Ugh... 92 Explorer Hell..

[MistahYebba]

Whatever the problem is, it must be amplified when the IAC is plugged in.. because with it unplugged it runs; but it runs iffy. When it's plugged in, it barely runs at all.

Which one of these would be amplified with the IAC plugged in? And subsequently, which one of these would be slightly pacified with the IAC unplugged? That's how we can all find this darn issue.

Vacuum leak?

TPS?

MAF Sensor?

Battery cables?

O2 sensor?

Spark plugs/wires?

FPR?

Fuel injectors?

Fuel filter?

I'm sure there's more to add to this list.

 

[natenkiki2004]

The MAF can be faulty. It won't have anything to do directly with turning the AC on/off but if the computer has an incorrect value on the amount of incoming air, the fuel trim will be off too and combined with extra load on the engine, could cause it to stall. Generally, unplugging the MAF will make the computer read from default values, enough to run the engine. Usually, if the engine runs much better with the MAF unplugged, it could be a sign of a bad MAF.

The only way you'll know is by either hooking up a multimeter to the MAF or running the onboard diagnostics. You need to have the computer respond to test mode, if it doesn't then your computer could be shot/faulty.

 

[MistahYebba]

Well in that case, if it was the MAF this whole time... If I reconnect the IAC and give it a go; everything would run well right?

So why does it still stall or idle real rough with the MAF unplugged and the IAC in?

 

[MistahYebba]

Could you give me a tip on maybe unhooking the battery to possibly correct any computer stuff? Like the proper procedure? Then I could try the self test again.

 

[natenkiki2004]

1st, use the edit button on the forum, you're making this thread way too long by posting several times.

As far as the battery, just disconnect the negative cable for 10 minutes.

 

[MistahYebba]

If disconnecting and reconnecting the battery fixes everything (it shouldn't)... what would the problem have been??

What is my next troubleshooting goal Natenkiki?

 

[natenkiki2004]

I never meant for it to fix anything, I only meant for it to reset the computer and buy your time so you can idle the engine up to temp and try to pull KOER codes without the engine dying. Hopefully, the computer would recognize whatever's going on if it's something sensor related.

 

[MistahYebba]

I know I know I wasn't thinking you said it would fix anything--it was hypothetical and being hopeful.

I need to try again to pull the codes now that I reset the battery. Unfortunately it didn't fix it...in case the IAC needing a reset was the problem.

 

[MistahYebba]

Okay so... the same thing happened when I reset the battery and tried to pull the codes.

When I connected the jumpers with a paperclip, I heard a click as if something worked..

went a did Key On Engine Off first.. it instantly started giving codes... I know there is supposed to be some sort of beginning phase?!

Then I tried Key On Engine Running next... once again, it instantly started giving codes! It totally skipped the portion where it flashes once to notify the driver to do a "goose test"... I know I'm not tripping, right??

So... because it skipped that phase... I tried again.. I shut off the engine and turned it back on to see if that made it do it correctly.. and then of course it did what it did before and just stopped being in test mode... showing only a solid Check Engine light like it always does :/

If it's to any avail.. it shows codes "998" and "579"... that's as far as I got since it's not asking for a goose test.

 

[MistahYebba]

Figured out why it's skipping the cylinder code...

Check it out..

"If you get a code 98 or 998 in place of the cylinder code that means the computer has forced the system into 'limp' mode. This means there is a serious problem and the computer is substituting or faking some sensor status in order to keep the engine running. There will be other fault codes as well."

Aha!

Okay... so let's keep diagnosing!

 

[natenkiki2004]

You need to have the computer respond to test mode, if it doesn't then your computer could be shot/faulty.

So, the big question now... what went **** up? Many people here say that the ICM won't throw codes and you'll only notice it by lackluster performance and a higher chance of pinging. In every thread where the computer has died, it's bad enough that the engine won't even start.

You mentioned dimming lights and other electrical issues... now the fun begins. I'm betting that everything is fine but you have a bad ground or connection or severely rotted battery cables. The computer isn't getting the right voltage for some circuit and is throwing fits. It could even be as bad as the 5v reference circuit having died.

Here's what I'd do;
- Check the reference voltage at the TPS and MAF.
- Check voltage directly at the battery then compare to voltage found at body ground and solenoid (the forwardmost post). If there's a difference, see below.
- Check the battery cables. If they're factory originals, replace them, no questions.
- Look for all connections, unplug them and squirt/apply a ton of dielectric grease in the female end. Connect, disconnect, reconnect. Make sure each one is getting a good connection.



*EDIT*
Looking online 998 seems to have a few possiblities;
- Shorted reference voltage (the 5v going to the MAF, ECT, IAT, TPS and more).
- Incomplete key on, engine off test (complete this test fully just in case).

Forgive my memory, didn't you get the 998 before you disconnected the battery too? If so, ignore the test bit. Whip out the multimeter and start probing. Without voltage going to the sensors, your computer has no idea what the engine temp is, how much air is going into the engine and how much throttle you're giving it. Basically... it has no idea of what's going on, it only knows the engine RPM.

 

[MistahYebba]

I'd be multimetering the wiring harnesses for each sensor, right?

