No Vacuum at lower RPM (RB25DET NEO)

[DTT_Eruc]

Is it possible that tight valve clearance on the exhaust side can cause little to no vacuum on idle...... This is regards to a RB25DET NEO i got...Re done the head installing tomei 1.2 head gasket and lapp over the valves however after that was done the intake side was at nissan specs of 0.012 and the exhaust is way tighter(0.014 to 0.015) on all 12 of the exhaust... will this cause such issue... secondly my last chance was to check to see if my timing was off

 

[NEO25T]

How much vacuum do you  have and what cams.

I just set clearences to what yours are with type b poncams and mine has 13-14 in vac, still have to set the ecu up properly too so might get a bit more

[DTT_Eruc]

Actually no vaccum at  all just show 0 on all gauges(ecu and boost gauge)....running tomei pon cam 262ex and 260in..... before i did the head work this never happened so i was wondering if is something to do with the clearances or timing .... but since the exhaust side has change was wondering if that would of been the cause 

[GTSBoy]

Look for the problem elsewhere. 0. Real zero vacuum and idle are incompatible.

[DTT_Eruc]

10 hours ago, GTSBoy said:

Look for the problem elsewhere. 0. Real zero vacuum and idle are incompatible.

elsewhere like? engine wont idle at 1000 rpm and if it try to will die and it shows zero value

[NEO25T]

What rpm will it run steady while holding throttle open.

Are all the vac lines connected properly, might wanna do a leak test

[DTT_Eruc]

1 minute ago, NEO25T said:

What rpm will it run steady while holding throttle open.

Are all the vac lines connected properly, might wanna do a leak test

checked all lines last time i try to make the car stay steady at idle was at 2000 to 2500 rpm or so.....am starting to think its more to deal with the exhaust clearance that causing it not to idle at lower rpm since the clearance is tight..but i just wanna confirm with yall....dont have leak down tools but only a compression tester

[Ben C34]

That's a big issue you have, but I don't think it's the tight clearances  causing it.

Unless they are non existant.

tight exhaust clearances will lead to burnt exhaust valves, so I would be addressing it first anyway.

[DTT_Eruc]

9 minutes ago, Ben C34 said:

That's a big issue you have, but I don't think it's the tight clearances  causing it.

Unless they are non existant.

tight exhaust clearances will lead to burnt exhaust valves, so I would be addressing it first anyway.

well i havent drove the car/ran it for long to say for it to cause any major damages but it ran for a while with no heavy load......but what do you suspect it maybe?

[Ben C34]

Intake leak, throttle not closing fully, timing heaps wrong.

Hard to guess

[DTT_Eruc]

2 minutes ago, Ben C34 said:

Intake leak, throttle not closing fully, timing heaps wrong.

Hard to guess

try a home made smoke machine had a very slight leak to the throttle body/tps......saw no other leaks from the intake(injector seals,gasket,vac lines) just the timing to check .... this engine produce vac before i took off the head but after i lap the exhaust valves(grit to fine) and due to human error on my side forgot to check clearance( first time dealing with head work on rb) lol...... but will the exhaust valve cause this issue being the clearance out of gap... 

[DTT_Eruc]

p.s this is my personal build and not a customer(dont do mechanical services) so everything am doing is trail and error on this project 

Edited August 11, 2019 by DTT_Eruc

[DTT_Eruc]

8 minutes ago, Ben C34 said:

Intake leak, throttle not closing fully, timing heaps wrong.

Hard to guess

oh i did check timing but i dont like using the crank pulley as it tends not to be 100% correct(believe mines getting worn out).... all marks seems to line up perfect and did the screw driver trick to make sure it was tdc and all marks line perfect ...... geeeeeeeez idk why little things does cause big problems lolzzz 

[Ben C34]

That could be your problem, you have to line up the dots on the pulleys, I dont recall if that is even at tdc as it doesn't really matter.

[DTT_Eruc]

2 minutes ago, Ben C34 said:

That could be your problem, you have to line up the dots on the pulleys, I dont recall if that is even at tdc as it doesn't really matter.

yeah all the dots are lined up perfectly ...just did the screw driver test for additional clarification ...... still my question havent been answered yet " will the current clearance value cause this problem also" or is it just intake related(intake cam,boost/vac leak etc)

[Ben C34]

People don't tend to stuff up the exhaust clearence then post results online. If they are just tighter than the spec, but still exist, I would say no way would it cause your issue.

What about ignition timing?

[DTT_Eruc]

3 minutes ago, Ben C34 said:

People don't tend to stuff up the exhaust clearence then post results online. If they are just tighter than the spec, but still exist, I would say no way would it cause your issue.

What about ignition timing?

havent got a timing light to know... i had it at the neutral position/stock...sooooo .....again i started the engine before i did the head removal and it showed vac and also the timing was at stock position and idle fine just dump alot of gas....reason for head removal had a slight bent valve on 11 and 12 exhaust(idk how it happened) but the engine was bought from someone etc etc etc 

[NEO25T]

Was it running with these cams prior or were they put in while doing the head.

Can you put an air fitting in spark plug hole while at tdc comp stroke and listed to see if valves are sealing.

Those clearences will not cause it to have no vacuum

[NEO25T]

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

[DTT_Eruc]

5 hours ago, NEO25T said:

Was it running with these cams prior or were they put in while doing the head.

Can you put an air fitting in spark plug hole while at tdc comp stroke and listed to see if valves are sealing.

Those clearences will not cause it to have no vacuum

yes it was running with those cams before and  the engine ran with vac perfect before i took of the head to replace the valves(two exhaust) ..... so your saying the clearance on the exhaust side wouldnt cause such ?