Noise on/from the flex fuel signal.

[S.Bretz]

I'm getting noise from the flex fuel sensor.
Its grounded to the same engine ground as tha the MS2 grounds to.
It casues the PW to jump from the 4ms range to the 8-10ms range and causes severe misfires.


Before I rewired the car, with the older BG 2.8X code, I was getting alot of noise on the FF sensor signal. It went away after I wired the TPS low ref ground (drain) to the MS. I wired the tps and all sensors back the MS, but this time the they ground to the engine whereas before the ground went to the back of the car to the battery in the trunk.

I also have a 1 farod audio cap in the engine bay. Should I try to wire to the cap or battery for ground....or should a leave the MS ground at the engine and seperate the flex fuel sensor ground to the cap or battery?

Here is an attach datalog that shows the PW spikes and the RPM jumping up and down.
Also is the MSQ is you guys would like to look at that.

extra 2.1.0d (latest release) with edis and a 1/2 working FFsensor.

I DO know this is the from the flex fuel, the history traces on my dash board will be really high and when I disable the FF input, it runs fine.

Anyone have any recommendations on how to 'clean' up the signal? Or a way to create a filter to get rid of the noise?

[S.Bretz]

Please don't respond about the flex fuel sensor yet.
Now its misfiring like an SOB with the FFsensor turned off.

It'll be ok for one pull after you mess with it to make you think you 'fixed' it...then on the second pull the miss comes back to piss you off.


I'll track down the misfire and then work out he FFS noise (it does have noise I would like to rid...but the misfire comes first)

Ordered a new coild, some plugs and will try a set of ford edis wires...as of now I have a coil with tower converters so I can put stock wires on.

[S.Bretz]

Ok, its time to pull this thread up from the dead.




I replace ignition components I was having problems with. Eventhing ignition wise is solid....no more misfires with flex fuel disabled. However, it misfires like crazy under high load with the flex fuel (FF) enabled.

I have the FF port set to PEO/JS7. It works fine at low rpms and low loads, but starts to misfire over, umm, say 3K and 133kpa. The signal just gets noisy.

I have the 12v power feed running off of a fuse block that powers the MS, the injector (with the flyback hooked to the injector 12 line), fans, a/c relays, gauges, nitrous, and the stock 30amp ignition circuit that was originally there (use the stock 30 amp ignition wire to just turn on a 100amp continus relay to power everthing esle) so I can imagine there is some noise here, but cannot determine without a scope. ( the DMM reads stead voltage, but may not refresh fast enough to pick-up fluctuations). The main power going to the relay is attach to a 0.5 farod audio capacitor to heldp reduce noise too.

The low refrence ground for the FF sensor is wire to the same ground point on the engine that he MS is wired to.
The ground on the engine goes to a ground point on the frame, then a seperate ground on the frame hooks up to the capacitor with some other stuff on the grounded to the cap as (nitroud, fans, a/c control relays).


What would be the best way to eleminate noise on the FF sensor line?

Should a install a small capacitor (22pF) between the ground and 12v on FF? Move the 12v off the fuse block?....move the ground to the battery or capacitor? I'm tempted to reroute the ground to the cap, but with the fan grounds already there, I can imagine is noisier then the engine.

[jsmcortina]

What input circuit are you using between the Flex Fuel sensor and the CPU pin itself?

James

[racingmini_mtl]

I wonder if this is simply due to the fact that the frequency is obtained through polling and that the interrupt latency and variation for the 0.128ms ISR will increase as RPM goes up.

I know Brian/Una is using flex fuel but with a hardware input capture on the Extender and I don't think he has any issue with the signal or had to do anything special to deal with noise.

Jean

[S.Bretz]

What input circuit are you using between the Flex Fuel sensor and the CPU pin itself?

James

PEO/JS7 . I have it wired like it says in the extra manual. It comes up through the CPU pin and jumpers over to JP4? (I can't remember off the top of my head, but its like stated in the manual).
I had it jumper onto JP4 (not going throught the CPU pin) and it was doing the same thing.

There was intermitten noise before, but nothing like this. If I remember correnctly, before I rewired the car the ground for the FF sensor went straight to the battery in the back of the car...so did the MS ground.

A few yeas back when I first install the FF sensor, I would get noise. But only during quick throttle inputs. The fix for that was to wire the TPS ground to the MS (I originally left the TPS wired to the stock ECU/PCM as it was one less wire to cut/deal with).

[karlo]

The FF code should probably have some noise handling code in place. I changed to code to handle noise better, since I was having similar problems. However, the hard disk crashed, so I don't have the code any more...

[S.Bretz]

A lag or some type of filter would be great. Even when I had mine working well with the old wiring, it would occasionally go from 10% ethanol and spike to something crazy around 300% while at a steady cruising speed. Some times you could feel the glitch, other time you could not.

