Working on little things, may have some questions soon

[1991 Corvette ZR-1]

Ended up going after my old oil cooler lines which have increased their leaking and what a fight that was. So I finally got a chance to take Jerry?s cooler lines out the parts bin and get ready to install. I do not advise trying this with the radiator shroud in place unless you are okay with a teaspoon of oil dribbling down the radiator. Had to pick up a 29mm socket and notch it to fit around the filter housing to get a good grip on the top fitting. They were on there! Used a two foot breaker bar plus a four foot cheater bar on it to break these things loose from the housing.

Anyway, figured I would post some pictures of what I am working on and also ask some questions as I work on some other parts of the Z. I do not have anything like what the factory used to seal the threads of the fittings. I do have permatex aviation sealant. Will this suffice? Worked well on the oil pressure sensor threads but these are considerably larger.

Next after the new oil cooler lines, I will be replacing the AC condenser, dryer, all AC specific O rings and oil in the compressor. Planning to recharge with R134 once I have put everything back together. AC blew room temp air since I first got it and the system was completely flat.

[1991 Corvette ZR-1]

Alright not to overthink things but I want the reassurance I am using the right stuff for this application. Jerry?s instructions say to use pipe thread sealant. I have permatex aviation sealant on hand. Does not appear to have a size limitation on the fitting sealed. Will this stuff work or is there a different product that should be used on the new fittings for the oil housing?

[1991 Corvette ZR-1]

Alright, put a pin in the question about proper thread sealant but I believe I will use permatex aviation thread sealant. Can someone school me on the AC switches? The FSM is not the most helpful on this part. I believe the black switch per the FSM is the AC compressor pressure switch, but does not state if high or low. The red switch is referred to as AC compressor engine cooling switch.

Then there is what I assume is the high pressure switch on larger tube on the upper part of the evaporator. What is what? Also, these are the old R12 switches so I am guessing they will not be compatible with R134a correct? Not sure what switches to replace these with. Would like some suggestions.

[1991 Corvette ZR-1]

Lots of views but I can?t be the only person who has gone through these parts before around here. Maybe it is some tough love to find the answers myself. Well find them I did! I leveraged my resources and reached out to Marc, who was kind enough to inform me of the answers to my questions. So I must confess, I got so engrossed in figuring out the AC switches, I glossed over the sealant provided in the FSM for resealing the oil cooler line fittings to housing.

It is Loctite 565. Marc informed me of this as well and it was only after reviewing the installation procedure again that I discovered this was there the whole time. So, loctite 565 has been ordered and on the way.

Next were the various switches on the AC hard lines. Again, these are per Marc who is an outstanding resource for everything on these cars. The large switch on the large upper tube to the evaporator, which I thought was high pressure switch is actually the low pressure switch and the replacement part is Four Seasons 35751. The red switch is the engine cooling switch per FSM and the replacement for it was Four Seasons 36669. The black switch was an over pressure compressor clutch cut off switch and not a direct replacement on that one short of a junkyard trip. And, you guessed it, I ordered all the switches I could.

Things are escalating. I was able to remove the oil psi sensor from the housing but the replacement sensor I have is a 92-95 sensor. So I will have to figure that out. I also unplugged the low oil psi alert switch connector and it is covered in oil! So, I may be taking off the remote oil filter housing entirely, as the water pump hose is out of the way along with everything else. I am also contemplating replacing the spectra radiator I have with a Dewitt?s single row now that all coolant is drained. Hmmm?

[Mystic ZR-1]

Go with the DeWitts 2 row radiator.
Fits great and has the extra cooling capacity.

[conesare2seconds]

Thanks for posting the AC switch info.

[1991 Corvette ZR-1]

Go with the DeWitts 2 row radiator.
Fits great and has the extra cooling capacity.

