[Gepetto]

It finally happened. I went to start my car Saturday...and I think the engine backfired into the plenum, shooting it upward and hitting the tea tray on my hood, sending it flying several feet in the air and narrowly missing an innocent bystander.

I've sorted the engine out and it's fine, but could use some advice getting the tray back on. I'm thinking some sort of epoxy to get the bolts back in place, but not sure which one to use. Any thoughts? Thanks in advance.

 

[alfaparticle]

Serpent autosport sell a very nice aluminum louvered tea tray that is held on with stainless nuts and screws.

Body Kits

Body Kits and Spoiler offerings

www.serpentautosport.com

 

[alfaloco]

Loctite or Permatex makes epoxy products that will re-attach those bolts. It looks like they were molded in to begin with, into a hex socket molded into the FRP panel.

Tip: You may already know, but there is a small adjustment screw on the front side of the throttle body, which sometimes gets fiddled with to adjust the idle speed (wrong...). It's located just next to the cable swivel. Check to see if the throttle plate is being slightly held open by this small screw. There should be a very small clearance between the throttle stop and this screw, you don't want the throttle plate held open at all, it could contribute to a backfire. (thanks Alfa BB...)

My son Mike really wanted that louvered aluminum tea tray from Serpent Autosport that Ed mentions, so he got one for his birthday and we installed it. Mike did want the bolts concealed though, so we put black plastic caps over the bolt heads. Charlie does a very nice job on the wrinkle finish black on those tea trays. And yes, a LOT of heat is expelled through there, especially with the AC running.

 

[Gepetto]

Loctite or Permatex makes epoxy products that will re-attach those bolts. It looks like they were molded in to begin with, into a hex socket molded into the FRP panel.

Tip: You may already know, but there is a small adjustment screw on the front side of the throttle body, which sometimes gets fiddled with to adjust the idle speed (wrong...). It's located just next to the cable swivel. Check to see if the throttle plate is being slightly held open by this small screw. There should be a very small clearance between the throttle stop and this screw, you don't want the throttle plate held open at all, it could contribute to a backfire. (thanks Alfa BB...)

My son Mike really wanted that louvered aluminum tea tray from Serpent Autosport that Ed mentions, so he got one for his birthday and we installed it. Mike did want the bolts concealed though, so we put black plastic caps over the bolt heads. Charlie does a very nice job on the wrinkle finish black on those tea trays. And yes, a LOT of heat is expelled through there, especially with the AC running.

Thanks! Does water get into the louvered tea tray when it rains? (Granted, I likely will not be driving the car in the rain, but I haven't gotten caught in the rain a couple times.)

I've heard of a new kind of epoxy that uses UV light to cure very quickly, but I don't know which brand is best. I may just do Permatex or Loctite (I've had good experiences with both their products).

I think I know what I did wrong to cause the backfire. The previous week, I rolled my car out of the garage to make adjustments to the steering wheel hub (horn wasn't working). Since it was on a slight incline, I turned the car on and moved it back inside. 5 or 7 seconds total from start to off (it was a cold start). I bet the extra fuel thrown in by the cold-start injector, and not actually being burned, contributed to this.

 

[Del]

Keep in mind that some of the heated air coming out of that open tea tray ends up going in the HVAC inlet at the base of the windshield, introducing hot air into the cabin.

I think that the tea tray idea came from when the engineers discovered that one could easily pop the intake plenum off if the driver tried to start the car with the throttle held open any amount, they decided to put in a release panel, ie, the tea tray, in order to prevent damage to the hood itself, much more difficult to repair if dented. Lol, our Milano, which has no such panel, has had for a very long time a very tiny bump in the middle of the hood. Yup, when we first got the car, I accidentally held the throttle open a little as I used to do on previous Alfas. Kaboom!

 

[alfaloco]

As to rainwater I purposely washed the car with the motor running to see if dripping water would affect anything, with no issues of misfire or stumbling. Now granted that was not a deluge test, which could maybe allow way too much water over the plug leads. In that case I suggested to Mike he keep some heavy gauge aluminum foil in the back, if he ever gets caught in a heavy downpour he could just cover the top of the motor across the plenum, tuck it under so it sits there.
Del mentioned the hot air getting pulled into the cowl vents, but I haven't noticed any difference. Probably because the louvers are centered on the hood., while the vents are on the L and R sides. Once the hot air blows out the breeze seems to disperse it anyway.

 

[alfaparticle]

I ran the louvered tray for a couple of years and it was on the car when I sold it. No downsides for me. I bought the un-painted one and painted it satin black to match the trim. Getting rid of some heat from around the plenum has to help.

