2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

Is my fuel cut defenser not working?

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Old Nov 25, 2005 | 05:12 PM
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From: lancaster pennsylvania
Is my fuel cut defenser not working?

I'm thinking my fuel cut defenser is not working because I am getting some bad hesitation around 5500 to 6000 rpms and around 8 or 9 psi. The hesitation is slightly jerky, not like a smooth hesitation. I was worried at first that it might be clutch slippage but this came on kind of recently (slipping clutch usually doesn't happen suddenly). Besides, I just replaced my entire clutch assembly about 2 years ago. I also just replaced all my spark plugs. If my fcd is malfunctioning, how can I check it? thanks.
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Old Nov 26, 2005 | 08:31 PM
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Old Nov 26, 2005 | 09:56 PM
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The RAcing Beat ones are adjustable. There is a trim screw in the box. Turn it til the clamping voltage is higher.

If you read and understand the article I''ve attached the url for, you'll figure out how to set the clamping volgage.
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Old Nov 26, 2005 | 10:12 PM
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the car tend to run real rich from 5750 up too...........................................
if you have big injectors, that might be a reason
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Old Nov 27, 2005 | 02:59 PM
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No, the injectors are still stock size. Plus, this is something that just recently started happening on its own, so it isn't a result of any modifications. Can somebody who has experienced fuel cut tell me what it was like so I can see if that is what is happening to me? also, anyone who knows how to do diagnostics to the fuel cut defenser would be a great help. thanks
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Old Nov 27, 2005 | 05:31 PM
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Read the article.

Want to feel fuel cut? Remove your present FCD and boost over 9 or so psi. Then you'll know.

Or....put a meter on pn 2B and go boost as high as you can go. The voltage should be clamped around 3.65 vdc, if I remember right. Read the article.
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Old Nov 28, 2005 | 03:05 AM
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hailers, the url you mention is not attached in your post. I'll will detach the defenser though and see if anything changes.
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Old Nov 28, 2005 | 03:13 PM
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I have just found a similar problem with mine. I have a Knight sports FCD. doing a 3rd gear pull resulted in a fuel cut, (car hesitated instantly).

Now i'm not sure if my FCD is working or not as well. One thing I did notice is that my factory boost gauge stopped working after I installed the FCD. The needle would jump around sometimes. Sometimes it would seem like it's working, but 99% of the time it just sits on the bottom. Is the stock boost gauge suppose to function normally after you install the FCD?

I'm assuming I installed it correctly. I just popped the hood, unplugged the harness from the stock map sensor and plugged the FCD in line.

Sorry, didn't mean to hi jack your thread, but figured this is similar.
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Old Nov 28, 2005 | 03:33 PM
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Originally Posted by Trike
I have just found a similar problem with mine. I have a Knight sports FCD. doing a 3rd gear pull resulted in a fuel cut, (car hesitated instantly).

Now i'm not sure if my FCD is working or not as well. One thing I did notice is that my factory boost gauge stopped working after I installed the FCD. The needle would jump around sometimes. Sometimes it would seem like it's working, but 99% of the time it just sits on the bottom. Is the stock boost gauge suppose to function normally after you install the FCD?

I'm assuming I installed it correctly. I just popped the hood, unplugged the harness from the stock map sensor and plugged the FCD in line.

Sorry, didn't mean to hi jack your thread, but figured this is similar.
Yeah.. the stock gauge should still work (it will, however, display a lower signal than reality)

Al the FCD does is take the signal from the boost sensor, limit it to 3.6 volts and then puke it back out to the ECU....

Take the FCD off and plug the stock connector back into the boost sensor.. if the gauge works now the FCD is screwed up...

If the guage is still wrong, you either have a bad boost sensor or a fault in the wiring somewhere. (or the stock gague is broke)

But, i suspect it to be a wiring/ connection problem bacause of the gauge jumping around thats telling me its getting an intermittant signal, like there is a loose or corroded conection or a ground fault somewhere
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Old Nov 28, 2005 | 03:44 PM
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The Dummy, me, forgot the ariticle url here: http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm

Like the decaying man said, remove the fcd and reinstall the plug to the boost sensor and the gauge and fuel cut should happen again. The gauge sits below zero because your pulling vacuum. When at atmospheric pressure or more, the gauge moves above zero.

I have a home built FCD and a RB one. I had to readjust the RB one because I didn't like the setting. I took the top off and I could see the adjusting pot screw. I used a meter to tap pin 2B and a hand pump attached to the boost sensors input nipple to create pressure and adjusted the output voltage to something close to 3.65 vdc. It was something on the order of 3.22 vdc.

If the gauge does nothing, then it ALMOST follows nothing is happening at pin 2B of a series four ECU. NOT good.
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Old Nov 28, 2005 | 04:13 PM
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I know the gauge works for sure with the FCD removed. That tells me that the ECU might not be getting a proper signal from the map sensor/fcd. Man that's not good. i've been driving around like this for the past week and a half. Going to remove the fcd and take it apart to see if anything looks fishy.
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