mikey k

i know there have been at least a million post regarding gauges but all of them are contradicting and don't really answer my questions. so, here goes:

on a car that is modded with a bunch of m2 bolt ons (including ecu) is an afr gauge good for keeping an eye on things? i've read a bunch about how "useless" they are, but those people seem to be looking for something that is a constantly accurate, tuning tool, not just for monitoring. i just want to have something to let me know if something unusual happens (clogged fuel filter or injector problems). i've already lost one engine, and i suspect it wasn't getting enough fuel.

next, i've read things that say that oil temp and water temp are not directly related. however, they didn't say what the difference is.

similarly, if an afr gauge is good for monitoring, how does a fuel pressure gauge differ? what are the advantages of each? if someone was to get one or the other, which should it be?

lastly, what problems cause high or low oil pressure?

now, i know many of you have strong feelings about afr gauges. you don't need to sit and tell me how useless they are. i've already read your opinion. i'm looking more for people who like them and WHY. not just "mine works great" and "those are useless".

thanks for your help.

rynberg

Any a/f gauge relying on the stock o2 sensor is worthless. The stock o2 sensor is a narrowband sensor, it doesn't produce a linear voltage as the a/f ratio changes. It is only meant to keep the a/f ratio near stoichiometric (14.7:1) during cruising conditions. This is why the engine computer does not rely on the o2 sensor readings once you start opening the throttle. There isn't any contradictory information -- just people that are deluded into thinking their a/f gauge is anything but a light show.

As far as for a fuel monitoring device, I think a fuel pressure gauge would be more useful. Let's face it though, if an injector fails (which is an INCREDIBLY rare event, except for some failures with the bored out 1300cc injectors) under boost, your motor is likely gone, it doesn't matter if you have a gauge or not. As far as a clogged filter goes, simply change it every year or two.

mikey k

that is exactly the answer i knew i would get. my question, however, is not dealing with "opening the throttle". i was wondering if it would show any trends during cruise (since, according to other post, that seems to be the only time it is accurate) that would indicate the car was starting to run lean.

evot23

iTrader: (17)

He did answer your question, you just didn't know it.

The a/f guage will not show any accurate trends in cruising. It will bounce all over the place from time to time and on deceleration. Mine says its lean at 2800 rpm cruising in third gear. The dyno says otherwise. Save your money, don't make a mistake I've made and
get a wideband if you are that concerned.

Fuel pressure gauges show you a baseline fuel pressure that is in your system. A Fuel Pressure Regulator makes sure that pressure does not go down with wide open throttle. Usually only really necessary when you upgrade your fuel system (bigger injectors, new or additional fuel rail, etc).

rynberg

Um...your car WILL be running lean during cruising conditions, that's the whole point of why cars have o2 sensors....

Also, how the hell does knowing what your a/f ratio at cruise is, have anything at all to do with what your a/f ratios under throttle are, which is the only time it's a concern. You can run 15:1 in vacuum and never blow the motor, it's under boost that you have to worry about.

adam c

iTrader: (2)

They are not directly related. Different conditions will produce different relative temps. For example, lets say you are sitting in traffic with a stock FD. The water temp and oil temp will continue to rise. At 226, the fans will come on to lower the water temp immediately. There is no oil cooler fan, so the oil temps will not drop quickly.

The oil temp gauge can be a better indicator of when your engine is truly warmed up, and ready to be pushed. The water gauge may say 180 degrees, but if the oil temp isn't up yet, the engine isn't completely warm, and may not perform to its full potential.

I have my oil temp sensor in the pan. It replaced the stock drain plug. When the gauge reads 200 degrees, I know the engine is ready for anything.

Hope this helps.

mikey k

thank you adam c. that's the kind of answer i'm looking for. so, is that to say that if you have one or the other (water temp or oil temp) you should go with the oil temp?

RotorMotor

iTrader: (5)

so if the A/F gauges are 100% useless why do they make them??? if they just bounce around non stop, how would companys still be able to sell them>

SpeedKing

iTrader: (4)

Why do they make them? So you can pay off the gauge company's president's mortgage and buy him a new boat, that's why.

rynberg

Go with water temp over oil temp. The only time to be really concerned with oil temps is when you are tracking the car (not auto-x, road course).

To add to what Adam already said, the oil temps will follow what the water temps are doing in typical driving, but they will be a bit higher (at least with the stock single cooler). On the track though, it can be a different story -- my last 2 track events saw water temps of 210F but oil temps of 250-255F. Obviously, Mazda put two coolers into the R1/R2 for a reason.