Secondaries not functioning

[TexasZR1]

My secondaries started acting up with the heat lately.


They work fine when cold, then after warm-up (anywhere from 5 miles to 20 miles) they stop functioning.

I first replaced the fuel pumps (they were original). Fuel pressure test shows ~40psi at idle and ~50 at WOT.

Injectors were replaced by the prior owner.

The vacuum pump is functioning properly (runs for about 10 seconds to build vacuum; cycles for about 1 second every 3 or 4 minutes).

When jumping the pink wire at the ecm to ground, i get intermittent function of the secondary butterflys when warm. When it's cool, everything works great.

I'm thinking it's the vacuum solenoid?

Wiring diagram shows only one vacuum solenoid for the secondaries. Is this correct?

I need to start ordering other parts (gaskets, etc) to pull the plenum.

As a sanity check, any other diagnostic I should do first?

Also, anyone have a parts list for stuff to order for the plenum RR?

Do I need to remove the throttle body to pull the plenum?

Do I need anything other than Jerry's "36 pc Fuel Injector Maint"?

I've also seen recommendations to block some coolant ports?

[Young1]

Because my Z is not a DD I always disassemble first, test and assess, then order parts. Maybe you have mice or lizards living in there! It is well worth the money to get Marc Heibecks DVD for your first plenum pull. zr-1 specialist.com

[Ccmano]

My secondaries started acting up with the heat lately.


They work fine when cold, then after warm-up (anywhere from 5 miles to 20 miles) they stop functioning.

I first replaced the fuel pumps (they were original). Fuel pressure test shows ~40psi at idle and ~50 at WOT.

Injectors were replaced by the prior owner.

The vacuum pump is functioning properly (runs for about 10 seconds to build vacuum; cycles for about 1 second every 3 or 4 minutes).
When hot?

When jumping the pink wire at the ecm to ground, i get intermittent function of the secondary butterflys when warm. When it's cool, everything works great.
Are you looking at both or just one?

I'm thinking it's the vacuum solenoid?
Its possible

Wiring diagram shows only one vacuum solenoid for the secondaries. Is this correct?
Yes Correct

I need to start ordering other parts (gaskets, etc) to pull the plenum.

As a sanity check, any other diagnostic I should do first?
You read this correct? http://www.zr1specialist.com/HAT%20Web/articles/Are%20The%20Secondaries%20Working.pdf

Also, anyone have a parts list for stuff to order for the plenum RR?
Just the plenum gaskets, replace the check valve while your in there it’s cheap and often causes problems.

Do I need to remove the throttle body to pull the plenum?
No

Do I need anything other than Jerry's "36 pc Fuel Injector Maint"?
injectors have already been replaced, no need to pull them again. Not part of the basic plenum pull process.
I've also seen recommendations to block some coolant ports?
Stick to one issue at a time although it does make a plenum pull a snap.

See my comments in RED above. With an intermittent and heat related problem like this and with vacuum holding when hot I’m inclined to think it’s more of an electrical issue. The solenoid is the only related electrical item under the plenum. I’m sure others will chime in. Keep us posted.
H
:cheers:

[A26B]

Certain DTC’s will disable the Secondary port throttles, i.e. full power. If that is the case, you should see a light in the panel, usually SERVICE Engine Soon.
I suggest you check stored codes, make note of them, then clear all. Drive the car again under the same conditions that have disabled full power until it happens again, then check stored codes again. You may have a bad/missing light in the panel. This procedure will at least eliminate the possibility without having to disassemble anything.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[TexasZR1]

See my comments in RED above. With an intermittent and heat related problem like this and with vacuum holding when hot I’m inclined to think it’s more of an electrical issue. The solenoid is the only related electrical item under the plenum. I’m sure others will chime in. Keep us posted.
H
:cheers:


Thanks much for your help and guidance!


Vacuum system is functioning well when cold and hot.

I've looked at both actuators, however, when it doesn't function, neither do. When it DOES function, both move.

I did read that diagnostic and a few others. I tried pretty well all I can with the plenum on I think. Given that grounding the pink wire works only when cold, the issue is almost certainly under the plenum.

I have checked for codes and its all clear (12). The SES light does work, but it never illuminated when I'm having the issue.

Power wise, I'm certain they are not opening (flat above 4500rpm).

I will order a set of plenum gaskets, pick up some coolant, solenoid and check valve and see if I can get this sorted.

Thanks everyone for the input! Will report back soon.

[TexasZR1]

I'm having a hard time locating a replacement vacuum solenoid.

Seems pn 1997222 is out of production and out of stock...

Did I read there is a near twin to this part with a different bracket that can be substituted?

[Young1]

https://www.rockauto.com/en/partsearch/?partnum=1997212

Type 1997212 into search of rock auto. This is what you need. Carefully change the bracket and cut a bit of plastic for the electric connector to fit. I did this myself about three years ago.

[TexasZR1]

Thank you! Part ordered!

I found some other things to tighten and clean up while in there, so the plenum pull will have been well worth it.

Leaking pcv cover, lose injector housing bolts, will look more tomorrow.

[Paul Workman]

*Power wise, I'm certain they are not opening (flat above 4500rpm).

Thanks everyone for the input! Will report back soon.

The stock "accordian" air hose between the air filter and the throttle body horn collapses under WOT and cuts off acceleration right at the 4500 +/- RPM you spoke of. It's a common issue with 26+ yr old plastic.

I fixed mine with a aluminum sleeve liner for that hose. Marc Haibeck sells some wire hoops to be inserted at intervals along the length of the hose, and Jerry's Gaskets sells a replacement hose which also adds to the esthetics.

Get back 2 us!

[Young1]

Zip tie every vacuum and pvc joint you can. I got small brass round stock at Lowe’s. Formed it around the air horn and popped it inside the pleats. I think I put in 3 pieces. Easy and cheap. Runs to the rev limiter quite often too. You are welcome!

[Paul Workman]

AND....Im sure you realize by now that it will run on secondaries FULL TIME. Many of us run on FULL ENGINE POWER, 100% of the time (above 1(?)% throttle input, IIRC). If you can pardon an old shade tree mechanics logic: "Parts that don't exist don't break, and they don't cost much!"

[Dynomite]

One of the reasons I have a ZR-1/LT5 is the LT5. An amazing engine which I found out once you treat it with a bit of respect in a restoration/maintenance it never quits (runs forever) :D

I replaced the complete secondary vacuum system on the LT5s for less than $100 (all those old rubber connectors are usually the issue as well as those old original injectors).

Lets not forget the old Fuel Pressure Regulators also replaced by Phil's new Fuel Pressure Regulator that can be changed out after initial installation without removing the Plenum (the original Fuel Pressure Regulators usually are a bit rusty inside) :thumbsup:

I would never eliminate a functional Secondary Fueling System which is the most unique features of an LT5 (The Full Power Key and all that Dual Fueling associated with the Full Power Key).

[TexasZR1]

Tightened everything up, new solenoid installed (in old frame), new gaskets, topped off coolant, runs like a dream! In my case, someone had already put stiffeners in the accordian.