Hope this is the right place for this. Car is a 98 FD3S

I recently got my car back from the workshop and tuner after completing conversion to single turbo, and I have found an issue, likely it wasn't happening when they tested and tuned it, its only in 2nd and intermittent too happening 70/30. 1st to redline no issue, 2nd, complete loss of power after 5500rpm, doesn't stall, its like click of your fingers and power is gone, as soon as it happens I change to third and power is instantly back no issue all the way to redline.

GTX 3582R 1.03 AR
Haltech 1500
IGN1A
Bosch 2x 1000cc primary & 2x 1600cc secondary injectors
Turbosmart GenV ProGate50 14psi External Wastegate
Turbosmart GenV RacePort BOV
Walbro 535 / 540 lph Fuel Pump High Pressure new fittings etc
Radium Fuel Rails & Damper
Replacement Mazda Engine Harness, new wiring etc.
Greddy V Mount
All the above is new. New Leads, New Battery, wiring etc. Plugs are under 500km old
The tuner has had a look and there is nothing in the tune, no cuts or limits that would cause this and all looks fine.
Its only tuned for 330hp. Pretty much everything is new except the keg which has good compression all around and the alternator and the Autoexe exhaust. Pipe is 3” till rear section and drops to 2.75”. ABS Light is on.
What could cause this to happen and only in second gear?
It is going back to the dyno in a months time (everyone's busy) for the experts to find the cause and fix it. But I was hoping someone might know what is going on that I can check and fix and I don't have to wait the month or more out.

 

Based on your description, the issue seems to be specific to second gear and occurs intermittently. The sudden loss of power after 5500 RPM, coupled with the immediate restoration in third gear, suggests potential electrical or mechanical issues related to the transmission or ECU controlled.

Possible Causes:

1. Transmission-Related Issues - Clutch Slippage: While less likely, it's worth checking.
   
2. ECU Logs - check for
   
   • Ignition System Problems: Check for a misfire
   • Fuel System Issues: Ensure there's no fuel pressure drop .
   • Sensor Malfunctions: Faulty TPS sensor, AFR sensor sending the wrong data to the ecu in 2nd resulting in cutting power.
   • ECU Safety cut: leaning out in 2nd causing an engine safety cut tripping an ign or fuel cut

Ultimately, a job for your builder/tuner to trouble shoot and resolve. All the best and be interested to see what the actual issue was.

 

Can you do a datalog to confirm there definitely aren't limiters active?

The fact it's happening around peak torque would suggest potentially an overboost limiter or something odd with traction control.

No mention of surge tank, does it still happen with full fuel tank?

Assuming this is a manual transmission there shouldn't be any switches active on or off in gear.

 

acceleration will be high in 2nd, might be bare wire spot that makes contact and grounds out then, but not otherwise

I actually had this issue on an FD3 way, way back in 1996, drove me crazy until I finally found it.
.

 

Thanks everyone for the replies. I actually have a working theory and i think its the fuel level.

I have been driving around for two days with 3/4 tank and it's been perfect. And when I look back the problem was only happening under 1/2 and close to 1/3. It didn't happen when I picked it up finished and it had a full tank. And when I said it was intermittent that night i put some gas in filled to just over a tank went out no problem and it only started happening on the way back when it went under half.

From searching it seems like this can be a thing that others have experienced in different ways. First FD so had no idea.

Still working on driving it with a full tank. But so far so good. I have to talk to the tuners Monday see what they say. It's weird because he checked the fuel log and afr and it was showing no issue. Can the haltech cut ignition if it detects lean or pressure issue before it will show on the log?

I'll fix it if that's it. See what happened in the tank. Probably get the radium surge tank or the feed baffle



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nice pulley, just need the rest lol

it's definitely fuel surge, very common for FD to surge under half and usually made worse by crappy fuel pump installs. ECU will only cut if it's setup to do so and most tuners seem to be lazy to do so.

 

When my power level went above 400 rwhp I had a similar problem but mine was real fuel cut not power drop at 1/2 tank or less.
A fuel pressure gauge will show fuel pressure dropping.
There are a few fixes for this but I chose a simple cheap one since I already have a rewired very good fuel pump with updated parallel fuel rails with modern larger injectors.
Holley Hydramat 16-111 (3x15) 11MM Outlet w/6 Lock Pin Position
https://www.speedwaymotors.com/Holley-16-111-3-Inch-X-15-Inch-HydraMat-Rectangle,287234.html?sku=42516111&utm_matchtype={ match_type}&msclkid=4d8eaef8370916e1cb6cc831796766 9a

Just drain the tank, remove the fuel pump assembly, and cut the front and rear surge tank walls so the filter will fit. Works with even 1/4 tank of gas.

 

I sort of forgot about hydramats, lots of good feedback, might use one in another vehicle, OEM pump is relatively new so was going to use it as lift to a surge tank but if I need to buy a better pump anyway for high pressure one pump and a mat filter is probably easier.