I do replace the air cleaner, spark plugs, spark plug wires, PCV valve, radiator cap, gas cap, serpentine belt etc and even change the oil occasionally. My cars are not quite as neglected as it may sound like from my posts ;-) I need for them to be reliable and I do take pretty good care of them. I just don't ordinarilly go around replacing parts that I don't know to be defective. I have also cleaned the MAF but I'm scratching my head right now trying to figure out what the IAC is.... Also the '97 has the same (basically) engine as the '91 and '92. Reading about everyone's problems with the SOHC scared me away from it.

 

Ok them. You have a good basis. The IAC is the idle air control valve. It lets air past the throttle valve at idle to make sure the motor doesn't die. From your post, I would not suspect a problem since you never talked about an idle problem. But why not take it apart and clean it if you are retired and these are hobby toys anyway. you can't make it worse by cleaning it.

 

I'm not retired, the truck is Semi-retired, that is. I'm busier than the proverbial one-armed paper-hanger with an itch. I'll take it apart anyway. That must be the thing that wouldn't unscrew without an impact driver...

 

Jharger,

I've been out of town a few days. Let me take in your message and sort through the info. Appreciate the advise. I'll drive the car the next few days and see if all is well or I can get it to repeat. And, no, I did not reset the PCM when I replaced the O2 sensors....should have known better, but it ran ok. Will get back to you. thanks.

 

Update:

OK, I've been driving car for a couple of weeks and it was running great......until today. I thought perhaps, the problem had been corrected. Foolish me. I started out of the subdivision and got about a 1/4 mile when it hiccuped and flashed the check engine light. I turned around and tried to make it back to house but engine died. It wouldn't start...first time that happened. I pushed it a block to get back close to house and then tried poping clutch and it started and then proceded to run normally, for what that's worth.
I hooked up vacuum and fuel gages and ran eec tests and all was as before..normal as I could tell. This is getting pretty frustrating, however, a couple of times the engine did hesitate and stumble but recovered. Fuel presure was 32-33, vacuum was 19-21 with some fluctuation.
The only thing I can offer is that the day before it rained throughout the day. I drove car well over 70 miles and all was well. I'm not sure if moisture may have seeped in over the night or not.

 

OK. Just reread everything. Man this is getting to be a long thread. kind of morphed off with the O2 thing but yeah back to the electrical engineer's issues.

Why did you pop the clutch to get it going - just because? I mean your battery and starter are OK and the motor will crank. right?

From before and now it looks like fuel supply up to the injectors is not problem. pressure looks right with and without the vac line attached to the regulator. I know you went and changed the wires and plugs. Can you go back and check the plugs again now? Pull every one. This is needed to know what is going on inside the engine. if they are black again, we're still too rich.

I mentioned the IAC - idle air control - valve before. Did you try to clean it. I can see it causing a bad idle. And even making the plugs black at idle. If the PCM tells it go open and then also sends extra fuel to compensate, but the valve doesn't open correctly and you get less air than the PCM thought, you will be rich. This is really only an idle condition potential though since once you open up the throttle, the MAF tells the PCM how much air and it uses realtime data to control the fuel delivery. At idle, it is all preprogrammed with no feedback from the IAC to the PCM (so it can't give you an error code either). The PCM never knows if the IAC actually opens or not. O2's would give some feedback of course but by then it's too late and the engine was already rich.

That would cover the idle but not the regular driving part. Hmmm...Did you check the throttle position sensor? It should give you a linear 0 to 5 V, more like .2 to 4.8 V actually. My scanner can read this real time. And on your 93, like mine, the OBD-I with the 3 digit codes allows you to see about 20 parameters real time too, with the right scanner. Otherwise, disconnect the plug and hook up your volt meter with key on and rotate the throttle plate.

MAF I think usually gets dirty but runs car lean not rich.

EGR system might have some affect. I've heard of bad DPFE sensors telling the PCM that more or less actual EGR flow is going to the intake and then the PCM doesn't correct the fuel requirements (more EGR, less fuel). But it sounds like your issue is worse than this.

That's about it from a controls perspective.
O2's, MAF, TPS, IAC, EGR/DPFE, intake air temp sensor, engine coolant temp sensor.
That's all you have on your car and you might not even have EGR.

Really need to know what the plugs look like right now. If you are still black, then it's got to be a controls issue. If they look good, then its more likely a physical/mechanical issue. The try that compression test you're so scarred of.

I need to do this on mine too. 170K miles and I'm going to get a custom chip programmed for it this afternoon. I should have done the compression test already but never got around to it. Last thing I want ot do is try an already weak condition somewhere by bumping up the timing and leaning out the mixture. Oh well. If I break it I'll have an excuse to pull it and rebuild it with that new cam I've been thinking about....

 

OK. Here's status. Popped clutch to see if it would start, yes, just because, but also I had an incline to get up in my driveway and wanted car under tree for cooler work. It started normally, that time. Battery and starter are fine, engine cranks normally.

