Stumbling Idle ... need assistance

[Mic_]

I’ve search for a few things to check, but need HELP!!

Situation: I have a stumbling idle.

First vacuum leak I found was on the fuel regulator.
Snapped that back on.

Still have a stumbling idle to almost to a die, but not quite.

Cruises fine.

I’ve cleaned the MAF and cleaned the IAT; and examined the IAC (looked ok).
Disconnected the battery for a while.
I’ve checked for other vacuum leaks and found none.

Please help

Prior to any work had these:
KOEO:54 35 43
CM: 32 75 43


After disconnecting the battery the CM’s went away but the
KOEO remain: 54 35 43
And KOER: 44 35 43

 

[dogfriend]

Here's what my book* says:

Code 54 - ACT(IAT) or VAT sensor fault, circuit open (KOEO or CM)

ACT is Air Charge Temp (aka IAT Intake Air Temp)

Code 35 - EVP /PFE circuit above maximum voltage (KOEO, KOER or CM)

EVP is EGR Valve Position sensor, PFE is Pressure Feedback EGR sensor

Code 43 - HEGO lean at wide open throttle (CM only)

HEGO is your heated oxygen sensor, it could read lean if the EGR were sticking open, for example.

Code 32 - EGR valve not seated or EVP circuit voltage low (KOER or CM)

I would check that EGR valve

Code 75 - BOO brake on/off circuit closed - always high (KOER)

Check the switch above the brake pedal

Code 44 - Secondary Air Injection system inoperative (right side) (KOER)

??? I'm not even sure you have this, aka Air Pump


I think that you could

A) Have a problem with the EGR valve (Codes 35,43,32)
B) Have a wiring issue that is generating some of the codes(Code 54,75,44)
C) Have Both of the Above
D) Have a Truck that may be possessed.

* Book is "Ford Fuel Injection and Electronic Engine Control" by Charles Probst

 

[Mic_]

As for a problem with the EGR, I concur.

These codes don’t narrow down if it is the EGR or the EGR solenoid, or do they?


Reason I ask is, because I disconnected the EGR solenoid from the EGR and hooked a vacuum pump right to the EGR port. As I drew a vacuum, the truck started to stumble.
So I believe you are correct in saying is has something to do with the EGR circuit.


PS. I have 144,000 mile on her

 

[badgett]

A 94 X I use to have did this. It ran down the road fine but idled really bad. It was the throttle position sensor. 20 bucks. It didn't turn my engine light on when it went bad. That's why it took me a while to find the problem.

 

[dogfriend]

As for a problem with the EGR, I concur.

These codes don’t narrow down if it is the EGR or the EGR solenoid, or do they?


Reason I ask is, because I disconnected the EGR solenoid from the EGR and hooked a vacuum pump right to the EGR port. As I drew a vacuum, the truck started to stumble.
So I believe you are correct in saying is has something to do with the EGR circuit.


PS. I have 144,000 mile on her

Codes 35 and 32 are both related to the EVP (EGR Valve Position) sensor, so you may have a problem with this sensor or the wiring. Code 32 could also be the result of the EGR not seating, so that is why you should check the valve itself.

Your test at the vacuum port would indicate ( I think) that the EGR is seating because it should normally be closed at idle, when you applied vacuum, you opened it and exhaust gas then gets sucked into the intake which causes the stumble. If it is opening on its own during idle, that would explain your stumbling idle. It is like having a vacuum leak.

 

[Mic_]

Your test at the vacuum port would indicate ( I think) that the EGR is seating because it should normally be closed at idle, when you applied vacuum, you opened it and exhaust gas then gets sucked into the intake which causes the stumble. If it is opening on its own during idle, that would explain your stumbling idle. It is like having a vacuum leak.

Makes sense...[on edit] I do not have a EGR positioner sensor.
Instead I have a DPFE with two ports (I think it accomplishes the same). (maybe that is bad).

Just thinking here...can I disconnect the EGR solenoid actuator with out ill cause (either for a short/lang duration w/o exploding the engine)?