I can tell you right now off of memory they all look plenty scuffed up... but if I recall correctly, one of the pins on the TPS harness looks "pushed up". What if it got unplugged too hard and bent one of the pins? Would this cause it? Just an example..

In other words, am I basically testing those 'lil pins in there?

So damn, now I need a multimeter. Think an autoparts store would let me borrow one? I'm broke til Friday.

Guess I need to add that to my growing mechanic's kit lol.

--------

Are you saying there is an order to the Self Tests that you must abide by? Do I have to do the KOEO test first before trying the KOER test? And yes, I did mention the 998 code earlier before I disconnected the battery.. but please note;

It seems as if I get "1 try" to do these tests... after it runs through "test mode" once, it seems like it doesn't notice the EEC Self Test having a paper clip in it... until I disconnected the battery and reset it.. then I was able to do the EEC Self Test "1 more time" if that makes sense?

Not to mention, earlier I had no idea what 998 meant.. so when I got it earlier, I was expecting to get 3 flashes to indicate my 6 cylinders.. but since I found that bit of information I felt so relieved.

**EDIT**

Let's pretend my TPS harness is screwed. Is there ways to replace those harnesses that plug into sensors?

 

[natenkiki2004]

One wire on each of the sensors has a 5v reference. That 5v is altered by the sensor and whatever is left of it is sent back to the computer. For example, the TPS may have a range of 1v at idle to 5v at WOT and smoothly travel between the two. Whatever voltage the computer gets back, it knows what the throttle position is.

What you want is the straight 5v. It may be 4.9 or 5.1v but somewhere in there. Hook your multimeter black lead to ground (make sure it's a good ground, touch the red to battery positive to verify). Then poke each one of the wires. Don't poke through the insulation, don't press into the female end of the connector, just rest the multimeter lead on the metal of the connector. Keep in mind, the key will have to be in the on position in order to perform this test. Chances are good too that if you get 5v on one sensor, all the others will have it. They all share the same 5v reference so if it's shorted, they'll all be dead. Personally, I'd test the TPS and MAF just for good measure, they're the big sensors in our engine computers and being at opposite sides of the engine, it's just good to verify.

& yes, you can buy new harnesses at most auto parts stores. For the love of all things holy, if you get to this point, don't use one of those crimp-on butt connectors. Solder it and heatshrink it, do it right, do it once.


All that said... I don't know why you'd be able to do 1 test but not subsequent tests. Many times I recall doing a test on mine, missing the numbers and having to redo the test. I could do them as many times as I wanted and in any particular order.

 

[MistahYebba]

Hmmm doing all that multimeter testing is something I'm gonna have to read about to understand haha. but when I get a multimeter I'll definitely give updates. I wouldn't be surprised if a harness was acting up or something...

but hey... tell me this!

if it's a harness being all corroded or even a pin being broken off at a harness for a sensor.. would that really cause all this?

Would most trucks be able to run with all sensors unplugged?

And one more thing.. since the IAC has to be unplugged for me to run the truck to pull codes, wouldn't that come up as a 998 code? Idk just fishing for info lol

 

[natenkiki2004]

Yes, a shorted 5v reference will all but kill the engine. The engine runs on a computer and that computer is utterly dependant on critical sensors. It absolutely needs the crank sensor, without that, the engine will never get fuel or spark. Aside from that, all the other sensors improve how well the engine runs. You CAN run the engine with all the sensors unplugged (except the crank sensor) but it'll run horribly... like yours.

You need to see if you even have the 5v reference. If you do then you need to look elsewhere. If you have no 5v then you need to start looking for areas where the harness would rub or short to ground.

Keep in mind, a shorted 5v reference isn't an absolute diagnosis but it's a quick and easy check. I'd hate to jump straight to BAD COMPUTER, that's expensive and unnecessary at this point.

Take some time to soak up some knowledge on testing sensors & electronics, ScannerDanner is good for that, just keep in mind that he mostly works on OBD-II vehicles so you have to do really dumbed down versions of what he does. Take a look at this:
https://www.youtube.com/watch?v=uyncVz_HAtA


*EDIT*
I'm not sure if the crank sensor just picks up a magnetic distortion or if it actually uses the 5v reference too. If it does use the 5v, then you can rule that out, the engine wouldn't even start.

 

[MistahYebba]

Just one question..

Wouldn't something only short out if it's plugged in??

In other words, let's say my TPS harness is shorting out because of "insert x reason here"..

If I unplugged my TPS sensor, it wouldn't be able to short out, right?

And therefore I could in theory unplug all of my sensors and re-scan and see if I get the 998 code again?? Or no?

 

[MistahYebba]

Not sure really where it would short besides at the harness or the sensor connection itself..

*edit**

sorry for not making this one an edit

 

[natenkiki2004]

You can short the wire by rubbing away the insulation. Watch the video I linked to, it'll get you thinking.

 

[MistahYebba]

In the mean time, any idea why everyone says "998" mean "limp -home mode" or "hard failure"??

 

[natenkiki2004]

In the mean time, any idea why everyone says "998" mean "limp -home mode" or "hard failure"??

Because that's what it is:
http://www.troublecodes.net/ford/eec-iv/