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I spent some time on the 944 this morning hoping to pinpoint the issue...I checked the gap of the spark plugs and re-gapped them to 0.029". I did notice the terminal threaded tops were loose so I carefully tightened them with some pliers. The plugs I installed are Bosch WR8DS and the wires were replace as well(Beru)...
I also cleaned the throttle body; which had a good amount of oil buildup, the throttle position sensor, and replaced the fuel filter, yet, there is still a hesitation at idle and "popping" from the exhaust... Attached is a picture of an old plug (all having the same wear) and the throttle body before I cleaned it...maybe they'll help diagnosis the issue.
Is there a vacuum line diagram available for the 944 8v? Maybe there's a hose/line that I was unable to catch...and speaking of vacuum lines/hoses, what's their purpose? I'm hoping the injectors haven't failed because they are quite expensive..Lastly, are there detrimental effects to the engine if I drive the car while I'm self-diagnosing it? At the moment it's my daily driver...
I believe the oil deposit in the throttle body is the precursor to the hesitation issue. There should be no oily deposit oinside the throttle body. Trace all the air piping connection upstream of the throttle body and determine what each connects to.
What is the source of oil? It is probably the engine crank case. What parts attach to the crank case? Is one of those parts letting excessive oil vapor into the intake because the internals of the part failed. Maybe a source of unmeterrd combustion air. Popping at exhaust indicated a lean mixture.
@T&T Racing Thanks for your input! Could you go more into detail about connection(s) "upstream" of the throttle body? What areas could let excessive oil vapor into the intake?
Also, I just realized my car was built for CA emissions. Are there specific settings/adjustments for these cars; for instance, idle speed adjustment? The car could be receiving too much air, creating a lean mixture, since I tinkered with the idle speed valve (on the throttle body) and installed a throttle response cam...
He's referring to the connections before the throttle body (other than crankcase venting via air/oil separator, air is flowing from air cleaner to throttle body, therefore before TB equals "upstream"
From my reading of the procedures in the workshop manuals, there is no difference between California cars and the rest of North America
He's referring to the connections before the throttle body (other than crankcase venting via air/oil separator, air is flowing from air cleaner to throttle body, therefore before TB equals "upstream"
From my reading of the procedures in the workshop manuals, there is no difference between California cars and the rest of North America
Hi PointFive, I believe the culprit is the air/oil separator and the outlet has a hose that connects to the air intake. Refer to https://rennlist.com/forums/924-931-944-951-968-forum/695981-oil-filler-separator-is-on-a-944-a.html, The air/oil separator is the unit with the yellow top where oil is added to the engine.
@Swenny I will have to make a note to replace the AOS seals as preventative maintenance. Thankfully, the air filter compartment/housing was very clean and dry. Nothing like the picture you posted...
@T&T Racing What could cause a lean mixture? Just today, I disconnected the o2 sensor (at the back of the engine) to see if there were any changes in the behavior of the car. At first, I thought I may have found the issue, but the popping/sputtering at the exhaust reappeared...several things I noticed during this test:
Lots of smoke from the exhaust (white/gray)
The engine hesitation/exhaust sputter started to happen more frequently as the engine was heating up
Again, to reiterate the problem here; the car has a strange hesitation and a "popping" sound can be heard at the exhaust. A strong smell of gas arises during hard acceleration. I've installed a throttle response cam and have adjusted the idle speed at the throttle body. At the top of this thread is everything that has been replaced/tested thus far...
My guess with the white/grey smoke and the popping from the exhaust is that you need a head job and/or rings. The AOS is the easiest thing to check first,the seals slowly fail until one day you're putting the petal down and then poof! Oil throughout the intake.You've checked that so a valve,ring job or even the worst case- worn out cylinders. A compression test and a leak down test could confirm that.
T&T Racing[/utag] What could cause a lean mixture? Just today, I disconnected the o2 sensor (at the back of the engine) to see if there were any changes in the behavior of the car. At first, I thought I may have found the issue, but the popping/sputtering at the exhaust reappeared...several things I noticed during this test:
Lots of smoke from the exhaust (white/gray)
The engine hesitation/exhaust sputter started to happen more frequently as the engine was heating up
Again, to reiterate the problem here; the car has a strange hesitation and a "popping" sound can be heard at the exhaust. A strong smell of gas arises during hard acceleration. I've installed a throttle response cam and have adjusted the idle speed at the throttle body. At the top of this thread is everything that has been replaced/tested thus far...
Leaking AOS seals allows air and crankcase vapors to enter intake manifold after the AFM, This is unmetered combustion air so it is increasing the volume/mass of air flow without an increase in fuel flow, ie lean mixture. The O2 sensor cannot not compensate for the mass of air flow increase.
I did, however, notice an additional bung next to the O2 sensor as I was under the car. I traced the metal pipe, coming from the additional bung, and it seems to have been plugged by the previous owner at some time in time...
The last things I plan on doing before taking it to the shop:
Replace AOS seals
Replace intake manifold gaskets
Check various hoses underneath intake manifold
I greatly appreciate everyone's input! I hope to resolve this issue soon!
I did, however, notice an additional bung next to the O2 sensor as I was under the car. I traced the metal pipe, coming from the additional bung, and it seems to have been plugged by the previous owner at some time in time...
The last things I plan on doing before taking it to the shop:
Replace AOS seals
Replace intake manifold gaskets
Check various hoses underneath intake manifold
I greatly appreciate everyone's input! I hope to resolve this issue soon!
Is this a common issue among Porsche 944's?
Are you talking about the pipe to measure CO2? It comes from a bung on the crossover pipe up into the rear of the engine. A blue cap? I guess dealers used to use it but I doubt anyone bothers today
Did you ever check that the fuel pressure regulator is working correctly? With exception of the grey sooty spark plug -- your symptoms mirrored ones I had with my 86. It turned out to be a failed diaphragm in the fuel pressure regulator. The vac system was sucking fuel past the failed diaphragm causing a rich condition that mimics your videos. Only diff was my plugs were dirty and wet. Try putting vac on the output vac line on the FPR and if you see fuel -- it has failed.
01-06-2019, 02:07 PM
