Guest Anonymous Posted September 6, 2002 Share Posted September 6, 2002 Hello all... I was referred to this site by a friend who said that it has provided him with a wealth of info. Well, I need some, and how! I have a 72 240Z that has an 83 L28DET motor. The car ran awesome! Then I put on a 1G DSM BOV and things have gone down hill considerably. Your help in idiod checking my thoughts will be greatly appreciated. Here are the details. I got the 1G DSM BOV from a 91 Eagle Talon. This is a parts car that I have for another project, but the BOV can be assumed to be good. I've been told that you should but the BOV as close to the throttle body as posible, do the flange is welded on the underside of the factory intake pipe (between Turbo and throttle body) on the short side of the 'J'. Yes, the BOV is essentially upside-down (for hood clearance issues). The BOV vents into the tube that connects the valve cover breather to the intake tube (between the AFM and the turbo). And here is where I think my fatal flaw *may* be. There is a vacuum line that runs between (what I assume to be) the vaccuum canister and the intake manifold. I tee'd into that line and ran in to the 'input' on the BOV. So here is what is happening... Car starts and idles perfectly... shows 15psi vaccuum at idle. Any attempts at positive boost acceleration causes the car to bog and buck and basically pitch a fit. 5psi of accuum actually seems to be the point at which this happens. So, I can drive the car, but I just cannot punch the gas without bad things happening. Any input will be greatly appreciated!!! I wanna go fast again!!! Thanks, John Quote Link to comment Share on other sites More sharing options...
JoshB 240Z Posted September 6, 2002 Share Posted September 6, 2002 John, I assume you have a stock EFI system. You will want the vacuum/boost reference line to run directly from the intake manifold to the BOV. You will then need to run the BOV return back into the intake system after the AFM but before the turbo. If I understand your description correctly you currently are running the excess compressed air directly into the intake manifold and valve/cam cover. I would assume that by routing the air around the throttle body and directly into the intake manifold would give you a lean codition as the EFI thinks the throttle body is closed and is not adding more fuel to make up for the extra air you are dumping in the manifold. Plus, you are defeating the purpose of the throttle body being shut by forcing air around the TB and directly into the manifold. Does this make sense? Josh Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 7, 2002 Share Posted September 7, 2002 Hmmm... now that you mention it, I am running the stock EFI system and this does make sense... but how can I account for this condition without boost? The system is still in vaccuum when this is happening. In theory, this would only lean out the car if the BOV was open due to throttle plate closure. If I crack the throttle more than a smidge, the motor stumbles. Good thought, though. I was just reading in the archive where someone recommends a check valve between BOV and valve cover. I will try disconnecting the breather tube from the valve cover and plugging the remaining holes and see if it still gives me problems. Thanks for the thoughts Josh and let me know if you have any more. John Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 7, 2002 Share Posted September 7, 2002 Well, I just plugged the breather tub and the hole that it came from. Slight improvement.... I can now push up to 0psi without stumble, but still has issues. Anyone who has a BOV... where are you getting the reference signal from? Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted September 7, 2002 Share Posted September 7, 2002 I run my BOV reference line from the manifold, it (bov)is connected to the line from the turbo to the intercooler, and it vents into a line that comes off the top if the valve cover and goes into the intake tube before the turbo. essentially tee'd in there. No issue's. If you are not running an intercooler and your set up is stock, you don't need a BOV, so why not take it off and see if that fixes your issue? Also you have to consider that a car with a flowmeter and you have a BOV, you have to plumb the vented air back into the system after the flowmeter. Here's why. The flow meter has already measured that air, and it is telling the ecu how to properly fuel the engine. When you vent it to the atmosphere, the ecu is fueling for the air in the system and the air you just vented out, and it makes your car run rich and stumble. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 7, 2002 Share Posted September 7, 2002 Hi Lockjaw, Nice 1/4 mi time in your sig... hope to be there someday. I agree that I probably dont need a BOV yet, but the next steps that I intend to take are as follows... intercooler upgrade injectors upgrade fuel pump turn up boost So my approach is always to take a step, get it right and move to the next. I am currently venting to the same location that you are. The reference signal for the BOV is coming from the manifold... teed into the main/purge line for the vaccuum canister. I'm starting to think that the BOV is not seating correctly when closing... would a constant flow of vaccuum back into the pre-turbo intake cause a stumbling? And another thought was that I might be having a fuel problem... since the problem seems to be most noticeable as it tries to build boost. I'm going to replace the fuel filter tomorrow and see if that helps, but I am just boggled! BTW my 1/4 mi times are between 14.2 and 14.8 on stock boost/setup. Dont know how this compares with everyone else, but I desperately want to be in te 12's!!! Thanks for the input! John Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 7, 2002 Share Posted September 7, 2002 Pic may help shed some light... http://jceagar.freewebspace.com/images/bovdiag.jpg Quote Link to comment Share on other sites More sharing options...
