Still No Secondaries

[Marccus]

I must have an open circuit on one of the wires going from the PCM connector to the IMRC connector at the end of the harness.

I've tried 3 different IAS (cylinder and electronics part) and no secondaries.

I've installed a new PCM. Still no secondaries. The PCM is new (well, newly manufactured when you buy it new, which is what I did). I doubt the second PCM is no good.

One of the wires reads 13 or so volts. (I forget which one right now.)

The other reads 0.45 volts. (Both should be at battery volatage from what I understand.) It jumps to 1.5 volts when I rev the engine past 4000 rpm.

Does anyone know the pin numbers for these two wires at the PCM connector? When I find the line that is open, I'll run a bypass wire from the PCM connector to the IMRC connector at the end of the harness.

Also, can you refer me to a drawing of the PCM pins and the numbers each pin corresponds to?

I remember seeing this one and I'll search again for it.

Thanks.

 

[Kens1992mtxSHO]

Probably a dumb question but did you check the black canister on the back of the intake?

 

[Lupo]

Probably a dumb question but did you check the black canister on the back of the intake?

The default position of the secondaries is "open". Engine vac keeps them shut until a small electric air valve releases the vac at 4K RPM causing them to open.

When you have no secondaries, do you mean that the butterflies always stay open, or that they never open?
If they always stay open, then a vac problem.
If they stay closed, vac release problem, i.e the valve, or whatever controls it.

 

[Marccus]

When I start the car, the secondaries stay in the same position as when it is off.

When I rev above 4000 rpm, the secondaries don't move.

I understand what you are saying, but I should be reading about 13 volts on both wires and I'm not.

 

[Marccus]

Are you saying that when the engine is off, the secondaries are in an open position - ie. their default position?

Then they are always open.

When I suck on the line from the cannister that goes to the secondaries, the butterflies close.

The vaccum from the cannister is very weak compared to the vacuum I create with my mouth that is necessary to close the butterfly valves.

But I've replaced this cannister and the electronics (solenoid) three times. They can't all be defective.

Should I check the vacuum line that goes to the cannnister? I believe it comes from the intake manifold surge manifold that runs the length of the manifold closest to the firewall.

The secondaries don't seem hard to open by hand, but perhaps they are too tight.

What bolts do I adjust to allow the butterflies to move more easily?

Thanks.

 

[SASHO91]

Pull the vacuum line that goes to both butterflies from the source, before the line makes a Y, back at the canister/valve. This will rule out a vacuum problem. But it does sound like an electrical issue.

 

[Marccus]

OK. I'll do that

 

[Marccus]

Actually, I've done that. When I disconect the line, nothing happens. The butterflies remain in the same position as when the engine is off - i.e. open.

When I suck on the vacuum line that goes to both butterflies before the Y split to create vacuum, the butterflies close.

It seems that since one of the lines to the connector is not reading 12 volts, then the butterflies will not close when I start the car from the default position of being open when the engine is off.

It seems that the vacuum is already released because one of the wires is reading 0 volts.

I guess that's why the vacuum from the cannister is very weak and is not enough to close the butteflies when the engine is started.

Thus the butterflies remain open when I start the car and rev above 4000 rpm.

When I suck on the line to the butterflies, they close.

It seems to be electrical.



But does anyone know the pin numbers on the PCM of the connector wires to the IMRC solenoid?

Then I can see if one of the lines is open and run a bypass line.

 

[itwonder]

Make sure you do not have the vacuum lines reversed on the cannister. There is a check valve on the port that goes to the vacuum source. You can connect the solenoid pins directly to a 12V source to test operation of the system.

 

[Denny]

Not sure if it'll make a difference or not, but what year is your SHO?

Let me check my database...be back in a few

 

[Denny]

Circuit 965 for the IMRC is a Light Green with Purple tracer.

On a 95 MTX it'll be PCM pin 32.

For a 95 ATX, it'll be pin 34.

 

[Marccus]

Sorry, forgot year.

1989.

I think the colors of my wires are different than later SHO models.

I think they are red and green. I'm not at my car now, but I'll check

Thanks.

