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| vacuum readings https://www.ausmini.com/forums/viewtopic.php?f=2&t=33240 |
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| Author: | Boostedmini [ Mon Jun 25, 2007 8:26 am ] |
| Post subject: | vacuum readings |
Hi all, last week i was playing with the car and noticed that my vacuum readings on my boost/vacuum gauge at idle dropped right off and site just below 0 (0 being Atmosphere) where previously the readings were around 15 to 20 inches or merc. i checked the readings on the megajolt unit and it had the same readings i checked over the lines and blocked some off and still the same. i have them connected to the little nipple at the front of the carb just in front of the done/bell. when i drive the car and back of throttle at above 2000rpm the vacuum readings go donw to 20 or so but then straighjt back to just below 0, same thing if i bring the revs up to around 1500 the vacuum readings go to 10 to 15 as soon as i take foot off the reading goes to just beow 0 again. any ideas? should i take the readings off the manifold instead off that nipple? but then again this is where i have always used. thanks Grant |
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| Author: | lovely2 [ Mon Jun 25, 2007 8:48 am ] |
| Post subject: | |
The front nipple, are we talking about the one that is closed by the butterfly at idle, the one which the ingnition advance usually comes off? |
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| Author: | Boostedmini [ Mon Jun 25, 2007 2:02 pm ] |
| Post subject: | |
yeah i am sure its the same one, if the butterfly closes it at idle how come i used to have a vacuum reading from it at idle? weird. although i used to get "correct" vacuum readings before. i will take some more readings later and see if this port does close off but i am pretty sure it doesnt GB |
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| Author: | lovely2 [ Mon Jun 25, 2007 5:09 pm ] |
| Post subject: | |
I don't have anything to back this up, it just a guess. a) i suspect your butterfly being made out of a softer metal than the body, has finally shaped itself to the throttle body. It werid thought. b) As i think you would only see vacum on that port (at idle) if the body is closed too much, so maybe its the buttlerfly that has worn out. Which carb do you have ? |
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| Author: | benjamin [ Mon Jun 25, 2007 5:29 pm ] |
| Post subject: | |
no idea why grant , but i have that nipple bolcked off and take my reading from the manifold. |
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| Author: | Spaceboy [ Mon Jun 25, 2007 6:03 pm ] |
| Post subject: | |
that nipple wont give an accurate vacuum reading as its too close to the butterfly, you have to put a new one further along on the manifold.. some manifolds have takeoffs for the brake booster |
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| Author: | Boostedmini [ Mon Jun 25, 2007 8:19 pm ] |
| Post subject: | |
Its a HIF44 turbo carb. i might put a "T" into the booster line for the boost/vacuum gauge, mega jolt unit and blow off valve, WAY to many thing on this dam thing. thanks Grant |
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| Author: | DOZ [ Mon Jun 25, 2007 9:14 pm ] |
| Post subject: | |
I would run one hose from the manifold to the megajolt, it's not really that important what the gauge says, it's important that the box of sparks is reading properly. I've had problems with consistent idle because my map sensor is picking the signal too close to the butterfly (not that I care much, it hardly gets to idle once it's warm) and I am moving this hose to the manifold where there is a bit less transient pulsing. As for the gauge and blow off valve, so long as they are somewhere after the throttle plate they should be alright, if you tap the blow off with the megajolt you'll find spikes when the valve opens. This may not affect engine running but over time it will affect the map sensor in the megajolt I'm sure. Daniel |
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| Author: | Boostedmini [ Tue Jun 26, 2007 12:33 pm ] |
| Post subject: | |
Good points Daniel, i have decied to tap the manifold for the Megajolt and run a T from the booster line for the BOV and gauge too. keep you posted Grant |
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| Author: | benjamin [ Tue Jun 26, 2007 5:34 pm ] |
| Post subject: | |
DOZ wrote: if you tap the blow off with the megajolt you'll find spikes when the valve opens. This may not affect engine running but over time it will affect the map sensor in the megajolt I'm sure.
Daniel really? i have every single line on the one take off |
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| Author: | DOZ [ Tue Jun 26, 2007 10:37 pm ] |
| Post subject: | |
Depends on the hose diameter I guess, you may not see the spikes unless you have a data logger of some sort but I have seen other problems with moisture collecting in the system and damaging the sensor too. Taking pressure readings doesn't involve moving much air, almost none in fact, so the hose size can be pretty small. If you used the same sized hose for your brake booster it wouldn't work, it's not big enough. The same sort of idea goes with the BOV, it moves a piston to work, if the hose is the right size it's probably ok but I would prefer to see a separate line for the sensor and another for all the other bits is all. I might add that this doesn't explain Grants problem, esp if it did work before, it's just my thoughts on the issue in general... Daniel |
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| Author: | Boostedmini [ Tue Jul 03, 2007 3:45 pm ] |
| Post subject: | |
ok well i have fitted a T in the booster vac line and have that going to the blow off valve and another T in that going to the boost/vac gauge, i have drilled and tapped a port in the manifold where i will run the Megajolt map sensor to. i am yet to start the engine to see how it goes but fingers xed hey, will keep you posted. Grant |
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