last weekend i took a trip down to U-Mass Dartmouth to pick up a friend of mine, and on the way i got some really weird fuel cut. i determined that i only get it between 3500 and 4000 rpm's on the highway, around 5 inches of vacuum - NOT in boost or at 0 vacuum.

i tried a bunch of times to replicate the situation and i was able to make it happen every time. although, i couldn't get the fuel cut to happen if, for instance, i was at 5 inches of vacuum in 3rd gear around 4000 rpm's. it only seems to happen in 5th gear on the highway.

i have the 96+ fuel system, s-afc, a missing link, AND HRC's FCD.

my AFC isn't set at all. right now it's all set at 0. i tried setting the pressure sensor at 6 in and 6 out vs. 7 in and 7 out, no effect on the fuel cut.

i have a missing link AND the FCD because a few months ago i bought the missing link and got fuel cut at exactly 0 vacuum, but NOT in boost or below 0 vacuum. so, i simply hooked the FCD back up and ran both. it was smoother than just the HRC "mystery box". maybe the FCD failed and it's tweaking or something?

i am getting a whole bunch of CEL codes. i know one of them is because i have the AFC and it usually tweaks because of that. the ECU probably has issues with me running way too rich too, i haven't had a chance to mess with the bleed valve on the s-fmu.

what do you guys think it could be?

I would remove the HRC FCD, and possibly clean out the Missing link real good. I got fuel cut a while back, and after cleaning the ML, the problem went away.

What injectors do you have?
What's your fuel pressure at idle? static? when you get fuel cut?
What rise rate/ SFMU disks are you using?


If you're running larger injectors, you HAVE to lean out your LO throttle at those RPMs cause otherwise you're getting so much fuel its not even funny. Especially in 5th gear/Overdrive, your throttle is usually at about 15-20% but the load is really high, so you're getting lots of fuel pressure...

i'm running the 415 cc/min injectors with the 3:1 s-fmu disk. fuel pressure is about 23-24 at idle and about 40 at 0 vacuum. i know that's a lot for 0 vacuum, but i haven't been able to really tune the s-fmu at all yet.

you can get fuel cut (or what feels like fuel cut) from having too much fuel? i thought fuel cut only happened when the MAP sensor saw boost, if you hit the rev limiter, or if you're running insanely lean. i'll give it a try... about what values should i be putting into my AFC for low throttle settings? i know that's a noobie question like "hey what do i put into my AFC to get 20 horsepower" because all setups are different, but i'm looking for a ballpark... 5%? 10% 15%? i'm guessing the correction should be highest at low throttle near idle and should go to 0 as it gets around 4500 rpm's. my datalogger isn't working for some stupid reason - if it was i would have certinly fixed this problem by now. would make tuning a LOT easier. right now i'd kill to be able to see my short and long term fuel trims and to also be able to see my timing situation.

well anyways, thanks guys. i'll try cleaning out the missing link and i'll fool with the AFC a little tomorrow when i get home from college.

>I would remove the HRC FCD, and possibly clean out the
>Missing link real good. I got fuel cut a while back, and after
>cleaning the ML, the problem went away.

How do you clean a Missing Link?
n00b question

take it out of the car and spray it with WD-40 and use some compressed air to get the EGR crap out of it? i don't know... maybe just putting it in some hot soapy water would do it too.

ML cleaning: I think you can just drop it in a can of paint thinner or gasoline... pretty sure they used all metal parts in that thing. I just use carb/throttle body cleaner on everything.

Fuel cut: Yeah I'm pretty sure if the ECU sees too much fuel, it will cut it. Could someone with technical knowledge back this up? A quick and dirty test would be to set the safc to like +20 at 2000 rpm.

As far as SAFC settings, tune your SFMU first!! Break out the datalogger, and get as close as possible to the perfect fuel curve. Then adjust the SAFC. I actually had to take out a little more at the highest RPMs cause it was too rich and stumbling at LO throttle, high RPM. Still need to work on that tho because my EGTs go sky high when I'm cruising at 90mph in overdrive.

Running 415 cc injetors, and having 40 psi of fuel at 0 vac, is WAY to much fuel. I will bet that your fuel trims are completly maxxed out. On my 310 cc injects, i need around 30 psi at 0 vac, which results in decent fuel trims, even a tad rich. That *could* be most of your problem. Oh an i agree with the above posts, get rid of the FCD entirly. Just run the missing link. Try running about 15-18 psi of fuel at full idle vacuum, which will bring you around 25 psi at 0 vac. Leave the SAFC totally disconnected and see what happens. IMO, you MUST datalog your setup to monitor your fuel trims and o2 voltages, to help you tune it properly.