View Full Version : MAF Voltage too High?

11-29-2004, 08:56 AM
Hey guys,

I'm wondering if someone out there can tell me what voltage I should be seeing from the MAF at full throttle, full boost. The S14 factory manual gives you values for both idle and 3,000 RPM, both of which I'm about 0.25 volts above. At full throttle, full boost on the freeway, I'm seeing 4.83 volts. I've got an almost totally stock S13 DET, running stock boost. From what I've found on this site, it looks like the MAF is good for a max of 5.11 volts. If I'm already seeing 4.83 at full throttle, full boost, it sure doesn't leave a lot of room for turning up the boost before I max out the MAF.

I took the MAF off and cleaned it up, sprayed off the wires with carb cleaner. That had no impact on the voltage. I'm hooking up my EBC in the next couple days and want to run 10 to 11 pounds of boost but I'm worried about maxing out the MAF.

I'm thinking I may just need to try a couple of different MAFs until I find one that reads more within the acceptable range. What do you guys think?


11-29-2004, 09:08 AM
Mmmm, I won't be suprise.. my friend maxed out his stock S13 redtop MAF by running stock boost around 4800rpm, it just pegged to 5V from that point up.

that's monitored by Techtom CMX100

11-29-2004, 01:57 PM
s13 sr20det mafs is same as s14 sr20de mafs.
s14 sr20de mafs is not the same as s14 sr20det mafs.

according to my jdm s14 fsm, the de mafs reads 1.6v @idle. 2.0v @2000rpm.
s14 det mafs reads 1.2v @idle and 1.7v @ 2000rpm.

if your readouts are from s13 sr20det mafs, then 0.25v above the oz s14 fsm figures should be acceptable.

mafs readouts are very sensitive to restriction or lack of, such as upgraded air cleaner and performance exhaust.

11-29-2004, 05:39 PM
Ah ha, interesting. Thanks for the feedback. I am in fact running a stock S13 SR20DET MAF. According to the FSM I downloaded from Zero-Yon, the S14 MAF limits are:

0.8 - 1.5 at idle
1.4 - 2.0 at 3,000 RPM

My readings are: 1.7 at idle (900 RPM) and 2.15 at 3,000 RPM.

Given what SRFiveTen stated, it sounds like I'm about where I should be for MAF readings.

So, my plan is to slowly crank the boost up and watch the MAF readings like a hawk. I have 2 more questions for the experts:

1) As I'm turning up the boost and watching MAF readings go up, what should be the upper limit of my "comfort zone" for MAF readings? As I stated, I want to run 10 to 11 Psi. If I'm at 11 Psi and 5.0 volts is that too on the edge? If I'm right at the edge of what the MAF can do and get a boost spike to say, 12 or 13 Psi, am I going to blow up the MAF, engine, etc?

2) Let's say I can't make it to my target of 11 Psi before the MAF maxes out. What are my options (if any) for going to a different MAF that DOES NOT require me to re-do intake pipes? Can I just drop in a, S14 DET MAF for example?


11-29-2004, 05:52 PM
The ecu injects fuel based on the specific voltage of the MAF, so if you change something, like swapping mafs, so the voltage is different for the same flow of air. You A/F is going to be changed as well. Most ecu's will go into a default mode when the MAF maxes out. If you max out your MAF voltage at 5.11 volts and you are close to redline at wot, then you are probably going to be fine. If you max out much lower than redline, you would be best to turn down the boost. You can replace the MAF, but you will need something like an AFC to correct for the different MAF signal.

11-29-2004, 06:05 PM
mafs voltage warning lamp can be set to light up when using an apex-i power fc, i believe 5.0v would trigger the lamp.

according to the tuning guideline offered in apex-i catalog, 0.7~0.8kg/cm2 or 10~11.3psi of boost should be attainable with light mods such as intake, exhaust and s-afc, yielding 210~230ps.

0.9kg/cm2 or 12.8psi is said to be the limit for stock turbo, 370cc/min injectors, stock s13 sr20det fuel pump and mafs.

11-29-2004, 06:49 PM
Good point about swapping out MAFs and not changing the ECU accordingly. Makes perfect sense now why people have a "Z32 MAF program".

It also makes sense that once you hit 5.11 volts from the MAF, the ECU goes into a failsafe type mode. I keep seeing posts about how your MAF will die if it hits 5.12 volts or your ECU will blow up, etc. Seems like Nissan would have been a lot smarter than that and programmed in a failsafe for such an occasion.

I like the idea of a 5 volt warning lamp! I think I could rig that up easily enough with a few bucks and a trip to Radio Shack.

As for mods, I've got a Walbro 255, Nismo FPR, Forge FMIC, 2 1/2 inch mandrel bent exhaust (I know that's small but it's the best I could do given the space constraints in the roadster), Greddy Profec B Spec II, stock 370 injectors, T25, and stock MAF. It sounds like I should be able to get pretty close to my goal of 11 Psi without blowing things up.

Thanks for the input guys. Much appreciated!