KOEO code 551 '93 ATX help

[CharlieR]

OK, so I pull this code. Translation is "intake manifold runner control solenoid circuit" problem. So where do troubleshoot from here? I pulled the IAC (new 2 yr ago), seemed clean and evidence that it works with movement and shiny area on the shaft. Problem is occasional stall on warm up when you pull up to stop sign when it is damp and cool. Once warmed up no problem. Also occasional "cough" or miss warm or cold cruising at below 2000 rpm. WOT performance fine. So the code sounds like it might actually be right. KOER tests fine. No stored codes.

 

[Mr Anonymous]

Start by looking at the IMRC (Intake Manifold Runner Control). It's located on the back of the intake manifold and controls the opening of the secondary intake runners. If the secondaries are staying open all the time that would result in a loss of low-end power. You can search the forum under 'imrc' for more information.

 

[Markus]

CharlieR:
OK, so I pull this code. Translation is "intake manifold runner control solenoid circuit" problem. So where do troubleshoot from here? I pulled the IAC (new 2 yr ago), seemed clean and evidence that it works with movement and shiny area on the shaft. Problem is occasional stall on warm up when you pull up to stop sign when it is damp and cool. Once warmed up no problem. Also occasional "cough" or miss warm or cold cruising at below 2000 rpm. WOT performance fine. So the code sounds like it might actually be right. KOER tests fine. No stored codes.

According to my Ford documents, 511 means, "Powertrain control module Read Only Memory test failure, KOEO self-test" The only solution offered is, "Replace PCM"

Mark

<small>[ April 10, 2003, 08:39 PM: Message edited by: Markus ]</small>

 

[projectSHO89]

My documentation matches that on the shotimes site - IAS/IAC circuit faiulure.

Not sure whre dalidesign got the IMRC stuff or where that "Ford" stuff came from.

Symptoms are of a problem with the IAC/IAS/ISC.

Steve

 

[Mr Anonymous]

(Markus, the code he reported was 551 not 511.)

Well now, it seems we have a genuine mystery on our hands... oh_my

The official PC/ED definition of 551 is: Idle Air Control (IAC) circuit failure KOEO.

HOWEVER, the PC/ED further directs diagnosis of a 551 code to the KT test routines, which are for the IMRC... HMMMMMMM......

Here is the specific diagnostic info and KT1 routine from the PC/ED:

KT1 DIAGNOSTIC TROUBLE CODE (DTC) 81/551:
CHECK IMRC SOLENOID RESISTANCE

DTC 81/551 indicates the IMRC solenoid output voltage did not change when activated during Key On Engine Off (KOEO) Self-Test.

Possible causes:

- IMRC circuit open.
- IMRC circuit short.
- IMRC solenoid.
- IMRC valve(s) assembly.
- Powertrain Control Module (PCM) output driver open/grounded.


- Key off.
- Disconnect IMRC solenoid.
- Measure resistance between IMRC circuit and VPWR circuit at the IMRC solenoid.

VERY Interesting...

<small>[ April 10, 2003, 11:47 PM: Message edited by: SHOooo ]</small>

 

[Markus]

SHOooo:
(Markus, the code he reported was 551 not 511.)

VERY Interesting...

Oops. Sorry

 

[projectSHO89]

Just looked more closely... "IAC" refers to the "Inlet Air Control" which, of course, is the IMRC on 93 and on cars.


Steve

 

[CharlieR]

OK, so I have learned much in 24 hours. I found the terminology change in the back of my '93 Shop Manual indicating compliance with a SAE directive J1930 where IAC is Idle air control from 93 on and IMRC was previously IAC as inlet air control. So the 551 code refers to the IMRC.
I thought the secondaries were purely vaccum controled, I now know they are open engine off, closed by vaccum engine on below ~ 3600 rpm and open by the IMRC solenoid opening the line to atmosphere above 3600 hence the secondaries open.
Now the puzzle. I think my secondaries work fine. I visually see them move slightly on key on (from vaccum reserve canaster) then suck shut on start up. I am reluctant to bump throttle past 3600-4000 to seem them open visually in the driveway - I fear that risks engine damage. But there is no doubt in my mind they open on the road - engine tone change accompained by the expected power boost.
So all indications in my mind are that all is well. SHOooo suggests problems that to me would result in either stuck open or stuck closed secondaries - I have symptoms of neither. I do not quite understand your intstructions to test the resistance of the solenoid and there are no ohm values given, I don't have the supplemental engine power control trouble shooting manual.
I can test the resistance to ground or the voltage at the terminal but have no idea what they should be.
And does any of this relate back to my engine symptoms (first posting)? Stuck open could do it I suppose but I should get other performance problems.
Thanks, this site is great. I have owned my SHO for 6 years, just found this site last week. Have had this problem for 5 years, dealer has replaced a multitude of sensors and the PCM, transient and intemittent change but it always returns. The dealer ate the cost of the PCM because he had not been able to fix with multiple new sensors.
I have a theory to do with coolant air lock in the throtle body/IAC loop producing the effect of old fashioned carb icing, but I'll leave that for another time, I am intersted in your response to this rather lenghtly post.

