[MLB]

Oh yeah, heater control valve of course, thanks MCL. HCV connection appears OK, havent had excessive cabin heat and the rubber elbow connector looks and feels fine.

I checked all the other vac line connections in the engine compartment (listed below)

Thanks to Bob/Flash for the reminder list and pointer to the sticker on the inside of the hood itself (forgot about that! :0)

 

Warmed up the engine (until both fans came on) and vacuum was a stable 13 in. Hg. but no more.

Engine RPM is stable and looks pretty close to 850-ish.

 

Anyway, from front to back roughly, here are the spots I inspected:

 

1. Supercharger blowoff valve

2. Heater control valve, next to cam sprocket cover

3. Top of Throttle Body

4. At ICV, under the front of the intake manifold

5. side of intake manifold, plenum chamber (I re-sealed this with epoxy)

6. vacuum valve in front of brake booster

       what about the adjacent vacuum solenoid / bleeder valve 944 605 240 02 ($200), #23 in PET 201-20?

       if that failed, would it be open or shut, and could that affect vacuum level?

7. Big hose - brake booster to back of intake manifold

8. Air / oil separator (AOS) and connection to back of intake manifold (PET 107-15)

9. Fuel Pressure Regulator (FPT) at the back of the fuel rail

10. firewall, behind engine, battery side, 2 vac lines pass into cabin via rubber elbows (these feel pliable and look fine)

11. Vacuum canister next to battery

12. vac actuators, either side of cabin air blower (underneath moulded plastic sheet)

 

I guess I need to check back at the fuel tank next? Never been under that cover before.

 

Thanks for the replies so far.

When I get to the bottom of this I bet the car will be running a lot better.

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[MLB]

AHA! moment:

As part of my reading and learning about vacuum related issues, my indie mechanic lent me a 22 yr old magazine article on the many things vacuum can tell you as a diagnostic tool. I may do a write up in a separate thread, but bottom line for my case:

 

a stable but low vacuum reading can often indicate valve timing is off....

BINGO! at least I think so, because

 

A few years ago I had the head refreshed and I replaced the head gasket (among other things) in anticipation of buying a D1R supercharger kit. The person who did the work has a lot of experience with these engines, and he suggested even more timing advance than the stock value published in the workshop manual. So I increased the timing advance by several thousandths, and the car seemed to run really well.

So maybe 13 in. Hg. is the "correct" vacuum value for my current timing setting, but the apparent excess oil consumption is leading me to rethink this strategy.

 

I plan to reset valve timing to the factory setting, and then check vacuum again. Previously it didnt occur to me that engine vacuum could be one indicator of the timing advance.

I suspect the factory setting will restore the stock vacuum level of 19 inches mercury, for what its worth, as Im confident i have no sizable leaks. This summer's driving will tell me if that worked.

 

 

Now, a second AHA! moment was reading flash's thread "stop smoking now" from 2011 in the forum archives. He used an oil additive "flush" and removed a lot of crud from the engine (some in the dirty oil that was then drained, some out the tailpipe) and potentially freeing gummed up piston rings.

 

So, I ask the current forum member-age for feedback; If I suspect rings could be a little gummy (tops of pistons were caked black and I cleaned them to a shine back when I had the head work done) should I consider one of the available oil treatments, where you idle for 10-15 min and drain the dirty oil?

 

Thanks

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[RS Barn]

Idle quality and engine vacuum can be affected by camshaft timing. More specifically when you move cams independently. You can widen lobe centers for more torque or close lobe centers for more top end. This will change vacuum. Adjusting cam timing on 968 move both cams at same time so that doesn't really come into play, but advancing cams together will increase low end and throttle response. I've also found the factory recommended setting has a serious power dip when the variocam switches at 5500. So I do advance timing a bit.

There are several tricks to getting the cam timing spot on. It's not easy. I've coached many individuals and shops and usually find a flaw in their process. Using a degree wheel is the only way to double check your settings.

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[MLB]

Thanks Pete, yeah I did find it difficult to set the timing with dial indicator gauges and achieve a precise value using the procedure in the workshop manual, along with some tips you provided, but I repeated the process multiple times in a row to test my reproducibility and I was satisfied I was getting very close to the same endpoint each time, based on dial readings.

