Weird Boost Gauge Phenomenon After FMIC Install

[RichB]

I have a boost gauge tapped into the vacuum line at the top of my turbosmart 50/50 BPV and I am getting something funny when I rev the engine at a traffic light.

When I rev the engine quickly at a traffic light my boost guage pins at negative 25 InHg (as low as it goes) then after a few seconds it goes back to the idle reading (about -21 inHg)

Can someone help me figure out what is going on? Does this mean my BPV is opening when I rev the engine like that? Do I have a leak somewhere?

I get all of my boost when driving but this thing at the traffic light is weird.

Thanks for your help!

 

[_MSprotegy]

i wouldnt worry about it if it reads a little higher, if it would read closer to boost is when you would have a vac leak. also it is always best to to have a "clean" source to tap into for your boost gauge.

 

[SwampAss]

God is pissed off at you for reving at a traffic light.

 

[StealthWyvern]

God is pissed off at you for reving at a traffic light.

What hes trying to race that honda! lol(silly)

 

[bykeryder4life]

should be all good man, I have a prosport gauge that goes to -30in/hg and I can get that sucker to bottom out sometimes on deceleration or a quick rev like you stated. As long as boost reads correctly and your fuel trims are under control you dont have a leak anywhere.

 

[RichB]

on my decelerations I never got that low before and I still don't now. This only happens when I do a rev while I am stopped. It also only started happening in general after my FMIC install. why is that?

 

[Speed3Rookie]

try another vacuum source.

 

[RichB]

try another vacuum source.

Thats the only one I know. Where are the others?

 

[chubbs]

check the gauges directions. some gauges like prosport and greddy(sorry only two i have ever owned) will peg to tell you diagnostics. maybe a connection came loose on install of fmic.

 

[RichB]

check the gauges directions. some gauges like prosport and greddy(sorry only two i have ever owned) will peg to tell you diagnostics. maybe a connection came loose on install of fmic.

Thanks I will check now!

 

[Darth Vader]

There is nothing to worry about here. It's normal for the gauge to spike higher on vacuum when the throttle is suddenly closed.

Changes in the intake piping can change the pressure variance between the back side of the throttle plate and the front side and change the reading. Idle is a controlled vac leak situation, where the air getting around the plate is controlled by the ECU. Decel and sudden closed throttle doesn't have time, or have to, activate the idle metering system so, you get a greater amount of vacuum reading.

 

[RichB]

I noticed the guage randomly pin to -30 inHG while I am cruising and not modulating the throttle. It does it over and over again. Could it be that the clear vacuum hose that came with my guage has gone bad and is smashing under vacuum?

I am going to see if changing it fixes the problem. Anyone know a good place to get some vacuum hose?

 

[chubbs]

for standard sizes autozone, kragen pepboys. just take in a piece as a reference and ask them to match it. i know my autozone has vac line in back so you have to ask for it.

 

[chubbs]

also is there a little circle thing, a filter and is it on the right way?

 

[Blitzkrieg]

There was a video someone posted on here that was having the same exact issue, I cant seem to find the post but from what i remeber reading he swaped the guage out and used a different vacum source and experianced the same vac spike, and after a couple 100 mile it just stopped. I had a similar issue ut my boost was spiking and that eventually after 700miles or so stopped as well. I would check all of your lines and give it some time and see if it stops

 

[RichB]

for standard sizes autozone, kragen pepboys. just take in a piece as a reference and ask them to match it. i know my autozone has vac line in back so you have to ask for it.

Thanks! I will check Autozone. You say you have to ask for it? They don't have it out on a shelf?

also is there a little circle thing, a filter and is it on the right way?

There is a filter on it but it looks bi-directional to me. It has worked the way it is for over a year.

Is there something on the filter that would tell me it's backwards?

 

[RichB]

There was a video someone posted on here that was having the same exact issue, I cant seem to find the post but from what i remeber reading he swaped the guage out and used a different vacum source and experianced the same vac spike, and after a couple 100 mile it just stopped. I had a similar issue ut my boost was spiking and that eventually after 700miles or so stopped as well. I would check all of your lines and give it some time and see if it stops

I drive about 100 miles a day and it does it one day and doesn't the next. I tried re-orienting my lines and it came back again. My next step is to replace the lines. Hope that works.

 

[chubbs]

yeah they tend to keep the line in back dont know why so go to the counter and tell them you need vac line, and how many feet or how much. the filter is directional if i recall. dont remember how to tell, also try removing it completely to see what happens. maybe it has a clog in itself and you can always replace if its still the same effect.