The double row is tempting. The current $100 Spectra seems to do a great job for my style of driving. From what I have read, the single row version is even greater cooling capacity over the factory rad. So the double row drops in with minimal to no modifications? I think I may continue to run the spectra rad for a while longer. I also got looking at the SPAL fan kit on Dewitt?s site. I think between the single row and the fans I would be at about $1,000. I do not track so maybe the double row is overkill?

I took the oil filter housing off. As expected, it was filthy. Look what I have access to now, the oil pressure regulator cover. Now I can change that gasket as well as the sight hole plug seal for the passenger side head. I do not think tightening those 8mm bolts did too much for the tiny leak it was appearing to have. Glad I bought the gaskets in advance. I will also restore the wiring harness running through here as it is oily and beyond filthy. Ordered some high temp split loom that mimics the factory coverings.

You know, I have to remove the plenum to pull the compressor. If I am that far into it, maybe now is a good time to eliminate the secondaries. Is there any HP to be found in the elimination? If any, I figure a couple at the most? Quite the rabbit hole from what was supposed to just be changing oil cooler hoses.

[Norwegianmopar]

Go with the DeWitts 2 row radiator.
Fits great and has the extra cooling capacity.I just bought the 2 row Pro Series for our car. Marc Haibeck told be it would be a very good replacement if I was buying a new one. Probably more than I need, but what the heck, I am upgrading more that isn't a must do because I want to [emoji16]

Sent from my SM-G955F using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[1991 Corvette ZR-1]

I just bought the 2 row Pro Series for our car. Marc Haibeck told be it would be a very good replacement if I was buying a new one. Probably more than I need, but what the heck, I am upgrading more that isn't a must do because I want to [emoji16]

Sent from my SM-G955F using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

Did it fit without isssue? Maybe you and Mystic are onto something. It is only a few hundred bucks more than the single row. I could have sworn I read something about fitment issue for double row but maybe that was an earlier model years ago. Guess I will look into the double row.

[secondchance]

Based on my experience, dual-row Dewitt, Spal fans and 200 amp alternator (to deal with Spal fans' increased draw) makes coolant overheating concern in 90 plus temp days thing of the past.:cheers:

[Subfixer]

The only fitment issue I had with the double row was the 1/4" spacers for the original fan shroud. They were a PITA to get in. Also, the bolts supplied are incorrect. They are sheet metal bolts vs metric threads. Solved with longer hardware store replacements. Otherwise, a direct fit.

Sent from my Pixel 4a (5G) using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[1991 Corvette ZR-1]

Not much of an update other than the secondary plates are off and I do not think I am going to miss them. The valves are pretty rough compared to the primaries. The screws holding the butterflies on were surprisingly easy to loosen. Some of the butterflies have seen better days. Hard to see in the picture but it has a nice thick hard carbon buildup.

[1991 Corvette ZR-1]

Just doing little things until I get two key items back. One is my updated chip from Marc for the eliminated secondaries. The other is a new set of AC compressor hoses from Ecklers. Site indicated they were in stock and ordered two weeks ago but still no update on shipment. Ecklers is two or three hours from me, so an order is usually a day two delivery for me. Probably call them to see what the status is.

I am VERY tempted to attempt bearing and shaft removal, but the heads are on the engine in the car, so not sure how doable it is without messing something up. I have the PVC box gasket to replace if I removed it and the other stuff in the valley, but I have a sneaking suspicion something will go wrong. Call it paranoia. Also, my sealing surfaces between heads and injector housings is lacking.

No matter how careful I am I installing new gaskets, every time it manages to seep through and weep down the valley. Also it is seeping through into the intakes I believe so that would probably solve my oil consumption issue some. On the new set of gaskets, I will be applying a smear of permatex ultra black to both sides before everything is torqued down to spec this time.


While I wait, I decided to tackle restoring a very oily and grimy wiring harness that runs down to the remote oil housing sensors, O2 sensor and crank position sensor. I have headers, so it made things easy to gently pull out the harness for the restoration. Oh and the old overflow bottle was retired. 31 years of service. Did not realize how worn it looked until the new one showed up.