I went to store this am and it ran fine to first store, approximately 10 miles. When I got ready to reposition to next store and got a check engine light and engine started running noticeably rougher, although not to the point where it stalled. I carefully went to next place just a block or so, went in for a few minutes and started up again. Check engine light remained on. I went home with engine continuing to run rough but not as bad as it was a few days ago.

I immediately put gages on it and code reader and got same results as before, fuel pressure 32, vacuum did fluctuate between 19 to 21, and code reader only showed 522, not in park or neutral. No other codes. I still haven't checked with another tester.

Pulled plugs on both sides and they were carboned up as before.

I had not reported, but a couple of weeks ago I did pull the IAC and MAF and clean as best I could. I noticed nothing that would indicate a problem and devices seemed to work correctly. I have just made the following checks: MAF, voltage close to battery with key on, engine off, connector removed. With connector on, engine on, signal voltage at idle was around .7 and increased with throttle movement.
TPS, reference voltage was present in plug, around 4.7VDC. With key on, engine off, plug on, idle, .76VDC and increased with throttle position up to 4.7
IAC, input voltage was normal, around 12VDC and resistance checks were normal too. No indication of internal short.

I can't find an EGR if I have one. I'd check it if I could find it.

I can do the compression test, but what I can't understand is, why would all the plugs be carboned up, if it were compression related. Also, it seems that I would have oil indications on the plugs if that were the case.

One other thing to point out is something that happened during these recent tests. As I was turning the ignition key on and off for the various tests, once, and only once, after I turned the key on, the valves started making irratically clicking noises(energizing/deenergizing) while the fuel pump continued to run. Normally, it briefly runs to build up pressure then turns off, but this time it stayed on. As I felt around to see what was clicking (think there were several things) I did notice the IAC clicking. So I then pulled off the plug and and it stopped. I then put the plug back on and it didn't repeat but there were other noises and the fuel pump continued to run. I think the other noise/s was the fuel seeping in the manifold, but not really sure. I turned of the key and back on and everything then worked normally again.
Don't want to start a new rabbit trail, but since the car was running rich, I can't help but wonder if this could have been happening when the car starts acting up.......

Guess I'll read up on the fuel system.

 

I've heard that turning the ignition on/off, on/off several times gets it to start a KOEO diagnostic. Not sure since I've never tried this method - always use my scanner. Why don't you go bu Autozone or the like and try a free code scan off another scanner. I would think you are runnin rich and the HEGO's not switching giving you the CEL. Like a 174 or 176 code - or right around those numbers (don't have book in hand right now).

I don't remember if you have changed the O2's lately.

I only suggested the compression check in case the plugs didn't show anything funny or funny in just one cylinder, perhaps. It looks like you have something affect both banks. So first would be the fuel pressure that we now know is good. MAF maybe second since it affects both sides too. Clean it and still rich. Maybe it's bad. Does it go all the way up to 4.7 V at WOT? 4.7V is the max per design. Dirty MAF's will give a lean motor, not rich. But a bad MAF can give either condition. TPS looks good from your reply.

The other control components are minor in their affect compared to these - air temp, coolant temp. Gee even the speed sensor is used to compute A/F mixtures as an input to "load" in the computer program. This could be bad but rarley reported as a problem.

I would either check the codes manually by jumpering the gray wire to the DTC connector and count the flashes. Or get another scanner on it to see what it says.

Not in park or nuetral...I wonder if the nuetral safety switch on Auto trans cars affects the A/F tables in the PCM...probably not. But if this is the only real code, then it might have an affect on engine performance.

 

Update:
I went to a local auto parts place and got them to read codes with their, much more expensive scanner. It gave the exact same results. That is, a 522, not in neutral error and nothing else. I did ask them to perform the engine running test as I never could get it to run with my scanner. Their scanner also would not run the test, but it gave a reason. Something like, could not find cylinder id.

I have changed the O2 sensors.


MAF voltage did get up to around 4.7.

My auto has amanual transmission and clutch switch will not let car start without it being engaged, but it will start with clutch in and in gear. I think this has always been the case and is so with all Explorers, right? I'll see if I can figure out which circuit carries the gear in neutral signal to the computer and check the switch or that set of contacts.

I have driven car a few days since last act up, it's running ok. Just pulled a plug on each side. Plugs are normal looking now. It seems they only carbon up when it malfunctions.

 

Of course - pop the clutch means you have a manual tranny - hard keeping all these threads seperated in my head.

EGR - saw on your earlier post you wanted the engine to get hot as to see the effect of the EGR...But for a 93 Fed ar I'm pretty sure you son' have EGR - and you now say you can't fing it so that should answer that question.

The only possible reason to get 522 is the car was in gear with KOEO test performed. If you did in fact have it in nuetral, then the nuetral safety switch is bad. You can test this by trying to get into 4WD low. the 4WD controller won't let it go into low unless you are stopped, in nuetral and have the clutch pedal pushed in. This is exactly how my 93 Cal Explorer works. This might be the reason KOER won't start - probably the reason I think.