 

[dogfriend]

Just thinking here...can I disconnect the EGR solenoid actuator with out ill cause (either for a short/lang duration w/o exploding the engine)?

Yes*, but you might set a code.
















* Shouldn't cause any problem, however, if you do explode your engine I cannot be held responsible.

 

[Mic_]

* Shouldn't cause any problem, however, if you do explode your engine I cannot be held responsible.

Been reading up on EGR operation and it is to lower combustion temps. So I thought bad thinks can happen if i were to disconnect it and run for a while.

 

[dogfriend]

Yes, the purpose of EGR is to lower combustion temps and therefore reduce the amount of NOx (Nitrogen Oxides) which is a component of smog. However, the EGR valve is only supposed to open during warm cruise conditions (engine warm, partial load on engine). Its supposed to be closed at idle and its supposed to close at WOT (wide open throttle). I don't think you would do any damage in disabling it for diagnostic purposes, as long as you take care to make sure you aren't getting any pinging (preignition). You shouldn't disable it permanently because you will be putting out more smog.

 

[Mic_]

Well guys, I made a mistake. My 94 only has 3 digit codes:
So revisisting my notes the code were
KOEO were 543 543
and CM 327 543

Now that my battery was disconnected I am only getting
KOEO 543 543
CM 543 543


Also, after reading about code543 (fuel pump power to pcm signal), I did some probing.
I checked the green with amber tracer wire all the way back to the pcm (passenger a-piller kick panel) and I get 12 volts on it, at key on as I hear the pump running. I know this by pushing a small nail thru the back of the harness as it was hooked to the pcm and reference to ground.

What else is there?

 

[dogfriend]

Doh!

My book says:

Code 543 - Fuel Pump secondary circuit failure (KOEO, CM)

No clue. I would check wiring and then think about dropping the tank (or selling the truck)

Code 327 - PFE/DPFE (EGR) circuit below minimum voltage (KOEO,KOER,CM)

The DPFE is a common problem on 2nd Gen X, so you should probably check it out.

 

[shamaal]

Regarding the 543: according to the Haynes schematic on the 4.0 SOHC, there is a wire that comes off of the Fuel Pump Relay (DG/Y) that goes to the PCM. The PCM senses the wire and determines the fuel pump relay closed.
The fact that the fuel pump's running (relay's good) would point to a faulty wire/connection on the sense line leaving the relay socket or at the PCM, a bad sense input on the PCM; or an old stored code that's no longer valid.

One other possibility, as it is a test, the relay may not be closing as fast as the computer expects e.g. 40 ms vs 10 ms. If persistent swap the relay.

 

[Mic_]

Regarding the 543: according to the Haynes schematic on the 4.0 SOHC, there is a wire that comes off of the Fuel Pump Relay (DG/Y) that goes to the PCM. The PCM senses the wire and determines the fuel pump relay closed.
The fact that the fuel pump's running (relay's good) would point to a faulty wire/connection on the sense line leaving the relay socket or at the PCM, a bad sense input on the PCM; or an old stored code that's no longer valid.

One other possibility, as it is a test, the relay may not be closing as fast as the computer expects e.g. 40 ms vs 10 ms. If persistent swap the relay.

Well I swapped relays and cleared codes. But to no avail they returned.

Truck starts..and I do get 12v at the gr/yellow wire (probed into back of harness as it was plugged into pcm) at the pcm when the pump is running (like at initial key on).

Do you think the pcm can have a sensor input go bad?

 

[MrShorty]

"Do you think the pcm can have a sensor input go bad?" Yes, I believe it is possible for an input circuit to go bad inside the PCM. If you've exhausted all other possibilitiesw for the code, then it is reasonable, "process-of-elimination", to believe that the circuit has failed inside the PCM.

 

[shamaal]

Hold on, let's not get too excited about this. Yes, the sense lines do go bad, but let's examine this before buying PCMs. I've attached the schematic from the 4.0 SOHC.
Mic_, if yours is something else, let me know and I can accomodate.