[1991 Corvette ZR-1]

Anyone reseal their AC compressor? Found a reseal kit and given how grime caked my compressor was, it might be a good idea. Also, no oil drained out of the compressor. Not a drop. They even have a walkthrough detailing the reseal.

https://www.shopcenturyautoair.com/store/p95/Denso_10PA15%2F17_Series_Master_Reseal_Kit_KT-10PA-SYS.html

[1991 Corvette ZR-1]

Finally figured out what the mystery blue ignition coils were on my car. They are Standard brand coils. Anyone use these? I am replacing them with coils from Jerry?s while I am in here but will keep them as a back up.

https://www.oreillyauto.com/detail/c/blue-streak/ignition---tune-up/ignition-coil/ignition-coil/90c5da72ae86/standard-ignition-blue-streak-ignition-coil/std2/dr39

For anyone that needs take these off, you need a 5.5 mm socket. Went into Autozone and they actually had one for individual purchase.

I can?t seem to find AC lines to save my life or at least verify newer 94-95 compressor lines will fit a 91 compressor and seal properly. On pictures I have seen of 94-95 compressors, there is no provision in the compressor to hold O rings. As such, the compressor lines have a recess for the rings to press into. On my 91 compressor, there is as recess for rings. My dilemma is if I purchase 94-95 lines and the rings seat in the mating surface of the lines, then I have a gap that is not properly sealed when I go to bolt them to the 91 compressor.

A helpful member showed me a picture of lines he got that were listed as 94-95 and they looked like mine but wondering if he got lucky? Can anyone confirm 90-95 compressor lines are all the same as far as mating surfaces go?

[1991 Corvette ZR-1]

Rebuilt the compressor and it is back on the LT5. It was not a bad job. I went slow with it and everything worked out. Big thanks to Century Auto Air. They provide the walkthrough videos and the rebuild kit. Videos offer tips and tricks the FSM does not have. Hopefully will have the new AC compressor lines by Friday.

[1991 Corvette ZR-1]

I am posting a little update with some info that hopefully someone may find useful one day should they decide to rebuild their AC system.

If you?re going through the trouble to rebuild the compressor, and it is your forever car, might be a good time to refresh some other items in the AC system. I got a set of compressor lines from these guys:

https://www.thepartsplaceinc.com/product/1991/1991-chevrolet-corvette-a-c-compressor-hose-assembly-ac-delco-15-30221-gm-10229061/63143

Although one review states they had to bend the lines some to get around the power steering pump reservoir. Mine show up tomorrow. I will update my thread with my findings as I install. The accumulators are pretty cheap at $30-$40. GDP model acquired off parts geek. The condenser I got off parts geek website was about $100. It required some bending of the tubes as it was not a direct mate up like the old condenser. But it beats paying $500 for the exact same kind from Ecklers or Zip.

I used the old shot condenser as a reference for how the new tubes would be positioned. Minimal bending required. It also comes to you pressurized. So the moment you undo a screw on plug, you?ll hear a lot of hissing. What that tells me is the condenser holds pressure. Mine sat in the parts pile for a year before I opened it up, so I feel good about the purchase so far.

Also, Bob with century auto air recommended PAG 46 oil for the compressor which should be compatible with the old R12 oil traces left after draining your compressor. I got this which has UV dye mixed in.

https://www.amazon.com/TSI-Supercool-P46-8D-Accessories-Fluid_Ounces/dp/B008PKWD3O/ref=mp_s_a_1_14?keywords=pag+46+oil&qid=1645746349&sr=8-14

Hope this helps someone in the future.

[XfireZ51]

Links not working

[1991 Corvette ZR-1]

Links updated so they should work now.