Can your scanner run a wiggle test? It's a seperate mode than KOER. KOER migh see a problem if the problem is ocuuring during the test. But it sounds like yours is intermittent. If it runs good most of the time but then all of a sudden craps out and then fixes itself, it's usually a loose conncetion. This is where the wiggle test comes in. If your scanner supports this try it. If not, try it anyway. You don't need a scanner to tell you your car is running bad. Fire it off and giggle all the controls devices. Start with MAF and TPS, then O2's - careful on the hot exhaust pipes. If you can get the problem to ocuur, then you know where to strat the fix.

This is really driving me naty - I can't imaging how you feel. But clearly, something is throwning the A/F mix off once in a while and tht is all computer controlled so it has to be a PCM input item.

 

Jharger,

Little by little, I'm getting more info on this. I was able to get a KOER test performed and all checked good.
Neutral position switch is a non related issue.

Here's what has happened the last couple of days. Yesterday car started acting up while I was driving it. I managed to get home and ran tests that came out with normal results. I left my fuel tester hooked up. Check engine light came on and stayed on initally, but somewhere along the line it went out. On one code test I got a 512 error, keep alive memory test failure, but subsequent tests were successful with no codes.
When I started to do the code test, as I turned on the ignition key to run position, the fuel pump came on like always, but stayed on. Normally it is powered on for a second and then shut off. While the pump was running I tapped the fuel pump relay and a couple of others for merit but nothing happened. I pulled out the relay and of course it stopped. Then put it back in and it resumed again. I pulled the PCM power relay and it stopped. I'm a little fuzzy here, but think it stopped when I put the PCM power relay back in. This happened about three times when I turned on the ignition key. On a couple of times the relay would chatter and some other noises came from other areas while nothing was happening and the key was in run position. I don't believe any sort of test was being run, this was a malfunction.
When I started the car, it continued to run rough and stalled a couple of times. Fuel pressure was normal except when engine almost died and it briefly jumped up around 36 or so and came back to 32.


My question for you is, could I have a pcm going out?

 

Funny you got a 512 code. I got this and a 511 code tody and a 341 - all when I swithced programs on my SCT chip to stock and bac to performance. 341 is the otane shorting coupler. It is defintely connected but I think SCT ignores it so it can run it's own timing advance 0 need to call them on that. And the 511 is a KAM memory error. So does SCT disable KAM memory codes? Need to ask that too. The 512 code came because I pulled the PCM fuse to try and clear the codes. Went away on second KOEO test.

So I am not a strong advocate of PCM replacement as the cure all. Some people can't figure it out and say - must be a bad computer. And many people don't understand computers either and then just asuume it must be bad. There have been a few posts recently where folks seem to have been able to fix their problems with a new PCM. And so I personnaly have had to reconcile that a PCM is more than a computer code reacting to inputs and outputs. But yes a PCM has electronic components that work in line with the signals from the sensors on an engine, and if say a resistor goes bad, then the wrong value may be input into the PCM and then it calculates the wrong output and the PCM in effect is causing drivability problems.

So double E. My ME is not going to refute your EE intuitions here. If you couldn't get any good indications from a wiggle test, it might behove you to find another like PCM to swap and see if all is OK. But be warned that all PCM are not created equal. You have a specific part number (F74F-12A650-ABC) and a code (COW1) for example, that must be matched to ensure the same controls parameters are programmed.

 

I wouldn't discount it, seen it before.

 

OK, one more question. All I can find is that when the ignition key is turned on to the run position, the fuel pump relay is energized for about one second. This seems to be controlled soley by the PCM. This morning I easily got the fuel pump to stay on, on the first try by turning the key to the run position. It did not cycle off after the one second delay. I wiggled everything I could find, related or not and tapped on the cover where the PCM hides and nothing. I pulled the pcm power relay and again the fuel pump stopped. When I put the relay back in, it came on and cycled normally, that is came on for a second and went off.
On another key cycle, the pump stayed on and on a couple of occations I could hear the fuel pump relay chatter a little.

Finally, my question, does this one second cycle get any input from anything outside of the PCM? From what little info I have, I don't see how anything outside of the PCM could be affecting it in a way that would cause the fuel pump relay to stay energized. Is there any schematic for the PCM anywhere on line? thanks

 

Additional info. I pulled the pcm out of mount and took off top and bottom. Nothing unusual and I couldn't get anything to change during the fuel pump cycling by tapping on components or wiggling wires. I did find that the IAC was also being energized during the fuel pump power time. When ever the fuel pump went off, the iac deenergized just after that. I checked the applicable pins on the pcm and the pcm was providing ground on each during the cycling and both pins went to power as the pump and iac stopped. Now, I don't know what that means other than the pcm was driving these actions.