83 Porsche 944 NA popping sound

[thomas944]

Recently replaced head gasket, put everything back in place and tried to start it. After few cranks, engine fired but wont idle so i pump the gas pedal to keep it running. I have my dad feather the throttle body ( i think thats the correct terminology). When doing this we both hear popping sound from the intake manifold area (#3 or 4 cylinder). What causes this to pop? Please help.

[GreenWater]

Could it be backfiring from one cylinder? Intermittent spark to one cylinder? Maybe distributor cap, if the terminals on the inside are worn, or one is worn badly, maybe that could do it. Does it pop when holding constant throttle or while gasing it, or while letting off?

[GreenWater]

Is the timing belt on right? Did you get the timing lined back up when you put the belt on?

www.only944.com/repairguides/ Awesome 944 parts

[alan6272]

how about correct firing order? Or maybe bad seal between mass air flow and throttle body rubber snorkel? Another thought could be maybe a valve or two not seating, a compression check will help there.

[porschetub]

My 2.7 did the same the PO had changed inlet manifold gaskets and one was completely unseated ,i could here the air leak @ this point.
Replaced all gaskets with thinner ones as the factory type are too think( IMHO) as the manifold will sink into them and the bolts become loose and cause a leak.
My other 2.5 motor had loose nuts also with the "thick"stock gaskets.
Have a good look for leaks in other areas as mentioned.

[thomas944]

Greenwater: The timing belt is on properly. Just checked that today. It does sound like it is backfiring from the 3rd or 4th cyl. Im pretty sure the distributor is ok because it looks like the PO had replaced it.(extremely clean). The popping sound comes while letting off the gas. The car only pops once while letting off. It doesn't pop constantly while losing RPMs.

Alan: Ive checked the spark wires too many times to count and they all look to be going to the correct cyl. Where is the rubber snorkel? Is it the large 3-4" black C shaped hose? We ran a compression check on all four cylinders and they were roughly the same psi. I dont remember what the numbers were. Do you know off hand what the range should be?

Porschetub: I do hear a hissing sound when the car is running usually while letting off the gas. That may be one reason it is popping or isnt idleing at all. I remember seeing that the gaskets on the intake manifold while tearing it down did have some kind of sealant on them. Could this be a solution to the hissing and popping? Could tightening the intake manifold bolts be another?

[porschetub]

Originally Posted by thomas944

Greenwater: The timing belt is on properly. Just checked that today. It does sound like it is backfiring from the 3rd or 4th cyl. Im pretty sure the distributor is ok because it looks like the PO had replaced it.(extremely clean). The popping sound comes while letting off the gas. The car only pops once while letting off. It doesn't pop constantly while losing RPMs.

Alan: Ive checked the spark wires too many times to count and they all look to be going to the correct cyl. Where is the rubber snorkel? Is it the large 3-4" black C shaped hose? We ran a compression check on all four cylinders and they were roughly the same psi. I dont remember what the numbers were. Do you know off hand what the range should be?

Porschetub: I do hear a hissing sound when the car is running usually while letting off the gas. That may be one reason it is popping or isnt idleing at all. I remember seeing that the gaskets on the intake manifold while tearing it down did have some kind of sealant on them. Could this be a solution to the hissing and popping? Could tightening the intake manifold bolts be another?

The inlet mainfold gaskets should be fitted without sealant,carefully try retightning but not too tight as you can pull the studs from the head,then you have a new issue.Best of luck,cheers

[alan6272]

Yes the snorkle is the c shape rubber hose, if there is a leak anywhere there it will greatly affect the way the motor runs. The computer reads the amount of air flow into the intake to properly ajust fuel and ignition.

[nynor]

you forgot a large vacuum hose at the bottom of the intake manifold. yep, been there and done that with my '83. IIRC, only the '83 (possibly the '84) has that particular hose.

[nynor]

timing belt/cyl head update

[thomas944]

Nynor: Is the hose between the head/block and the intake manifold or somewhat visible from right of intake manifold when looking at the engine from the front of the car? Hopefully its some stupid but important hose not connected.

[nynor]

the hose i am referring to is literally on the bottom center of the main part of the intake manifold. i think that if you take the airbox and intake hose off, you may be able to reach under there and feel the nipple on the intake.

[nynor]

the top half of this picture shows what i am talking about. the manifold in the picture is oriented upside down:

[thomas944]

Ok. Ill make sure to check for that this weekend. What is the difference between the two? Is one for an earlier model or what?

[nynor]

the upper manifold is most likely from an '83. the lower is from a later car, like i stated in my first post on this thread.

[thomas944]

Sorry for not following up on this but I did find the leak and it was exactly the hose nynor had pointed out. Your help is greatly appreciated. Thankyou

[nynor]

my pleasure. i hope it is all sorted.

darell