Hi Everyone..... Is there supposed to be a "check valve" of some sort within the oil seperator (item 14) as operated by the vacuum pipe back to the plenum (item 19). Image Unavailable, Please Login NOTE - There are 2x item 14's on the schematic but, you know which one I mean I bought myself a smoke diagnostic machine and pumped smoke into the throttle body and saw that the smoke just billowed out of the pipe to the air box (item 10). Therefore there is seemingly a direct connection between the plenum and the other end at the Airbox. Curious about this, I assumed that when the engine was running, a check valve would operate using the vacuum from the plenum to shut off this connection. I tested this by pinching the pipe from the plenum (19) with the engine running (warm) and the revs dropped which shows that this connection to the plenum just constantly sucks in unrestricted air from the airbox. Is this correct ? The car runs perfectly well and idles rock steady at 1000rpm when warm but the interesting thing is that the air bypass screw at the bottom on the throttle body only has, say, 1/16th of a turn from fully closed to get the idle up to 1000RPM.... suggesting that air is perhaps being sucked from elsewhere, hence the interest in the vacuum pipe to the oil seperator. I have read articles that suggest that the vacuum from the oil seperator could be used to scavenge oil vapour and burn them within the combustion cycle which is possibly better for the environment than straight venting. it just seems to be a relatively uncontrolled and variable factor to govern the air intake ? Any thoughts or expeerince would be much appreciated Steve
This may be a totally dumb comment from a total newbie so apologies if this contributes nothing but confusion, but I thought I read that the K-Jetronic was regulating air intake and mixture on the injection models. Does that somehow make the throttle body screw less relevant in those mechanicinjected engines?
No check valve between the separator and the intake plenum but the diagram is kind of confusing as there are two item #14.
I don't think so (which is surprising as it is an air path into the engine that does not go thru the K-Jet airflow metering unit). See the text on page 77 of your 260/83 OM which indicates that the engine is always sucking in oil vapors "at the idling [sic] as well as in all other conditions" from the blow-by system.
Thanks you guys for your comments.....I too am surprised that unmetered air can get into the plenum via the oil seperator inlet. The rate of vacuum is possibly variable depending on the condition and performance of the oil seperator and not more precise like the air metering unit. I thought this open port to the plenum was the source of my low vacuum but I guess that the air metering is therefore set in mind of this baseline "vacuum leak" from the oil seperator. The smoke test also revealed smoke leaking out of the throttle plate spindle bushes once l blocked off the Vac to the oil seperator. Quite a lot of smoke actually but could this be enough to almost render the bypas sir screw ineffective as a means to adjust the idle to 1000 rpm (Only 1/16 turn from closed). Is it worth the cost of replacing the bushes / spindle to cure the leak which is perhaps being compensated for by the air bypass screw.....thinking not ? I am just trying to recover every last stock HP I can from this thing. Cheers, Steve
Understand what you are saying and you are right....I think the throttle body screw is perhaps just a fine tune adjustment for the warm idle speed.
I just cleaned and repainted my oil separator, and was surprised to discover it's just an empty can, not even a simple screen inside. But on my car there was no appreciable oil coming into the airbox.
What is the warm idle RPM when the air bypass screw is fully closed? I believe it should be about 700 RPM (or even a little less). If it is, and it only takes 1/16 of a turn of opening the air bypass screw to increase it to 1000 RPM that seems strange. However, if it is higher than 700 RPM with the air bypass screw fully closed (maybe because the throttle plate shaft bushings are leaky) = the throttle plate adjustment screw would be adjusted to reduce it back down (assuming all else is OK, like the AAV is fully closed when warm).
#14 is a clamp. The oil separator is #1. The small line to the plenum is there so that the separator will still maintain some function at idle when the throttle is shut. I don't think there is any false air circuit because it's a closed loop. Alfas use the same type of system and they are plumbed identical to this.
This is indeed the correct way to set things up for a proper idle. There appears to be misunderstandings about what the air bypass screw adjustment is for.
Is it? There is a tube from the atmosphere (at the air filter) into the separator, and then into the plenum.
Yea I see that Brian but I was thinking that there are probably some complex delta P's going on in that circuit when the engine is running. Even at idle there is air flowing through the filter housing so it's lower pressure than atmosphere. The size difference between the two hoses could be a factor as well as some positive pressure from the crankcase. But hey, I could be wrong.
I also do not get any oil in the airbox and am therefore assuming that I too do not have a blow by issue.