fl327 Posted September 7, 2002 Share Posted September 7, 2002 12s out of the turbo setup will require a lot of upgrades to the system. i would check out the fuel pump, i had a problem like that where it would stumble and buck like a bronco except when boost would come on, and i just sprayed the pump with battery cleaner and problem went away. i previously degreased the rear suspension and got dirt on the leads im sure. i have to run a bov with a line back to near the turbo on my setup as well, i remember when venting to atmosphere it would automatically stall out as soon as i got ready to shift into the next gear. im running a bosch bov, and it vents at idle, and has to be routed back behind the afm to not stall out the car. ive had a lot of stumbling issues to get the car to run right, but its cool now, if not a little bit slow to me, but i dont care, its a awesome driver and thats what i do, i drive, a lot. once i take care of other issues not car related, im gonna make it a better driver, and turn up the boost to about 10psi with an ic and drive a little faster, btw. one of my buddies ran 13.4 @108 with a stock turbo setup, starion intercooler, and 15psi and no traction-i didnt see it but i believe him, hes a good mechanic and trustworthy. Quote Link to comment Share on other sites More sharing options...
JoshB 240Z Posted September 7, 2002 Share Posted September 7, 2002 Oops. I misread the first post. The BOV is vented to the hose that runs between the valve cover and AFM to Turbo hose? Duh! For some reason I thought the BOV was vented directly into the intake manifold behind the throttle body. I appologize. Josh Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted September 7, 2002 Share Posted September 7, 2002 It looks like you are set up like me. What you may have is what some friends have commonly referred to as mystery turbo death. Usually disconnecting the harness at the ECU and cleaning the plugs and ecu pins with brake clean and reconnecting will cure it. Another thing that helps is to make sure the fuel pump is grounded properly. Mine is grounded to the chasis. You may also need to check the BOV and maje sure it is working ok. I have the little HKS one, and had to shim the spring in it. You can get down into the 12's, it just takes some time and patience. The first pass I made in this car was a 14.1 at 101. That was after I spent a ton on building the motor and getting the JWT set-up in it. Ended up at 13.5 at 105. Then I added a 3 inch exhaust (best mod for the money on turbo engine in my opinion), and electric fan, and Jacobs plug wires and dropped down to 12.93 at 109. Added drag ta's and swapped to 3.90's in the back to get current best, on a sick turbo. Next round of mods will be a different turbo ( more turbine same size compressor), a slightly larger cam, and a ported exhaust housing. I want to upgrade to a bigger intercooler and 2.5 inch lines to, and hope all of that will help me drop a little more. I would upgrade your fuel pump. A walbro or peirburg from cartech would be a good way to go. I cannot remember what kinf of car you have, but if a 240, you will have to get a larger return line made and run if you add a larger pump. Quote Link to comment Share on other sites More sharing options...
awd92gsx Posted September 7, 2002 Share Posted September 7, 2002 Have you plugged off the vent line going to your valve cover too see if that changes anything? You should not dump back into the valve cover. You should dump back into the intake (between AFM and turbo) or into atmosphere (this may cause some richness between shifts) Quote Link to comment Share on other sites More sharing options...
