Weird vacuum issue,blow off valve question need help.
01-10-11, 04:48 PM
#1
Weird vacuum issue,blow off valve question need help.
I am having this weird problem that i cant figure out.If i am cruising on second or third gear and i get into the 25 to 30 vacuum range right after i get of the pedal the car stumbles runs really rich and my vacuum drops from 15 that pulls at idle to like 12,to get rid of the problem i have to rev the engine a bit and it goes away if i dont do that it takes like a minute to go away.It only happens at really high vacuum not under boost.All the vacuum lines are AN fittings,motor has 90psi on every face,starts right up pulls great under boost and it was running fine until this started happening,my blow off valve is HKS knock off and is installed next to the throttle body(third gen setup)and i am thinking that it might be the problem maybe vacuum is opening the valve and causing a rich condition when the air gets out of the intake instead of going to the engine,Does it makes sense?Motor is a halfbridge running a 78mm turbo on microtech.,Any other ideas?
01-10-11, 08:13 PM
#2
I've heard the HKS knockoffs don't seal for about 30 seconds after venting. If I recall, by design the HKS SSQV is ridiculously sensitive too, so when you hit that 30"Hg, it triggers the valve. Then you'll have an open hole in the intake after the AFM. But that should lean it out, right?
There's a fix for those I believe, you'll have to google it.
There's a fix for those I believe, you'll have to google it.
01-10-11, 09:04 PM
#3
no AFM i am running a lt10s,BOV is right on my greddy elbow maybe 4or5 inches away from the throttle plates.Okay so if my map sensor is reading 25"hg and the valve pops open air will leak out the intake track and then i wont get all that air in the chamber and it will run very rich cause the MT already injected fuel for the X amount of air,is that how it works?I think that the greddy valves work backwards,boost wont push there open but vacuum will,isnt that right?I am thinking about disconnecting the charge pipe so that way i am running NA so if the valve is staying open it wont affect anything cause the intake track is not under pressure and if i do get the same problem is something else then.
01-11-11, 01:24 PM
#4
No, the blowoff valve is on the wrong side of the throttle body to affect engine vacuum. The blowoff valve doesn't just open when it hits a certain vacuum, it opens based on differential pressure of the manifold and intake charge pipe. Microtech... I missed that part. So that blows my AFM theory out of the water. Do you have any datalogging capabilities with that ecu? I'm not too familiar with that, so you might want to post this problem in the microtech forum here.
Do you think that the problem may not be when you reach that certain vacuum, but when the throttle butterflies shut? It would only make sense that you'd reach almost 30" on decel with the throttle shut, so it may be linked to a TPS issue. I know on megasquirt that you can calibrate the TPS. You have to floor it and log the values, then let off the gas and log the shut value. It records numbers based on voltage. However, if by any chance that "shut" number dips below the lowest recording (completely possible) it'll go to a default "limp mode" and cause it to run all funky.
Just food for thought.
Do you think that the problem may not be when you reach that certain vacuum, but when the throttle butterflies shut? It would only make sense that you'd reach almost 30" on decel with the throttle shut, so it may be linked to a TPS issue. I know on megasquirt that you can calibrate the TPS. You have to floor it and log the values, then let off the gas and log the shut value. It records numbers based on voltage. However, if by any chance that "shut" number dips below the lowest recording (completely possible) it'll go to a default "limp mode" and cause it to run all funky.
Just food for thought.
01-11-11, 01:36 PM
#5
tps
No, the blowoff valve is on the wrong side of the throttle body to affect engine vacuum. The blowoff valve doesn't just open when it hits a certain vacuum, it opens based on differential pressure of the manifold and intake charge pipe. Microtech... I missed that part. So that blows my AFM theory out of the water. Do you have any datalogging capabilities with that ecu? I'm not too familiar with that, so you might want to post this problem in the microtech forum here.
Do you think that the problem may not be when you reach that certain vacuum, but when the throttle butterflies shut? It would only make sense that you'd reach almost 30" on decel with the throttle shut, so it may be linked to a TPS issue. I know on megasquirt that you can calibrate the TPS. You have to floor it and log the values, then let off the gas and log the shut value. It records numbers based on voltage. However, if by any chance that "shut" number dips below the lowest recording (completely possible) it'll go to a default "limp mode" and cause it to run all funky.
Just food for thought.
Do you think that the problem may not be when you reach that certain vacuum, but when the throttle butterflies shut? It would only make sense that you'd reach almost 30" on decel with the throttle shut, so it may be linked to a TPS issue. I know on megasquirt that you can calibrate the TPS. You have to floor it and log the values, then let off the gas and log the shut value. It records numbers based on voltage. However, if by any chance that "shut" number dips below the lowest recording (completely possible) it'll go to a default "limp mode" and cause it to run all funky.
Just food for thought.
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