Hi Steve When the bypass screw is fully closed, I recon the Idle speed is about 800. This is with the throttle plate tight / fully closed aswell. I recon all the air to support warm idle iat 1000 RPM s coming from the oil seperator and whatever is leaking through the throttle plate shaft bushes. Again this is not so much of an issue as I can achieve a rock steady Idle at 1000 RPM albeit not by manufacturer design. So the question is possibly...is it worth spening the money on fixing the throttle plate bushings so that I can better control the warm idle through the air bypass ? Is there any other performance benefit from doing this ? Cheers, Steve PS the AAV works and performs as per design. PPS Are there anu other useful tests I can perform with my smoke machine. I have already tested all the other Vacuum tubes from the plenum and they all "hold a vacuum" (incl the brake Servo pipe)
I can't recall a single thread where someone disassembled a 308/328 throttle body (and I haven't done it myself) so can't really comment on the level of hassle/cost required to fix it. I will say that when Ferrari/Bosch wrote the Mondial8/QV WSM, the original procedure was to leave the air bypass screw fully closed and just use the throttle plate adjustment to set the warm idle speed -- consequently, if you aren't having any operational problem, I would say it isn't a critical thing that you need to fix immediately. However, I do think that you should at least use the throttle plate adjustment screw a tiny bit to not have the throttle plate rest position be determined by the throttle plate hitting (and wearing) the bore of the throttle body (even if this further reduces the amount that the air bypass screw is opened to get the 1000 RPM warm idle). Since you have a 1983 euro 308QV, I believe it would have a VLV (Vacuum Limiting Valve), and like the AAV, it should be fully closed at warm idle so, like the AAV, if you pinch, or block, one of its large hose closed, the warm idle speed should not drop (i.e., it should not be letting any air leak thru it at warm idle).
I need to maybe correct myself. I'm unsure if/when the VLV was added to a euro 308QV -- the OM doesn't show it, but the online SPC does (but no notation about at what chassis no.). I should've written, "If your 1983 euro 308QV has a VLV, it should be fully closed at warm idle...".
Hi Steve, Can't say I have ever seen or heard of a VLV and pretty sure it is not on the Euro. I did the unscientific testing on the AAV from cold buy removing the pipe to and blocking off the take-off on the air metering body. Then, by covering the pipe to the AAV with my thumb, it had a good strong vacuum was obvious when cold and the Vacuum became undetectable as the engine reached temperature. The following day, I connected a vacuum gauge instead of using my thumb and again...strong vacuum when cold (20 cm Hg) However, when properly warm I get a reading of 10 cm Hg. (When warm, the idle speed was not affected if the pipe to the AAV is open or blocked) A-ha...another vacuum leak...or is it supposed to be like this? The mechanical valve in the AAV surely isnt supposed to provide an air tight seal when warm...is it ? my guess is the the warm idle is designed in mind of all the various vacuum leaks (from oil seperator and the AAV) and as mentioned before the air bypass screw is just for fine tuning when the "designed in" leaks vary for any reason....makes sense I did notice that I can buy a repair kit from Germany for the AAV but the kit is basically only the moving aperture cover and a spring. Possibly a pointless expense seeing as when I block off the AAV pipe altogether it has absolutely no effect anyway. I guess I should relax in the knowledge that I have a steady idle at 1000RPM despite leaks. Any money spent would not affect the performance of the engine as the Vacuum at this point is overwhelming governed by the air metering. Anyway....hours of fun with the smoke machine to ultimately invent problems that are of no consequence Cheers, Steve
I'd agree with that -- it's not the most perfect sealing valve arrangement (being all sort of "hard" components). Agree -- as long as the amount of air leaking thru the AAV when warm is so small that it doesn't affect the engine RPM = it's working correctly. The online euro 308QV SPC does show a VLV present, but the way that it's done you can tell that it was a later addition IMO -- an added view to show it, and the item numbers for the components are all added to the end of the list (i.e., they are all very high numbers, and not logically grouped with other items around the throttle body). Yours being a 1983 is fairly early in the span of 1982-1986 euro 308QV so yours not having one isn't surprising.
Since you measured about 800rpm when the bypass was closed, I would adjust throttle butterfly screw to close the butterfly up a bit on idle, and bring the idle down to 650rpm. This assumes you have the adjustment range on the throttle butterfly adjusted slightly open to begin with. Then open the air bypass to get you back to 1,000rpm. This in turn all presumes your mixture richness is set correctly, which can be done with a gas analyzer. Once you do the throttle and bypass adjustments noted, you then measure the mixture. You then adjust lean or rich as required, and then redo the throttle butterfly and air bypass adjustments. These three adjusting parameters are all interactive, you change one and you may have to adjust the others. You itterate this until you find the balance of all three adjustments giving proper mixture and idle. Just spitballing, but if you need very little air bypass to get to the 1,000rpm, you may be running too lean. Most people do not have access to the gas analyzers to test for correct mixture. These fuel injections can compensate within a range of mixture and still run ok, especially off idle. I would bet very few cars are actually set up with proper mixture, as gas analyzers are now hard to come by. However, good (meaning patient) mechanics can get very close by ear and response feel. One thing we seem unable to confirm is how much air leakage at the throttle butterfly shaft to body is normal. The "seal" appears to be hard parts of metal spindle against bushings, presumably both could wear and be replaced. Probably dismantling and greasing with a thick grease may seal things up if the wear is more marginal. It does seem you are doing a useful checkup on the whole system, and might be discovering some wear and adjustment items to tinker with. But on the whole your car seems to be running well, so one way or another you are probably running within the tolerance these systems can adapt to.
Thanks Steve for your feedback, all great information and advice. I would just love to get access to a Gas analyser and am pretty sure my trusted mechanic has one and is Ferrari trained and so has the "ear". Job for today.....grease the throttle spindle bushes Cheers, Steve
