: N* Injectors and Fuel Pressure Regulator

11-05-07, 10:43 AM
I have a 2001 SLS. Does anyone know the fuel regulator pressure range? And also the fuel injector capacity?

I have noticed that ever since I modified the air intake, my car has been running very lean. I had thought that the PCM would adjust, but it doesnt look like that is the case. Now, I am looking at possibly upgrading the injectors and/or regulator to compensate. Any thoughts on doing so?


11-05-07, 12:42 PM
Just sticking a so-called CAI on should not alter the air-fuel ratios. One of our resident mechanics will come up with fuel pressures and lb/hr injector ratings, but the PCM controls injector pulse width = flow, so changing injectors probably won't make a bit of difference. Fuel pressure is constantly controlled, partly by manifold vacuum, and the existing regulator has a fairly broad pressure range.

Did you do anything to "modify" the MAF unit or throttlebody ? If so, it's possible that the air/fuel compensation for low-midrange flow/mixture is now outside the PCM program range. A common occurrence with intake modification is a slight to moderate stumble or lag in low and midrange response due to too much air for the rpm/load range.

What gives you the impression that the mixture is lean ? Are the spark plug electrodes and insulator tips burned white after a full power run and shutdown/throttle closed at redline ? Either an exhaust gas analyzer or spark plug reading are the only sure ways to diagnose fuel mixtures across the rpm curve.

11-05-07, 04:13 PM
Don't know about injectors, but fuel pressure should be about 45 psi.

11-05-07, 05:55 PM
checking in

11-05-07, 06:30 PM
The plugs stay white! And i mean printer-paper white!

And I have modified the air intake quite a bit. And I am about to have my father fab an aluminum duct to go from the bottom of the intake box to behind the front grill. Might be a waste of about $200 (which I am sure many on this forum would tell me!!!), but at least I can say I have "ram air"!

My thought was that increased fuel pressure via an adjustable regulator would (if the injectors can handle it) increase the amount of fuel delivered with each pulse. Otherwise, I would need to get new injectors along with the regulator.

The plugs tell me that it is running very lean.. But I still need to get a capable ODB-II reader or Tech II on it to know for sure. But even there I would need a stock SLS to compare it too.

11-05-07, 06:41 PM
You WILL waste $200. Won't see any "ram effect" till somewhere over 100 MPH, probably well over.

11-05-07, 07:00 PM
It just so happens that I have the speedo over 100 just about every day!
So is it a good investment now? :D :D :D

I know what you are saying though. i will have to do the math to see what air volume I would need to see any difference. Very well might not be possible.