79 911 SC sputtering

[kmlco]

recently bought 911 , 109,000 miles , engine sputters @ all gears on acceleration low rpm. I replaced all injectors, sleeves, and o rings. / new plugs, checked for obvious vacuum leaks, no improvement. engine will not idle up or down after taking off oil cap. All emission control devices have been removed: pump, check valve, and diverter valve. On cold start engine will idle up , then after warm up will idle down, but after highway warm up normal operating temp , engine will not idle down. Main concern right now is solving the sputtering , seems to go away @ higher rpm's. Need help.

[ossiblue]

Originally Posted by kmlco

recently bought 911 , 109,000 miles , engine sputters @ all gears on acceleration low rpm. I replaced all injectors, sleeves, and o rings. / new plugs, checked for obvious vacuum leaks, no improvement. engine will not idle up or down after taking off oil cap. All emission control devices have been removed: pump, check valve, and diverter valve. On cold start engine will idle up , then after warm up will idle down, but after highway warm up normal operating temp , engine will not idle down. Main concern right now is solving the sputtering , seems to go away @ higher rpm's. Need help.

Please be a little more specific in what you mean by "sputters." Is it an engine miss, hesitation, or backfire/pop through the intake or exhaust?

Though you checked for vacuum leaks, your symptoms still indicate a vacuum leak, especially because they appear after the engine is warmed and the fuel mixture has been leaned out by the WUR. Taking off the oil cap with no change in idle also indicates there is unmetered air entering the intake. First step, IMO, would be to do a comprehensive check for vacuum/air leaks as I'd wager you still have leaking air, somewhere.

[kmlco]

none of the above really. sputtering only occurs while driving , cant hear it when just throttling up in neutral.
no backfire , hesitation , or misfire indicating electrical that I can determine.
faulty ignition wire?
when i rev engine in neural I hear some slaping noise near distributor , could it be worn?

[kmlco]

sputtering or like popping thru exhaust would be more like it.

[kmlco]

sputtering more like popping out of exhaust ,not really misfire or back fire like an electrical problem.
since all injectors and o rings replaced what is best guess on where air leak could be?

[kmlco]

sputtering or more like popping thru exhaust , not really misfire and doesn't backfire like and electrical problom. since all injectors , sleeves and o rings replaced, what's best guess on where air leak is?

[kennykimk2]

My need a new CDI. I had similar situation where the car cuts off at idle. Replaced the CDI and now runs like a champ.
Hope you get the SC running right.

[kmlco]

what did you mean by cuts off at idle? Mine idles fine just a fast idle @ normal temp. Possibly aux air valve?

[kmlco]

not up on abbrevations/ CDI?

[Bob Kontak]

Originally Posted by kmlco

what did you mean by cuts off at idle? Mine idles fine just a fast idle @ normal temp. Possibly aux air valve?

Skip the dead box right now.

You have a moderate air leak. Don't try to speculate. It is of no value. You are simply sucking air and you are confusing the system. Find the leak.

Get a couple cans of brake cleaner at the local auto parts store to test your air seal integrity.

Since you are absolutely sure there are no issues with the injector o-rings, start there first. Put the skinny plastic line on the can and spray into the o-ring area. Just a spritz. Idle will change if you are sucking air there. My experience is the idle will drop if the fluid can slide by. Don't know why. Just what I have observed.

Next, spray at the base of the intake runners where they meet the heads. For me, this is the only potential air leak area where I have found the exhaust to "putt-putt" semi-backfire from an air leak.

Open your air-box (air cleaner). Spray around the pop-off valve base.

Then start to expand. Where runners meet air-box. Sides of air-box. Back of air-box. Bellows mating to air flow sensor and throttle body.

Don't be a pig with spraying. Just a spritz in the right place will do the trick. Idle change.

On the 79, there is a fat rubber tube that goes from the back of the bellows to the oil tank. Inside this tube near the oil tank mating there is a restrictor. This allows you to check your oil level with engine running but not kill the engine. If you pull it off the oil tank, you can look into the end of the hose and see a cone that reduces the air allowed to be sucked into the system. Both ends need to be tight. Oil tank and bellows.

Then you have the brake booster fed by a hose from the engine to the front of the car. Occasionally a problem.

None of this as effective as the pressure test where you force air into the system with engine off - not lots - just some air - reverse shop vac - 10psi from an air compressor - and use kids bubble blowing liquid in a spray bottle and look for bubbles that appear as air escapes.

