Stumblin Bumblin Z - ZR-1 Net Registry Forums

1963korvette · 06-12-2012

Need help. In the last 6 months, at different times, I've replaced the Coils, Injectors and fuel pumps. Now, when I'm in Full Power mode it gets to 3,000 rmp's and goes no where. It gurgils and sputters along. I have checked the vacuum, no leaks. I've checked the fuel pressure 42 steady revs it and it goes to 50. Checked the secondary injectors they read 14.8 across the board. Looked at the secondary through the pellum and they seem to be working although the right side seemed a bite slow on the first try, than got better on 2 & 3 pulls. I'm thinking that it might be the secondary system in general. Could the linkage for secondary be fubard. Would like to narrow it down before I pull the pellum. Oh there are no codes. Any thoughts.
Rich

XfireZ51 · 06-12-2012

If the motor is stock, then 3000rpm is the magic number for secondary issues. Opening on 2nd or 3rd pull isn't exactly what you would define as high performance.
Typical secondary issues:

1. Pump Key On, does it keep running?
2. Is system holding vacuum?
3. Solenoid operating?
4. Cannisters binding?

QB93Z · 06-12-2012

Is your secondary vacuum pump operating properly?

Turn the ignition key to ON with engine not running. You should hear a brief period of operation of the vacuum pump located below the passenger-side headlight. If it doesn't run, repair it or replace it.

If it runs continuously, there is a vacuum leak or a leaking check valve in the secondary vacuum system. Post up if this is the symptom and we can do further trobleshooting.

If the vacuum pump runs for short periods (2-3 seconds) and stops and then repeats, there is a slight vacuum leak in the secondary vacuum system.

There is a pressure switch in the vacuum system that tells the ECM if the secondary vacuum system is not operating properly. What year is your Z? Recently, I have seen two ZR-1's with bad pressure switches with symptoms similar to yours.

I recommend some more analysis before you do the plenum pull.

Jim

1963korvette · 06-12-2012

Yes, the vacuum pump is working, although it is squelling. I also checked the rest of the system and it holds vacuum nicely.

1963korvette · 06-12-2012

Oh! 1990

tomtom72 · 06-12-2012

Quote:

Originally Posted by 1963korvette

Yes, the vacuum pump is working, although it is squelling. I also checked the rest of the system and it holds vacuum nicely.

The motor bearings may be dry in the vac pump. Not to be a wise guy, but when you say the system holds vacuum nicely did you do individual checks while you were under the plenum doing your injector work? Or are you using the connection from the vac pump at the right bank? I'm asking because sometimes you have to rotate the actuator canisters so that the arms move freely when vacuum is applied. They should be fully open between 6" & 8" Hg, and their movement should be smooth and linear, not choppy.

Some of the symptoms mirror a DTC 61: secondary vacuum failure. Is the motor still resisting that 3k rpm barrier? That is what happens with a DTC 61. The cause could be a leak, a bad secondary MAP or it's hose, bad tank, bad check valve ( doubtful ), leak in the plastic tubing or at either of the actuator canisters, leaking 2* solenoid.

Tom

1963korvette · 06-12-2012

I used a mity vac to check the vacuum. I did a visual from the top of plemum to see canisters opening when i grounded the pink wire in the ecm.

QB93Z · 06-12-2012

On a 1990, the secondary system pressure switch is located on the bracket under the ECM. You can test it by disconnecting the vacuum line, connecting a vacuum pump and then use a ohm meter to verify that it operates at the correct pressure setting, (which I don't remember but it is in the Service Manual.)

If you have access to a Tech 1, there are very good tools available to verify the operation of the secondary system. I see that you are not too far away from WAZOO. If you could get over here, we would be glad to help troubleshoot your Z.

If you are convinced that the secondary system is holding vacuum and that you can see the secondary actuators move in the open direction, I would move to troubleshooting the secondary injector relays and the secondary injectors wiring.

Jim
jim@gizmosart.com

1963korvette · 06-12-2012

I will check the presure switch when I get home tonight. As far as the actuators go the one bank seemed a little lithargic, but it did open. i do not have a tech 1, got a snap on. I will also look into the relays and wiring you mentioned. thanks

secondchance · 06-12-2012

Last time I had a similar problem my Z was also throwing a code 56 (I think...). Referenced code indicated Pressure Differential Sensor (Jim, perhaps you remember the terminology?). In essence this is a sensor that looks a lot like the MAP sensor but compares differential pressure and allows for activation of 2ndary system. For 94 model this sensor is mounted under side of the plenum.
I will go through my manual tonight and clarify further.