[1991 Corvette ZR-1]

Well the fit is horrible on the new lines right out the box. I spent about 30 minutes bending the lines to negotiate around the power steering reservoir just enough to actually properly bolt up to the compressor. Once fully secured to the compressor, it was very easy to gently bend the hard lines to properly clear the power steering reservoir. Definitely not for the crowd that wants as close to factory looks as possible but it will work for me.

[tiegsd]

Lots of good info in here. Appreciate the effort to document, need to do some of this stuff myself in near future.

[1991 Corvette ZR-1]

Lots of good info in here. Appreciate the effort to document, need to do some of this stuff myself in near future.

Glad I can contribute in someway. I will also add the next time anyone is in the valley to take a look at the alternator plug. Mine crumbled to pieces when I removed it from the alternator to upgrade to the 200 amp power master. It gave 31 years of service and many heat cycles in 94K miles. The replacement pigtail can be had from various sources but I got mine from Autozone. It is Duralast #237. 14 bucks I believe. I have terminal pick tools, so I removed the wires it came with.

Then I surrounded what was left of the old rotted plug in a shop towel and with a pair of channel locks, I gently cracked it like a walnut. All original terminals intact unharmed. After that it was just a matter of gently plugging in the original terminated wires into the new plug. No splicing required. A few pics of that and where my lines ended up once the radiator shroud was back on. Waiting to test drive it to give the loctite 565 close to 24 hours to cure on the oil filter housing fittings.

Also, because I eliminated the secondaries and all the associated hard lines, no more vacuum line on the driver side of plenum. I just used a nipple cap to seal it.

[Matt B]

Great information, thanks for your efforts. This threat could be linked into our knowledge database, no?

Only I always find it sad when Secondaries are eliminated. Though I fully understand the motivation (and there is plenty) it's something only our ZR-1 have. So it's eliminating are piece of uniqueness and coolness.
Personally I even asked Marc to calibrate my chip in a way that low power mode remains standard at start up so I can/have to use that ultra cool power key to unlock her horses [emoji3]
But again, I understand there are good reasons to pull them.

Question: from your recent experience would you say that removing the whole oil filter assembly, cleaning and resealing it can be preferred over only replacing the sensor without pulling the while unit?

[1991 Corvette ZR-1]

Great information, thanks for your efforts. This threat could be linked into our knowledge database, no?

Only I always find it sad when Secondaries are eliminated. Though I fully understand the motivation (and there is plenty) it's something only our ZR-1 have. So it's eliminating are piece of uniqueness and coolness.
Personally I even asked Marc to calibrate my chip in a way that low power mode remains standard at start up so I can/have to use that ultra cool power key to unlock her horses [emoji3]
But again, I understand there are good reasons to pull them.

Question: from your recent experience would you say that removing the whole oil filter assembly, cleaning and resealing it can be preferred over only replacing the sensor without pulling the while unit?

I agree on the secondary operation. I enjoy it as well and I get a kick out of the noise the actuators make when you release vacuum and all the butterflies snap back shut. A few things made me eliminate them, lack of readily available repro actuators and putting eyes on the valves after the butterflies were removed. They were rough! And this is a higher mileage car and definitely driven by the previous four owners.

The method I chose was to leave the throttle shafts and bearings in place. Marc provided small brackets to keep all the shafts in the open position. So technically, it would be easy to convert back to the butterfly setup if desired. But I agree 100 percent with you, if it were feasible to keep the dual performance mode intact I definitely would.

On the oil filter housing, if it is your forever car, I say go for removing and restoring. Jerry?s has the replacement gasket as well as all sensors. I went with a 93-95 oil temp gauge sensor. So I removed the screw in bushing and threaded in the larger late model sensor directly into the housing. It ACTUALLY reads oil temp now on the gauge I can?t believe it. Old sensor after a two hour drive would barely be off the peg. I have heard that it is common for the low reading on the gauge, but I took a chance on a new sensor and glad I did!

