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1985.5 Porsche 944 Engine Hesitation

Old 01-06-2019, 03:07 PM
  #31  
pointFive
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Feeling a bit disheartened...

Still haven't been able to identify the root cause of the hesitation/sputter...

Over the Holiday's I had time to do the following:
  • Replaced engine mounts
  • Replaced intermediate steering shaft
  • Replaced brake booster
  • Replaced brake master cylinder
  • Tested AFM and re-positioned wiper arm
  • Tested AFM relay
Here are some things I think "may" be the culprit to the hesitation/sputter after everything I've done so far:
  • Water temp gauge fluctuates. Had thermostat replaced in August (rated for 80░C/176░F). At times it'll hit 100░C...
  • Cam tower gasket oil leak
  • Incorrect adjustment after installing TPS sensor?
  • Incorrect idle speed adjustment tuning? (referred to Clarks-garage. Adjusted idle after running the engine for 10 minutes...)
  • O2 sensor out of spec?
  • Possible intake and exhaust manifold leaks?
Any additional input would be very helpful!
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Old 01-06-2019, 04:41 PM
  #32  
pointFive
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I've started a photo album, for visualization...

https://photos.app.goo.gl/gAbFuiRryGrdn3r6A
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Old 01-06-2019, 06:29 PM
  #33  
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Originally Posted by pointFive View Post
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.
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Old 01-08-2019, 06:51 PM
  #34  
pointFive
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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...

Thoughts?
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Old 01-08-2019, 07:16 PM
  #35  
Dan Martinic
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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
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Old 01-08-2019, 07:24 PM
  #36  
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Originally Posted by Dan Martinic View Post
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.
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Old 01-09-2019, 12:29 AM
  #37  
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When the AOS seals fail you'll know it. Oil throughout the intake system.
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Old 01-10-2019, 09:17 PM
  #38  
pointFive
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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...
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Old 01-11-2019, 12:17 AM
  #39  
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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.
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Old 01-11-2019, 09:32 AM
  #40  
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Originally Posted by pointFive;15557109.

[utag=110213
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.
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