Battl;ing Code 81: IRMC

[Marccus]

I've replaced the existing IRCM twice on my '89 with used ones off of junked SHO's and I keep getting the same error.

As suggested by others on the forum. I flicked the throttle above 4,000 rpm and beyond and the buttterflies did not open.

There is vaccum going from the intake manifold going to the small grey cylinder (I don't know what it is called - vacuum buffer reservoir?) attached to the manifold; there is vacuum coming out of the cylinder and going to the electronic assembly; there is no vaccum coming out of the electronic assembly to the main tubing which splits to the diaphragm of the butterflies.

When I suck enough (no wise guy comments on that last phrase) on the main tubing to the butterflies, both butterflies open all the way, and when I hold the suction the butterflies remain open - that is there are no leaks in the tubing or diaphragms.

So the only conclusion I can make is that the electronic module is not working by not allowing vacuum to open the butterflies.

I checked all the grounds I found and they are all good. I'll look for some more or run some grounds from other bolts on the manifold to the body.

If I can't find a ground problem, then I guess the problem is in the wiring / connector to the electronic module.

Can anyone advise on how to troubleshoot the electronic part and the connector wiring; what are the voltages I should find on the connector?

I've been battling this problem for about 6 months and it is really irritating and frustrating. :banghd:

Thanks.

 

[projectSHO89]

Both wires at the connector should read battery supply voltage at idle. If not, there is an open circuit between the IAS and its supply.

At 4K, the PCM should ground one of the lines to energize the solenoid and to switch vacuum to the secondary vacuum motors.

If both lines stay at battery voltage at 4K, then either the PCM is defective or there is an open circuit between the IAS and the PCM.

The IRCM has no involvement in the operation of the secondaries.

Steve

 

[Marccus]

Wow! How do you KNOW all this??!!

Can you supply more detail on the operation of this mechanism or refer me to a source?

PCM = Power (train) control module Computer.
IAS = ??? (Idle Air Supply???)

"... engergize the solenoid ..." ... the electronic module as part of the IRMC?

"... secondary vacuum motors ..." what I called the "diaphragms" on the secondaries?

... what is the PRIMARY vacuum "motor"?

"The IRCM has no involvement in the operation of the secondaries"

.. this means the secondaries are essentially opened by the PCM when the RPM reach 4K?

If so, I would understand this (maybe incorrectly!), that the IRCM responds to another signal to energize its solenoid (what I called the electronic module with the connector) "to switch vacuum to the secondary vacuum motors"

... i.e it doesn't perform a control function .. it responds to a control signal and to my intrepetation, it is still involved in the operation of the secondaries.

OK. Now you can slam me for questioning you! :scared: :scared:


:thankyou::thankyou::thankyou::thankyou::thankyou::thankyou::thankyou:

Both wires at the connector should read battery supply voltage at idle. If not, there is an open circuit between the IAS and its supply.

At 4K, the PCM should ground one of the lines to energize the solenoid and to switch vacuum to the secondary vacuum motors.

If both lines stay at battery voltage at 4K, then either the PCM is defective or there is an open circuit between the IAS and the PCM.

The IRCM has no involvement in the operation of the secondaries.

Steve

 

[projectSHO89]

The IRCM is well and completely documented in the stickied thread in the Electronics forum. Refer to my post in it so you can understand what it is and what it does.

IAS= Inlet Air Solenoid. That is the electrically operated vacuum switch that is mounted on the firewall side of the intake. Its purpose is to control the switching of vacuum to the secondary vacuum motors under the control of the Powertrain Control Module (PCM) aka ECM & ECA. Memory is hazy, can't recall if the solenoid passes vacuum when de-energized and blocks it when energized or if vice-versa. Been awhile.


Do not confuse the IRCM (Integrated Relay Control Module) with IMRC (Intake Manifold Runner Control) . IMRC is the nomenclature used starting in 93 for the IAS. I suspect you have done so and have confused the issue with the wrong terminology.

Steve

 

[Marccus]

Yes, yes. sorry, I meant IMRC not IRCM. The IRCM is located under the flap on the radiator.

Since my car is an '89, I shouldn't use the term IMRC, but IAS.

Do you know the pin number on the PCM connector for the IAS?

I can then check continuity between the pin on the zpCM connector and the terminal point on the IAS connector to see if there is an open in the wire.

If so, I can just run a bypass wire and see if this works without changing out the PCM.

:thankyou: