Rough Running, both cold & warm, both idle & under power

[motopsycho650]

Hi, I'm new to this forum, but I am having issues with my '92 XLT.

About a week ago, I went to start my Explorer in the morning, and it sounded like it was running on 4-5 cylinders, Very Rough. After warm-up the rough running improved a little, but I could feel power cutting in & out while going down the road. The last weird symptom was, while sitting at a stop light for about 30 seconds, the RPM's would drop from the normal 700ish to below 500. Then it would cough a few times, and eventually return to normal RPM's, although still rough. Oh, and there is no Check Engine Light.

First thing I did was changed the fuel filter, and pulled the plugs. All the spark plugs were very black and rich looking. I cleaned them, checked the gaps, and put them back. I also sprayed out the Mass Airflow Sensor with carb cleaner, and disconnected the battery to clear the computer. Some of this helped a little, but not enough. It is still running rough cold or warm.

So, I found this forum, and was looking at different posts about a 4.0L running rich. I read one that said to check my thermostat, since the computer could be keeping the truck choked, trying to warm it up. Well, that was right, my thermostat was broken. Replaced it, started it up again, and again next to no change in running. While I was driving around, warming it up, I finally got a check engine light.

Came back home and pulled the codes from the computer. All I got was a 172 - Oxygen Sensor Reporting "Lean" code from the stored memory. So, I changed out the O2 Sensor. While I did that, I did a good inspection for vacuum lines, all of which look okay & dry. I also reset the computer again.

The O2 Sensor did make a change while it runs, but did not fix the problem entirely. Now, running cold is still rough. When it warms up, and is moving, it becomes a very rhythmic miss fire. The power is steadier, not cutting in & out like it was before, but still only 75% of normal. While sitting at a stop light, I still get the RPM drop after 30 seconds or so of sitting & idling.

I have two guesses left, but since I don't have much money to waste, I thought I'd ask you guys. 1st. The EGR Valve. This makes sense to me with the RPM Drop at stop lights, but how much does this have to do with fuel mixture? 2nd. The MAF Sensor. I did a test, and while the engine was running, I disconnected the MAF. There was no change in the way the engine ran with the MAF either connected or disconnected. The CEL did come on when I un-plugged the MAF, and turned back off as soon as I plugged it back in.

What does anyone think?? If you have any questions about my long story here, please ask... I appreciate anyone trying to help...

 

[explorinitup]

it does sound like it could be a mafbut thay can be expensive.in te closed loop for morning warm up it would disable a lot of sensors such as maf and o2s your miss can u see any one cylinder that isnt hitting when u pulled out your plugs u might have a coil pack out or maybe with the idle could be iac

 

[motopsycho650]

I 100 % agree my problem is during "open-loop" or before warm up. I knew the O2 sensor didn't make sense, but I had to try.

All the spark plugs look the same, all black & rich. There are none that stand out as being the faulty cylinder. The plugs & wires are only about 20,000 miles old.

So The Mass Air Flow Sensor is only used after warm up? I think so is the EGR Valve... I'm going to remove & clean the Idle Air Control Valve, and see if that makes an improvement... If so, I may replace it.

 

[motopsycho650]

I removed & blasted all the crap out of the Idle Air Control Valve, and it had no effect on how it runs. I pulled codes again, and I get nothing but normal 111 on the KOEO test. Then I still get a 172 - O2 Sensor says Lean on the KOER test.

Also, while it was warm, I pulled the plug on the MAF sensor, and the engine quickly choked & died, so I think that has been eliminated.

I'm going to pull the plugs again, and have a look once it cools down. Other than that, I have no idea what else to do...

Update: Now, according to the plugs, it is running lean. All the plugs are completely burned clean from before I changed the O2 sensor. There is on plug, the #3 cylinder according to the Haynes book. That plug is not burning as hot. Actually, it looks perfect compared to the other five. But, it still has a very bad miss all the time.

 

[marragtop]

Have you tried to isolate the miss to an individual cylinder by pulling the plug wires one at a time?

 

[motopsycho650]

No, haven't done that yet. I was out testing the Throttle Position Sensor. All voltages there are in spec.

 

[MrShorty]

I think we can eliminate the EGR as a possible cause, because your '92 doesn't have an EGR system.

One thing I'd probably do would be to check the vacuum line to the FPR for gas and check fuel pressure. Make sure fuel delivery is up to spec.

 

[motopsycho650]

No EGR System on a '92? Well, I hadn't gone looking for it yet, just remember it being mentioned in the book. Fuel Pressure is going to be the next test. My cousin is comming over with a gauge in a few.

As far as pulling plug wires one at a time, all of them made a difference in the way it ran. There was not any one cylinder that acted any different than any of the others.

 

[motopsycho650]

Ok, so my cousin, who is a very good mechanic came over. He re-did the test of pulling the plug wires, this time we had it in gear with the engine under load. We found a dead cylinder. Tomorrow, I'm going to check compression, and test the injector. I personally think it's the injector since the plug is dry and has no fuel on it.

