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Haltech Engine Protection - Fuel Pressure Setup (and avoiding false negatives)

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Apologies if it has already been covered in the Engine Protection webinars or in another thread on this forum, but I am having some issues with the Haltech Engine Protection setup for Fuel Pressure.

Car is a T04S single turbo FD3S fitted with a Honeywell MLH150 pressure sensor just before the aftermarket FPR (after the fuel rail) and a stock fuel system. The MAP is the onboard Haltech, so has a bit of vacuum hosing involved from the intake.

I turned the engine protection function on, with it being activated via the Fuel Pressure Sensor - Operating DTC. Initially just turned the default settings on - Deadband 30kPa, Precondition TPS 50%.

I found with this setting that the engine would enter protection mode on throttle blips and quick transient throttle movements. Presumably, the MAP was picking up quicker changes in manifold pressure than what the fuel pressure sensor was seeing. Looking at the logs confirmed that under boost conditions, the fuel pressure sensor was consistently lagging MAP by 10kPa, and possibly more in transient conditions.

I changed this value to a Deadband 50kPa, precondition TPS 50% and precondition MAP 20kPa. This time the engine protection function kicked in after changing gears at redline and coming back onto WOT.

Is there a better way to set this up? Or is there genuinely an issue in my fuelling system that needs to be remedied?

Have you tried datalogging your fuel pressure, MAP and RPM to see if you can pin point exactly when this is happening?

Hi all,

7 months later and I'm still having headaches with this.

What I have tried so far

- Installing an aftermarket fuel pump (Pierberg 360lph) to replace the OEM unit (which was probably near its limit and definitely saw an increasing loss of fuel pressure with rpm). The fuel pump is wired directly to the cabin mounted in the rear hatch.

- Installing a surge tank to prevent fuel surge

- Replacing the SARD (or SARD replica) FPR which came with the car with a Tomei Type L FPR

- Replacing the vacuum hoses that run to the FPR

The issues I am having

1. I still consistently see fuel pressure sitting at 25-30kPa below target (MAP + base fuel pressure) at 1 bar boost. It's closer to target on vacuum, cruise and atmospheric pressure but diverges proportional to boost.

2. On transient events, such as fast throttle application at high rpm, the fuel pressure lags MAP and engine protection can activate, killing what is often a potential PB lap at the track.

Haltech engine protection set up with the following:

- Deadband (fuel pressure error activation): 50kPa (which seems way too much to properly protect the engine)

- Minimum throttle: 50%

- Minimum MAP: 30kPa 30kPa minimum MAP

With these settings, I still get the engine protection kicking in occasionally during fast throttle application at high rpm. MAP will quickly spike as boost builds quickly, but the fuel pressure will lag a bit and I'll briefly see an error of 40-80kPa. See attached image.


See attached image which has two snippets from a log file shown in MegaLogViewer. The "Target Fuel Pressure" and "Fuel Pressure Error" fields are calculated by taking the MAP value and adding 350kPa (base fuel pressure).

In the first example, you can see that measured fuel pressure both lags the target fuel pressure on transient events, and falls short by around 25kPa at full boost. Towards the end you can see when engine protection kicked in on a fast punch of the throttle, where fuel pressure error spiked to 60kPa.

For the second example I decided to try logging Battery Voltage to see if there was anything happening there, keeping in mind that battery voltage is measured at the ECU which is closer to the alternator, while the fuel pump voltage is after the current travels down long cables from the alternator back to the battery in the rear.

Anyone have any ideas of what this could be?

- Is this normal behaviour and do I just need to change the settings on the Fuel Pressure engine protection?

- Is there anything else in the fuel system I need to fix?

- Is this issue on the sensor side (Honeywell MLH100) of things?

Driving at WTAC in Clubsprint in 1.5 weeks, so would really appreciate your help! Would hate to see a good lap spoiled by going into "limp mode" again...

Attached Files

Even with a properly designed fuel system where everything is up to task and performing as expected you'll still see some spikes on transient throttle application so I'd personally say that what you're seeing is typical and nothing to worry about. It's the interpretation by the Haltech that is causing your issues. When looking at the performance of the fuel system I'm more interested in what the fuel pressure is doing through the rev range under sustained full throttle operation. Here you 'should' be able to maintain a fixed differential fuel pressure within 5-10 kpa.

I'd stop beating yourself up over this and make the engine protection work for your application. In this case I'd be inclined to use the protection function above perhaps 80% throttle and above perhaps 70-80 kPa boost so that the ECU ignores the transient conditions.

I've attached some data from our 86 on track so you can see what the fuel pressure does in our system. The channels include the calculated differential fuel pressure, as well as the fuel pressure and inlet manifold pressure (note that I've offset the fuel pressure here so that it aligns with inlet manifold pressure just so you can see the latency in the system so please ignore the actual values as they aren't real. As you can see, our 86 would suffer an identical fate to your car.

Attached Files

Hi Andre,

Thanks for your prompt response (and apologies about my own delayed response).

Great to hear that this sort of behaviour is normal. I have been getting frustrated and stressed out of this for a while now, and probably should have asked before I went and changed my FPR!

I noticed you said 5-10kPa would be normal, however I am getting more like 20-25kPa at only 1bar. Would you still consider that to be something not to worry about?

I think your threshold values will resolve the issue though. Testing them in Excel, I can't see any instances where putting in a MAP restriction of 70kPa will lead to fuel pressure error exceeding 50kPa. I suppose the question is how well this will protect the engine against a fuel leak or dying fuel pump.



Also, if you're at WTAC again this year, feel free to drop in by the Project 7dere garage to say hi.

You won't miss it. Just listen for an RX7 with a poorly tuned idle that keeps stalling. :-P

Attached Files
  • 20776700-807749436102370-5351028556947523305-o.jpg
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When the fuel pressure initially hits the expected target at low rpm and then tends to fall away as the rpm (and fuel consumption) increases, this normally indicates the fuel system is a little light on fuel flow and essentially struggling to keep up. Assuming you're still able to achieve your lambda target and you've got plenty of injector headroom I'd say it isn't ideal but not necessarily something to worry about.

Have you checked the voltage at the fuel pump during a full power run? In terms of FPRs I find the Turbosmart are probably one of the most stable regulators I've used.

We will be attending WTAC so we will make sure we come say hi! Good luck for the weekend!

We usually reply within 12hrs (often sooner)

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