90 - Running out of breath at 5000 - No Codes

[scottfab]

Originally Posted by dondon

....snip....

My gut feel says and the secondary vacuum number is the big clue, does anyone know perhaps if it stays at 0 kpa like mine does, and at which point that changes. ie does it change when the secondary pump charges the system or some other time. All I can think is something under the GD plenum is preventing Vac from getting to the Vacuum sensor under the ECM... there may be other issues as I recently replaced the solenoid, reservoir tank and spider hoses... so who knows.

There is so much info on this forum about the code 61, you would swear I was deaf to something or overlooked something.

I'm going to propose a negative test. That is a test where you force a failure and see if the outcome is what is expected. Pull the power to the vacuum pump and go for a WOT. Do the secondaries pull at all? When does it give out? (in rpm)
If the only vacuum to the actuators is the pump then the secondaries will not pull in at all.

[XfireZ51]

If the secondaries are shutting down due to lack of vacuum, should be getting a 61 if full power is ON. Have you shut down Full Power and run it up that way?
Does it still "run out of breath" and exactly what does that mean?
Bucking, stalls, breaking up simply not accelerating as much?

[scottfab]

Originally Posted by XfireZ51

If the secondaries are shutting down due to lack of vacuum, should be getting a 61 if full power is ON. Have you shut down Full Power and run it up that way?
Does it still "run out of breath" and exactly what does that mean?
Bucking, stalls, breaking up simply not accelerating as much?

From post #27

Originally Posted by dondon

...snip...
.. I reset it and went for another test drive just to hopefully confirm the problem... Code 61 - Secondary Port Throttle.
...snip...

Also in post #6 he states all runs smoothly with power key off.

With the pump disabled I would expect a flattening of power earlier than 5000rpm. If that happens then we know the pump is helping but what if the pump vacuum capacity is diminished? or???? The data point is finding out what happens with the pump unplugged.

[Franke]

Dondon, what Scott is suggesting has merit especially since the vacuum required has to remain above 41kPa to operate the SPT valves. 41kPa is about 12 inches HG. Code 61 is set in FP mode when the vacuum monitor senses vacuum below 21 kPa (3.5 in HG). When you mash the accelerator, the manifold vacuum drops toward atmospheric value (very low vacuum) and the vacuum pump starts to supplement the manifold vacuum in the vacuum reservoir to keep the SPT valves open. I would test the vacuum pump to verify its capacity to pull at least that much vacuum. Chart C-2D on page 6e3-c2-32 and 33 may be helpful. This is an attempt to eliminate any external items before plenum pull as suggested by Ripsher to get at that check valve underneath.

[dondon]

Originally Posted by Franke

Dondon, what Scott is suggesting has merit especially since the vacuum required has to remain above 41kPa to operate the SPT valves. 41kPa is about 12 inches HG. Code 61 is set in FP mode when the vacuum monitor senses vacuum below 21 kPa (3.5 in HG). When you mash the accelerator, the manifold vacuum drops toward atmospheric value (very low vacuum) and the vacuum pump starts to supplement the manifold vacuum in the vacuum reservoir to keep the SPT valves open. I would test the vacuum pump to verify its capacity to pull at least that much vacuum. Chart C-2D on page 6e3-c2-32 and 33 may be helpful. This is an attempt to eliminate any external items before plenum pull as suggested by Ripsher to get at that check valve underneath.

Happy Chart C-2D everyone. Following the instructions led me right to:
Faulty Hose or Blockage in hose or faulty check valve.

The pump pulls at 14HG is anyone is interested... so anyway, it looks like the plenum pull going to become a reality. When I had it off last, I replaced the original spider assembly with one I ordered, so now I must pull it apart and test the plastic pipes until I find the blockage / check valve / faulty hose. I'm a little nervous to reorder from same vendor given the problem (has never worked since the rebuild), but that may just be par for the course... I'll likely assemble hoses from my previous set to make it work well.

This sure does explain the 0kpa on the vacuum sensor.

I will let everyone know once its back together to let everyone who know whether this was finally it... or there are more issues - I really hope I can just enjoy the car now for a bit.

[Franke]

dondon, I used steel brake line to replace many of the under plenum pipe and the one that comes out to the vac pump. Just a thought. Just another thought of something else... Could the check valve be installed backwards since you replaced the stuff?

[rkreigh]

plenum pull is a little intimidating, but do some searches and there are MANY step by step tutorials, with lots of nice pics. another recommendation is to buy marc haibecks DVD

once you watch it, you'll be more confident. you can even use the "top tool" as it fits but it's best to get a nice long shank torx

anyway, you are doing great troubleshooting the car and are almost home

I had the same exact issue, and it was the secondary act switch that went bad. it would only "code occasionally" until it went "all the way bad"

but I consitently have problems with the stumble at WOT and the car would buck and fall on it's face.

if you run into problems or don't want to attempt the plenum pull. mosey on over to see Aaron Scott at SGC and he's have you back on the road in nowtime

plus, Thomasville is nice this time of year.

hey, anyone going to SGC????

[rhipsher]

Don I bought my 1990 Z knowing before I wrote that $22,500 check that there was something wrong with it running out of breath at 4k. And was on the fence about buying my first Chevy that could turn out to be a lemon. But I was already a shade tree mechanic and felt confident or cocky enough that it was just a bad component somewhere and I could fix it. It took me a month and several plenum pulls until I found that the bad component was the secondary vacuum solenoid. And after I buttoned the plenum up fully expecting the same ole running out of breath at 4k and throwing another code 61 ses light. I was shocked when I mashed the gas peddle. There was no doubt it was fixed. The acceleration difference was undeniable. No ses light ever again. Acceleration all the way up passed 7k and really fast up to 7k. So hang in there. You will get it. It took me a month to figure it out. Sometimes finding the fix doesn't happen over night.

[dondon]

I think I'm out of ideas. Today I pulled the plenum... It was quite pleasurable. Anyway, I connected each vacuum pipe individually and tested for a blocked pipe, I tested the check valve. It all appears in order. I then took some volts off the battery and heard the solenoid operate. Continued testing.

In FSM on page 6E3-A-83 - the code 61 error chart. I went through the motions.
"Faulty Connection or Open CKT 930 or Faulty ECM" is where I ended up this was after the connect terminals A and B and enable "Field Service Mode" with "Scan" tool is test light "On" step.

CKT 930 is the connector to C17 (prior to removing plenum during previous diagnosing). Which when shorted operates the actuators... so can it be assumed from the above I have a bad ECM or are there some other tests I can run to avoid a potentially unnecessary parts spend or is it a case of just suck it up and try to source an ECM?

I have the plenum off and will likely leave it off until I'm sure I've tested everything that could be a miss. So any other good tests to get through would probably be good to get out the way.

Thanks Again

[Franke]

Judging from what you just described it appears that you have good voltage to the solenoid but don't have ground coming from the ECM when commanded by tech tool to enable field service mode. I would verify the c17 pink wire (ground) from the ECM at the ECM connector to see if it is resistive or open and then test continuity on that wire from the ECM connector (C17) back to the PTV solenoid. After all this testing the only thing left is the ECM.