Alright, this is about my Black GT in sig...it has 30 lb injectors, which I know are too big, but it was supercharged. I probably would be better off w/ 24's, but could I just keep the 30's and lower the pressure? Right now, the pressure is at 38 psi vac off and I have to hold the gas pedal for it to start (running rich, right?). I really don't want to change injectors simply because I don't want to spend the money if I don't have to. I'm going to play w/ the pressure when I have time, but thought i'd throw this up before-hand. The idle problem could be a timing issue as I had it idling well, but tightened the dist. back down and put spout in and it'll run for about 10 sec and die. I've checked timing half a dozen times and it's at 12-ish*.
Can I Keep my 30's and lower the fuel pressure?
- Thread starter TheUser
- Start date
Michael Yount
Mustang Master
It won't hurt to play with the pressure - you can always set it back if you make things worse. But pressure changes are usually only temporary. The ecu has the ability to 'learn' and make changes - adapative strategies they're called. In closed loop it's gonna adjust pulse width on the injectors til the O2's are reading what it wants them to read - within the range of it's ability to do so. So if drop the pressure to lean things out, and it wants things richer, it's simply gonna increase the pulse width (hold the injector open longer). You could use a chip to make changes to solve the starting problem - withhold/shorten/reduce that initial amount of fuel during startup. Supercharged applications do that all the time.
86Cobra
Founding Member
Michael Yount
Mustang Master
To 86Cobra's point - if your mass air was a ProM calibrated for a supercharged application, the transfer function is probably entirely different than for a naturally aspirated set up with the same injectors. That could be contributing to your drivability and idle difficulties.
wrathchild
Founding Member
Michael Yount
Mustang Master
70 mm MAF sensor. I'm not positive that it's calibrated for the 30's because I bought the car w/ it on there, but i'd assume it was. I thought MAF sensors were calibrated for injector size only - didn't think N/A or Forced Induction came into play? It's not supercharged now. I have not pulled codes, however I was thinking about that and I will try to do that ASAP. I forgot to mention that it still has the FMU on it from the supercharger, but as I understand it, the FMU only kicks in during boost, so that shouldn't cause problems like this, right? I plan to pull it off, but i'd like to have the car running well if possible and then pull it off as to not open my range of possibilities even more.
86Cobra
Founding Member
Meters are calibrated for injector size, EEC, and induction system. Many possible ways for it to be wrong. The only 70mm meter for a Mustang I'm aware of is the 93 Cobra meter which is calibrated for the 93 Cobra EEC using 24 lb injectors.
Michael Yount
Mustang Master
I'd pull the FMU sooner rather than later. To 86Cobra's point, what type (not size) of maf is it?
I really am not sure what type of MAF it is. I bought the car with this stuff, and didn't get any paperwork or anything. I looked and cannot see any brands or anything on it. I ran the numbers on the MAF through google and came up empty - but one time, I thought I did that and found out it was a 70 mm MAF. I'm not sure what all it's calibrated for, however. I dropped fuel pressure as low as it would go (40 psi vac off). I'm not sure why it won't go lower, but that's where the screw starts to come out of the FPR. I started the car up and the first 2 times, it died right off, but the 3rd time, it bounced around and jumped from 1000 rpm down to 800, then 700, then 600, and I made sure to keep it running. Ran it at 2000 RPM for a couple min to warm it up to pull codes. Realized the SPOUT was out, put it back in and the car still ran the same. I tried to pull codes w/ a paper clip and the check engine light and nothing happened, so then I used a test light and still nothing, so I don't know if it just doesn't work or what. Shouldn't it say something if there are no codes?