If you are seriously into getting you car running correctly this (pressure test) is the method boyt911sc (AKA Tony) recommends. Tony = CIS God. It takes some time to set up but once set up, you can go to town with the bubble mix and you won't even set yourself on fire - which is a risk with the brake/carb cleaner, starting fluid if you get silly.

Go to search then advanced search then load boyt911sc into the member name field and enter "CIS pressure test" into the left hand side search criteria.

Your best bet is to read right now. Maybe, try the spray trick for finding a big "honkin" air leak fast.

Just do yourself a favor and invest even an entire weekend into eliminating air leaks. I cannot stress this enough.

It's nothing from a dollar perspective. OK, kids bubble solution.

It will set you free even if your aux air regulator is not functioning correctly and that is something we can guide you on.

Good luck. Chin up and all that. Bottom line, suck it up and kill the snake that is biting you....False air.

[kmlco]

now that's the advice I'm looking for !Thanks Bob

[kmlco]

update 79 911sc sputtering /putt-putt noise out of exhaust. /
after spraying brake cleaner @ all suspected areas mentioned , no change in engine idle.
Finally set up shopvac for air vacuum test, no bubbles @ injector seals,sleeves o rings, thankfully since I replaced all of them. No bubbles @ intake runners @ heads or @ air box that I could tell.
After a few more tries, found some leakage /bubbles not major coming out of left side of air box where all four phillips screws fasten box together. Could this slight leakage cause the constant popping / putting noise out the exhaust @ acceleration?
Is there some type of sealant I could try on plastic before getting new gasket for box?
If I have to go that route, what is the most efficient way to replace gasket w/th taking whole injection system off , since I already installed new injectors,sleeves, and o rings.?

[pmax]

Air leakage from intake manifold sleeves

Here's a similar thread from last week ...

[tirwin]

You should thoroughly check the airbox for cracks. Blown airboxes are not uncommon.

Here is a thread that discusses what type of glue to use.

Air Box Repair Myth or Reality ??

Not sure about the longevity of the proposed fix but definitely cheaper than a new airbox.

Also, if you have a pop-off valve installed, make sure it has a good seal around it. Sometimes whatever the installer used to bond or adhere it to the plastic cracks or deteriorates with age and heat cycles and it can eventually let air by.

[Zaz]

I'd go underneath and check the exhaust, esp if it's old, and look hard at the muffler gasket flanges.

[theiceman]

if those screw holds are strained and leaking I am thinking that airbox as been under some extreme trauma, if its cracked underneath in the air chamber it will be really hard to find.

a couple of things you can check ..

make sure the distributer shaft does not rock back and forth and inspect the distributor and rotor. make sure you don't have a worn bushing.

You may just want to check your head studs since the car is new to you , did you get those checked before purchase ?

[Bob Kontak]

Originally Posted by Zaz

I'd go underneath and check the exhaust, esp if it's old, and look hard at the muffler gasket flanges.

+1. If you can get under while idling you can put your hand near the various flanges and feel for exhaust leakage on top of visual.

When I had the putt putt noise that ended up being an air leak at the base of the intake runner, this was mentioned as a potential cause for a slight backfire. I sort of remember the symptom being a slight back fire on decel though, vs acceleration. Can't remember so don't take my word on it.

It's another due diligence check that will payoff.

[Bob Kontak]

Originally Posted by theiceman

if its cracked underneath in the air chamber it will be really hard to find.

Do the removal of the oil tank cap when the car if fully warm. Idle will not drop when cold. If it does not drop when warm, air leak still.

Another test is to screw that big fat dime sized air bypass screw in all the way when warm. If you can bottom it and your car is not dead or near dead, air leak.

Good job on finding the first air leak, BTW.

Like I mentioned before, it's worth a weekend confirming your false air situation.

[kmlco]

adjusted the air bypass screw while engine a normal temp, and sure enough I was able to idle it down to stall, so my attention turned to exhaust leaks. I asked my son -in -law who has a good mechanical ear to listen @ tailpipe while I hit the gas, he said sounds like exhaust leak , proceeded to check all exhaust gaskets , the heat exchange gaskets looked suspect , so I took them off to replace w/th new gaskets , then took off exhaust valve cover and low and behold @ #1 cylinder head was a broken head stud and its allen nut fell into my hand . I guess there in lies the main problem! So now what Porsche fans ? The only good news is the main problem is solved.

[kmlco]

good call on head studs, didnt hear the poping sound when I bought the car, just my luck.