Help on seconadry system

[lt496]

I have just purchased a 92 Zr1. Its a fixer but complete.
I notice the vacuum pump runs non stop, I disconnected the line near it and there is a vacuum leak pry under the plenum.
The full power switch does light when switched to on but there is no "full engine power" light on the screen.
Ran ran the car full throttle in regular mode then switched the power switch on no difference at all.
I got a ses light that went on for a brief time at full throttle.
Can i get some point to start on this?

 

[bradslt5]

if your car is like my 92 then you dont get a full power light on the message center . i get that on my 90 but not on my 92. do you have a vac cker ? you will need one to find the offending part . the secondary thread is great for finding what is wrong . but you will most likely need a set of plenum gaskets . do you have a scanner to ck for trouble codes . you most likely have a code 61 port throttle selinoid failure . you could just have a lose connection under the plenum . just follow the thread and you will find her .

 

[lt496]

if your car is like my 92 then you dont get a full power light on the message center . i get that on my 90 but not on my 92. do you have a vac cker ? you will need one to find the offending part . the secondary thread is great for finding what is wrong . but you will most likely need a set of plenum gaskets . do you have a scanner to ck for trouble codes . you most likely have a code 61 port throttle selinoid failure . you could just have a lose connection under the plenum . just follow the thread and you will find her .

thank you for the reply. I will get a hand vac and scanner. i have been reading all the posts about seconadary problems even before i got this.
I got this from a saleman that got it from the dealership wasnt good enough to put on the lot but kept it for himeself. he did all kinds of stuff like ball jionts all New clutch/flywheel gaskets oil pan gaskets, starter, even main bearings were done when they pulled the oil pan gaskets.

Where is the main connector to find codes on the 92?
My vacuum pump was running non-stop so disconnected the power to it until I can pull the plenum. will obtain the 1990-1993 service update by gm for the lt-5 should thet do?

 

[Rob]

If you haven't done so already, check out this thread:

http://www.corvetteactioncenter.com/forums/showthread.php?t=14272

 

[Hib Halverson]

First, you need the factory service manual for a 92 because it has information in it to troubleshoot the seconday port throttle system.

Secondly, per the service manual, using the IP display you can read the fault code that turned on the SES. You do not need a scan tester.

Thirdly, as stated above, if a plenum removal is necessary you need plenum gaskets along with the FSM for its instructions on how to remove the intake.

 

[rhipsher]

Take a paper clip. Locate the diegnostic port right below the steering wheel. Ground terminal A and termial G. Turn you key all the way but don't turn the car on. You should get a code C12 first then you should get a code 61. C12 just means the port is communicating.

 

[Hib Halverson]

Darn...I wish you guys would get your facts straight before you post.

It is true that you can also get a 92 to flash codes with the SES light, but you don't ground pin A or Pin G, you ground pin B, the ECM diagnostic pin (top row, fifth from left when you look at the connector with its indexing tang pointing up) or connect pin B to Pin A, the ground pin.

With the key on, engine off and Pin B grounded, the check engine light will blink the codes in a sequence of sequences. Each code is two digits made up of two groups flashes. For example code 12 (which you get if the ECM can send data) will be one flash, followed by a gap, followed by two flashes, like this: F--FF. Each code is followed by a longer gap and is repeated three times. Each sequence of codes is bracketed by a DTC12. For example, if code 61 is set you see:

F--FF---F--FF---F--FF---FFFFFF--F---FFFFFF--F---FFFFFF--F---F--FF---F--FF---F--FF

It's easier to use the IP display to show codes.

DTC61 is only one of the fault codes which can set if the port throttles are not working properly. It is suggested to have the factory service manual for its information on SPT repair. Haynes and Chilton manuals have little useful information on diagnostics and what they have is partially inaccurate.

 

[rhipsher]

I've never met Hib Halverson, But I respect his word greatly. Now I don't know about anything other than the 90 ZR-1 I have. I tried grounding terminal A to B and all I got was a series of dash flashes that didn't mean anything to me. And somewhere else on the internet I was able to pull up something else on it. And it said ground terminal A to G. I did it and it worked. First I saw C12 flash then H61. On my 90 the diegnostics port has 6 pin holes on top and 6 pin holes on the bottom. You stick a paper clip or a bobby pin in the far right top pin hole and the other end in the far bottom left pin hole and turn your key I guarentee it will work. I can even make a video of my doing it and post it hear. And then Hib Halverson can explain to me why it worked. Or why it shouldn't of worked. I'm not going to get on this forum and make crazy statments unless I've done it myself and can prove it. I'm all about facts. Not Fiction.

