Average Vacuum Gauge reading??
01-19-12, 09:17 PM
#7
I guess I could've said "When your car is at idle and you then apply the throttle enough to reach a constant 1.5k RPM what does your vacuum gauge read?"
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01-20-12, 07:51 AM
#8
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Hold the idle how you currently are and then get someone to spray starter fluid around the engine. If there are leaks, rpm should increase on its on. Then just look in the area that caused the rpm to rise.
01-20-12, 12:38 PM
#9
01-20-12, 02:55 PM
#10
nobody will give you an answer because quite simply, its irrelevant. nobody has an idle at 1.5k. holding the throttle open to get to 1.5k will screw up the reading anyway.
a healthy stock port car will hold 17in/hg at idle. a healthy ported engine can be as low as 10in/hg. whatever reading you get at 1500 is pointless. do work to rule out leaks. if you cant work on it to 'rule out a leak' then how are you going to work on it to fix a leak?
a healthy stock port car will hold 17in/hg at idle. a healthy ported engine can be as low as 10in/hg. whatever reading you get at 1500 is pointless. do work to rule out leaks. if you cant work on it to 'rule out a leak' then how are you going to work on it to fix a leak?
01-20-12, 04:04 PM
#12
His car doesn't idle. that alone tells you it has a vacuum leak... althought there are other things that can cause non-idle. 99.99 percent of the time, on an FC this old, that cranks and runs but dies as soon as you let of the throttle HAS A VAC leak.
There's no point in doing any more diagnosing, you have one, if you want to double confirm it.. then do it when u can propane/starter fluid it..
There's no point in doing any more diagnosing, you have one, if you want to double confirm it.. then do it when u can propane/starter fluid it..
01-20-12, 06:43 PM
#14
Well instead of being an ******* heres some help for you dude
Cranking Vacuum: should be 3-6 in/hg (Thats inches of mercury),
Normal at idle: 17-22 in/hg, 23-25 is possible.
At 1500 rpm in neutral: The engine should show a steady vacuum reading at a higher level than idle, approx 17-22 in/hg
Vacuum that drifts at idle : say from 15-20 constantly indicates a lean mixture, minor vacuum leak
Fluctuating Vacuum at idle: Continued fluctuations of 1-2 in/hg can be an ignition problem
Steady Low Readings: Between 10-15 in/hg can be caused by over retarded ignition timing, large vacuum leak or low compression
Restricted Exhaust: Record the vacuum reading with the engine at idle, slowly increase rpms to 3000 rpm. Hold at 3000 for 1 minute. Engine vacuum should be equal to or higher than the reading at idle. If the vacuum decreases at higher rpms, its the indication of a restricted exhaust.
Theres everything you could possibly need to know about vacuum readings.
Cranking Vacuum: should be 3-6 in/hg (Thats inches of mercury),
Normal at idle: 17-22 in/hg, 23-25 is possible.
At 1500 rpm in neutral: The engine should show a steady vacuum reading at a higher level than idle, approx 17-22 in/hg
Vacuum that drifts at idle : say from 15-20 constantly indicates a lean mixture, minor vacuum leak
Fluctuating Vacuum at idle: Continued fluctuations of 1-2 in/hg can be an ignition problem
Steady Low Readings: Between 10-15 in/hg can be caused by over retarded ignition timing, large vacuum leak or low compression
Restricted Exhaust: Record the vacuum reading with the engine at idle, slowly increase rpms to 3000 rpm. Hold at 3000 for 1 minute. Engine vacuum should be equal to or higher than the reading at idle. If the vacuum decreases at higher rpms, its the indication of a restricted exhaust.
Theres everything you could possibly need to know about vacuum readings.