 

[itwonder]

Actually, I've done that. When I disconect the line, nothing happens. The butterflies remain in the same position as when the engine is off - i.e. open.

When I suck on the vacuum line that goes to both butterflies before the Y split to create vacuum, the butterflies close.

It seems that since one of the lines to the connector is not reading 12 volts, then the butterflies will not close when I start the car from the default position of being open when the engine is off.

It seems that the vacuum is already released because one of the wires is reading 0 volts.

I guess that's why the vacuum from the cannister is very weak and is not enough to close the butteflies when the engine is started.

Thus the butterflies remain open when I start the car and rev above 4000 rpm.

When I suck on the line to the butterflies, they close.

It seems to be electrical.

:

You need to take this step by step.

If you have weak vacuum from the cannister, but vacuum in the line from the engine to the cannister is normal, then more than likely you have reversed the input and output lines at the cannister. There is a checkvalve in the cannister so that air will flow through it only in one direction. So get that working first.

Next, you speak of one line on the connector missing 12V. That is as it should be. One line on the connector is 12V, switched on and off by the PCM, and the other lead is Ground. The solenoid coil completes the circuit.

When the connector is hot with 12V, then the solenoid is on, and vacuum flows through the valve to operate the actuators on the secondaries. When the 12V is turned off, the vacuum is blocked, and the acutators are released.
You can test this part with two clip leads. One solenoid pin connects to ground, and the other you touch to the battery + terminal (preferably through an inline fuse).

Do these basic tests to verify the systems components are working properly. If all checks out, then consider a wiring problem. The first wiring problem to check for is a missing ground on the ground lead in the connector.

 

[Denny]

Sorry, forgot year.

1989.

I think the colors of my wires are different than later SHO models.

I think they are red and green. I'm not at my car now, but I'll check

Thanks.

Hmmm, no 89 manuals online. I'll have to see if I can find a EVTM book somewhere.

 

[Marccus]

You need to take this step by step.
.
.
.
Next, you speak of one line on the connector missing 12V. That is as it should be. One line on the connector is 12V, switched on and off by the PCM, and the other lead is Ground. The solenoid coil completes the circuit.

When the connector is hot with 12V, then the solenoid is on, and vacuum flows through the valve to operate the actuators on the secondaries. When the 12V is turned off, the vacuum is blocked, and the acutators are released.
You can test this part with two clip leads. One solenoid pin connects to ground, and the other you touch to the battery + terminal (preferably through an inline fuse).
.
.
.

(1) When the key is in the start position or the engine is on, the red wire reads 12v and the LG/P wire reads 0 volts but the secondaries are open (no change from when the engine is off) and there is no movement above 4,000 rpm.

But you state that the secondaries should be actuated when one wire reads 12v and the other is 0v. (that is, they should close from the open position when the key is the start position or the engine is on).

But, I will proceed based on your instructions.

You seem to be ahead of my post I made today Aug 11 and have already made the diagnosis.

It seems like I am missing a ground connection for the LG/P wire as there is no continuity between this wire and ground.

How would I correct for this missing ground from the LG/P wire at the connector? Splice a ground into this wire?

I had read on the forum, that both wires read 12v when the secondaries are open. Then one of the wires is shorted to ground by the PCM when rpm exceeds 4,000.

I guess this is wrong.

Lastly, you state to test with alligator clips.

Should the engine be off or on or the key in the start position?

Do you mean to use the alligator clip to pierce the red line while the connector is connected and run a wire from this clip to the battery, when the rpm is below 4000?

This should make the secondaries close.

Am I following you correctly?

 

[itwonder]

(1) When the key is in the start position or the engine is on, the red wire reads 12v and the LG/P wire reads 0 volts but the secondaries are open (no change from when the engine is off) and there is no movement above 4,000 rpm.

But you state that the secondaries should be actuated when one wire reads 12v and the other is 0v. (that is, they should close from the open position when the key is the start position or the engine is on).

It seems like I am missing a ground connection for the LG/P wire as there is no continuity between this wire and ground.

How would I correct for this missing ground from the LG/P wire at the connector? Splice a ground into this wire?