 

[lt496]

Thanks for replys. I have the 92 service,and lt5 supplement on the way.
I did the paperclip to a-g and a-b. I get the C-12 codes only.
Ive disconnected the vacuum pump so it dosent run non stop until i pull the plenum.
I know the secondary system vacuum isnt working. Vacuum was leaking but wouldn't the engine still flood out? No codes.
You input is very helpful thanks

 

[Hib Halverson]

The the SPTs are not working..not just the vac pump not working...but the secondaries are not opening, then a code should set.

Understand that the vacuum pump is not always required for secondary actuation. The only time it's needed is when long periods of low MAP exhausts the SPTs vac. reserviour, then the pump runs to keep the port throttles open.

Either your port throttles are working but the pump isn't or the SPTs are not working and the ECM diagnostics are screwed up such that no codes set which is unlikely.

 

[bradslt5]

when you disconnected the vac pump and tried it did you have the valet key set to on ./ if you didnt then the secondaries wont activate .

 

[lt496]

yes valet key was on with WOTH. Injectors not on line

 

[Hib Halverson]

I've never met Hib Halverson, But I respect his word greatly. Now I don't know about anything other than the 90 ZR-1 I have. I tried grounding terminal A to B and all I got was a series of dash flashes that didn't mean anything to me. And somewhere else on the internet I was able to pull up something else on it. And it said ground terminal A to G. I did it and it worked. First I saw C12 flash then H61. On my 90 the diegnostics port has 6 pin holes on top and 6 pin holes on the bottom. You stick a paper clip or a bobby pin in the far right top pin hole and the other end in the far bottom left pin hole and turn your key I guarentee it will work. I can even make a video of my doing it and post it hear. And then Hib Halverson can explain to me why it worked. Or why it shouldn't of worked. I'm not going to get on this forum and make crazy statments unless I've done it myself and can prove it. I'm all about facts. Not Fiction.

It works because you're looking at the IP display and not the check engine light.

There are two ways to get codes out of the ECM on a late C4. One is by "flash code diagnostics" where you ground the ECM diagnostic pin on the DLC then watch the check engine light flash. The other is through "CCM" diagnostics where you ground the CCM diagnostic pin and read the module displays on the IP.

The reason I, at first, said: it wouldn't work was I thought the discussion was about flash code diagnostics, which it was...read the earlier thread and you will see that's what I was talking about.

Those are the facts...not fiction.

 

[lt496]

Codes

Yes I have used both methods for getting codes. A-G and A-B count the blinks. Both function with the c-12 but no stored codes other then a h64. I disconnected TPS sensor And started car, diagnostic system displayed the proper code so the system seems to work.
In my case there is a vacuum leak under the plenum but minor so im not setting codes, and I don't think the secondary injectors are coming on line.
Whats next? I think i need to see if the ecm is even sending the command to go into full operation?

 

[ecss]

Try this. Re attach the power to the vacuum pump.

On the driver side middle of the plenum is a black colored vacuum hose yellow arrow pointing to it in the attached picture.

Pull the hose off at the plenum. Turn the ignition to On. The pump will come on. Place your finger over the vacuum hose and see if the pump stops after a couple of seconds. If it does, there is a vacuum check valve under the plenum that is bad. You can fix the problem without pulling the plenum by adding a vacuum check valve to the end of the vacuum hose and plugging the other end back on to the plenum.

You can at least drive the car and use full power mode and pull the plenum at a later date if you want to remove the defective check valve. If the pump continues to run most likely the Vacuum Port Throttle Valve Solenoid is bad. To fix that does require the plenum to be removed.

Also note before the ECM commands the secondaries to open some parameters must be met.

Valet key in Full Power mode.
Engine coolant and oil temperature must be at least 68 degrees F.
System voltage greater than 10 volts.
No Service Engine Soon bulb lit.
Throttle position sensor must exceed a certain value.

 

[lt496]

Well thanks for the info. yes if i plug the line like you mentioned, I have no vacuum leak. what can i use as a valve until I get under the plenum.
Also i get a code H64 from the module 9 (abs). Is this the throttle sensor?

