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No Vacuum at lower RPM (RB25DET NEO)

DTT_Eruc
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DTT_Eruc Enthusiast

DTT_Eruc

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5 hours ago, NEO25T said:

Did you hold the intake cam on the hex with a spanner while removing/installing the cam gear?

If not it might be jammed advanced and could probably cause something like this

yes i did that remove it with a spanner in place to remove the vct gear 

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DTT_Eruc Enthusiast

DTT_Eruc

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5 hours ago, NEO25T said:

Last thing I can think of, my fuel map need adjusting after tightening the valve clearences but it still ran and idled

you know whats funny now.... i checked the cam specs card to see whats the clearance of tomei 262 should be and it fell within the range the clearance of it and i personally wanted it to be in nissan specs so thinking i have it at a tight valve when tomei requested it to be so without me even realizing it....now it have me wondering it can be really something else geeezzz :/ 

  • 2 weeks later...
DTT_Eruc Enthusiast

DTT_Eruc

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Ok buddies... i have finally got the time to check the timing and did a compression test and so far on the timing its on spot so far , the compression test showed the same value for the cylinders 2-6 of 125 but cylinder 1 was a bit lower but thats due to valve 1 of the intake being 0.011 when the others are 0.012.... so my last check is to do a proper smoke test.. what yall think?

DTT_Eruc Enthusiast

DTT_Eruc

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2 hours ago, Ben C34 said:

Cam timing or ignition timing checked?

cam timing is on spot but havent checked the ignition timing...also what i forget to mention is that the compression tester took a while to build up the reading so it have me wondering that its looking like a valve seating issue... could be wrong ?

DTT_Eruc Enthusiast

DTT_Eruc

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On 8/24/2019 at 10:04 PM, Ben C34 said:

Cam timing or ignition timing checked?

lolllll i came to harass my sau buddies once again..... finally took of the head saw nothing to really say A BIG issue.... Took some gas and put it on all 6 chambers of valves and all seems to be well sealed except for one but very slow .... so now am left to believe due to the shim clearance settings i got for intake and exhaust can be causing the problem... 

Intake - 0.012(Nissan) Tomei Requires - 0.018

Exhaust - 0.019(Nissan) Tomei Requires - 0.015

what i currently have is the intake side of nissan and the exhaust side of tomei so am wondering to have the intake of tomei to see if it makes a differences .....

GTSBoy Grand Master

GTSBoy

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There is no way that slightly tight clearances can cause NO vacuum. Slightly less vacuum perhaps. But not none.

You definitely have something very weird going on, and in my experience of these threads, it always turns out to be something that no-one could have guessed.

DTT_Eruc Enthusiast

DTT_Eruc

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3 minutes ago, GTSBoy said:

There is no way that slightly tight clearances can cause NO vacuum. Slightly less vacuum perhaps. But not none.

You definitely have something very weird going on, and in my experience of these threads, it always turns out to be something that no-one could have guessed.

ok let me say again..... its very hard for the engine to idle at 1000rpm so high rpms it idles but with no vac... if it trys to go 1000rpm its gonna cut off sure.... did a compression test and it took long for the results to build up wasnt like the first pulse it jump to a 60-90psi reading and then settle to another high number...

DTT_Eruc Enthusiast

DTT_Eruc

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Just now, GTSBoy said:

Let me state again.....how the hell can slightly tight clearances cause the effect you're seeing? It's just wrong to think that they can. The problem is elsewhere.

am moving away from the "tight clearance" cause i saw it still wouldnt cause that issue, what i  really wanna know what IF the clearance settings i posted a little while would cause a change in overlap .... am not no genius in this cause currently search results is limited to my question so i hadda fetch from all over and then put it together to see if it makes sense .... Timing correct,did a smoke machine test no BIG leak, compression test done(but slow build up) 

DTT_Eruc Enthusiast

DTT_Eruc

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22 hours ago, GTSBoy said:

Will change overlap, but only by a tiny amount.

I'm thinking that something really big is wrong and you should take it apart. This is generally how these threads go.

Well i did and so far i havent seen anything wrong,valves are sealing properly..... so just for a piece of mind i did the intake clearances to tomei spec and so is the exhaust.... now its just to time the engine and am not even gonna start just run a compression test again and see whats popping...am starting to wonder maybe the engine was just a tooth off and could of been part of the issue even doh i checked a million times   if that doesnt work welllllllllllllll idk lol

DTT_Eruc Enthusiast

DTT_Eruc

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On 8/11/2019 at 2:43 AM, NEO25T said:

Did you hold the intake cam on the hex with a spanner while removing/installing the cam gear?

If not it might be jammed advanced and could probably cause something like this

And yes i held it in position in removing and installing.This might be my last bet.. If its stuck open it will create much more overlap = low vac. Correct me if am wrong.

How can i tell if my vct is stuck.....

Ben C34 Grand Master

Ben C34

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2 hours ago, DTT_Eruc said:

And yes i held it in position in removing and installing.This might be my last bet.. If its stuck open it will create much more overlap = low vac. Correct me if am wrong.

How can i tell if my vct is stuck.....

Still won't cause what you are experiencing.

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