 

My best efforts settled on 18 thousandths timing advance, instead of the factory setting of 15.2 thousandths, or 0.39 mm.

But this might not have been the exact spot for optimal performance. This time around it sounds like using a degree wheel is in order, so thats something new for me to figure out.

It just occurred to me, is there any hope of doing that with the engine in the car?

 

For now, are you saying that further advancing the timing on my car by using just the WSM procedure might not be expected to alter vacuum to as low as 13?

 

You traveling near Madison any time soon?

;0)

 

--Michael

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[Waylander]

I was considering doing this as my HG is still the original at 153k and 26 years, 

 

this cam timing seems to be the hardest part of the while job,

 

is it easier with dial gauges or with degree wheels, i think a few 1000ths off in any direction has a huge effect

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[RS Barn]

There is an absolute cam timing to get best torque and not have HP droop after variocam switches. That said, the timing isn't that critical if it within 2-3 degrees from ideal. The power band just moves around a bit. Every .002" change on lifter setting is close to 1 degree.

Vacuum shouldn't drop from .018 valve setting.

 

I use degree wheel to check settings on modified cams. So if I set intake at .030" with modified cam, what degree does it open. Once I know for a particular cam, I just use dial indicator to set next one.

You really don't need degree wheel for setting stock cams.

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[Waylander]

One of those jobs I think I will get to, when I have no choice

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[MLB]

Sounds good, I'll gladly stick with dial indicators for the stock cams.

Also should note that the D1R supercharger (mine is stage 3) was designed for, and requires, stock timing advance so that was a mistake on my part to leave the bit of timing advance in after I installed the SC (and recommended single-prong iridium spark plugs).

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[RS Barn]

I recommend the cam advance , especially for Superchargers. This closes the exhaust valve at or just before TDC. Most cams designed for SC or Turbo close exhaust valve way before TDC.

I would also use a short tip plug that doesn't extend too far into combustion chamber. Less chance of detination.

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[flash]

I've been sitting back watching this, but now I have to step in.  

 

NO!    Do not alter the cam timing on a car with my SC kit.  It would require a complete retune.  Cams designed for forced induction are very different than these.  The SC kit is designed and tuned specifically for the overlap that is there.  Reducing that overlap can cause serious damage.  I don't want to go into it here, but anybody with any questions can contact me via email.

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[94SilverCab]

I've been sitting back watching this, but now I have to step in.  

 

NO!    Do not alter the cam timing on a car with my SC kit.  It would require a complete retune.  Cams designed for forced induction are very different than these.  The SC kit is designed and tuned specifically for the overlap that is there.  Reducing that overlap can cause serious damage.  I don't want to go into it here, but anybody with any questions can contact me via email.

 

D1R Supercharger users follow the designers advice...it is a specific SC system that was tuned comprehensively...

 

There are other SC designs that were designed differently and so should be tuned differently.

 

Jay

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[RS Barn]

Advancing cams doesn't alter overlap. I though smart people knew that.

I was offering my opinion based on cam timing experiments I have tried and tested. The stock cam timing isn't ideal for turbo or SC.

Even though I would recommend advancing the cams, car was tuned for stock cam timing and should be maintained there. 

Just do it with precision.

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[flash]

sigh - i had hoped to avoid this.

 

perhaps the wrong term is being used then.  there is a very significant difference between cam timing and ignition timing, just as there is between static timing and dynamic timing.  while, on this car, they are inter-related to some degree, they are all very different things, and in discussing them one should take care to be clear.

 

if you alter the rotational relationship of one cam to the other, you alter the overlap.  that's just basic mechanics.  overlap is defined as the time during which both cams hold valves open simultaneously.   because they are connected by a chain, if you rotate one cam relative to the other, you alter the amount of time the cams are holding the valves open.  this has effects on exhaust gas pressure, and intake pressure.  this can have deleterious effects on a forced induction car that should be obvious.

 

cam overlap can have significant benefits on a normally aspirated car.  it helps with lowering emissions, and can help with low end torque.  altered without thought to the resultant changes in pressures, it can cause serious problems in a forced induction car.

