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Under The Plenum

Rob

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lt5_under_plenum.jpg


For those of you wondering what it looks like under the plenum of a ZR-1's LT5 engine, here you go. Unfortunately, I'm chasing down a secondary port throttle vacuum leak which I discovered last night.

So....what is all that mess under there you ask?

Starting from left to right:

1. Those red wires are the ignition wires going to the 4 coil packs that basically are the car's distributor...so to speak. Underneath that, is the starter motor which you can't even see. This should give you some idea of how deep the valley is on an LT5 engine.

2. In the middle of the picture you see two very large tubes. Those are the crankcase ventilation hoses. To the left of the top hose you see a shiny metallic cylinder. That is a secondary port throttle valve actuator. When enough vacuum is applied. the valve opens via a mechanical linkage and it opens the secondary port valves which you see at the top and bottom of the picture. There is another secondary port throttle valve actuator on the opposite side which controls the other bank of secondary port throttle valves.

3. To the lower right hand corner, you see a large black cylindrical shape with vacuum hoses on top. That is the secondary port throttle vacuum reservoir where vacuum is stored to control the secondary port throttle system.

4. In the upper right hand corner the large silver motor is the AC compressor and below that is the alternator.

Incidentally, in order to replace the starter, all that stuff in the center there pretty much has to come out. There is an intricate system of vacuum tubes which you can sort of see running in there. It is that vacuum system with all it's check valves which has my vacuum leak. This will be the second time I have replaced the system and it's not an easy chore.

Unfortunately, due to the intense heat that can build up under the plenum....these types of things are prone to failure. The nature of the beast so to speak.
 

Ken

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I don't know Rob. I think I'll take the standard small block anyday. What a PITA to reach anything on that engine of yours. :L

_ken
 
S

Steel Half-Shafts

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Rob,
Thanks for the excellent pictures and info on what's under the plenum on the LT5.

I havn't had to become a member of the "Plenum Pullers Club" yet with my 1990, but it's nice to know what's under there and how it's setup just in case.
:beer
 
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Nice lesson professor, now when is the next installment of LT5-101:D. Sheesh Rob, I'm beginning to think twice about tha ZR-1 goal of mine:L.

- Eric
 
G

grkzr1

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Wow! This is the cleanest under the plenum area that I ever saw!
What did you use to clean it that well?

--John
 
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Rob

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John,

Back in 1999, I replaced everything under there except for the starter and coil packs. Everything came out of the center there. I had to replace the crankcase baffle cover gasket which was known to possibly leak on earlier ZR-1s. Mine was leaking so there was a fair amount of oil and gunk built up in the valley.

This is not good because there is a drain hole drilled into the back of the block near that starter that acts as a drain to prevent water build up in the center of the valley. This drain hole was not drilled large enough on earlier LT5 engine and as a result can plug up. If water gets under there, it can corrode the starter contacts thus leading to starter failure.

Although it's rare for water to get under there, it can happen. As a result, I replaced that crankcase baffle cover gasket and cleaned up any crud that built up under the plenum. What you see is basically how it looked after I finished 4 years ago with the exception of a little dust. Before I put everything back together again, I'm going to vacuum the dust out of their and I've already polished the fuel rails to a chrome like finish. :D

Incidentally, I tracked the vacuum leak down to a failed vacuum solenoid. More pictures to follow.
 
R

rhanselman

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Rob,

Great post!

I have to make sure I save it for when I need to track down leaks! I wonder if anyone has tried to replace the rubber with stainless components?

Cheers,
RH

:)
 
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Rob

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rhanselman said:
Rob,

Great post!

I have to make sure I save it for when I need to track down leaks! I wonder if anyone has tried to replace the rubber with stainless components?

Cheers,
RH
:)

Good question. I'm not sure if anyone has or not. Keep an eye on this thread. I'm picking up the new vacuum solenoid tomorrow afternoon and I'll hopefully have the the engine put back together tomorrow night. Once it's all done, I'll post some followup photos as well as some simple diagnostic procedures that you can do to help troubleshoot secondary port vacuum leaks.
 

