Troubleshooting a FRPP SC install. Looking for advice.

Rickycardo

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So about 3 weeks ago I finished installing a Ford Racing supercharger on my 2015 GT auto. I've never done this install before but have been building engines for many years. Long story short the car runs greats except I get a slight stumble at highway speeds and I haven't found the cause yet.
When driving the car in 5th or 6th at a steady speed above 40mph the engine has a sight stumble. You can just barely feel it. Watching the vacuum gauge you see it bounce around a little and the a/f gauge will run13-14 then bounce up to 15-16 then back. When the cruise control is on and the car goes down a slight grade you can really feel it. Otherwise the car runs great. Good power, smooth idle, drivability is good, even fuel mileage is good. The car has 51k miles and runs perfect and always serviced regularly.
I have suspected a vacuum leak somewhere but after replacing all the hoses I've yet to find anything. I pulled the throttle body and supercharger body and checked for a bad seal but didn't visually find anything.
Has anyone else run into this after doing an SC install? I don't want to take to a tuner and pay just to find I've missed a vacuum fitting somewhere. TIA.

 

ZenkaiRacer

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Sounds like the supercharger bypass valve may be fluttering at low vac for some reason. Would triple check the vacuum to the bypass valve actuator.
 
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Rickycardo

Rickycardo

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Thanks, I'll look at that too. According to the vacuum gauge I'm running 18-20 inches at speed when it happens. It will run around 20 and bounce down to 14-15 and back. It was happening this morning on my way to work in 4th gear. It seems to happen when the engine isn't under load, flat cruising or downhill. It goes away as soon as the engine is under load again.
 
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Rickycardo

Rickycardo

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Wait, is thew bypass supposed to open at low vacuum or high?
 

ZenkaiRacer

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It should open under vacuum. So higher vacuum such as at idle it should be open more.
 

Cory S

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Could be tune related.
 
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Rickycardo

Rickycardo

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I may have found my problem in the dreaded aspirator. I went through the instructions again and verified my vacuum plumbing. I think I had the hoses switched. I replumbed it and it seems much better now. I still need to do a highway test to make sure.
 

 
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