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420A I need help 420a turbo

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Michael Snipes

Probationary Member
14
1
May 20, 2020
Tucson, Arizona
I have a 420a with a custom manifold and when I hit boost it will stutter when it switches from vac-boost. Then I’ll get a really bad fuel cut around 4500 rpms. Please help.
 
I have a 420a with a custom manifold and when I hit boost it will stutter when it switches from vac-boost. Then I’ll get a really bad fuel cut around 4500 rpms. Please help.
You are probably running rich or have a bad air leak somewhere how have you tuned the car and what other upgrades?
 
If it still has the stock ecu controlling the fuel and spark then that’s the issue. The stock MAP sensor can’t read positive intake manifold pressure. It causes the ecu to cut fuel because it thinks somethings wrong.

That’s a stab in the dark though. I need more details to help further. Like how are you tuning it. What was done to turbo it. Any pics of the engine bay.
 
You are probably running rich or have a bad air leak somewhere how have you tuned the car and what other upgrades?
No tune. I got the cat how it sits and yes I’m assuming to lean. But what do I do. It’s 2020. I can’t afford ms right now. Missing link is like unheard of. Fcd are out of service. So should I get a adjustable fpr?
 
An adjustable FPR will not solve the issue of it cutting out. It’s cutting out because the ecu is seeing positive intake manifold pressure.
 
So what do y’all recommend. I’m not doing well enough to afford mega squirt or a stand alone.
 
FCD + FMU is probably the cheapest option. You can still find both of them on eBay.
 
Not tryna be this guy but ok.

fcd- electronic or missing link?

I’ve been reading a lot of forums trying to figure this out. Could you link what you think is the most bang for its buck on eBay. I’ve been looking and it’s like 150$ for a fcd and 220 for a fmu.
 
Thank you so much. I probably can’t get the sfmu yet but the fuel cut defender I should be able to get.
 
I've had better luck with electronic FCD's. There's a used HKS unit for under $50 here:

https://www.ebay.com/itm/HKS-Fuel-Cut-Defencer-FCD/254460367706

I've also seen a few HKS knockoffs on AliExpress for about the same price.

There's actually an S-FMU--which will give you more flexibility than an FMU--listed for $150 shipped right now, which is a pretty good price:

https://www.ebay.com/itm/Vortech-Super-Fuel-Management-Unit-s-fmu-sfmu/333742251395
Do you know a How to video or no?
 
Thank you so much. I probably can’t get the sfmu yet but the fuel cut defender I should be able to get.
Just FYI, you will destroy your engine if you try running boost without some way to also control fuel, whether it's an FMU or otherwise. Adding an FCD without fuel management is asking for trouble.

Do you know a How to video or no?
No, but there must be a million threads about how to install FCD's and FMU's in these forums.

And that doesn’t look like the correct fcd. Is it the same?
The same as what? It should work for your application. It looks like an older model, but I was trying to find something cheap for you.
 
Just FYI, you will destroy your engine if you try running boost without some way to also control fuel, whether it's an FMU or otherwise. Adding an FCD without fuel management is asking for trouble.


No, but there must be a million threads about how to install FCD's and FMU's in these forums.


The same as what? It should work for your application. It looks like an older model, but I was trying to find something cheap for you.

didn’t look like the same. But okay I’ll order that. And thanks guys. So get the fcd and a sfmu ASAP.
 
So update I have a missing link and vortec fmu 12-1 and still experiencing fuel cut. I don’t have map sensor code or any other codes.
 
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