6 replies to this topic

[LumpyVR4]

Hey all, this one has me stumped. My idle vacuum sits around 7 in hg and I have no idea why.

I have boost leak tested to 25psi and the pressure holds fine. The car drives fine with the Meek chip it came with, but I'm trying to get ECMlink going and I'm sure this is making things harder than they should be.

Most of my vacuum lines are gone. I only have the two off the manifold, and the booster. Everything else is capped.  EGR is sealed. I have tried removing and capping the booster feed, and clamping the vacuum lines to the WG and FPR in case there is a leak that seals under boost. I've also replaced the biss oring and tried the finger over the hole test. None of this makes any difference.

My cams are a mystery as the specs have disappeared through previous owners. With them straight up the idle is a little rough, and if I close the LSA by a degree of intake advance it becomes a full rump. I tried splitting the LSA by 6 degrees and it had zero effect on the idle vacuum although it did idle like stock.

I've done a compression test (which I should redo because the engine was cold) but all cylinders were around 135. Engine does not blow smoke or pop its dip stick under boost.

 

Next thing to try is squirt a little WD40 here and there to see if that shows any vacuum leaks.

At this point I'm open to any suggestions as to why my idle vacuum is so low / how to find the leaks?

[Cranked]

Big cams will affect vacuum as there can be small overlap. My car is generally 10-12psi at idle.

[vr401]

135 compression is a bit too low for vr4 ???

 

timing at idle will affect vacuum. Bigger cams require a bit more timing at idle too. And idle should be around 900rpm on bigger cams.

 

Cheers

[LumpyVR4]

The compression test figures are low, but the engine was dead cold, so I should redo it at normal operating temp. I believe it should be around 145 - 155 fully warmed up.

 

My idle is 1000 rpm. The base timing is dead on 5.

 

I'll try adding a little timing into my map in ECMlink when I get a chance and see what happens.

[CLuTZ]

Might be a silly question, but where is your gauge tapped into?

[LumpyVR4]

Never know, I might have had it wrong forever.

 

All of the points on the throttle body are capped. Pressure gauge and FPR are off one of the two vacuum points at the top of the intake runners, and the waste gate and BOV are off the other one. That's it. While googling I came across this, which is the way I have my vacuum, apart from having my crank vent hooked to the manifold still, and my MBC is a bleed rather than block type.

 

Edited by LumpyVR4, 11 October 2016 - 10:40 PM.

[bazeng]

I think the Tb has 1 nipples that is open. Which can be used for the Bov / Guage.