DAW Posted September 8, 2002 Share Posted September 8, 2002 Think about what the BOV is for and you can figure out how to plumb it. The vacuum signal to the canister diaphram is wrong. That signal is ported vacuum and that's not what you want so reverse that hook-up and start over. You want an intake manifold vacuum signal to your BOV, take it right off a manifold fitting using a tee. When you let up on the throttle, the plate closes and the manifold signal shoots right up as the cylinders are sucking against a closed chamber (the manifold). This opposite of this condition is happenning simultaneously on the other side of the plate as the wound-up turbo is suddenly faced with a pressurized column of air it created which has no where to go now, and works to try to stop or brake the compressor wheel from turning. The BOV vents that pressure and allows the turbo to stay spun-up so that you'll have pressure availablr when you reopen the throttle (at which point the BOV vacuum signal falls and the BOV stops venting). Vented air from the BOV should be rerouted into the system since it is metered air which has some proportion of fuel matched to its passage through the AFM. If you do vent it into the PCV intake, then do it as close to the large air intake hose for the turbo as possible, and use a "Y" fitting to direct it into that larger volume air hose rather than into the smaller volume PCV (valve cover-connected) hose. DAW Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 8, 2002 Share Posted September 8, 2002 Hey All, Thanks alot for all of you responses! I think that the problem is licked, now. DAW, very good explainatiion! What is 'ported' vaccum? I found a place on the maniflod that was capped off as a result of the conversion and went directly to that vaccuum source. Things have definitely improved. I am a little concerned that the fitting was alot smaller than the fitting for the reference signal on the BOV, but I was told by a friend that this will have a minimal effect. Can you confirm this? I'm not sure about the physics involved, but my gut says that it just might. For the record, the problems that I hve been having MAY have been complicated by a fuel delivery issue. In addition to the vaccum problem, I was careless enough to let the car run out of gas. I refilled it and moved on, but it seems that I may have clogged the fuel filter as well. I replaced the filter today and PROPERLY hooked up all of the vaccuum lines to the BOV. I took the car for a quick run arond the block and it seems fine, but my debatably useles autometer mixture gauge is telling me that I am running very lean at 5lbs of boost. I will put this in a seperate post later, but I just wanted to clarify this for the archives. LEN, very respectable time. I hope to get there soon! I have a T-5 and a 3.90 LSD that are waiting to go into the car. I'm weighing my options right now, though. I have a mechanic buddy that will help me do it if I want to go the DIY route. There is also a local Z shop that will do it for around $800. Not sure if it's worth it... but I think that the deciding factor will be whether or not I can get access to a lift. Any thoughts? i know this is off topic, but... Quote Link to comment Share on other sites More sharing options...
Drax240z Posted September 9, 2002 Share Posted September 9, 2002 $800 sounds like a lot to me! You can definately do the diff without a lift. I just did one on my 260 and it took about 8 hours start to finish, fom parking the car to the first test drive. (in this case removing an R180 and installing an R200) No lift necessary. Throw in a few more hours for a tranny swap while your on the go.... Its definately doable in a weekend with a couple of guys. (I could have saved a couple of hours with another set of hands I am sure) Buy a haynes and dive in! Quote Link to comment Share on other sites More sharing options...
DAW Posted September 10, 2002 Share Posted September 10, 2002 "Ported" vacuum is a signal source at the throttle plate from a slot that is masked at closed throttle, then gradually exposed during throttle openning such that the resultant signal is roughly proportionate to the degree of throttle openning. So you can see why that wasn't working well...you wanted just the opposite type of signal, and more of an all-or-nothing type signal rather than gradual. As to the vacuum fitting/connection, I would try to approximately match the lumen of the fitting/hose of the BOV. If you mismatch to too large a fitting, you'll lose responsiveness of the BOV and defeat its purpose. If the mismatch is to too small a fitting it could lead to increased turbo lag because the vacuum in the top of the BOV won't be able to release quickly if it has to flow through a tiny orfice/restrictor. The turbo will freewheel until the BOV has the signal released so pressure is allowed to build again in the turbo hoses. There's a single fitting in the top of the manifold, about 1/3 of the way from the front that is about the size of the BOV port. That would be a good vacuum source for BOV signal. It would be best to find a metal Tee port that threads in to replace the single port connector. DAW Quote Link to comment Share on other sites More sharing options...
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