Massive Air Leak After Plenum Pull

[ThisIsSparTTa]

Alright guys, so I got through my first plenum pull a couple weeks ago. I did: Plenum Coolant Line Bypass, EGR Bypass w/o Removal, AIV delete, Valve Cover gaskets redone, new injectors.

She cranked up first time, but had a massive air leak. I initially thought it was a suspect IACV>Balance Tube hose, so I got a new one on. I was also suspect of the EGR Valve vac line leaking, but have since eliminated that as a possibility. Read some more on looking for leaks, and got some soapy water and a vacuum tube up to my ear.

What I'm finding is the hissing seems to be coming from the drivers side in between where the upper plenum meets the rest of the engine and the intake valve cover. I have checked all vacuum connections in the area. The hissing seems louder at the rear, but can be heard all the way up to the front. I do have about 1/8" of plenum gasket sticking out of that side (it was a PITA to get the plenum holes to line up right and i had to shift it around some). I'm thinking right now that my upper plenum isn't sealing properly. 2nd suspect is possibly a bad intake valve cover seal, but that gasket is rubber (and OEM New) and all the screws are down plenty tight. Lastly, even though I used new fuel rail insulators, I guess its possible I could be leaking air out around the injector? I don't think it would be as steady if that was the case, and it would smell terrible.

So, has anyone ever had their plenum not seal back up right? Any other ideas? I don't want to tear my plenum back off unless I absolutely have to right now...

[Ace2cool]

Spray some starter fluid around the engine bay to localize the leak. Wherever the idle changes when you spray it is the exact leak location.

[Oh Em Zee]

Lets list the stuff to check as well:

Balance tube- 3 o-rings, Carbon canister vac line, IACV line
IACV\AAC - 4 hoses (8 points of potential leaks)
Plenum gasket
Plenum fittings (2 on drivers side, 1 on back of passenger side)
Brake booster hoses
PCV hoses
All of the intake piping near throttle body (2 fittings on passenger side, 3 on drivers side)
Fuel regulator and dampener
Also check the caps on the balance tube.

[ThisIsSparTTa]

Thanks, I was going to grab some starter fluid today. Can you better define the "Plenum fittings"? I probably know what you're talking about but the terminology is throwing me. Also, what caps on the balance tube? Right now I haven't deleted enough to have a vac line cap on it, but maybe you're referring to something else.
Also, while I definitely have the possibility of other smaller leaks in those locations,that I will try to be investigating soon, this one is HUGE, and I think from the Plenum gasket. The starter fluid or similar should help verify that today.

Also, for reference here is my current vac hose arrangement:

[t.mcginley.jr]

He's talking about the brass fittings that screw into the sides of the plenum, like the one for the recirc valve and brake booster. They look like this:



or this



But I doubt that's your problem if you didn't remove them.

Your problem is most likely the gasket between the plenum and lower intake, like you think. It's easiest to sit the upper plenum down on the gasket if you have a helper. You can buy some studs to help too so that you just lower it down on the studs and then replace the studs with bolts. But you can also just have a helper hold the other side of it, put a bolt thru one hole in the back and one in the front and then both of you slowly lower it. Then just make sure you each have the bolt lined up with a hole before lowering it completely. Kinda hard to describe it in words..

[ThisIsSparTTa]

Thanks for the verification. I didn't mess with those and they aren't the source of the huge leak, but I will be getting a boost leak tester soon once everything runs decent. I will actually have a helper when I do it this time, but I may also pick up dome studs today while I'm out and about.

[t.mcginley.jr]

It's the easiest way and you only need like 4 of them but I guess you could get all 8 if you wanted. Just make sure to put the gasket on over the studs so that they hold it in place while you lower the plenum on

[KornFlakeZ]

On my engine, i used a little bit of gasket maker on the lower intake manifold then put the gasket on top and let it dry. Then i lowered the plenum on top without worrying about the gasket moving and developing leaks. You could try that if you want... to be on the safe side you know

[ThisIsSparTTa]

Long story short, did starter fluid test, pinpointed a small area, did plenum pull, tried using all ultra-grey liquid gasket instead of the paper-based on what I've seen mentioned other places, used studs and a helper to lower plenum. Got back together, still massive air leak, basically in the same spot. I'll show a diagram soon to better explain and ask for help, but I am swamped with work atm. I have a second suspect, and I've seen that fuel rail insulators (i used new) can get pinched causing a vac leak, which could be why the leak remained in the same place, or could be bad luck. We'll have to see. I'll give more updates soon.