The cicuit in question is the Fuel Pump Relay. You can follow the DG/Y line down from pin 5 of the relay to splice 127 where it branches to the fuel switch and fuel pump etc. We know these lines are good because the pump runs. The other branch goes to the PCM pin 40.

I believe, the logic is that the PCM energizes the relay which closes and sends power to the pump and to the PCM. I then speculate that the PCM senses the +12 volts and sets the corresponding error if not present.

Note I said I speculate this is what happens, it's what I would do if I was designing this. Mr. Shorty, if there's a flaw here, an alternate algorithm or even the factory spec, I'll defer to your experience. I thought that maybe if the fuel tank pressure sensor was hokey, the PCM could assume that the fuel pump isn't coming up to pressure and set the 543, but I'm guessing the pressure sensor fail bit would be set, so I discarded the idea.

At any rate, I do not see this problem, annoying as that light is, would cause the stumbling idle. I'd work the code 327.
Incidentally, do any of the autoplaces check PCM's? That may be a possibility.

 

[dogfriend]

He has a 94, so he actually has a 4.0 OHV engine. There is a 94 schematic here See Fig 29.

I agree that its possible to have a bad PCM, but it is usually unlikely. They are very reliable, but it is possible. I agree that you must eliminate all other possibilities first.

The easiest way to rule out the PCM would be to substitute a known good unit, but you would need to find another 94.

 

[Mic_]

dogfriend,

Yes that is the circuit I have in my book.

I stuck a small nail along side the gr/y wire from the back of the harness as it was plugged into the pcm for testing.

Then I cycled the key and got 12volt on the dvm as I heard the pump run ( not starting it).


I am really at a loss here.

My other code has not returned after fixing the vacuum leak (line to fuel regulator popped off ...why ???) but it does not sound like it idles as smooth as I believe it used to.
Have not had a stumble in 3 days not, but I can not figure this open batt to pump circuit.

The though crossed my mind to look for a junk yard pcm....but what if any gaurantee to I have from them...(probably not much).

 

[MrShorty]

I looked in my gtest.pdf file (taken from Mitchell for a '95 Explorer) and found an interesting thing. Never would have thought of this on my own:

20) Code 543
Code 543 indicates fuel pump secondary circuit failure
between B+ circuit and FPM connection to POWER-TO-PUMP circuit.
Following are possible causes:
No Start:
* Open circuit between B+ and FPM connection to POWER-TO-PUMP
circuit.
* Fuel pump relay contacts are always open.
Engine Starts:
* HO2S short to power (dual HO2S models).
* Faulty PCM.

(emphasis added).

You should probably find the same information for your '94 4.0, but it appears that a fault in the driver's side O2 sensor could possible cause that KOEO 543, and cause the rough idle. I think the next thing I would do is go to the library and hopefully get a hold of a good manual and see if the pinpoint test for a '94 4.0 KOEO 543 said the same thing. If it did, then follow the pin point test to check the O2 sensor.

 

[dogfriend]

Wow. That's weird.

 

[Mic_]

I looked in my gtest.pdf file (taken from Mitchell for a '95 Explorer) and found an interesting thing. Never would have thought of this on my own: (emphasis added).

You should probably find the same information for your '94 4.0, but it appears that a fault in the driver's side O2 sensor could possible cause that KOEO 543, and cause the rough idle. I think the next thing I would do is go to the library and hopefully get a hold of a good manual and see if the pinpoint test for a '94 4.0 KOEO 543 said the same thing. If it did, then follow the pin point test to check the O2 sensor.

If I follow correctly, circuit 359 GY/R (sensor signal return? also accessable at the data link connector) receives a modified/adjusted voltage from the O2 sensor(s) via pins 43/44 (plus spliceS136) and uses it in the pcm at pin 46 to control air/fuel?

Would the pcm 'see' either of these wires shorted to power; and that is what is causing it?