In the recent days I’ve come to learn some things about the fuel temp sensor.

For starters, many of us toss/lose the stock fuel temp sensor when we get an aftermarket fuel rail for bigger injectors. This is a big deal. Without the sensor afr can be impacted by up to 4%. So running an aggressive tune can make you dangerously lean without anyone knowing, including the tuner.

it’s water under the bridge for me since my fuel rail doesn’t have the sensor. My question is, what is involved in getting the fuel sensor added? Is there a solution for this that isn’t a major operation? Or do I need to replace the rail entirely? If that’s the case I will stick to a conservative tune targeting low 10s afr which is unfortunate.

I am running 750/2100 cc injectors. Or was it 700/2100. I forget.

 

Its not as critical as people make it out to be. If it were, they would be standard equipment. The only other place I've seen a fuel temp sensor is on a z32. What it and the fd have in common are fuel rails that are in wildly hot locations.

According to the power fc, its a 2% difference at PEAK which is 60C (140F). I can think of no situation where a rise in fuel temperature would be the only or the decisive factor in a circumstance that would require such a correction. Not like a rise in air temp while sitting still. If you car is tuned to the wall where a 2-4% difference in fueling due to FUEL TEMP matters..... you have bigger problems.

For the fuel to get hot enough and not have anything else going on that would affect a tune is very unlikely. That would be indicative of an issue with the fuel pump getting too hot in the tank or the exhaust running too hot and cooking the gas. Even if the pump was getting too hot due to actual extreme use, a fuel cooler would be (should be)(better be) installed on that car and it more than likely wouldn't be pump gas in that system. Also the exhaust being too hot that far back is a problem on its own.

Im not saying the power fc base settings are great or anything but its the only ecu map i can think of that has base fuel temp corrections built in. Even on a link ecu with the z32, it suggests you to use the fuel temp sensor wire as an additional input for something else lol

This sensor is seriously not making or breaking any tune, especially on a street car. Although I don't label myself a tuner, I can tune and do tune cars other than FDs and at no point has fuel temp played a role or has been a variable. Granted, I'm not a big hp person so that's probably why

/rant

 

its 4% and that’s enough to lean up a map if aggressive.

and it’s not ok just bc everyone does it. The gm map sensor is sold by everyone and very common. Yet it’s not compatible with Pfc

 

Mazda engineers would not have included the fuel rail temperature sensor on the FD if it was not required to maintain stable fuel injection. The issue is generally not whether or not the engine will get damaged, but whether the ECU is able to hold the tuned AFRs stable throughout the year and independent of under hood temperatures. The Apexi PFC default compensation setting of 2% at 60 degrees C is inadequate (wrong) and the correct fuel compensation values are applied by FC-Tweak. ECUs with no such compensation should not be used on the FD. Gasoline fuel density changes are higher than most people would think. For example going from 20C to 50C, gasoline density changes by -4%. This amount of variation can be observed by seasonal temperature variations, meaning that any RX7 which has no fuel temp sensor will run richer or leaner by approx 4% depending on the season it was tuned in. This does not take into account the heat soaking component of the fuel rails, when fuel density changes may indeed result in engine failure if the engine is tuned on an aggressive map with no such sensor.

 

This is wildly inaccurate and misleading. It would behoove you to start doing some basic research before posting your verbal diarrhea. Until then, please just stop.


~ GW

 

You have a couple options to add the fuel temp sensor back. The easiest is to buy the race only fuel rail which has the fuel temp sensor port and will work with emission/ non emissions / stock primary rail / aftermarket primary rail. It can be found here. -https://www.raceonly.com.au/product/raceonly-fd-13b-rew-secondary-rail-step-up-kit/

Another option is to add a “T” fitting in with the fuel temp sensor in one of the ports. Radium engineering has all the fittings needed to do this including the adapter for the stock fuel temp sensor. I had mine done this way for years on a single turbo car that had ffe rails who omit the fuel temp sensor. I am using the more elegant solution being the race only unit on another car that’s sequential twins. Do recommend that unit.


Another thing that people don’t realize is the power Fc uses the fuel temp sensor to calculate when to activate the hot start function along with adjustments of fuel density changes. Xavier’s explained it very well above. It’s worth the work to add it back in.


~ GW

 

which part? help me understand

 

It is standard equipment.

 

Rotary Performance makes a cast aluminum secondary rail with the fuel sensor retained. It will fit a standard stock twin car and will even allow you to keep all the air pump stuff including the ACV or emissions stuff. I have this rail, and it is great.
Mike