JT ZR-Won

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Very cool post Rob. It's funny you posted this because I just pulled the plenum off mine a couple of days ago. I'm replacing my stock LT-5 wires with a nice set of MSD 8.5mm wires. I like the idea of the polished fuel rail covers:)

Jay
 

Rob

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JT ZR-Won said:
Very cool post Rob. It's funny you posted this because I just pulled the plenum off mine a couple of days ago. I'm replacing my stock LT-5 wires with a nice set of MSD 8.5mm wires. I like the idea of the polished fuel rail covers:)

Jay

The polished fuel rails look awesome once the plenum is back on. Whenever I remove the plenum, I use the opportunity to do some extra cleaning and polishing that is normally hard to get to with the plenum on. ;)
 
G

grkzr1

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Rob,
I replaced the solenoid in my car also. When I received the part I realized that it is different from the original one. You can not install the flat filter on it. You have to order PN 10159525 which is a tubular filter. But I bet that you know that already :)

--John
 

Rob

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Update

Well.....I installed the new vacuum solenoid tonight. Put everything back together, took the car out for a test drive and am not happy with the results. The solenoid works perfectly....the system holds a vacuum well, but as soon as the secondaries come online, they shut right down. It literally feels as if the car hit a wall and secondary operation is not smooth. They open abruptly and the car jerks. The last time I tested it, the secondaries shut down and the check engine light came on for a few seconds and shut off.

I threw the car back in the garage, double checked for vacuum leaks which there are none and shut the door in disgust.

Tomorrow, I'll grab the Tech 1A diagnostic scan tool and find out what the trouble code is.

:( :( :cry :cry :cry
 
G

grkzr1

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I know the feeling :cry . Maybe a bad actuator? or a bad pump? I hope you resolve this problem soon. Please keep us posted.
Good Luck

--John
 

Rob

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Nope....actuators and pump are working....and I'll verify the actuators later today when I rip the plenum off....again..... :( The only thing I can think of is that I forgot to plug an electrical connector somewhere under the plenum as there are several. It's the only thing I can think of. That trouble code will be key to the problem as soon as I read it later today. I'll keep everyone posted.

-Rob
 
G

grkzr1

Guest
I had a similar problem but I had no error codes. It was the actual full power key switch. It was going on/off because it was loosing connection. Did you also checked the fuses of the secondary injectors?

--John
 

JT ZR-Won

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Man Rob I know that's aggravating. Good luck on finding the problem and keep us posted......

Jay
 

FrankUrbinati

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FWIW....the new solenoid is bad.

Just got done checking the secondary system with a vac. pump. The notorious MAP sensor line WAS leaking a bit. A tie wrap was the easy fix. Now she will go from 20in vac. to 15in vac in 6 minute's. The vac. pump go's on for abou a second once every 16-18 second's. With the key in the On position. Good ??
 

Rob

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Wonderful......so....even though the solenoid, can still hold a vacuum, it can still be bad? Unfortunately, I stripped one of the plenum torx bolts so I can't even get the damn plenum off the engine. I also can't find anyone who knows what the part number is to the bolts....not even the dealer!!

As for the engine code, it was a code 61 - port throttle problem - no kidding.

:eyerole

I'm aggravated beyond belief. The weather is going to be awesome this weekend and I have two events I was going to bring the car to and now....it doesn't look like it's going anywhere unless I can get the damn plenum off the engine and somehow come up with another solenoid if that is indeed the problem.

I have a feeling I'm just going to make an appoint. with the dealer and let them figure out what's wrong with it.
 

FrankUrbinati

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Rob... Take it easy. Relax a while. Even stay away from the car for a while if you have to. By all mean's when your ready go back to work on the car. Help's for me when frustration set's in.
You think the dealer can do better ? You'll get it.
 

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