I was going for a mostly complete refresh. I wanted to pull the housing because it was filthy and I did not want to torture myself trying to finesse a custom cut socket down there to remove the oil temp sensor. Also replaced the low oil PSI switch while I had it off. I even sourced the temperature element if I decided to crack the housing open but decided to hold off. If I need to in the future it appears to be accessible from the front while still mounted on engine.

The big catch is you have to drain coolant and remove the water pump hose to get access to one of the three bolts mounting the housing to the block. Attached a few pics of the temp element used inside the housing. This same bag and part numbers have appeared on eBay by different sellers for roughly $500. I believe I got it for $20 but do not recall the site. I have had it in the parts pile for a year or more.

[1991 Corvette ZR-1]

Moved onto something more fun I guess you could say. I cannot take credit for discovering these as it was ZuggZR1 who referenced them in a headlight upgrade thread. So figured I would give it a try. Weight difference also shown between Wagner glass bulb and the LED. Also picked up some load resistors to pair with the LED headlights. They get very hot from what I have read, so mounting them to something metal near the lights will be preferred.

Good news is the lights came with an extension piece that helps out. I want to try my hand at NOT hacking up the factory wiring, so that this is reversible if desired.

https://www.amazon.com/gp/product/B014Q6HSOY/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1


https://www.superbrightleds.com/moreinfo/flashers-load-resistors/headlight-load-resistor-kit-h4-led-headlight-bulbs/2179/5079/

[1991 Corvette ZR-1]

Well I paused the headlight switch for the moment. Something wonderful decided to rear it?s ugly head. So did a couple of little drives post putting everything back together and 25 minutes into the drives, I am smelling gas. I pull over and check the cap and sure enough it?s venting pressure. I slowly undo it and get the classic outward blast of pressure.

I definitely plugged in the fuel vapor solenoid during reassembly and there are no trouble codes. I can blow through the vapor line unplugged from the passenger side connection and can pass air all the way out the hard line out back unplugged from the canister. So I took apart the rear wheel well housing and pulled the canister and check valve. I applied vacuum to the check valve and no matter how hard I try to push air through, barely anything comes out the other end. I found a replacement Duralast part PV111. Says on the Autozone website it does not fit, took my factory valve to the store and it is a carbon copy. Minimal vacuum required to actuate the diaphragm.

https://www.autozone.com/emission-control-and-exhaust/canister-purge-valve/p/duralast-canister-purge-valve-pv111/68757_0_0

Also ordered a new charcoal canister. I am already in there and the one on there now has been in place going on 32 years. Part number VC120

https://www.autozone.com/emission-control-and-exhaust/canister-purge-valve/p/duralast-canister-purge-valve-pv111/68757_0_0

Going to pick up the canister later today as the new check valve was put on last night. To make sure I am not crazy, I applied vacuum to the new valve and was able to blow air through it no problem. They also have the purge solenoid and you guessed it, I may be ordering one of those as well. Because I will go through this and my luck it will end up being a cooked purge solenoid. But wouldn?t a faulty solenoid throw a code? I guess if it?s energized but clogged, the ECM will not recognize an issue. I may have to go back under the plenum.

https://www.autozone.com/emission-control-and-exhaust/canister-purge-valve/p/duralast-canister-purge-valve-pv118/45380_0_0

[1991 Corvette ZR-1]

I have not updated this in a while, but I figured I would provide one. Combination of a new check valve, vapor canister and vapor solenoid under plenum did the trick. No more fuel smell and yep, I pulled the plenum again just to switch out the old solenoid with a new unit. The old unit worked fine after applying voltage and blowing air through the tubes, but if I went through the trouble of pulling the plenum, I was going to replace the old part anyway. When Pete did my top end porting, he plugged the TB coolant passages in the injector housings and I have to say that one update made a WORLD of difference for working on the Z.

I ended up saving the headlight wiring and not having to splice anything. The only wiring that got modified were the adapters that came with the resistors for the headlights. Everything is reversible on the original factory wiring. My motors also ran about ten seconds after opening or closing. So I rebuilt the motors while in there.