Vacuum reading at idle

[Kit2523]

What are the normal vacuum reading at idle? Mine are as the following:
-Transmission in Drive 16 inHg (-7.8 psi)
-Transmission in N or P 18.5 inHg (-9 psi)
Engine fully warmed, AC on, at sea level.
Interested to see if you guys are getting similar idle vacuum reading.

Thanks in advance

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[MasterCylinder]

Your good to go. Most any engine depending on atmospheric pressure where you live, should be 14-18hg. We use to tune for optimum performance and timing using a vacuum gauge. Personally (Im old gear head) keeping a record of real vacuum gauge readings from an early stage can help you keep track of sneaky and pesky future problems. Record engine temperature, outside temperature, rpm, idle readings , cruising readings at steady rpm and deceleration readings which is when highest (22+hg). Turbos will change readings compared to older naturally aspirated engines most notably under acceleration of course. Just some helpful thoughts.

NOTE: I failed to mention. Do Not rely on the on board diagnostics, (OBD port) for your vacuum readings. Those are supplied by various sensors (like MAP, MAF, TPS etc....) feedback and a correlated feed back processed from the ECU. Use a real vacuum gauge connected past throttle plate which reads the intake vacuum to rely on.

 

[superj]

i haven't put it on my truck but i always tuned my carb'd vehicles with a vacuum gage so i got the best performance. set the timing and carb with it

 

[hand-filer]

That's almost identical to the numbers I'm seeing on my 2.7

 

[Kit2523]

Your good to go. Most any engine depending on atmospheric pressure where you live, should be 14-18hg. We use to tune for optimum performance and timing using a vacuum gauge. Personally (Im old gear head) keeping a record of real vacuum gauge readings from an early stage can help you keep track of sneaky and pesky future problems. Record engine temperature, outside temperature, rpm, idle readings , cruising readings at steady rpm and deceleration readings which is when highest (22+hg). Turbos will change readings compared to older naturally aspirated engines most notably under acceleration of course. Just some helpful thoughts.

Thank you very much for the info!!! From what I gather, vacuum reading is a good indication of engine health. This RR is my first GTDI in a long time (came from diesel world). I will keep an eye on the perimeters you mentioned. Thanks again.

 

[MasterCylinder]

i haven't put it on my truck but i always tuned my carb'd vehicles with a vacuum gage so i got the best performance. set the timing and carb with it

Yes indeed. Good old days and the tricks we learned. Fun in the sun and the smell of burnt rubber! If we went racing somewhere and the atmospheric pressure was quite different a little touch up was sometimes warranted. Interesting note is, the first thing tuners do is change those perimeters within the ECU to get more umph! Some of the most basic tunes, it's all that is done within octane limitations. Old school rules, just how you go about has changed because basic engine functions have not, an engine is still an engine! Lol

 

[MasterCylinder]

Thank you very much for the info!!! From what I gather, vacuum reading is a good indication of engine health. This RR is my first GTDI in a long time (came from diesel world). I will keep an eye on the perimeters you mentioned. Thanks again.

You are 100% correct. Vacuum readings can unmask simple vacuum leaks to the more serious piston ring seal or valves leaking and even leaking head gaskets to a clogged exhaust especially since the catalytic cover came about. I encourage all to learn about vacuum and engine functions, you might be surprised just how useful a simple tool can be. Even diesels vacuum can be checked. Enjoy that ride!

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