 

[rhipsher]

ecss is right about bypassing the check valve. When your ready to take the plenum off and fix the check valve here's how. All the check valve has in it is a little bebe ball that allows air flow in one direction. If it has any dirt in it this will allow flow in both direction which is not good. All you do is take the check valve off and spray carb cleaner inside the holes. Then blow it out with air really good. Then spray WD40 in it and blow it out again. Again this is something I've had to do myself and it works. Also take a look at your vacume solinoid. It has a little filter on one end. And when it gets old it just crumbles apart and allows dirt to be sucked into it and will cause it to fail and will also throw up a our favorite code 61. But this part is only $34.00 bucks no big deal. A vacume pump is your best freind to check and make sure your actuators are opening when you put a vacume on them and to make sure your vacume system under the plenum is air tight. When I went through this it took me a month to narrow it down to having a bad secondary vacume solinoid. When I put the new solinoid on I took the car out for a drive. I fully expected the car to run out of breath at 4000 rpm's and throw up an SES light just like before. But not this time. When I hit 4000 rpm's it rocketted all the way up to 7500 rpm's. I wasn't ready for that and almost lost control of the car. Fixed. ZR-1's have nothing below 4000 rpm's but above 4000 they really shine. Between 4000 and 7500. Thats where all thier magic is.

 

[ecss]

I don't see how that ABS code could affect the secondary system.

You could get the original GM check valve and install in on the outside of the plenum.

The universal replacement check valves I've bought have strange size input and output nipples. The check valves can be purchased at any auto part stores in the Help section. I've purchased packages of hose barbs to get the vacuum hose to fit.

Be careful when you mess with that vacuum hose. The hard black plastic gets brittle and you don't want to crack it.

I've never tried it but I don't see why it wouldn't work. You could plug the vacuum port at the plenum and plug the end of the disconnected vacuum hose. The vacuum pump would be the sole source of vacuum for the secondary. The purpose of the pump is to supplement the vacuum for the secondary system when engine vacuum isn't enough.

The reality is how long and often are you really going to be in full power mode?

I'd think the pump alone could handle the secondary vacuum.

If not there's a vacuum sensor that monitors the secondary vacuum so if there's not enough vacuum it will shut the secondary system down and set a code.

Here's a link with some pictures of a vacuum check valve.

http://www.partsamerica.com/ProductList.aspx?CategoryCode=3110

 

[lt496]

Thank you for the replies. The running out of breath and check engine light after that is exactly what this does. Very informative and will do as advised.

 

[rhipsher]

I know what your going through it496. It's a pain in the but to get it figured out. But there are only about six things that have to do with the secondary vacume failure. But your going to have to pop the plenum to get to them. When you pop the plenum there are actually two check valves under there. The second one is on the passengers side toward the back of the plenum valley just remove both of them and clean them like in my above thread just as a process of elemination. Next unplug both your vacume actuators. Plug in your vacume pump (which should come with all kinds of different male/female tips) to the actuator and start pumping until you see the actuator arm start to pull back. Once it does you should be able to look down and see your secondary butterfly valves openning. Keep pumping until you reach 13hg then stop and see how long it holds a vacume for if it drops to zero within the first minute then your actuator is toast. But if it only drops a few hg within 2 to 3 minutes its good. Then once you've determind there good or bad replace them. Then plug everything back in and put your plenum back on. The last thing you need to do is disconnect the line going to the vacume pump. You should be able to disconnect it right about where the alternator is. Then plug your vacume pump to the end going under the plenum and start pumping until you reach 13hg if it holds then your vacume system is air tight. Your plenum gaskets are good. Both check valves are working and only allowing flow in one direction. Take her for a test drive and punch it all the way up to 7500 rpm's. If it works, you'll damn sure know it. If it does the same thing as before then I'm 99% sure it's the vacume solinoid located under the plenum toward the front of the car. After removing your plenum 5 or 10 times you'll be able to have it off in about 5 minutes. Now once you fix it depending on how long the secondaries have not worked you will have to get your injectors cleaned and flow tested. After years of the secondary injectors not in operation they will gum up. I took the car to Corey Henderson and he said my main injectors were dirty. But my secondaries were horendously dirty. So he cleaned them and flow tested them for me. Let me know how it goes. If your actuators are bad I've got two extra ones that are in excellent shape. I'll send you.