mlx8

Ok, so I've run a forum "search" and found very limited results, eg https://www.rx8club.com/showthread.p...ghlight=starve

I've been track the Rx8 fairly frequently since I acquired it last July. As I've moved from stock to stickier tires etc., and my lap times improve, I've now gone from where this was an issue when the gas gauge reach the 1/4tr tank level, to 1/3rd+ and now approaching 1/2 tank.

On long, sustained high speed turns, turns to the right seem to be particularly susceptible, but then that may just be a consequence of most of the tracks I have been to with the car seem to be running in a clockwise mode, I will loose power and stall when the fuel level in the tank drops below, now approaching the half tank mark.

Needless to say, this is exceptionally annoying, and in some cases down right dangerous.

Anyone else experiencing this; talked to their dealer or MazdaSpeed about it; or most importantly GOT A FIX for it?

Thanks
mike, denver

expo1

Do you still have the same Spark Plugs in the 8 ? Also have the coils been checked?
I had something simillar happen to me at Watkins Glen.
https://www.rx8club.com/showpost.php...2&postcount=45
Dealer just changed the plugs. I have not been at the strack since so Next Sat @ Pocono I will see if it's been fixed.

RenKat

I had the same thing happen when I was at Laguna Seca.
It was right around 1/4 tank.

Lock & Load

The style of the fuel tank being a saddle type either side of the drivetrain causes this when the tank is low on fuel , the pump cannot extract fuel quick enough , found the same situation on track at Wakefield its a 2.2 km race track in Goulburn Australia the track has a slight slope being at the side of a mountain .

cheers
michael

murix

Same problem for me too. What is speedsource doing about it? Do they run a fuelcell?

Razz1

Same here, I thought it was 1/4 of tank, but it was actually less.

Speed Racer

I run into the same problem at 1/3 of a tank at Watkins Glen. The gas tank really needs some baffles to keep the fuel from gravitating away from the fuel pump pick up during sustained high G turns.

mlx8

Other factors (i.e., one unexplained "check engine" light I suspect related to altitude changes occassioned during driving the car down from Denver (5,280+ feet) to Heartland Park Race facilities (@ 1,000 feet or less); and a flooding event) have caused at least two new sets of plugs to be put in the car. The starvation is more related to the position of the gas gauge and extent of latteral g's occasioned in long sweeping corners than anything else.

I'm pretty confident this is a fuel pick up and pumping issues, not something else.

mlx8

I'd be willing to bet that as you move up to stickier tires, and faster cornering speed, you'll be experiencing this at increasingly higher tank levels.

mlx8

Ok, so has anyone taken this to MazdaSpeed or Mazda?

Does anyone one have an aftermarket solution (i.e. catch can accumulator or some thing like this)?

Does anyone know if any of the higher end or more experienced tuning shops , i.e. Racing Beat SR etc. have seen this as an issue and may be working on a solution?

howardteets

In most saddle tanks of this nature there is a transfer pump which moves fuel from one side to another. Usually working on some kind of venturi. Sometimes if this transfer pump can not keep up with the engine demand you can get a starve.

mlx8 you said that it is more susceptable during right turns. This I find curious. Since the main electric pump should be located on the fill side of the car (left side or driver's side for the 8), you should not be seeing this during right turns, except for extremely low fuel levels. During a right hand turn the fuel will have a tendancy to slosh to the left side of the car, which would bury the pump in fuel. During a left turn the fuel will slosh to the right, away from the main pump causing a dry condition in the immediate area of the pump. At this point the engine is relying on transfer flow from the right side of the tank to the left to supply the engine. If this transfer flow rate can't keep up with the engine demand then you may see a fuel starve. This is more likely during a increasing radius turn where the exit is gradual. A sharp corner and sharp exit is less likely to see this kind of starve.

I'm not sure of the specifics of the 8's fuel system, but I have seen this problem in other cars.

Richard Paul

iTrader: (5)

Run with 3/4 of a tank! It will not hurt you as much as the cutting out will.

Speed Racer

That is hard to do when it is easy to get less than 7 MPG on the track.

Heck, some times I wonder if I even have 3/4 of a tank after I pull away from the pump. :p

expo1

That’s why I will now bring 5 gallons of gas with me just in case. Usually I can do the first two runs in a full tank then fill up again during the lunch break. My incident at the Glen was unique as I don’t think I will be in a run group again that gets a whole hour of track time. At 7 MPG that hour will take up more than half a tank. I was below ¼ when my 8 cut out, So long as your above ¼ I think things will be ok.

Speed Racer

I've found that I can run two 25 minute sessions. Then during my lunch break I head to the pumps and top it off so that I can run the next two sessions without incident.

But there is no way I could make it through 3 sessions without running into fuel starvation issues through the high speed turns.