[t.mcginley.jr]

When you get a chance, start it up and then try smelling around where the fuel injectors are. Like get your nose in there and smell. If you smell fuel then something isn't sealed right.

[ThisIsSparTTa]

It doesn't really smell. If the engine runs for a long time it smells slightly like exhaust, but it's still not strong. I haven't smelled any fuel smells. Still, if there was a vac leak around the fuel rail insulator, it would be pulling air in, so would I expect a gas smell?

[ThisIsSparTTa]

Below is the synopsis of what we've found. Ignore the yellow and green circles. From using a straw with the starter fluid the leak seems to be focused in the red area. The blue arrows represent targeted sprays with the starter fluid. Note that even using the straw, the stuff spreads around, so its tough to get an exact location of the problem.



I've also sprayed a lot of other stuff too. Passenger side seems to have no problems. Sprayed all over the IACV/AAC assembly, no results. The sound and the starter fluid reaction seem to be focused in this area. I personally think its odd that the plenum didn't seal properly here 2x in a row. I guess technically its within the realm of possibilities the upper plenum got cracked, warped damaged or something while it was out, but I would consider this doubtful. The lower plenum was basically untouched as far as things go, so I'd be confused if a problem developed down there. Do note that before my plenum pull I definitely did not have this massive leak. Also, above I noted that I did do the valve cover gaskets. I've targeted the valve cover a lot, with no results.

I think my plan at the moment is to order new fuel rail insulator, upper o-ring and lower o-ring for injector 6. I will also reseal the plenum again with RTV ultra-grey, but this time I will let it sit longer. However, I will gladly accept any other input.

[Ace2cool]

You're still using the plenum gasket, right? Not just RTV? Just want to make sure.

Sounds like you've got a good plan.

[ThisIsSparTTa]

After some reading and some advice from a local z32er that did his with just RTV, we did just got with RTV-only this time. We were thinking that RTV+Paper could make problems too. I do still have an extra paper plenum gasket from one of the kits I ordered before though.

And yea, put in the order for the stuff above and some IACV/AAC connectors to CZP this afternoon. Props to Coz. I wasn't sure which fuel rail insulator I needed (91 engine but with injector adapters), and it was $1.5 more to add both, and I didn't feel like calling in, but he noticed that and called me and asked what I was up to and saved me $1.50 haha.

[Z-owned]

I have seen before where people when putting the plenum back on pinch the det sensor wire between the upper and lower plenum at the back of the engine which would cause a huge vacuum leak.

[ThisIsSparTTa]

Someone before me cut the knock sensor wire right off the wiring harness (didn't even bother resistor trick). There is actually a little bit of the sensor wiring insulation sticking out but it's not in a place to get in the way. Thanks for the thought though. I'm still open to ideas. The last thing I want to do is do another pull and have the problem remain.

[t.mcginley.jr]

Did you make sure that the fuel rail ground strap isn't pinched between the upper and lower intakes? It's attached to the bolt in the center of the area you highlighted. Although I doubt it, the metal connector on the ground strap could've gotten pinched and caused a vacuum leak.

[ThisIsSparTTa]

Yup, sure. Its actually connected to the VTC screw holes (I didn't do this) because the hole for the ground screw is stripped

[t.mcginley.jr]

Hmm. It's almost like either the upper or lower intake is warped, but if it sealed right originally there's really no way for that to happen while it's off the car.. It has to be something related to the fuel rail because there's nothing else in that area. You didn't actually take the lower intake of did you?

[ThisIsSparTTa]

Warping or crack I think has to be in the realm of possibilities at this point, but I agree I don't know how this would have happened. I did not take the lower plenum off, so it shouldn't have had anything that could have damaged it. The upper plenum was off, and did get moved around some as I cut off the opening for injector #1 for the late style injectors, but even at that, I doubt that could have warped or cracked the upper plenum.

I am going to check both upper and lower much more closely when I get it back apart for anything suspect. I'm also going to replace fuel rail insulator and o-rings for injector #6 just to be safe. I'm also going to probably be a little extra liberal in the problem area with the RTV. Not so much to make a mess, but enough that there should be no doubt. I'm also going to give it longer to set this time before cranking.

[ThisIsSparTTa]

A quick update for those following. Pulled plenum off. My all-RTV seal looked solid in the region of interest, but I guess its possible it didn't seal properly or sit long enough. No visible cracking/warping to upper or lower plenum, but I'm going to do a better inspection on Wednesday. Then I will redo the fuel rail insulator and injector o-rings and put this bad boy all back together and hope for better results!

