Low Vacuum - Idle is fine...

[97gst_spyder]

I have replaced a ton of parts on my car over the past week.

- IM Gasket
- Both TB Gaskets
- Shaft Seals
- Plugs
- Wires
- Coil Pack
- CAS - again. This time with a 1g 98-91 with the wires coming out. First one was a green top with a plug, same issues...
- All exhaust gaskets
- Injector seals
- Timing belt

I have 12-14 inhg vacuum at idle which is at 850rpm. BLT, no leaks but pressurizes the crank case alot. We tested it from the turbo inlet. Compression is 190 across the board. So I'm at a complete loss. We also re-did the timing belt, nothing.

So issues are Low vacuum, miss fires at idle, will not start the first, second, possibly the 5th time. Then starts....

 

[Zack Huffman]

PCV valve? Did you pinch off the VC breather hose when you BLT'd?

 

[DeadlyScone]

Sounds like what my cars vacuum sits at. Though it doesn't miss. We blt and can't find any. Although recently we can hear a bubbling sound in the engine when we blt. We suspect the seals on the turbo.

 

[97gst_spyder]

We blocked off the Pcv and breather. Removed and capped brake booster off, nothing.

 

[007jimmy]

Do a boost leak test on the piping right after the turbo as the seals are known to leak and cause gurggling in the oil pan. Block your PCV and make sure you block off your MBC ports. Do you have all your emissions hooked up? Could be a simple vacuum leak from one of the intake manifold hoses/TB hoses.

 

[eclipse gsx]

im in the same position ????????

 

[Zack Huffman]

If you can figure out why it's pressurizing the crankcase, you'll probably also find out why you have low vacuum.

I'd start doing more BLTs, start near the TB and work your way back towards the compressor.

 

[97gst_spyder]

No emissions. Everything is capped off. But I'll try a blt at the tb.

 

[007jimmy]

Is your EGR blocked off, or did you just unhook the vacuum lines?? A clogged EGR could be stuck open \closed causing issues also. Just a thought.

EDIT: do you have larger cams???

 

[97gst_spyder]

EGR is blocked off. Stock engine.

 

[775TSI]

Just curious. Where are you tapped into for your Vacuum. Are you reading off your Boost / vacuum gauge or an actual vacuum tester.

 

[97gst_spyder]

The boost gauge is on the 'p' port on the tb. Same as it's been for 3 years. Also my Omni power 4 bar in the mdp location reads the same.

Update - vacuum was at 5.7psi, 11.4inhg. After bumping the idle up to 900 rpm's we got it to 6psi, 12inhg. Can a tune really fix something like this if there are no mechanical issues?

 

[Zack Huffman]

Can a tune really fix something like this if there are no mechanical issues?

Highly unlikely that a tune causes this. To maintain idle speed the engine has to produce just enough torque to keep the speed from changing. If your ISC is maxed closed and idle speed is still above the lowest acceptable speed then the low vacuum is most likely a physical problem and not a logical tuning error. However, if your ISC is not fully closed at this low vacuum level, you may need to increase your timing advance at idle just a little. Are you running extra lean at idle? I really doubt that timing is your problem. If you have any idle quality at all, I'd have to assume that the low vacuum is a mechanical issue.

Does the vac reading flutter or wander up and down at all? Rapid short sweep flutter at idle can be worn intake valve guides, rapid flutter at all engine speeds can be headgasket or worn and weak valve springs. Do you have bad lifter tick?

One test you can do is the short throttle blip. If vacuum goes over ~20inHg right after you let off and then falls back to 12-14 as engine speed drops, then you may have worn rings. A leakdown test would then be needed as opposed to the compression test you already did.

A steady low vac at idle is almost always either rings, a vac line leak or a gasket somewhere on the manifold.

 

[97gst_spyder]

We went over everything again. Nothing...

Thanks Delta! The only thing we have not checked was the mani bolts again.... If that does nothing, then leakdown test I guess.

 

[775TSI]

Due to delta's response my day is now ruined. Everything you just said about rings fit my car's issues and vacuum perfectly.

 

[El Cuervo]

Due to delta's response my day is now ruined. Everything you just said about rings fit my car's issues and vacuum perfectly.

. Same here. It seem that delta has also ruin my day J/K delta
Though I still have to do a leakdown test to verify. There is still a slight glimmer of hope.

 

[775TSI]

Just look at your vacuum issue this way. My idle is 1000 and inHG is a floppy 7 at idle and 9 at cruise with a A/F reading of 15.9 at 30mph. When i hit 30 mph today my inHG went to 5 and this is a cruise no load.

 

[Calan]

Just to toss this out there... valve overlap can also play havoc with vac readings. Adjustable cam gears, non-stock cams, excessive material removal from the head/deck, and similar conditions can all contribute to it.

 

[97gst_spyder]

Well after going through the engine again with a few DSM buddies all night and morning. We came to the concution that A, the intake cam was out of time some how.... After 5 tries we got it timed correclty. Also, its an auto now. So if the car is in P/N the vacuum is 17.4-17.5 at 900 rpm. In R/D/2/1, its at 14-15 with an idle of 800-850.

 

[bradselph]

How far was it outa time?
It was dead on when i looked at it

 

[Calan]

... the intake cam was out of time some how....

That would definitely fall under the "similar conditions" I mentioned.

Was the t-belt just off a tooth or something? It didn't jump time did it?

 

[bradselph]

must have been off a tooth because we retimed it friday night when we changed the lifters.