Unplug the wire connector from the DPFE Sensor. The fuel pump should cycle normal. Engine should run ok but will use more fuel. Sounds like the DPFE sensor is bad to me.

 

Double E - I would first try a new fuel pump relay. It might be getting stuck open.

The PCM will first drive the fuel pump on for a second or two when you hit "on" of ignition switch. (This is to make sure fuel is totally pressurized.) Then, the engine RPM signal to the PCM tells the PCM to keep the fuel pump running all the time - it never turns off when the car is running.

I think you might be suggesting the PCM is occasionally telling the fuel pump to keep running when you only cycle on the key to "On". A software program wont do this - act different at different times with all else the same. And there is only one input to the PCM at the "on" only position (car not running) to tell the PCM to run the pump. So if the ignition switch is not flickering on/off/on/off when in the "On" position, it must be the fuel pump relay. If the ignition switch was alternating on/off/on/off - other things on the dash would be lighting up like the ABS light, parking brake, oil pressure... all the same stuff that light up when you first hit the key.

 

PS = backin - you taught me a good lesson - I am learning...

 

OK. I don't have a dpfe. That started a year or two later than model I have. EGR is a mistery, I can't seem to find one, if I have one.
I know your tired of hearing from me with more questions.
When I have fuel pump 'sticking' on, I pull fp relay and reinsert, the relay definitely reenergizes, so I'm sure it is not sticking. But pulling pcm power relay and reinserting will cause it to stop after the one second.

When you say there is only one input to pcm to start this cycle, I assume you mean the ignition circuit completing to the on position providing power through the pcm power relay to the pcm? This in turn through the software you mentioned, runs the one second fuel pump routine. I just checked with it still intermittantly messing up and, there is a constant 12vdc to the pcm while it stays on and while it cycles the fuel pump on and off irratically. While this happens all lights and gages stay as they are, that is the check engine and charging light stay on constantly.
Seems to me, if fuel pump is being powered on by pcm, (I know the pcm provides a ground to the fp relay) the pcm must be suspect. pls tell me if I'm looking at this wrong, before I order a pcm. Local parts place says it could take a week, up to a month to get one. $140.

 

Have you tried replacing the PCM relay? Should only be a couple of bucks. I'd also replace the fuel pump relay as well.

 

Good idea. I swapped out the pcm relay with the heater relay as they were the same and same thing happened. I pulled the fuel pump relay completely out and the system still malfunctioned. I could tell this by the iac valve and some other I couldn't locate, which would click intermittently. Normal ops would be for the iac to click once just after turning key on, but as key stayed on for a few seconds the iac sol. started acting up, indicating to me that the problem is still there and the fuel pump/relay circuit aren't involved. Back to pcm?

 

For some reason not all the words come through on this site when posted. Above, I pulled out the fuel pump relay completely.

 

Not sure how well this will work but let's look at the schematic.



No you have no EGR system on a Fed 93 Explorer - not until 94 did all 50 states get an EGR. You can stop looking.

Per the schematic, the PCM controls the fuel pump by being the ground to the primary or low voltage side of the fuel pump relay. So when you first turn the key to "on", you can see the PCM relay is energized and the Fuel Pump relay is energized at the same time. Then the PCM is supposed to open up the fuel pump relay ground to turn off the fuel pump. On your car this is staying on. So the PCM would normally turn it off unless there are RPM's present. RPM's is the only logical system input that would say, we need fuel. There is no actual fuel pressure monitoring - it's all manually calibrated into the fuel pressure regulator. So then the PCM does not turn pump on/off to maintain a pressure. So then if RPM's is the only other reason to ground out the fuel pump relay, then the PCM is 1) sensing RPM's even though the motor is not turning or 2) PCM is wacked out and giving the wrong outputs.

If it is sensing RPM's with the motor not turning, this comes from the ignition control module. There are 2 for some reason. I think one goes into the PCM and the other comes out. PCM pin 4 is "engine RPM sensor input" and number 56 is "ignition Module RPM input". You may tray another test and wiggle this ignition control module connector. Didn't I suggest a wiggle test already? This unit is located right in front of your battery so you'll have to pull the battery and see if you can get the unit out and reinstall the battery - maybe leave battery on the floor and use jumper cables. Now if you are having you figgity items attack with the key to "on" and you pull the ICM connector off and everything stops figgiting, then the ICM is likely bad...or maybe the crank position sensor as this is the primary source of RPM indicators.

With the "on" self test the PCM initiates first when youturn the key, several functions are checked. The IAC you mentioned for example. Yes the PCM opens this up 100% and leaves it there. This is because it thinks if you turned the key to "on", you just might be thinking of actually starting it. Wouldn't it be nice to have some air to help it start? So when you said this valve is also cycling at the same time the fuel pump stays on, it makes me trink bad PCM too. Even if the ICM is sending RPM's signals when it should not, I would think the PCM would still hold IAC wide open until it senses 2000 R's and then it would slowly drop the R's down (close valve down) until it hits 650 or whatever. And when it closes the valve, it actually cycles the solenoid open/closed - just really fast. But when I say wide open I mean no cycling - 12V full time to the valve.

