IPK mode 19 sub section 6 verified

[T-Cut]

@Typhoon190
You could be right and my write-up is wrong. I've never been convinced that I understood Section 6 properly and it hasn't been 'translated' from BMW to MGR correctly. That's why we need as many people as possible, with and without faulty tank sensors, actually doing the tests and reporting the numbers. Over the years, this part of the HowTo has been taken as gospel instead of the a starting point. I've asked for help in testing it since writing it up, but few have responded so I kinda lost interest. So, this renewed interest is welcome and might eventually point it in the right direction.


TC

[Mickyboy]

Well today has been quite an interesting day in this investigation, as I had a vehicle that had a faulty sender unit with a fuel gauge fluctuation issue. T4 didn’t highlight a fault.
During the IPK section 6 test I noted this one was displaying 1.6.2 that would indicate from my previous tests that the sender unit on both sides was sending out a signal, however yes it was sending out a signal as I measured the resistance for both feeds on the terminal pins located on top of the pump and had resistance values of 46 for the passenger-side and 62 for the driver-side. However on the IPK diagnostics it only displayed the total quantity of fuel at approximately 15 L _ _0150 it didn’t display a figure for both sides as the BMW E90 models do, I then removed the sender unit and found this issue.

First picture shows the sender unit at its lowest position producing a resistance value of just over five ohms

The second picture shows it at its full mark producing a resistance value of 199.5

Now the third picture is far more interesting as if you look at where the float contacts meet the pump markers you will see that the surface where it measures resistance is faded quite considerably between a quarter of a tank or just below up to around half a tank

Last picture shows the resistance value at 5.5ohms when it is at the empty position


So it appears to me that where the contact surface has worn why the resistance values become in accurate hence it then sends an accurate measurement to the fuel gauge and causes the needle to “float around”
So in relation to test 6 it identifies that you can still have 1.6.2 And have a 40 sender unit due to the fact that it is still putting out a signal but the signal has become correct at certain points due to wear where the resistance gets measured

Hope this has been of benefit to people reading this and helps identify issues that people may have with the floating fuel gauge issue

When a fuel sender unit was fitted from another vehicle I have that did not have that type of wear on it the fuel gauge stopped floating so to speak.

I also now believe that section 6 test 1.6.2 only indicates remaining fuel as a total rather than per side Ie _ _0xyz I will be checking this with various other vehicles to confirm my findings but from my investigation today I’m fairly sure this is the case
Mick

[T-Cut]

At last, a clear reason for faulty gauge readings and your earlier strange results. It confirms the basic recipe that the prefix 1- or 2- indicates rheostat condition as 'on' of 'off', but not 'wrong'. I believe the wear and tear effect on the contact arc is a new finding.

I also now believe that section 6 test 1.6.2 only indicates remaining fuel as a total rather than per side ie: _ _0xyz. I will be checking this with various other vehicles to confirm my findings but from my investigation today I’m fairly sure this is the case

Which goes some way to explain some notes I made a few years ago when testing my 1.8T. There was something wrong with what I was seeing and what I'd translated from the BMW stuff. So, a few more steps forward.

It'll now be interesting to see what 1-6.2 shows with both sensors working normally.

I have an old rheastat around somewhere so it'll be interesting to check how the resistance varies over the range. The 'full' tank resistance is quoted st 155ohms so clearly it's designed not to butt up at the top end.

TC

[slovcan]

Good morning guys,

This thread - especially with recent additions - could prove to be a gold mine. My fuel gauge shows the 8:00 position when full and subsequently shows 6:00 (empty with NO low fuel light) as the level drops towards 1/2 tank. Actually, it COULD be showing 6:00 when it is somewhere between 1/2-3/4 full, because I am sure it is currently over 1/2 full and showing just "above" the empty mark (maybe the 5:27 position). I'll watch what happens as I use more of that fuel.

I did the section 6 diagnostic test a few days ago and got a 1_6.2 which sort of baffled me. Mick's results today may be the answer. I will edit this in a minute with the full results from a few days ago.

Edit: the readings for section 6 are --6.0 (top left) & --0384 (bottom right), --6.1 (top left) & ------ (bottom right), 1-6.2 (top left) & --0397 (bottom right). These figures are from my good, but very short memory. The quantity numbers are close, but I will do the test again when I get a chance. I think they should be the same - or nearly so - for 6.0 and 1_6.2.

As an aside, my wife's cousin is taking apart a ZT CDTi right now, but I am sure it has a 2 pump system (mine is a single pump). Are the sending units the same?

Cheers,
Glenn

[picky747]

Checked mine yesterday when the low fuel light came on and it read 5.4 litres. I take it that faulty readouts due to track wear on the sender will increase with mileage due to the number of fill/empty cycles

[KWIL]

Obviously.

[T-Cut]

So, I had a look at the float rheostats on my spare pump and filter modules to see if there is any wear and tear on the windings. They both actually look pretty good as you'll see in these photos. These are for a petrol tank.

This is the pump unit:



The wirewound rheostat is compressed flat to the white plastic plate and a brush of springy copper/brass presses onto this and the concentric ground arc. The latter is just a thin metal arc. Details on how this brush system fits together can be found in the excellent HowTo by rich17865. Unfortunately, the official HowTo is under PhotoBucket's ransom, so the images need recovering: https://the75andztclub.co.uk/forum/s...d.php?t=194156

Here's a closer look at the rheostat.



I checked the resistance of this at each end of the float arm range and got the following results.

'Empty' =147 ohms

This fell to around 130 ohms after cleaning up the contacting surfaces with cleaner spray. The figures also vary according to how much contact pressure is applied, so all the results are relative.
'Full' = 4.7 ohms

The filter module rheostat is of similar construction, but much smaller in size, maybe half that of the other.



The resistances here were;

'Empty' = 4.7 ohms
'Full' = 153 ohms

I watched the resistances change between empty and full for each one and they seemed near enough linear. So, these are in good nick and will be kept as spares.

[Mickyboy]

I did some more testing today I actually forgot to take a photograph after filling up the tank completely, only remembered once I had got home after doing quite a large sum of mileage however I am convinced now that when it shows 1.6.2 is identifying the total fuel quantity in the tank and it does not show both sides of the tank just the total sum as seen in the photograph below



I also found on every car I tested, I did test multiple vehicles, and 6.1 only brings up dashes (Like this _ _ _ _ ) so I think this does not give any reading of any significance on our vehicles

Mick

[Mike Noc]

Originally Posted by picky747

Checked mine yesterday when the low fuel light came on and it read 5.4 litres. I take it that faulty readouts due to track wear on the sender will increase with mileage due to the number of fill/empty cycles

Wonder if the type of fuel also has a bearing on the wear rate?


I've had a couple of high miler deisels and never had any problems with rheostat track wear.

[T-Cut]

Originally Posted by Mike Noc

Wonder if the type of fuel also has a bearing on the wear rate?

Quite probably, though I think any wear needs a pretty high mileage to become apparent. I guess a diesel system will wear more slowly than a petrol one.


TC