.

 

[Glacier991]

Some of the 93's had the test connectors inside under the dash

 

[fearsome]

I found the connectors. They were stuck to the back (firewall side) of the power distribution fuse panel and slightly under it. Now I pray that I can make it to the parts store again to read the codes.

 

[Infragate]

check the vaccuum hoses on the vaccuum spider/tree. It sounds like one may have popped off or is cracked badly or loose. Make sure they are all attached to the tree. Ive seen this before, a cap comes off and it runs as you describe.

 

[MrShorty]

No need to go to the parts store to borrow a code reader (unless you don't have any paper clips lying around). See www.dalidesign.com/hbook/eectest.html and use the Check engine light to read the codes (Check engine light will flash in the same way a voltmeter or test light will).

 

[zach9989]

My dad had a problem like this with his explorer, turned out to be the oxygen sensor.

 

[karl_burns]

I had something similar too once

Come to find out there was a hole in the silicone elbow of my intake. No vaccuum, no air into the engine, no spark.... you get the idea.
Check that while you're checking the MAF.
Karl

 

[fearsome]

OK, I did the CEL counting method (thanks MrShorty) and came up with this.

TEST 1
KOEO:
111 157 176
KOER:
116 136 538 536

TEST 2
KOEO:
111 157 176
KOER:
136 167

TEST 3
KOEO:
111 157 176
KOER:
136 167

I feel that the second and third ones are more accurate, I'm not sure that I hit the brake or gave it gas during the first KOER test. I did disconnect my battery the other day after I replaced the IAC and before I drove it the 1 1/2 miles to the parts store. I'm leaning toward a faulty oxygen sensor, what does everyone else think?

 

[fearsome]

I did check the vacuum hoses. All are there and appear to be in good shape.

 

[MrShorty]

The initial 111 indicates that it passed the KOEO test.

KOER 136 = One O2 sensor indicates lean.
KOER 167 = Almost always means you missed the "goose" test. Make sure you goose the throttle at the right time, and don't be shy when goosing it -- 3/4 to full throttle.

The other codes from the KOEO test are continuous memory (CM) codes.
CM 157 = MAF signal low. Likely an intermittent fault or something, because this code doesn't show up in the KOER test. Or possibly bad MAF data is the cause for the KOER 136.
CM 176 is essentially the CM equivalent of KOER 136

Overall analysis: A faulty O2 sensor is certainly one possibility. I would at least check the wiring between the O2 sensor and the PCM before replacing the O2 sensor.

 

[Diff Whack Daddy]

Clean the MAF. This is commonly a cure for this problem. The best way is to remove the two security torx screws from the MAF housing and clean the small wire with carb cleaner. With the KOEO test, it tests good, so it the PCM uses the data from the MAF when the KOER. Basically, the MAF is good, but with it being dirty, it sends incorrect data to the PCM and causes poor idle and stalling at idle.

 

[fearsome]

I did clean the MAF filaments with a q-tip and alcohol. They didn't look bad, a little carbon came off on the q-tip. Could it be passing the KOEO test because I took the ground off the battery and haven't driven it much since? Also, since an O2 sensor showed up in both tests it seems that checking the sensor and wiring would definitely be the place to start, correct.

I'll try the engine test later and try to get the throttle. The KOER test gives the engine code, I brake and turn the wheel. Then, it runs for approx. 45 seconds while the idle fluctuates from 1000-2000 rpm. It then flashes once (goose?) and I give it gas, most of the way to the floor. After a few seconds, the fast codes flash and then the test starts. Am I missing something? Also, after the test completes, can I start the cylinder balance test?

Thanks for everyone's patience and input!

 

[MrShorty]

You're hitting the goose test at the right time. Test the TPS to see if there's something wrong with it.

 

[liqhx2]

a faulty FPR will through this also check your fuel pressure and make sure it is not dumping fuel into the vacum system also another thing that can cause the O2 sensor to show lean is missfires all the O2 sensor is looking at is the amount of oxegen that is coming down the exhaust and when the motor misses it pushes alot of air out the exhaust the O2 sensor does not see the amount of fuel that is there only oxegen i would check wires plugs coil pack CPS and coil pack when you read engine codes it's not a magic thing that will show you exactly what is wrong it just gives you clues good luck

 

[fearsome]

It finally stopped raining today. I check the resistance between the gray/white and brown/white leads on the TPS and the resistance went up to around 6 ohms. While I was opening the throttle it seemed to bounce around a little but I am not sure I even tested it correctly. Will it hurt anything to do the voltage test by piercing the insulation on the wires? I hate to do that if I don't need to. Also, what wires am I supposed to read from. Thanks!

liqhx2 suggested it may be the FPR. Can I test that?

 

[MrShorty]

I don't think piercing the insulation would really hurt anything, but I prefer to backprobe a connector instead. If the resistance is jumpy, that would indicate a worn TPS.

FPR can be tested. 1st test is to pull the vacuum line off of the FPR and see if there is gas in that vacuum line. Gas in the line means the diaphragm inside the FPR has ruptured, and the FPR needs to be replaced. 2nd test is to get a fuel pressure gauge, attach it to the fuel rail, and see what the fuel pressure is.

 

[fearsome]

When you say backprobe I assume you mean to insert the test leads into the connector from the side the wires enter. If so, I tried that and was unable to get a reading.

I did check the FPR. When I pulled off the bottom "hard" vacuum line there was some fuel in it. I don't know if there was alot, but I would think that any in there is bad.

 

[liqhx2]

yes any fuel in the vacum lines is bad sign that your FPR is bad only remedy to that is to replace the FPR good luck