I had read on the forum, that both wires read 12v when the secondaries are open. Then one of the wires is shorted to ground by the PCM when rpm exceeds 4,000.

I guess this is wrong.

Lastly, you state to test with alligator clips.

Should the engine be off or on or the key in the start position?

Do you mean to use the alligator clip to pierce the red line while the connector is connected and run a wire from this clip to the battery, when the rpm is below 4000?

This should make the secondaries close.

Am I following you correctly?

The red wire should have 12V on it whenever the ignition key is in the On position. That seems to be okay from your description. The PCM switches the solenoid on/off by toggling the ground side of the circuit, the LG/P wire. The PCM toggles LG/P to ground when the engine is below 4,000 RPM. This allows vaccum to flow and close the secondary butterfly valves. Above 4,000 RPM, the PCM opens the LG/P wire so it is no longer connected to anything. The circuit is no longer complete, and the solenoid de-energizes. This shuts off the flow of vacuum, and the secondaries open. If you were to check voltages above 4,000 RPM, you would still see the +12V on the red wire. You would also see +12V on the LG/P wire. Why? Because the solenoid is nothing more than a coil of wire. As long as no current is flowing, and there isn't any because the PCM opened the circuit by removing the ground path, you will see the same voltage at both ends of the solenoid coil.

So what tests are possible?

Test #1. - Bypass PCM control altogether.

Unplug the connector from the IMRC connector. Carefully connect small clip leads to each pin of the solenoid. Take care they are not shorted. Connect one lead to ground. Connect the other lead through an inline fuse to +12V. If you listen carefully , you should hear a slight click. Start the car. The vacuum should flow, and the secondaries should be closed. Unhook either the +12V lead or the GND lead, it does not matter which, and the secondaries should open. This test will verify your solenoid and vacuum connections are normal.

Test #2 - Bypass PCM switching of LG/P wire

As before, unplug the IMRC solenoid connector. Connect one end of a clip lead the the pin on the solenoid that normally corresponds to the red wire. Use a paper clip, or other suitable piece of wire to connect the other end of the clip lead to the red wire terminal on the connector. Take care nothing is shorted. Connect another clip lead to the remaining solenoid terminal. Turn the key to On and verify you have 12V on this clip lead. This verifies the red wire side clip lead is connected correctly. Start the car and alternate the second clip lead between GND and open circuit. This should close/open the secondaries. This will verify the red wire from the PCM is supplying an adequate 12V current to operate the solenoid.

If those tests pass, then that isolates the problem to the LG/P wire not being properly switched between a solid ground and open circuit. You can bypass the wiring harness with a separate wire from the LG/P terminal on the connector to pin 32 (MTX) or pin 34 (ATX) at the PCM .

 

[projectSHO89]

Itwonder's assessment of how the circuit works is correct. That is, the red wire is always hot in RUN/START and that the LG/P wire is switched by the PCM. Below 4K, the switched wire should be ungrounded and should read the same as the red wire. At 4K, the PCM grounds that wire, energizes the solenoid, and closes off the vacuum supply to the secondaries' vacuum motors, allowing them to return to the open position.

Measure the resistance of the IAS solenoid coil. Verify it is not open and neither pin is internally shorted to the case.

Unplug the connector to the PCM and verify continuity from PCM pin 32 to the LG/P wire at the IAS solenoid. Verify resistance to ground exceeds 10K ohms.

Steve

 

[Marccus]

Unplug the connector to the PCM and verify continuity from PCM pin 32 to the LG/P wire at the IAS solenoid. Verify resistance to ground exceeds 10K ohms.

Steve

I did disconnect the PCM wiring harness and checked for open in the lines.

There is continuity between Pin 32 on the PCM connector and the LG/P wire on the pin at the connector to the solenoid .

Likewise ,there is continuity between Pin 37 on the PCM connector and the Red wire on the pin at the connector to the solenoid.

I'll check that ground resistance exceeds 10k ohms.

Thanks

 

[projectSHO89]

Check the coil continuity also. Probably around 30 or 40 ohms, from memory

 

[Kens1992mtxSHO]

PM Sent...