I asked for a filter a couple years back when I first incountered the problem (when I had noise from the TPS ground not being at the MS) and Grippo (maybe it was Bruce) said that they would not implement it into the 2.8 code, but possible the MS3 stuff.

If something was implemented that would limit the amount of change in a short time, it would help alot. If you fill the tank going from e10 to e85, is still takes about 20 seconds for the ethanol numbers to settle after you start it...so quick changes are not needed.

Karlo, do you at all remember what you changed/added to help with noise?

[jsmcortina]

What input circuit are you using between the Flex Fuel sensor and the CPU pin itself?
James

I had it jumper onto JP4 (not going throught the CPU pin) and it was doing the same thing

How does it connect from there to your FF sensor though?

James

[karlo]

Karlo, do you at all remember what you changed/added to help with noise?

I implemented a lag filter or sorts, restricting it to change only 1% on every sample. This fixed all my noise issues, and would still go from min to max fuel correction in around a second, which as you point out, is quite sufficient.

- Karl

[S.Bretz]

That saounds like it would work perfectly.
Can you try and save the data from tha crashed hard drive. I would like to see how you did it.
I can make some changes here and there to the ini, but I have no idea how to change the code to include lag filters.

[Faster7]

I implemented a lag filter or sorts, restricting it to change only 1% on every sample. This fixed all my noise issues, and would still go from min to max fuel correction in around a second, which as you point out, is quite sufficient.

- Karl

We'll be using the flex fuel sensor later in the summer after the car is tuned better on gas, and this would be a great addition to prevent noise issues. I can code a little but certainly if you still have any of your code revisions that would give me a head start!

[karlo]

I made an attempt at redoing the changes I had before the harddisk crash. These changes are absolutely untested, but it compiles. The intention of this code is to only allow the frequency from the flex fuel sensor to move 1Hz every 7ms (150Hz), the maximum frequency of the flex fuel sensor. This should dampen out most of the noise, but will still move between min/max ethanol content and vice versa in 2/3s of a second, enough for all practical purposes. There are other and probably better ways of eliminating noise as well, but I didn't investigate that at the moment. If your signal is extremely noisy, your fuel correction will be pulled upwards artificially.

This also fixes an issue with cranking. Currently, the flex fuel code would not be run at all on cranking, so starting may be hard when switching from 100% petrol to 100% E85. Also untested!

- Karl

[jsmcortina]

As I asked before... what input circuit are you guys using?

James

[S.Bretz]

IDK if you didn;t read my post or not...or are asking these guys.
...but as I stated. Its coming in on the JP4 and I have TS set to PEO.


If you are asking how its' built...the circuit is build like it states in the manual; to use a pull up resistor off the 5v on the proto board and hook up to JP4 on the MS2 card.
like this:
http://www.megamanual.com/ff_wiring.gif

[S.Bretz]

What input circuit are you using between the Flex Fuel sensor and the CPU pin itself?
James

I had it jumper onto JP4 (not going throught the CPU pin) and it was doing the same thing

How does it connect from there to your FF sensor though?

James

Umm....with a wire? I'm confused with your question. Can you state it another way?

[jsmcortina]

So you have the flex fuel sensor directly connected to the MS2 card? No resistors or capacitors in between? That's your problem right away.

The input needs a protective and smoothing circuit.

James

[S.Bretz]

Its constucted like recommended in the megamanual.

see link in this post...its has the wiring diagrahm I used.

IDK if you didn;t read my post or not...or are asking these guys.
...but as I stated. Its coming in on the JP4 and I have TS set to PEO.


If you are asking how its' built...the circuit is build like it states in the manual; to use a pull up resistor off the 5v on the proto board and hook up to JP4 on the MS2 card.
like this:
http://www.megamanual.com/ff_wiring.gif

hmmm, link isn;t working....






umm....niether is img..../img.



Ok....the wire come in throu SPR1, and goes to the JP4....there is a 10kohm resistor that is spliced into the signal wire before it runs to the JP4. The other end of the resistor goes to the 5v source on the baord.

The picture of the diagram is all the way at the bottom of this page:
http://www.megamanual.com/flexfuel.htm

[jsmcortina]

Well, Megamanual or not, that's a really dangerous circuit and I urge you to change it as soon as possible.

Try the following.


James

PS. The images you linked to earlier didn't work due to the Referr and other access bans that some of the other Megasquirt sites implement.

[racingmini_mtl]

Just to confirm and emphasize James' message about the need to filter and protect the input, the circuit used in the case I mentioned before does have an inline RC filter with values very similar to what James proposes (10K Ohm and 0.001uF).

So using the resistor and capacitor should go a long way towards eliminating your noise issue.

Jean