When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a stock 2001 NB, with a MS3PNP recently added, about 120,000 miles on the car.
On two occasions now it has cut off fuel delivery in a regular ~30 sec off, ~1.5 min on pattern, repeatedly for many miles. Independent of acceleration, and even when at a standstill.
Both times fuel in the tank was low, about 1/8, and the tank took 35 L to fill (40 L capacity). So it still has ~1.25 US gallons in it when it is acting up.
I am highway driving, straight line, no hills. I have never had a car "run out of gas" this way before, and my 99 spec miata does not do this, even on the track.
I tested it, giving 62 psi at idle, dropping to 61.5 when revving hard at a standstill. Holds 50 psi when turned off after 5 min. So all within spec.
Is this sign of a failing fuel pump? Over heating when it is not fuel immersed? Plugged? Faulty sock in tank?
I have heard of fuel pickups being finicky several times over the years. It often is resolved with repeated test fitting and occasionally switching pickup sock shape or angle. But I haven't dealt with it myself.
Do you have a datalog of when it happens? Did you have the same problem before adding the MS3?
Yes there is data log. The problem starts at about 418.306 seconds. A link to a google drive upload of the file is given below.
It never happened before adding the Megasquirt. file
The on/off cycle is so very regular I am having trouble picturing it being a problem with the sock, but I won't know for sure without opening the tank.
I thought I would add a picture of the data log. The cycle is much faster than I thought, about 4 sec on, and 4 sec off. When off, there is no fuel flow. But strangely, there is also no alternator control, and the voltage drops to the battery value of 12.3 V or so. You can see the MS3 is still controlling pulse width for fuel delivery (Seq PW 1), but there is no fuel getting to the engine, and AFR is > 18. However, since it is still rotating while cruising along, I don't see why the field in the alternator would collapse.
These problems make it seem electrical, but they were solved by filling the tank, making it seem like a fuel pump or pick up problem, since there was 5 L in the tank when it happened. But I don't see why the fuel pump delivery problem would be coupled to the control of the alternator, or why the field would collapse when the engine is still rotating at significant rpm.
Your VVT is also going crazy. That can cause the oscillating MAP and will also effect AFR. EGO correction does nothing so it is not over correcting. These can all be connected to the changing voltage.
So it happens since you got the MS3 and that controls your alternator. I have no idea how it works, I got the westfieldmx5 board that does it outside of the software. But your control duty stays on 0 even when the oscillation starts. Can you upload your tune so people can look at those settings?
Your VVT is also going crazy. That can cause the oscillating MAP and will also effect AFR. EGO correction does nothing so it is not over correcting. These can all be connected to the changing voltage.
So it happens since you got the MS3 and that controls your alternator. I have no idea how it works, I got the westfieldmx5 board that does it outside of the software. But your control duty stays on 0 even when the oscillation starts. Can you upload your tune so people can look at those settings?
Yeah, all the various readouts and controls are shifting, but as you say, I believe that is due to the voltage changing by 2 V every time the fuel cuts out. Nothing else actually turns off, it just does not give the same delivery because it is voltage dependent. Even the injectors keep firing, but they don't deliver any fuel.
I wrote to DIY about this, and they said the alternator control readout is not the one that is doing the job. They set it up with a high frequency control, which is one of the menu options, and there is no recording done of the PWM 3 line they use for that task. They suggested bad wiring or a bad alternator, but wiring to the alternator is secure, the wiring to the MS3 is secure. That does not mean there is not a bad wire in the harness, but the wires are secure.
The thing is, it happens when the fuel is at about 1 gallon in the tank, but I don't see why the alternator cuts out, when the fuel stops being delivered. It does not make sense to me that the two things are coupled. An overheating fuel pump could possibly do something like this, and maybe it is triggering the fuel cut relay. But being coupled to the alternator control is decidedly odd.
An earlier version of the tune, with a lumpy VE map, is posted at the end of the first post in the linked thread. The VE map has been improved since then, but the relevant things in the tune are the same. tune
Isn't the alternator PID controlled? That oscillation does look like a over correcting PID circuit. Maybe being low on fuel gives a sudden electrical load 'somewhere' that starts the oscillation. PID control is then to aggressive to calm it down. The swings get bigger as time progresses.
The Fuelpump is done through the ECU -> Fuelpump relay and is triggered on rpm only. Alternator voltage has nothing to do with it.
Can you post a screenshot of your alternator settings?
The alternator settings don't give a whole lot more info.
No clear info on what control algorithm is being used.
These are the settings that came with the MS3PNP files.
Just to be sure: Put a lower value into WOT TPS%. That will enable those WOT values below WOT TPS%. Replace the 12.5 WOT target voltage with 14.0 so that it does not accidentally trigger. Then put the value af 101% back to WOT TPS% to disable the values again.
There were instances where a greyed out setting in tunerstudio still worked even if they should not work..
05-27-2020, 01:00 AM
Unusual Fuel pick up issue
0
