Popping intake plenum 95 3.6 stock non-vario

[midnight911]

My intake plenum pops and separates. not frequently, but enough to annoy me, especially this time of the year. yesterday, i go out to cold stones to cool myself down and the plenum pops on the way home. tarmac was hot, engine was hot, 10 minute job to put the plenum back together but soaked in sweat, feeling like i had to go back for another ice cream.

how are people preventing this happening? I saw couple of posts around this but the threads did not take me for tips.

CIS motor had pop-off valve trick. something similar can be done for the backfire to escape through?

[Bill Verburg]

There's something wrong w/ your car.

I've seen the intakes pop off during a spin on track where the motor is forced to rotate backward, but never in normal use.

[midnight911]

Bill, hey, ummm, thanks. the list is short but i can handle something a little longer... :-)
the other thread discussed a broken dizzy belt but mine is fine.

[bri450sl]

I have a stock 95 non-vario 993 and have never had this problem. I don't believe I've ever heard any popping and have never had anything separate. How does it seem to run? I would lean towards resolving the popping as I don't think that is normal. Sounds like we have similar setups so ask me anything and hopefully I can be more helpful.

[midnight911]

the difference i have on my car from most stock 993 is that i have a chip from protomotive including some compensation for light weight flywheel. may be this is causing unnatural unburnt fuel in the intake somehow popping between the intake valve and the throttle vane?

I also have a very short exhaust to fit the motor into my 84 chassis. 993 stock HE with two after market cats with a muffler.

what else could "something" be?

[mamut]

Leaking injector, bad lifters.
Stef.

[bri450sl]

Originally Posted by midnight911

the difference i have on my car from most stock 993 is that i have a chip from protomotive including some compensation for light weight flywheel. may be this is causing unnatural unburnt fuel in the intake somehow popping between the intake valve and the throttle vane?

I think you may have hit it on the head right there. If its been altered from stock, I would have to take it to a specialist or a performance shop and let them tell you what they find. It sounds like it may need some tweaking that's out of my expertise.

[Green993]

Does this occur on start-up or just randomly while driving? Has any work been done on the car prior to this happening?

If on start-up it could be a leaking injector. It could also be a timing related problem. I had this very intake popping problem on my 95 993. Mine happened only on start-up and it was NOT the injectors. I tried various things - very frustrating - it would happen randomly every week or so. Ultimately, it was fixed by one of two things. I did them both at the same time so I'm not sure which fixed the problem.

1. Replaced dizzy caps and rotors. The old ones had a black carbonized ring inside.

2. I re-adjusted the flywheel reference sensor. I think it got outta whack during a recent clutch job. From the manual:

The air gap between the sender and the
flywheel ring gear is adjustable and must be
1.0mm plus/minus 0.2 mm.

[Vandit]

Did OP resolve the issue?

[kojo911]

Had this happen a couple times, turned out to be a loose spark plug wire forget which cylinder. Not sure why this would cause pressure back through the intake but it cured it.

[rsscotty]

Check your vacuum line to the fuel pressure regulator to see if there is fuel in it. Regulators can leak fuel into the intake causing such problems as you are experiencing.

[midnight911]

thanks for the inputs. i did find one of the ignition wires tad loose at the distributor but i don't think i ever go to the root cause. i'm just driving with less blipping and that helps unwanted back fire at the wrong timing. the intake has not popped lately.

i'll check the vac line to fuel reg per rsscotty's suggestion...i doubt reg is leaking, but...

thanks again,

[mamut]

Check the spark plug wiring sequence on the lower s/plugs, it might be out of wack.Stef.

[sheriong]

I have been having a similar issue but I think mine is because I have turbocharged the car. However, was advised to go with the rubber sleeves for the 993 Turbo as they are reinforced. Just order a complete set; dealer only part.
biggles