Last thing - you heard something else clicking but could not isolate. There is one mor solenoid in your system - the gas vapor purge canistor solenoid. It is located underneath the upper intake manifold, on top of the lower manifold. It's a bitch to see. If you take your intake tube and the plastic throttle linkage protector off you get a glimpse of it from the front. Now how this operates I haven't a clue. I think when at full RPM or decelerating...something condition triggers the PCM to open this solenoid and let the throttl body suck all the vapors out of the canister. I would think this would ever open if the car motor is not turning because it would release fuel vapors potentially into the atmosphere. So if this is clicking too, pointing again at a bad PCM. Or maybe the PCM is seeing RPM's from a bad ICM?

I found a spare PCM on eBay for $48 delivered. You need to watch what you get. The part number F37F-12A650-YB, or if you had yours updated under TSB, F47F-12A650-CMA (yours might be different) and the code. Like COW1 of another 4 digit, 3 letter, 1 number code. These are on the PCM itself. If you don't match both these numbers, you might end up with a california PCM that's loking for an EGR input...or just the wrong program for your car.

Let us know what you find.

 

Thought I had it. Reread your message and wanted to check out all I could before changing pcm. I did wiggle on icm and nothing. Then crawled under car and found crankshaft sensor. It was pretty oilly and wiggling wires did nothing. I tapped on sensor with key on and fuel pump running and walla it stopped. I managed to cycle the pump a few times by tapping on sensor. I pulled plug off and cleaned with contact cleaner and ohmed sensor while tapping and nothing abnormal. Put it back together and repeated problem. Bought and installed new sensor, unhooked battery to reset then test drove. Almost immediately the check engine light came on and driving for 15 minutes was rough with engine missing, rpms dropping betwieen shifts quickly, etc.
Talking about frustrating. I found and removed the speed sensing plug off of sensor and still nothing.
I know tapping on old crankshaft sensor caused fuel pump cycling, but now I'm not sure where I am except to change out pcm. ????
Got car back home and stopped engine, turned key to on and fuel pump would not go off. Pulled off every sensor cannon plug I could find with no change. THat includes the icm and the connector to the ignition module. Pulling fp relay and putting back in same as before, it runs, but pulling pcm pwr relay and putting back in the pump obviously quits and then starts back up without stopping when relay reinserted.

The only thing I am not sure about now is the camshaft sensor, if I have one. There is a sensor? directly below the throttle valve which I also tapped during the runaway fuel pump and unhooked with no changed, but not sure if that's it. Schematic doesn't show sensor.
I think I'm out of options.....

 

Just to for the hell of it I went out to the garage and yes, my 93 fuel pump starts for 2-3 seconds when key goes to "on" , then stops.

To late now for me to go through the previous pages - did you ever replace the fuel pump relay? It could be getting stuck open and would stay open regardless of PCM primary side grounding- just because the key is on giving it power.

But that does not explain the rough engine performance - unless the relay is then opening up and not giving gas when expected.

Cam sensor I think you do have - passenger side just behind the valve cover next to the firewall - but this is a condition signal for a spout output and not part of initial start up or fuel pump running.

If you can isolate the fuel pump relay as good - only thing I can think of is a wacked out PCM. What are you numbers? Look on eBay.

 

f37f.....yb. ebay didn't have but found a site with one for about $100. Will probably order one in next few days.

 

hey double e. I can't believe between your EE and my ME degrees we can't figure this out. But I asked about your PCM # to check something. It is on the 1995 TSB recall for PCM's - well it wasn't a recall but a warranty issue. You can also use a F47F-12A650-CMA. There was one of these on eBay a couple months back for $40. PM me your email and I can send you the TSB. So now you have 2 to look for. As far as the tunin code, I think they are all the same with the same part number. I got another one by part number and it had the same code number so you'll probably be safe just matching to your or this other part number I just gave you.

 

Take a look at this thread. https://www.ford-trucks.com/forums/s...18#post3040518
A little different symptoms but a new PCM fixed it.

 

By the way, I did swap out the fuel pump relay and same malfunction happened again. Also, the fuel stays on constantly now anytime key is on. I even plugged in old crank sensor to see if tapping changed anything, and it did not.

 

Got your email but not sure if you got my response since the FTE web system says you don't accept emails. So your middle initila must be "B". LOL. Now I get it!

Here's what I emailed you:

You see when I inquired about a chip for my PCM, the chip dealers wanted to know my PCM code - 4 digit number. Usually 3 letters and a number. This is how the refer to the SW programmed into the PCM. So then that tells me that the code needs to match so that you have the same SW when you swap the PCM.

But the TSB didn't list these codes. But it does list a Ford engineering calibration number so I thought this was a different Ford reference number for the same 4 digit code.

OK. I bought a used PCM off eBay solely by the part number and the 4 digit code is the same as mine. So I'm not sure if a 4 digit code ever varies from part number to part number. But I do know those 2 part numbers will work in your truck. TSB list it for a 93 Explorer, MT, 49 state. Sport or 4WD don't matter.

It was wierd that you affected the fuel pump with the crank sensor but can't replicate it now. If you want the TSB, send me you email adress - type it into you message.