VersaTune User Forum

A friend of mine and I were playing around with his Speed3. We decided to log the difference between The Stock Tune, A Hypertech Tune, and then a Cobb Stage 1+ Tune. We notice an interesting Dip in his HPFP. It's not there with a Cobb tune. You can see it's there with stock but not as bad. The only modification his car has is a MazdaSpeed CAI. He bought the car brand new so there's no question or worries about unknown modifications or service history. What do you guys think? Signs of a worn out HPFP? Or is there hidden fuel pressure regulator tables?

Oh, these logs were captured with VersaTuner. I exported the logs to CSV format and then set them up so I could import them into HPtuners scanner.

Can you rather post the .csv files instead of these graphs?

here you go.

CrazyCanadian wrote: ↑July 25th, 2021, 7:14 am A friend of mine and I were playing around with his Speed3. We decided to log the difference between The Stock Tune, A Hypertech Tune, and then a Cobb Stage 1+ Tune. We notice an interesting Dip in his HPFP. It's not there with a Cobb tune.

Apart from the Hypertech tune which commanded (or allowed) a bit higher load targets, the Cobb and the factory tune commanded the same load at the same RPM and the same fuel rail pressure (FRP).
The fact that the dip was not there with the Cobb tune was just a matter of luck, but it will be in there if you insist and will eventually cross that limit where at this point the leaner AFRs commanded by the Cobb tune saved the situation.
There is nothing different that the Cobb tune would or can do to prevent the malfunctioning of a mechanical device, only by commanding a bit leaner AFRs that tune simply demands a bit less fuel (about 8%) at the same air flow/load, that's all. But it's a matter of time until the problem will arise with that tune as well, because 8% is not a whole lot by any means and leaner AFRs + FRP dips will result faster in ZZB while with richer AFRs from the factory or HT tune you will feel that bucking or wavy pulling which will make you back off and make you understand you actually have a problem or at least make you wonder and look closer.

Also the fact that these fuel rail pressure dips appear at loads a lot lower than 1.9 at OEM AFRs is a clear indication that the HPFP needs servicing badly, 3 years ago.
For good measure I'd keep an eye on the FRP after servicing the HPFP just to make sure the relief valve (PRV) is not actually the culprit, which is hard to say for sure at this stage, but by how it looks the HPFP is the problem 95% sure.

I am always fascinated by this kind of stuff. One thing we haven't checked on his car is low side fuel pressure. I haven't seen anyone talk about it when it comes to high pressure pump issues. As a mechanic this would be one of the first things I'd check to confirm this is in fact an issue with the high pressure pump getting weak. I am curious as well about the injection tables and how they work for our cars.

What you are talking about in terms of fuel volume being used, the different loads makes sense.

If you had any issues on the low pressure side the car wouldn't even drive well and would idle roughly.
However as a good measure you should change the in-tank fuel pump filter, that tends to clog over time if the gas stations you get gas from have dirty tanks.

I posted this more for curiosity and to build a more out of the box conversation. I am not really looking for silver bullet fixes. The diagnostics end of whats going on isn't something I am new to. I've specialized in drivability diagnostics for almost 15 years.

I asked the question about the hidden high pressure fuel pump regulator command tables because I've see varying levels of data from different scan tools. It's also interesting and valuable in my mind to show how different tunes can net different results. It would be interesting to see data that supports what you are talking about with the leaner A/F command and how it's changing the demanded volume of fuel. I believe you are right.

CrazyCanadian wrote: ↑August 1st, 2021, 7:49 pmIt's also interesting and valuable in my mind to show how different tunes can net different results.

It all comes down to two things:
1. how worn and/or clogged the HPFP is;
2. the amount of fuel demanded in the 3000-4500rpm area where the number of strokes per second of the fuel pump piston simply are not enough to move the requested amount of fuel.

At stock AFRs a good/new factory HPFP will run out of steam at about 1.92 load around 3700-4200rpm. If tuned properly with a bit leaner AFRs they will hold up to load 1.98-2. These are just some points of reference, and you can never estimate the lever of wear or clogging on a specific car especially if it was not driven fast enough all the time, it used factory spec 5w30 ACEA A5 or C3 oils and cheap brands or all sorts of crap, so you never know.

To add to what Mituc has posted:

The HPFP is a positive displacement pump and the flow rate is tied directly to RPMs (and is impacted by things that plague all such pumps like cavitation, etc). Since it's tied to RPM, there is a point (~7000 RPM) where the factory pump can outflow the injectors (which are time limited, not flow limited).

The reason why pressure dips at about 3500-4500 RPM is because that's usually where peak torque (and thus peak fuel consumption) is. You absolutely *can* tune around this, and (though I don't recommend it) I've run full E85 on the stock injectors and HPFP but was only able to make about 12 PSI at the ragged edge. The funny thing about that tune is it made the same power and torque as my maxed out pump gas tune, but with a LOT less airflow.

I've done some work figuring out the HPFP stuff, and learned alot along the way; I don't know what the stance is on linking other forums here but I have a big fat thread on how fueling works for the 'Speed cars on MSO.

Here's a sample (stock HPFP setup):
https://imgur.com/pwq4E1z