Popping fuses / bucking

[2eighTZ4me]

I got a "decent" VE table from Cygnus X1 that has a very similar setup to mine. A little rich - but still fairly close. Whenever I get in to boost, I go a little richer (10.0ish) and then poof - nothing. I pop the Inj2 fuse. If I get in to the throttle gradually, it is smooth. When I "get on it", the car bucks like a bronco - like there is a dead spot in the TPS, but that can't be since a smooth gradual acceleration yields good results. The car fires up and idles great (still a little rich). I am running 7.5A fuses for the Inj1 and Inj2 slots. It only pops the Inj2 fuse. Should I go up to a 10A fuse? I can't really do data logging without blowing a fuse. Even at 100% duty cycle, I still shouldn't be popping fuses should I?

 

 

So - based on the above, are there any "glaring" entries that would cause the car to buck/die under abrupt throttle changes?

 

Also - if I want to go leaner, do I up the numbers, or drop them? I tried dropping them and the car went even a little richer. Will try the opposite today.

 

Any help would be greatly appreciated. I need boost and I need it now!

[S130Z]

First off, what size injectors are you running? Second, did you calculate your required fuel under the fuel injector characteristics table? The bucking under accel is caused by lean fuel mixtures. You will have to change your settings in your Accel Enrichment tables to eliminate the bucking. Before you go messing with Accel Enrich, make sure your VE tables are dialed in correctly. In the VE table, the higher the number, the more fuel is added.

 

Also, can you give us a little more info on your setup?

Edited April 17, 2010 by S130Z

[2eighTZ4me]

Injectors are of the 440cc Arizona Z-Car variety. Bone stock ZX NA (dished piston) motor (with 130K on it). MS1 - fuel only. Spark controlled by Electromotive HPV-1. Lonewolf intake, AZC FMIC w/3" pipe. Garrett T04 .60 trim. 3" mandrel exhaust to Borla XR-1 muffler. I did calculate the required fuel - maybe I did it wrong? Will recheck today.

 

If I'm going lean, it sure doesn't show on the wideband. Perhaps it's such a sudden spike that the wideband isn't picking up. I went up to a 10A fuse, but haven't had a chance to get in the boost yet to see if it will blow. In boost, it's around 10.5 - plenty rich - but then the fuse goes.....damn.

 

Thank you for your insight. I will triple check everything today.

[S130Z]

If you know you are going rich in a certain area when the fuses blow, take some fuel out. Your setup is very similar to mine, except I am running MS II 3.57. Start a data log before you start driving, then post the log up for us to see.

 

I also have the same AZC fuel injectors, from the looks fo your fuel maps, your required fuel seems way too high. Recalc your req. fuel so it is about 6.5. Doing this will result in leaner fuel mixtures, so be very careful while tuning! Take baby steps through the rpms and log everything so you have a good idea of where to correct.

[2eighTZ4me]

OK - reran the numbers and required fuel came out to 6.0. I was running 8.3. At 6.0, the second I got off idle, it shot AFR straight to 18+. Reset it to 6.5, and still lean. Went up to 7.5 and while it's still a little rich, I was able to get some decent pulls. The bucking has subsided a bit, and I got up to 12psi of boost comfortably. There's still a few "dead spots" upon abrupt throttle transitions, but either I'm learning how to drive around it, or something is indeed getting better. I have not popped the 10A fuse. All appears to be well - and no burnt wires or anything.

 

I'm trying to attach a log file, but the forum says I'm not permitted to upload this kind of file. I changed it from .msl to .log and still no joy. Any ideas? I can put it out on my website for download, but don't want to make it a pain in the butt to get at.

[z-ya]

Are they low Z injectors? Are you using a resistor pack? What are your PWM settings? Do you have three injectors on each driver?

 

In the log, do you ever hit 100% duty cycle?

 

Lets assume the injectors are low-Z and in the 2.4 Ohm range. Let's also assume that you have three wired in parallel on each injector driver. Thirdly, lets assume that you do not have a resistor pack, and you are using the default PWM settings (OK, we are making a lot of assumptions here, and I think we all know what happens when you ASS-U-ME).

 

The DC resistance would be:

 

1/(1/2.4 + 1/2.4 + 1/2.4) = 0.8 Ohm

 

Ohm's Law:

 

I = V/R = 12V/0.8 Ohm = 15A

 

So using my assumptions above, yes, you would blow the fuse if you hit 100% duty cycle.

 

If you are using a 5 Ohm resistor in series with each injector, it results in 4.8A. Which is just below the recommended 5A injector fuse size. If the PWM settings are correct, it will limit the current well below 5A.

 

Pete

[2eighTZ4me]

I spoke to Matt at DIY Autotune. He had me measure the impedance of my injectors to make sure one of them wasn't fried. All 6 measured out right between 2 and 3 ohms. All good there. He then stated that these injectors would draw about 7 amps a piece when opening, so he recommended going to a 20A fuse for both Inj1 and Inj2. He also stated that I needed to go into TS and set the PWM Current Limit(%) to 30%. Mine was set at 75%. He thinks that is why I was popping fuses. I have made the changes but won't be able to test until tonight.

 

Just an update.....

[2eighTZ4me]

Thanks Pete - wow - our posts were 3 min. apart.

 

You're pretty good at this "assumption" thing I take it - as all your assumptions were 100% dead on the money. Going to see how it does this evening. I'm a little hesitant to hit more than 15psi until I have it properly tuned next Tuesday, but my mix is fairly rich, so I'm not hurting anything. We'll see how she does tonight!

[z-ya]

Thanks Pete - wow - our posts were 3 min. apart.

 

You're pretty good at this "assumption" thing I take it - as all your assumptions were 100% dead on the money. Going to see how it does this evening. I'm a little hesitant to hit more than 15psi until I have it properly tuned next Tuesday, but my mix is fairly rich, so I'm not hurting anything. We'll see how she does tonight!

 

 

I would keep the 7.5A fuses in there for now. If they don't blow, then switch to 5A. Easier to replace a fuse than an injector driver....

 

Also check your log to see if you hit 100% duty cycle.