[SOLVED] Throttle/Boost Cut/Misfire on Partial Throttle?

Brado

Brado

Problem Encounterer
Greenie N00B Member
I've recently been experiencing an issue where on partial throttle (mainly) my BOV will activate randomly and quickly, to where the car sounds like it's sneezing. The pedal position is constant however the wastegate appears to get the signal to dump the boost momentarily before it builds back up and possible does it again.

This of course jerks the car and is no fun to experience. I'm wondering what the issue is and managed to get it on log and video at the same time.

Datalog:
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Video:
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Does anyone have any info or suggestions?
 
What Bov are you running? Probably needs the correct spring for your vacuum. Or could be failing ebcs what brand ebcs, what turbo.
 
Awafrican said:
What Bov are you running? Probably needs the correct spring for your vacuum. Or could be failing ebcs what brand do you have?
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HKS SSQV BOV. It's been on the car for years and no parts have changed, so I don't think that's the culprit.
 
Awafrican said:
Which ebcs / turbo? Any recent maintenance?
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MAC 3 port EBCS and a BNR S3. I replicated the issue several times today and all of them show the Throttle Position (%) dip when the issue occurs. Since my Accel Pedal Position looks good I'm leaning towards a connection issue with the throttle body itself.

Here's a datalog that I got today and the corresponding video.
Throttle Issue.png
Video:
Template public:_media_site_embed_youtube not found. Try rebuilding or reinstalling the s9e/MediaSites add-on.
 
Brado said:
MAC 3 port EBCS and a BNR S3. I replicated the issue several times today and all of them show the Throttle Position (%) dip when the issue occurs. Since my Accel Pedal Position looks good I'm leaning towards a connection issue with the throttle body itself.
Click to expand...

Excellent diagnosis on your part, thumbs up to you.

The throttle body connection is known to have problems (as far as I have seen its the pins on the connector), as is the throttle body itself.

The symptoms line up as well, your APP shows a higher value, while the throttle closes up. The ECU will see a higher load (or boost) and reference the fueling required, but with a surprising lack of air (due to throttle close) and you see a rich condition, as per your logs.

First thing I would do is check for damage and really closely inspect the harness side connector going to the throttle body.
 
The_big_dill said:
Excellent diagnosis on your part, thumbs up to you.

The throttle body connection is known to have problems (as far as I have seen its the pins on the connector), as is the throttle body itself.

The symptoms line up as well, your APP shows a higher value, while the throttle closes up. The ECU will see a higher load (or boost) and reference the fueling required, but with a surprising lack of air (due to throttle close) and you see a rich condition, as per your logs.

First thing I would do is check for damage and really closely inspect the harness side connector going to the throttle body.
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Glad I'm on the right track! I've got an...interesting connector that's seen better days. I'll inspect the pins on both ends and see if anything immediately stands out. On one hand I hope it's the connector because the throttle body is expensive, but on the other hand wiring issues are a pain in the ass.

upload_2021-4-26_21-7-13.jpeg
 
What in tarnation is going on with that connector...even duct to tape could very well be it coming loose
 
SharksInSpace said:
Why does it have a zip tie around it, is it physically damaged?
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To my understanding the red lock connector tab is broken/missing so it has never clicked into place. The zip tie is simply there to try and prevent it from coming off completely.
 
My throttle body connector looks similar, heat cycles made it brittle and the clip crumbled on me when I tried to unclip. Check the pins are still lined up on both sides, throttle body and cable.
 
Yes, the yellow zip tie looks aftermarket haha.

If you are having trouble seeing the pins in the connector, that red retaining tab with the pin holes in it is removable. A pick/screwdriver/pliers can be used to pry it out. Just be gentle, especially with the pliers.

The good news is that you can get a replacement pigtail connector, all you need is some soldering skills and basic tools:

https://www.bmotorsports.com/shop/product_info.php/manufacturers_id/3/products_id/4478

In terms of a throttle body, you can likely source a used one from a yard or the forums. I may have a couple throttle bodies laying around as well that I won't charge much for.

Good luck!
 
The_big_dill said:
Yes, the yellow zip tie looks aftermarket haha.

If you are having trouble seeing the pins in the connector, that red retaining tab with the pin holes in it is removable. A pick/screwdriver/pliers can be used to pry it out. Just be gentle, especially with the pliers.

The good news is that you can get a replacement pigtail connector, all you need is some soldering skills and basic tools:

https://www.bmotorsports.com/shop/product_info.php/manufacturers_id/3/products_id/4478

In terms of a throttle body, you can likely source a used one from a yard or the forums. I may have a couple throttle bodies laying around as well that I won't charge much for.

Good luck!
Click to expand...
I love Ballenger Motorsports! I got my EBCS pigtail from them and it was perfect. Great to know they have our pigtail for the throttle body! Granted, the wiring for the throttle body probably won't be as nice/fun as the simple EBCS pigtail...

Thanks for the help!
 
Alright so I took some better pictures of the connectors, both male and female ends, however I think I may bust out the DSLR for even higher resolution photos when I get a chance. Nothing strikes me as immediately obvious, especially with the throttle body male pins, but let me know if anything looks out of place. If I really had to nitpick I'd say maybe the two left most pin holes on the connector look loose?
IMG_3135(2).png IMG_3132(1).png
And of course a video of the connector for a sense of depth:
Template public:_media_site_embed_youtube not found. Try rebuilding or reinstalling the s9e/MediaSites add-on.
 
Brado said:
HKS SSQV BOV. It's been on the car for years and no parts have changed, so I don't think that's the culprit.
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HKS sucks at part throttle. I could never get it to drive the way I wanted and it would like half open and leak unless I was doing WOT which at 600+ hp was not something I could just do all the time. @alexwlwsn had similar issues. I got the precision 50mm and never looked back.
 
JohnnyTightlips said:
HKS sucks at part throttle. I could never get it to drive the way I wanted and it would like half open and leak unless I was doing WOT which at 600+ hp was not something I could just do all the time. @alexwlwsn had similar issues. I got the precision 50mm and never looked back.
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HKS does suck for driveability, but I've never experienced this very annoying issue until recent months. If I could afford a GFB BOV I'd give it a crack, but I'm not sure it would fix the throttle cut issue.
 
My car would do this also when the pressure relief valve was going out. As soon as it tried to get into boost and command fuel it would not be there so it would cut out.
 
JohnnyTightlips said:
My car would do this also when the pressure relief valve was going out. As soon as it tried to get into boost and command fuel it would not be there so it would cut out.
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I recently cleaned out my relief valve and after looking at the datalog for the triple boost cut above I see the fuel pressure is there.
Here's that datalog:
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issue.png

I do see the MAF giving off some weird numbers, but I can't tell if that's because of the throttle position or if it's visa versa. Guess it couldn't hurt to clean the MAF again and just see if there's a difference.
 
JohnnyTightlips said:
My car would do this also when the pressure relief valve was going out. As soon as it tried to get into boost and command fuel it would not be there so it would cut out.
Click to expand...
It is, yes. I've heard aftermarket ones can be hit or miss. That said, it could very well be the original MAF for all I know.
 
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