I've talked with a few friends that race and they say that this is not uncommon. The normal fix is to put a couple of baffles in the tank to keep the fuel from sloshing away from the pump.

Razz1

Man and I thought I was the only one. I swear I got lees than 6 mpg on track day.

BlueRenesis82

Did anyone else notice that their exhaust was unusually clean after tracking the car? Almost like the extreme exhaust temps burned the soot out of the pipes

Speed Racer

Yeah, my exhaust pipes turn chalky white after being out on the track all day.

BlueRenesis82

I was super surprised to see how clean they were...I thought i was going to have to spend at least a half hour cleaning those bad boys

mlx8

Some of the tracks (well, one) do not have on-site fuel available; or if available the system may not be turned on. I find it a little inconvieneint, and as my margin for starvation seems to be increasing occasionally disconcerting if not a bit dangerous to have the car stall while being followed at speed by others. What started out as a 1/4tr tank or less problem last year on OEM tires and a stock suspension has now progressed to a 1/3rd and most recnetly just below 1/2 tank issue as I've progressively changed over to (a) slightly wider & stickier tires (255/35's); a set of Racing Beat front & rear stabilizer bars and MazdaSpeed upper tower braces; and probably just gotten more comfortable and improved driving skills with the car. It may just be me, but I find a car, designed and presented as the Rx8 is as a "sports car" that can't keep itself in fuel with 1/2 a tank ~ heck with a quarter tank ~ rates as a defect. Don't get me wrong, I really, really like this car. It will and has surprised a lot of more "snobish" performance pretenders, and much more powerfull cars at the track by giving them a lot more of a run than they thought it ever would, but running out of steam at the half tank level .... come on, that's just not right.

BTW, you've got the machining and fabrication capabilities. If no one else is, how about looking into fabricatiing a small baffled gas catch can reservoir system to act as intermediate stage accumulator between the engine and the main tank?

Cheers
Mike

howardteets

Once again, not sure of the specifics of the 8's fuel system, but there is probably a kind of "catch can" already.

Most cars now-a-days have "Fuel Pump Modules". These can be very basic and also get complex. Filters, regulators, jet pump, check valves, integrated ROV's, FLVV's. This all depends on the geometry of the fuel tank and of course the requirements of the OEM.

Typically the fuel pump is seated in a resevoir or bucket that is designed to keep fuel surrounding the pump at all times. The reservoir also helps with low fuel restarts. If the module is not able to fill the reservoir with fuel from transfer flow from other side of tank, low fuel pick up points, return flow from regulator (if system is return or short return system), etc... faster than the engine can burn it, fuel starves can happen. Another possibility is that the reservoir is not large enough. In which case a baffle system or larger "catch can" may work.

Sorry if this doesn't make too much sense. I've never tried to put all that in words. I'll try to make up a sketch to explain if anyone is interested.

Does anyone have an exploded view of the fuel tank assembly showing the fuel pump? I may be able to add a little more insight knowing more about the fuel system in the 8.

mlx8

Ask & you shall recieve. I've scanned & will try to attach part of the section taken out of the Factory Rx8 Official Workshop Manual, Section 01-14 pages 1 through 10 (of 31 total) detailing the fuel tank and related fuel system, including injectors etc.

There are several view & diagrams fo the tank and various connections and fittings.

FWIW, one of the things I've notice re: the starvation issue is that once it occures, it can take several seconds for the sustem to "clear" enabling a restart ~ i.e., one can NOT rely on just dropping the clutch to jump start the car as once the system has ingested some air, it at least feels to me like it needs several moments to clear that void or air bubble in the lines before one can get the motor to re-start. When one is on the track, the better course of action often is to run clutch in at least until you clear the "fast line" Trying to jump the car by letting the wheels turn the motor runs the risk of bring you to a dead stop before the fuel system can catch up with providing the engine with gas again. ? One possible negative to the single line, no fuel return system?

attachment (or an attempt at one) pdf file

Nope, upload refused. File too large. The 10 page pdf is @ 852k, limit is 200. I have dnlded a shorter 2 page version w/ tank illustration etc.

Razz1

Yep and that's exactly what happened to me!

Took me a few minutes to get the fuel back into the system.

howardteets

The vehicle is actually stalling!!!?!?!?!?! The case I've seen before was only stumbles. There was some fuel in the line and only loss of power occured, never a complete stall. What would help regain power was to shake to car left and right to get the fuel to slosh back over to the main pump.

If you're stalling out completely, all the fuel in the lines has been spent. Dropping the clutch to bump start it will not work because you have no fuel in the line. Bump starting will only work if you have pressurized fuel in the lines.

Speed Racer

I had the same situation where the engine stalled with no hesitation or warning before hand.