 

[boxandboat]

Sometimes, I think every single GTV6 with a stock plenum will pot it underneath.

 

[alfaparticle]

Popping off the plenum seems to be an L-Jet thing. It was never a problem for me after I installed Megasquirt.

 

[planetmojo2]

Since the original question seemed to be about fixing the tea tray, I've repaired a few of those over the years. Usually, 1 or 2 nuts has frozen up on the studs and the head of the stud breaks away from the plastic. As Loco mentioned, the studs are molded in. My method of repair is to get some stainless metric bolts that match the nuts, and are about the same length as the originals. Easily found at a hardware store or Home Depot. The hex heads on the bolts, as I remember, are a bit larger than the stud heads they used in the molding process. So with a Dremel tool I open the pockets in the plastic a bit so that the hex heads sit flush. Then bond them in place with epoxy. I've had good luck with JB Weld Plastic Bonder. If you want to get a clean flush 'mesa' on the epoxy, you can put a film of Vaseline on a washer (as a mold release) that has a fairly snug fit to the stud diameter. Push the washer over the stud so it's flush to the flange on the perimeter of the plastic before the epoxy starts to kick, and remove washer after the epoxy has set. Saves some time in not having to whittle away any extra epoxy that may be above that level. After you've replaced all the studs, you can add some extra epoxy around the base of any bonds that look like they could use a bit more reinforcement.

Also, there is a white foam gasket that sits in a groove near the perimeter if your tea tray is complete. Doesn't look like it would be very effective as a seal to keep water out as it's porous. But you can replace that with a similar foam, or maybe a 'noodle' of rubber would make a better seal.

 

[Zinhead]

911's of the same vintage had a similar problem to the extent that the aftermarket developed a pop-off valve to relieve pressure in case of a backfire. I wonder if this could be adaptable to our cars.

911 Pop Off Valve

 

[alfaparticle]

Those 911's had K-Jetronic so maybe my L-Jet theory is wrong?

 

[alfaloco]

911's of the same vintage had a similar problem to the extent that the aftermarket developed a pop-off valve to relieve pressure in case of a backfire. I wonder if this could be adaptable to our cars.

911 Pop Off Valve

I looked at that 911 pop-off relief disc when I was researching a way to minimize or eliminate the V6 plenum pop. That solution is ideal since it installs into the airbox, whereas space is limited on our cast aluminum plenums. It's simple, spring loaded and has a seal. The ribbing on the top of the plenum and the limited hood clearance makes it tough to come up with a similar pop-off disc. Any effective pressure relief device must fit downstream of the throttle plate, which is bolted right onto our plenum flange.

 

[Baz70]

anyone filmed a backfire with the plenum popping off? just curious to see it....

 

[alfaloco]

anyone filmed a backfire with the plenum popping off? just curious to see it....

It might be a wee bit hard to catch that event!

 

[Del]

A cam in the windshield, like many seem to have these days? If it happened it would be caught by the cam.

 

[alfaloco]

Guys I'm not curious to see it again, after all its pretty rare. What I did was to make modifications to hopefully prevent it.
But I'll look up the photos and put that in its own post. Suffice to say it's a nice little bang when it does happen. It just blows the plenum off the intake tubes.

 

[yvesmontreal]

Those 911's had K-Jetronic so maybe my L-Jet theory is wrong?

Porsche shops do sell the pop off valve for CIS (K Jetronic) 911s.

When I got my GTV6, the tea tray had been sealed from the inside with some house sealant. The fellow who had worked on the car for the PO explained that he found plenty of water in the V of the engine block, which had dripped from the tray surrounds. He did the sealing. He had also found the spark plug tubes on the left bank full of water. I later found out that the resistance on ignition wires 4-5-6 was way out, needing a new set of wires. Having the built in resistors soaked in water for a while didn't do them any good.

 

[Gepetto]

anyone filmed a backfire with the plenum popping off? just curious to see it....

I wish I had. In my garage, with the echo, it sorta sounded like an M80. (Maybe I'm exaggerating, but not a whole lot).

 

[cda951]

To all of those asking about why this happens, see my post #5 in another recent thread:

#5

Cliff's Notes version: the Bosch L-jet and K-Jet (CIS) systems use the exact same primitive system of a single, crudely modulated cold start injector, which causes uneven distribution of the air-fuel mixture. Combine this with old, flaky wiring, thermo-time switch, sticking auxiliary air regulator, vacuum leaks, etc, then you have a recipe for a pop-back