 

[projectSHO89]

Charlie,

It is unlikely that the 551 code is related to your stated symptoms.

From looking at the schematics of the engine control circuit and looking at the KT1 diagnostic routine that SHOooo posted and your posting, I am surmising that the 551 failure is due to a fault in the internal circuitry of the PCM that is used to monitor the transition of the voltage at the IMRC control (pin 34 of the PCM). Your description of driving the car is that you feel the secondaries open at 4K when driving. Also, note that you cannot rev an ATX equipped engine to 4K while sitting in the driveway. The computer won't allow it.

During operation, the RED wire of the IRCM solenoid (remember, we are NOT talking about the Idle Speed Control/Bypass Air (ISC/BPA) here, but the valve on the rear of the intake manifold that is called the IAC (Inlet Air Control)) is normally at battery voltage. The solenoid is energized by applying ground to the other wire (a LT GRN/PPL wire) by the PCM, most likely by an open collector transistor or equivilent driver chip/gate. There is most likely an internal connection from pin 34 back to an input port on the microprocessor that allows the uP to monitor if the output state of pin 34 changed from a HIGH (batt voltage) to a LOW (0) Volts. I suspect that this internal test mechanism is what is actually defective and causing the CPU to report that it did not detect a change of state when the CPU commanded it to do so.

My advice: ignore the 551. Just accept it as one of the things that give your car its character.

Back to your original reported problems.... my suspicion is still on the Idle Air Control/ Bypass Air (IAC/BPA) valve. On the other hand, that suspicion would not be strong enough for me to go spend the money on the newer part that was released in 96 by Ford. Remember, that valve is responsible for the idle speed maintenace and for dashpot control.

Damp/cold could be a spark misfire. They tend to be most common under damp conditions.

Given that several members have taken to disconnecting the coolant loop for the throttle and the IAC/BPA without reports of performance problems like you have encountered, I wouldn't suspect the situation you described to be very likely.

Steve

 

[CharlieR]

Thanks Steve,

That would be my thinking, nothing to do with secondaries. So the secondary solenoid works on 12V red line hot with energizing by grounding. Is it either open or closed or is there a part way position with say 6V?
Back to my problem, I am going to change the 10 yr old ignition wires. Problem is too connected to damp weather to ignore that aspect. Plugs are new. The IAC looks clean to me and I think if that was it I should have idle problems warm or cold. Is there a way to test the IAC? Should I just apply 12 V and be sure it moves fully?
Also has original O2 sensors, does it make sense to just replace them anyway as some would advise? '93 ATX stock 86,000 mi.

Thanks,
Charlie

 

[projectSHO89]

I believe the IMRC solenoid is supposed to be either on or off. Nothing in between.

Definitely replace the plug wires. At 10 years old, they're due and are a good suspect for causing the

I would replace the throttle bypass valve since that is what is primarily responsible for controlling idle speed.

Steve

 

[CharlieR]

Steve,
I forgot to mention in last post that the IAC was replaced about 2 yrs ago by the dealer attempting to fix this problem. EOM part by dealer should be the new post '96 version. Seemed to help for a bit but the problem returned after I replaced the sparkplugs (? so maybe because of handling of sparkplug wires?) I figure it is a 12 V solenoid so I will just remove it at apply 12 V and make sure it moves freely. It does not seem gummed up. I do not have easy access to the Taylor wires mentioned in this forum ( 6-8 wks order) but can get Accell wires, 8mm , dual silicone, stainless steel coiled conductor, custom fit - half the price of the Motorcraft OEM wires. I think they should do.

Charlie