01-20-12, 07:09 PM
#15
no one is being an ******* here actually and your figures are high for the most part.
vacuum is based on atmospheric conditions and is also affected by dynamic sealing of the engine, the higher you are off idle the less any issue will be shown in a vacuum reading. the higher in altitude you are the air is less dense/compressed than at lower altitudes so the vacuum readings will be even lower. porting will also lower vacuum readings as will ignition timing.
so it being off idle and all the above, this thread will not be helpful in any way shape or form to him in the direct question he was asking for an answer to.
this question was also just answered in the 3rd gen section, while the motor series may not be the same the readings will be nearly the same to be expected.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/acceptable-vacuum-hg-984167/
vacuum is based on atmospheric conditions and is also affected by dynamic sealing of the engine, the higher you are off idle the less any issue will be shown in a vacuum reading. the higher in altitude you are the air is less dense/compressed than at lower altitudes so the vacuum readings will be even lower. porting will also lower vacuum readings as will ignition timing.
so it being off idle and all the above, this thread will not be helpful in any way shape or form to him in the direct question he was asking for an answer to.
this question was also just answered in the 3rd gen section, while the motor series may not be the same the readings will be nearly the same to be expected.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/acceptable-vacuum-hg-984167/
Last edited by RotaryEvolution; 01-20-12 at 07:17 PM.
01-20-12, 07:37 PM
#17
I wasn't referring to you Karack, your definitely a respectful member with often helpful info.
I suppose I didn't really word that right, lots of sarcasm really. That information did come directly almost word for word from one of my information sheets from school. And I read that thread, at the guy said close to what I gave. Also I assumed the OP has no issues with altitude, though he could be from Northern California. Engine sealing affecting vacuum readings is a given in my mind, thats why I didn't say anything about it. Frequently I forget that I'm not talking to owners of the same training level as I.
They may be high for a rotary engine but its at least some good general guidlines. If I remember correctly the last time I measured vacuum on a rotary was on a Renesis 4-port which was about 15 in/hg.
I suppose I didn't really word that right, lots of sarcasm really. That information did come directly almost word for word from one of my information sheets from school. And I read that thread, at the guy said close to what I gave. Also I assumed the OP has no issues with altitude, though he could be from Northern California. Engine sealing affecting vacuum readings is a given in my mind, thats why I didn't say anything about it. Frequently I forget that I'm not talking to owners of the same training level as I.
They may be high for a rotary engine but its at least some good general guidlines. If I remember correctly the last time I measured vacuum on a rotary was on a Renesis 4-port which was about 15 in/hg.
01-20-12, 08:06 PM
#18
steady 15-19" is average for lower climates at idle of 750-850RPMs and depending on porting. the 500whp FBP TII that left the shop idles at 1500rpm w/~10"Hg. 
if a guage starts creeping to or above that i suspect it's faulty and they usually are.
i usually don't look at bio info for basis, it usually bites me in the *** and the car would be at 6k ft elevation somewhere in bfe. so in the end the numbers will vary by a wide margin, unless bouncy it likely won't tell you there's a leak unless the reading is extremely low. even then you have to plumb the gauge near the leak, say if you measure vacuum on the primary rotor runner and there's a leak at the booster hose on the secondary rotor runner, the gauge reading won't be as low.
if a guage starts creeping to or above that i suspect it's faulty and they usually are.
i usually don't look at bio info for basis, it usually bites me in the *** and the car would be at 6k ft elevation somewhere in bfe. so in the end the numbers will vary by a wide margin, unless bouncy it likely won't tell you there's a leak unless the reading is extremely low. even then you have to plumb the gauge near the leak, say if you measure vacuum on the primary rotor runner and there's a leak at the booster hose on the secondary rotor runner, the gauge reading won't be as low.
Last edited by RotaryEvolution; 01-20-12 at 08:12 PM.
01-21-12, 01:35 PM
#19
Why is it that nobody understood that I was at work and had an idea to rule something out? I don't know what industries you guys work in (with the exception of Karack) but in the scenic artist industry its frowned upon to work on your car while painting. I very much Disney would let me bring my noisy *** rotary on Tom Sawyer Island while I was repainting some logs. I am very capable of working on my car to find and fix a leak just not at work and definitely not on location.
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