06-12-2012	#1
1963korvette Join Date: Jul 2009 Location: Washington Township NJ Posts: 49	Stumblin Bumblin Z Need help. In the last 6 months, at different times, I've replaced the Coils, Injectors and fuel pumps. Now, when I'm in Full Power mode it gets to 3,000 rmp's and goes no where. It gurgils and sputters along. I have checked the vacuum, no leaks. I've checked the fuel pressure 42 steady revs it and it goes to 50. Checked the secondary injectors they read 14.8 across the board. Looked at the secondary through the pellum and they seem to be working although the right side seemed a bite slow on the first try, than got better on 2 & 3 pulls. I'm thinking that it might be the secondary system in general. Could the linkage for secondary be fubard. Would like to narrow it down before I pull the pellum. Oh there are no codes. Any thoughts. Rich

06-12-2012	#2
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,708	Re: Stumblin Bumblin Z If the motor is stock, then 3000rpm is the magic number for secondary issues. Opening on 2nd or 3rd pull isn't exactly what you would define as high performance. Typical secondary issues: 1. Pump Key On, does it keep running? 2. Is system holding vacuum? 3. Solenoid operating? 4. Cannisters binding? __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

06-12-2012	#3
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,689	Re: Stumblin Bumblin Z Is your secondary vacuum pump operating properly? Turn the ignition key to ON with engine not running. You should hear a brief period of operation of the vacuum pump located below the passenger-side headlight. If it doesn't run, repair it or replace it. If it runs continuously, there is a vacuum leak or a leaking check valve in the secondary vacuum system. Post up if this is the symptom and we can do further trobleshooting. If the vacuum pump runs for short periods (2-3 seconds) and stops and then repeats, there is a slight vacuum leak in the secondary vacuum system. There is a pressure switch in the vacuum system that tells the ECM if the secondary vacuum system is not operating properly. What year is your Z? Recently, I have seen two ZR-1's with bad pressure switches with symptoms similar to yours. I recommend some more analysis before you do the plenum pull. Jim __________________ If it isn't fun, you aren't doing it right! 1990 Black ZR-1 - sold 1993 Quasar Blue ZR-1 1994 Competition Yellow ZR-1 1995 Dark Purple ZR-1 Maryland State Coordinator WAZOO Member

06-12-2012	#4
1963korvette Join Date: Jul 2009 Location: Washington Township NJ Posts: 49	Re: Stumblin Bumblin Z Yes, the vacuum pump is working, although it is squelling. I also checked the rest of the system and it holds vacuum nicely.

06-12-2012	#5
1963korvette Join Date: Jul 2009 Location: Washington Township NJ Posts: 49	Re: Stumblin Bumblin Z Oh! 1990

06-12-2012	#7
1963korvette Join Date: Jul 2009 Location: Washington Township NJ Posts: 49	Re: Stumblin Bumblin Z I used a mity vac to check the vacuum. I did a visual from the top of plemum to see canisters opening when i grounded the pink wire in the ecm.

06-12-2012	#8
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,689	Re: Stumblin Bumblin Z On a 1990, the secondary system pressure switch is located on the bracket under the ECM. You can test it by disconnecting the vacuum line, connecting a vacuum pump and then use a ohm meter to verify that it operates at the correct pressure setting, (which I don't remember but it is in the Service Manual.) If you have access to a Tech 1, there are very good tools available to verify the operation of the secondary system. I see that you are not too far away from WAZOO. If you could get over here, we would be glad to help troubleshoot your Z. If you are convinced that the secondary system is holding vacuum and that you can see the secondary actuators move in the open direction, I would move to troubleshooting the secondary injector relays and the secondary injectors wiring. Jim jim@gizmosart.com

06-12-2012	#9
1963korvette Join Date: Jul 2009 Location: Washington Township NJ Posts: 49	Re: Stumblin Bumblin Z I will check the presure switch when I get home tonight. As far as the actuators go the one bank seemed a little lithargic, but it did open. i do not have a tech 1, got a snap on. I will also look into the relays and wiring you mentioned. thanks

06-12-2012	#10
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,723	Re: Stumblin Bumblin Z Last time I had a similar problem my Z was also throwing a code 56 (I think...). Referenced code indicated Pressure Differential Sensor (Jim, perhaps you remember the terminology?). In essence this is a sensor that looks a lot like the MAP sensor but compares differential pressure and allows for activation of 2ndary system. For 94 model this sensor is mounted under side of the plenum. I will go through my manual tonight and clarify further.