Boost cut? such a thing?

[droppinbottom]

Well I finally got the car on the dyno today. I managed to get it to 288awhp @21psi with no knock so we decided to up the boost a bit and as soon as I hit 22psi it felt just like fuel cut but the operator mentioned it as being boost cut. I have never heard of boost cut. I can post the log of it when it happened if anyone wants to see it. When it happened we were at around 4k and the idc was still low. Any ideas? All my mods are listed in my profile.

Thanks for the help and sorry if this is a rather newbie question.

 

[zippyshoe]

I have never heard of the term "boost cut" either. You very well could have experienced fuel cut. Fuel cut is strictly based on airflow (actually airflow per rev) that the ECU sees. When this airflow (airflow per rev) exceeds a pre-programmed value, the ECU responds by cutting fuel to the cylinders, hence the term "fuel cut". I see in your profile you are using an SAFC piggyback type fuel controller. These type of controllers will simply delay the onset of fuel cut - they will not eliminate fuel cut as provided by the factory ECU. Since fuel cut is based strictly on airflow, with upgraded injectors you can reach fuel cut even at low IDC's. If you look at the log at the point of this event and see your IDC's suddenly drop to 0%, then this is a good indication that you reached fuel cut. Hope this helps!

 

[droppinbottom]

That is what I thought as well. Yes the idc's went to zero as soon as it happened. So the only way to fix this problem is to get rid of the afc and step up to link or aem if I am understanding this correctly.

 

[zippyshoe]

That is what I thought as well. Yes the idc's went to zero as soon as it happened. So the only way to fix this problem is to get rid of the afc and step up to link or aem if I am understanding this correctly.

To reach the power goals I think you have in mind, you will be flowing a lot of air. Since fuel cut occurs at a fixed airflow per rev value, your only options are:

1. Further delay the onset of fuel cut by upgrading to larger injectors, which will allow you to adjust SAFC so that the ECU sees even less airflow.

2. Switch to another fuel control method such as a "chipped" EPROM ECU which is custom-programmed for a particular injector size, DSMLink, AEM, etc. DSMLink completely eliminates fuel cut and I'm sure a "chipped" EPROM ECU could be programmed to eliminate fuel cut as well.

I would probably opt for number 2 because there are practical limits on what size injectors can be tuned using SAFC. I think some people have also used a combination of SAFC and a "chipped" EPROM ECU which extends the capabilities of SAFC with larger injectors. My personal favorite option is DSMLink, but this can be a bit pricey. AEM standalone system is powerful, but requires extensive knowledge and time to tune properly. Good luck in your decision!

 

[CanadianTSi]

What are your S-AFC settings like?

And Have you done a boost leak test recently?

 

[droppinbottom]

^^ I did a boost leak test the night before dyno since I was working on the car and off the top of my head the afc settings are in the -20 range (I dont remember every one off the top of my head) and my a/f is a bit rich down low 10.7+/- and from 4k on they are around 11.3

Zippy, I am planning on getting link but first I am looking for a eprom since my 90 ecu had to be replaced by a previous owner and it is not eprom. As soon as I get a eprom I am going to get link and I think I have enough old stuff sitting around to offset the cost of link. I was also hoping that if I held off long enough they might release v3 and I could possibly get rid of the translator. Guess it is going to come sooner than I thought.

 

[zippyshoe]

As you probably already know, you will also need a laptop in order to use DSMLink. If you already own a laptop, then you can check this off of your list of expenses. Good luck with whatever fuel control option you go with!

Also, CanadianTSi raises a good point about boost leak testing. If you have a boost leak, then the ECU will "see" a higher airflow than what is actually entering the cylinders while under boost. The air that is not entering the cylinders is escaping through the leaks. This may cause you to reach fuel cut prematurely. This will also cause you to run rich.

 

[scottsee]

Just for refrence, the popular term "fuel cut" occurs around 2.55g/rev. Good Luck..