 

in an of itself, cam timing has nothing to do with ignition timing.  that is an entirely different discussion.  while rotating the cam's static position can alter ignition timing, the ignition timing is determine by the ECU.  the variocam also play in, as it shifts the relative cam position at specific points.  the position of the cam also determines how the hall sender interprets "zero".  both of these can influence ignition timing.  this may mean having to alter ignition timing to compensate for cam timing.  this may be where the confusion arises.

 

that being said, the system is specifically tuned for both cam timing and ignition timing as well, and altering either on my SC system can have dire results.

 

the original question posed by MLB was about oil consumption.  he has one of my SC kits.

 

i think we have now adequately addressed the issue of altering timing (both cam and ignition) on a car with one of my kits, and have proven it to be a bad idea, unless one is willing to completely retune likely all 20 maps involved.

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[94SilverCab]

So, we all agree that your comments are specifically related to D1R SC kit, and I have already stated that owners of that kit should follow your directions implicitly.

 

This thread was added to a fora for "OEM Repair and Technical (Not Modifications) - Engine", which the D1R SC kit clearly is not.

 

Thank you for stepping in and providing support for your kit.

 

Jay

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[ds968]

Not 968 related but engine oil related : DO NOT TEST THIS m.o. on your 968 , or for that matter on ANY car !!!!


I bought a 2011 Nissan Sentra for my son replacing his Altima ( which I had serviced) and he put 90,000 miles on the Sentra since then I also relied on him to have this car serviced. I JUST found out yesterday that he NEVER had an oil change on that car . The car runs perfectly, just as if it was practically new. I looked at the dipstick and it was down less than a qt., but the oil was as black as charcoal. Did not smell weird though . Keep in mind that also means the oil filter is the original one . I don’t know what to think, I told him to take the car and have the oil changed immediately, but the fact that the engine did not sear itself at 90 K miles with the same oil is nuts ! To make this even crazier, I’m pretty sure it’s conventional oil, not synthetic.

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[pdxmike]

The simple answer is that someone must have been topping it off. No way he'd only be down under a quart after 90K. The oil capacity on that car is 4.3 quarts, so if it got a quart even every 3K miles, then it essentially, sort-of got a change every 12-15K.

 

I would pay a dollar to see what that insides of that filter look like, though...  

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[ds968]

Yeah, he said he did check the dipstick occasionally ( but very rarely, maybe once a year , or every other year .. ) and he just added oil when it looked as if there was almost nothing left at the tip of the dipstick ( I told him who the real “ dipstick “ was in that equation ) but had no clue it needs to be “changed“. The word car is just not in his vocabulary. At least he has the tires replaced before they’re totally bald. But I’m shocked the car runs at all, with that filthy and old oil and filter in it , regardless of how often was topped with fresh oil. I drove it today for about ten minutes just to hear and feel how the engine is, and it runs just fine, smooth and quiet, pulls very well. Although I have little doubt the bearings must be in pretty bad shape, but what can one say ; simply built, simply engineered , basic car car Japanese engine - those things are bullet proof and made run a million miles..maybe this one will wear out prematurely at only a quarter million miles .

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[J.Elenbaas]

One should think he missed an extremely necessary educational part during his childhood 

 

I think that when you take the engine apart you would be more surpised to find the bearings are still in good shape.

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[ds968]

This is a post from a guy on the Maserati forum ( posted on the oil change interval thread )  :  "  I had a 91 Honda accord I changed the oil every 30,000-40,000 miles I put 367,000 miles on it sold it to a guy down the street it's still running like a champ. I used conventional grade ( 15-40 ) same oil we run in the Detroit and Cummins at the company I worked at. We changed the oil every 75,000 miles , so I figured if these trucks can go that much pulling the loads they did, then my little car could go a lot too.   "   I hope the hell he does not treat the Ferrari engine in that Maserati the same way he treated his Honda. He said in another post that today's synthetic oils are so much better that they keep their viscosity easily 4 X or 5 X longer than conventional ones. That may be so, but I don't think today's filters are that much more improved...            

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