[t.mcginley.jr]

You'll be able to tell if the injector o-rings got messed up because they WILL be shredded looking (ask me how I know )

As for the RTV, unless either of the surfaces is warped, the paper gasket should be enough to seal it. So it is possible one or the other is warped.

[ThisIsSparTTa]

I think I figured it out! When I pulled the #6 injector (from the problem area), the o-ring had rolled up from the adapter cap onto the area where the fuel gets sucked into the injector. This would explain both why the cylinder wasn't firing, and the air leak. I presume the ring was effectively blocking the fuel from getting sucked in, while simultaneously the injector wasn't sealing properly, hence the huge air sound. I guess I'm pretty lucky that something worse didn't happen. Here's a pic of the injector with the ring in the normal place, and then imagine that ring rolled up onto the fuel input area:



Anyways, as far as other things, the upper/lower plenum doesn't appear cracked or warped. I don't see any other defects that would have been causing this. For now, when I ordered new o-rings, I didn't get that middle one that had rolled up. I'm going to call CZP tomorrow and see if they think I can reuse it since the engine has only run ~1 hour on it not under load. I'll probably just end up getting a new ring to be sure, because I don't want to do this again. After some heli-coiling on the lower plenum, this will probably go back together the weekend after this, and we're going to hope there's no more massive leaks!

[t.mcginley.jr]

Yeah that was definitely your problem, simultaneous fuel blockage and vacuum leak. As long as the o-ring isn't shredded or broken at all it should be fine, but better safe then sorry.

[ThisIsSparTTa]

So, replacing the o-rings definitely fixed the air leak problem, and I just went with a paper gasket. After tinkering with the PTU wiring a bit I was back running on 6 cylinders, and everything appeared fine. So mark, the topic of this thread done.

Unfortunately on my test drive I developed what I believe was rod knock, which we'll explore in another thread soon. Long story short, result was engine cut straight out, no stumbling, etc at a stop light and wouldn't start again. I will have to do some troubleshooting on the starting and fuel system, but I'm thinking once I try to turn the engine by hand its going to be seized.

So, after probably 50hrs of work and a nice sum of change, I got to drive my Z for 25 minutes, then get her towed home. Pretty bummed about that.

[t.mcginley.jr]

Wow man talk about the worst luck. How many miles are on your car/engine anyway?? are you sure its rod knock?

[ThisIsSparTTa]

Not 100% sure. Going to solicit opinions from the internet via a video I took before the engine completely died. It was definitely a mechanical and consistent noise that followed the RPMs, including at idle that definitely wasn't there before. Initially as we were driving it, I noted that I had lifter tick before, and it did sound louder than I remembered, but I hadn't driven her in 3 months and only had her 3 months beforehand. The further we drove, the louder and more distinct it got where I was pretty sure it wasn't lifter tick. With the hood up, my friend that was with me helping out said he had heard the sound before and it was a rod knock on someone else's 300ZX. Anywho, like I said, I will cover that topic in a new thread soon, probably once I do some troubleshooting on the fuel and starting system.

[dayjavid]

I apologize if this is a bit too late and since his original problem was resolved.
In the most recent update, I see that there was a subsequent problem.

Could someone either point me in the right direction to that discussion (if it exists) or let me know if this could be caused by not replacing the injector o-ring?

I had been doing some other reading as I recently did my first plenum pull and I found this..

Install new OEM upper and lower O-Rings.

Note: This step CANNOT BE SKIPPED. It's not one of those things where you can think "I know I should, but I don't have the time/money/patience to so I will in the future." Injector O-rings are a compression type that can only be used once, and after they've been removed, they cannot be used again. Failure to replace these o-rings will cause a fuel leak, and a fuel leak into the cylinder can (and will) hydrolock the motor, which can cause complete engine failure.

Source: http://z32.wikispaces.com/Fuel+Injector+Replacement

Could that be the issue that was experienced? Again, I apologize for posting to an older thread.

Thanks all

[ThisIsSparTTa]

I replaced all o-rings and fuel rail insulators with new during the original pull. As far as the subsequent mechanical failure, I'm certainly suspicious of problems caused by the injector/o-ring, but the engine did have 165k on it...so it might have been its time. I never drove the car with the air leak problem, although it probably ended up running for ~1hour with the problem basically at idle. Once I got all 6 cylinders firing properly and the leak fixed etc, the engine was idling normally. The problem built up slowly over several minutes of driving.

Anyways, I've put in an order to IPP for a new Stage 1 shortblock and working on getting my engine to get pulled at the moment. It's definitely a good bit of work, but I'm hoping it will all work out alright in the end. It will probably be mid-June before I get everything put back together completely.