Car doesn’t want to idle anymore after supercharger install

nbeyer2000

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Sep 7, 2018
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So this past week I installed a Powerdyne supercharger into my 91 fox. Since I’ve got it installed, the car doesn’t want to idle anymore. If I get the car going 20+ it’s just fine and drives good and has great power, but as soon as I slow down to a stop the car starts to drop very low in rpm and feels like it wants to die( and sometimes it does die). The kit I bought came with a pro-m MAF sensor and I’m wondering if there is any way to tell, without sending it in and paying 50$, to see what it’s tuned for. I put 24lb injectors in the car awile back before I had the blower, and today installed a 255 lph BBK fuel pump and it now starts good, but it still wants to die at low speeds. Any help would be awesome!
 

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jrichker

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You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 

John Dirks Jr

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It's important for the MAF to be calibrated for the specific size injectors you are using. Post a picture of the numbers on the MAF. Sometimes the numbers tell what it's calibrated for. Mine does. In this pic you see M93-30. I have 30lb injectors.

77672594-0668-4476-B86F-D96EFFBE1F2E.png
 

nbeyer2000

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It's important for the MAF to be calibrated for the specific size injectors you are using. Post a picture of the numbers on the MAF. Sometimes the numbers tell what it's calibrated for. Mine does. In this pic you see M93-30. I have 30lb injectors.

77672594-0668-4476-B86F-D96EFFBE1F2E.png
I don’t remember it having a sticker or anything like that, but I’ll send a pic when I’m home from school. Thank you!
 

Mstng93SSP

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When I was first starting out working on cars, there were no computers, no internet, nothing like that. You are fortunate with the infinite amount of information on the web. If someone suggests something like doing a base idle reset, and you don't know what that is...search google for "mustang base idle reset". It will easily guide you through what you need to do.
 
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nbeyer2000

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Sep 7, 2018
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When I was first starting out working on cars, there were no computers, no internet, nothing like that. You are fortunate with the infinite amount of information on the web. If someone suggests something like doing a base idle reset, and you don't know what that is...search google for "mustang base idle reset". It will easily guide you through what you need to do.
thank you for the help!
 

John Dirks Jr

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That looks like a 30lb MAF to me according to the labeling anyway. With the SC you'll need bigger than 24lb which you currently say you have. I have 30lb on my setup and they're maxed out. It's not the recommended setup but I am cheating by turning up the fuel pressure. I've been lucky to get away with it so far.

You might want to go with 42lb and a calibrated MAF
 

nbeyer2000

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That looks like a 30lb MAF to me according to the labeling anyway. With the SC you'll need bigger than 24lb which you currently say you have. I have 30lb on my setup and they're maxed out. It's not the recommended setup but I am cheating by turning up the fuel pressure. I've been lucky to get away with it so far.

You might want to go with 42lb and a calibrated MAF
Okay. So what kind of 30lb would you recommend? And thank you a lot for the help.
 

John Dirks Jr

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First of all, I’m not ready to recommend 30lb injectors. You may need something bigger, maybe not.

What is the rest of your engine setup and how much boost do you expect to make with that blower?

No matter what size injectors, I see another potential problem. You have a cone filter attached directly to the maf inside of the fender. That’s turbulent air at that point. Some mafs are designed to be used like that and some not. Some need to be further up the tube.

Where did you get this stuff? If you bought used stuff you don’t know for sure what you have. I’m not the best for giving advice on these matters but even experts would be chucking darts if they don’t know what you’re working with, or what your expectations or goals are.

What about your head gaskets? Are they up to snuff when it comes to significantly increased cylinder pressures that boosted engines see? My head gaskets failed repeatedly until I pulled the engine, decked the block, heads and used Cometic gaskets with ARP head studs.

I’m sorry to complicate the matter for you, but me throwing darts on injector size is sketchy at best, and only a small part of the big picture even if I was correct.
 

Boostedpimp

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It all depends on the power out put planned for the car. If your looking to swap a pulley and push some boost through it and break stuff then you will need to toss the FMU, 24lb injectors and MAF for some 42lb or 60lb injectors, maf and a tune.. and like mentioned above the head gaskets will be your failure point. Plan to eventually experience the thrill of replacing them.


If it's a simple stockish street cruiser with out of the box powerdyne, then you should be able to get away with the FMU, 24lb injectors and calibrated 24lb MAF.
 

Blown88GT

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The Powerdynes were 6 psi. 24's will be fine. You need a maf matched to 24's. The "maf matching" is only an issue if using the factory ECU (EEC-IV), with no chip.
 

jrichker

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@nbeyer2000
Evidently you didn't follow the link to Surging Idle Checklist.
The no cone filter inside the engine compartment is one of the big "No No's" given in the checklist. You should thank @John Dirks Jr for noticing that problem.

Do the checklist, you will find and fix the problem a lot quicker than randomly chasing rabbits her and there. The reset base idle is one of the procedures given in the Surging Idle Checklist.