 

[fixxxer]

Don't rule out the wiring from the ECU, the injectors get their signal from the computer, you could have a bad connection at one of the connectors.

 

[motopsycho650]

Hey, Does anyone know... On an '92 explorer, does the computer send the injector pulse through the positive wire? Or does it pulse the ground? My cousin wasn't sure for my explorer and said some vehicles work either way.

Basically what I'm thinking is, if I test light the positive, and get a pulse. Then ohm the ground to make sure it's ok, that should prove the injector bad, correct?

 

[muhl5443]

actually he does a have an egr valve in a '92. every vehicle made after about '85 has an egr valve.

 

[MrShorty]

Injectors have a constant +12 V power supply and the computer is a ground side switch. On your '92, they are also "batch" fired three at a time. A wiring diagram (even the one in Chilton's) would be useful for seeing this relationship.

 

[MrShorty]

actually he does a have an egr valve in a '92. every vehicle made after about '85 has an egr valve.

In school, they taught me that, when answering a true/false question to watch for words like every, all, or none, because all you have to do is think of one exception to make the statement false. One exception I know of is in my garage.

 

[motopsycho650]

The lack of EGR debate is correct. My '92 does not have an EGR. It has a charcoal canister that re-circulates the fumes. We went to a junk yard and pulled injectors from a '94, and it did have an EGR valve.

All said & done, I had a bad injector on the cylinder #3, according to the Haynes manual. The injector wires have a constant 5 volt supply on one wire. The other wire is a reference wire that fires the injector. My mechanic cousin told me a good trick to test the injector wiring. Unplug the injector, hook a 12-volt test light to the POSITIVE battery terminal, (yes that's weird). Start the engine, and check each wire connector. One will be a constant light (dim since it's 5 volts on a 12 volt light). The other wire should flicker on & off. That proves the wires are providing a good signal.

Anyways, a used injector from a junk yard, a lot of cleaning things, and the sucker runs better than it has in years. Not bad for 180,000 miles. Also, aside from the injector, the lower gasket below the fuel rail was blown at the front, cylinders #1 & #4. Not sure when that happened, but it wasn't helping...

 

[SuddenDeath]

I'm having a smiliar problem. I'll have to try your test with the light. Mine was getting pretty bad with the coughing and RPM drops, after a good bottle of fuel system cleaner she got better...but not all the way. I'm wondering if maybe the fuel injectors are really caked up, instead of one being dead? Way I see it, if one was simply not working, the Fuel System Cleaner wouldn't have helped at all. Is my logic sound? Should I just gather up my buddies and do a full clean of the injectors and electrical systems?

 

[boggs1227]

if your replaceing one injector then it may be a good idea to buy all new orings for all of them seeing that you have to almost take all of them off to remove a single injector .seat them useing plain old 30w motor oil and no silicone based oils ....silicone may cause problems with the injectors.

when you got the fuel rail off replaceing the bad injector it also may be a good idea and time to clean the fuel rail to just spray the piss out of it with carb cleaner and then get air compressor to dry and clean it good .

just a few ideas while you got every thing apart plus could not hurt either.

 

[motopsycho650]

My explorer ended up getting 2 used injectors, a complete set of injector o-rings (10 bucks), and two new intake gaskets, one above and one below the fuel rail.

I replaced the injector that was bad, and found one other with a small crack in the lower plastic end cap. I saw the old o-rings, and wasn't even going to mess with them. I cleaned everything as best as I could, and used a finger dab of motor oil to lube the new o-rings. That made them a lot easier to push in, as well as seating the fuel rail.

According to my cousin, that test light trick for the injector wires is doing the same thing as the "Noid" light mentioned in the book. It's just a lot easier since most people don't have a Noid light.

For SuddenDeath: Injector cleaner will not do anything for a dead injector or cylinder, unless the injector was totally blocked, and the cleaner happens to clear it. Another trick to try that my cousin showed me during this process; With the engine running, spray carb cleaner completely around the base of the plentum & fuel rail. If your rough running issue clears up for a few seconds, you most likely have a blown intake gasket. If you don't notice anything in park, set the parking brake, CHOCK THE WHEELS, and repeat the test with it in reverse or drive. That puts the engine under load. This trick is only good for automatic transmissions.

I guess explorers are known for blowing intake gaskets. Mine were blow and I have no idea when. I've had a rough idle for years, and now it's running as smooth as I can ever remember.

 

[boggs1227]

congrats on getting it running good ...all tho i did not blow my upper intake gaskets my lower intake is leaking coolant ( in the common area for them to go at) ......it will be interesting to see what the intake manifold looks like after 14/15 years of wear and tear when i remove it for the repair.the upper intake manifold was so bad on mine when i got it ,when i took it off the engine 2 big golf ball sized chunks of carbon fell out of it ...after i soaked it in a big plastic tub with 4 gallons of gas over night it got all the carbon deposits out and in the hard to get to areas as well .