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Discussion Starter #1
having issues with my boost jumping around. as a result of its fluctuating, its causing issues with my injector pulse width. here is a photo of my recent datalog


i just put brand new precision waste gates in. i was previously running some chinese gates when the issue started so i switched to precision but it did nothing to fix the issue. boost jumps up and down about 2psi. what could be going on here?

another issue i see is that rpm dropping from 6k to 4500 right as the boost its 257kpa. over boost was set to 275 for this run so i couldnt have hit my boost limiter, yet the motor stumbled
 

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Are your bypass/blow off valves leaking? What type of boost controller are you using?
 

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how do i test if my BOV is leaking? the issue only happens at high boost so i doubt i could foot brake the car into enough boost to hear a leak and even if i could the motor would be so loud i wouldnt hear a small amount of air leaking.

no boost controller. that boost is set by the springs in the gates. i plant to run an EBC so i can turn the boost up about 10psi more but no reason when i cant even get low boost to work correctly.
 

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If one or both of them are leaking you'd generally hear them, though you might have to have your head under the hood to hear it. They'd make an audible hissing or hooting noise under part or full throttle.
 

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took the BOV out completely and made a couple pulls. made no significant difference. boost still fluctuates by about 1.5psi i know the boost wont hold rock steady and its going to fluctuate some, but how much is acceptable. at this point, i have ruled out the BOV and the wastegates
 

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Mine fluctuates about 1.5psi at 25psi.
I don't know how rock solid it can actually get and what's not acceptable but for now I'm not worried about it.

ks
 

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having issues with my boost jumping around. as a result of its fluctuating, its causing issues with my injector pulse width. here is a photo of my recent datalog
...

i just put brand new precision waste gates in. i was previously running some chinese gates when the issue started so i switched to precision but it did nothing to fix the issue. boost jumps up and down about 2psi. what could be going on here?

another issue i see is that rpm dropping from 6k to 4500 right as the boost its 257kpa. over boost was set to 275 for this run so i couldnt have hit my boost limiter, yet the motor stumbled
I am not convinced that the boost fluctuations caused the injector pulse width to change.

There are a lot of considerations, including differences in level of precision and lag times between different types of sensors, response to changes in battery voltage, mechanical properties of the springs in the wastegates, delay time and resonance of the hose to the MAP sensor, etc.

Some discussion that may help:
Megasquirt Support Forum (MSEXTRA) ? Internal MAP sensor considerations (View topic)

Also, the datalog doesn't show target AFR or spark timing. Those might help you figure out why the injector pulsewidth appears to be dropping.

Also, if the boost control is all mechanical, did you calibrate it against the electronic pressure sensor? 275 is only 107% of 257. It seems likely that the tolerance of each component is big enough that the wastegate could have opened while the sensor was reading 257ish.

Also, 23 psi is low boost to you? Whoa.
 

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kevin that makes me feel a little better. i cant feel the power level changing, pulls like a freight train all the way to 7000rpm......wants to pull past 7k but i wont go any higher.

mazza, i made an adjustment to my deceleration enrichment (change it from 90% to 100%) and the dips in the injector pulse width went away completely. one problem solved. 23psi is low boost when you plan to add another 10 or 12 on top of that >:)

the fluctuations started when i went to bigger turbos, perhaps the twin 38mm gates arent enough to run boost this low. ill probable stick a bigger spring in the gates, see what boost it hits and then hook up the EBC and go the rest of the way up with that
 
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kevin that makes me feel a little better. i cant feel the power level changing, pulls like a freight train all the way to 7000rpm......wants to pull past 7k but i wont go any higher.

mazza, i made an adjustment to my deceleration enrichment (change it from 90% to 100%) and the dips in the injector pulse width went away completely. one problem solved. 23psi is low boost when you plan to add another 10 or 12 on top of that >:)

the fluctuations started when i went to bigger turbos, perhaps the twin 38mm gates arent enough to run boost this low. ill probable stick a bigger spring in the gates, see what boost it hits and then hook up the EBC and go the rest of the way up with that
That's interesting. Now that you said that, when I look at the RPM trace closely, I see some small dips in RPM that correspond with the drops in injector pulsewidth. So the computer definitely did drop the pulsewidth on purpose.

Next question would be, why is RPM dropping at all when you are at full boost? Maybe the wastegates really are the start of the issue. If boost lets up, maybe the engine can't maintain speed.

Does it do this on the track and on the dyno? If only on the dyno, maybe the loading could be inconsistent?
 
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