Testing quality of combustion using idle speed smooth running control

I have been thinking about ways of assessing how well our choosen fuel is combusting.

Using VAG-COM and looking at measuring blocks group 013 you get 'idle speed smooth running control'. This shows the ECU modifying fuelling to each cylinder to balance combustion - the ECU measures the time it takes for a magnetic trigger on the flywheel to pass a sensor. If a given cylinders combustion event pushes the flywheel faster the ECU reduces fuelling.

I think I'm right in saying A3/B4 models show three values
1st is comparison of cyl 3 and 4
2nd cyl 2 and 3
3rd cyl 1 and 3

A4 models (what I've got) show a value for each cylinder
From taking and graphing a few logs of my vehicle it appears the values for cyl 1 and 4 mirror each other as do 2 and 3..... Both of these 'mirrors' have a different offset from zero which appears to change slightly over time.....

this block has specified values at warm engine idle for my engine between -2 and 2

Bosch state that

Excessively high values point to a low compression or contaminated injectors.

Low values to high compression or leaking injectors.

Anyway my thinking is that if my fuel is not burning well and I activate the glow plugs combustion should improve.....

If I activate one glow plug I should be able to see the difference using block 013.

A quick test running on diesel after a coldish start (I had run the car a few hours before this) showed the post glow running for three minutes with a coolant temp of 15deg C. glow plug bits show 10110000 when after glowing or 11010000 if rpm is above 2500

I then used a jumper from the battery to glow plug 4 and noticed the 0.47 - 0.49 value fall to 0.45 - 0.47 untill I removed the lead when it rose back to 0.47 - 0.49

Of course it is possible to log these values when not at idle....

I am going to do some more experimenting with this and different fuels. I will post my results.

If anyone else tries this I would be interested to hear results.

Also I searched on tdiclub and did not find much about using this potentially usefull measuring block.

I had previously found it being used under full throttle acceleration to tune timing for performance in a 1.8tubo SI engine -
http://www.revotechnik.com/products/pdf/SelectPlus_AdvancedUserGuide_V0707.pdf

Keeping an eye on this data set should be useful for an early warning of failing injectors or gumming rings.

Best

Darren

This is a bit beyond my expertise, but I can appreciate the basic idea. I have a good VAG-COM unit, so if you end up simplifying the procedure for noobs like me, I would love to check my readings and post what I find.

Regarding low compression on 1 cyl .... a member suggested
to try group 013 test ...to have a confirmation>> by the qty..of fuel injected from 1to4 .
Here is what I get on my 2000 .....(.05, -0.09, 0.09,-0.09 )
(.05 -0.09, 0.12,-0.07)
(.02 -0.07, 0.12,-0.07)
Will use some additifs & look for numbers next time.
Very usefull measuring block indeed.

"I then used a jumper from the battery to glow plug 4 and noticed the 0.47 - 0.49 value fall to 0.45 - 0.47 untill I removed the lead when it rose back to 0.47 - 0.49"

I assume this means the hot g.p. aided combustion because less fuel was necessary to maintain RPM.
But you were on diesel. (?) I guess it helps on diesel too.
You have a stock TDI right?

"glow plug bits show 10110000 when after glowing or 11010000 if rpm is above 2500"
Above 2500 it's presumably off.


Hope you have your Durotherms, ( slow glow ) g.p.'s ;-)

Wish Ihad more time to reproduce your experiments.
I did make the blow-by monitor suggested by crossbones.
I drilled out an valve cover oil cap for a 1/4" barbed nipple.
Waiting to borrow a friends low pressure gauge to see what blow-by is at idle and start.

I then used a jumper from the battery to glow plug 4 and noticed the 0.47 - 0.49 value fall to 0.45 - 0.47 untill I removed the lead when it rose back to 0.47 - 0.49

Click to expand...

Which cylinder changed? Was it #1 or #4?

Cylinder 4 fell.

I must admit this was a quick test and maybe I saw what I wanted to see.

The problem is my VAG-COM lead was not long enough to let me sit the latop under the bonnet although I could set up something up which would allow me to view what happens the second I power up the plug - although I expect it may take a short while for the plug to heat enough to make much difference.

I'll have a bit more of a play and post more.

This is a stock Tdi 1.9 AGR engine (90) I was running on UK pump diesel - probably winter grade fuel I put in when I last used it - February. this was just after start up with a coold(ish) engine. In the process of this experiment I noticed that the other three glow plugs were not working..... I started without the glow plugs 'harness' attached so there would not have been post glow on any cylinder.

" "glow plug bits show 10110000 when after glowing or 11010000 if rpm is above 2500"
Above 2500 it's presumably off."

I didn't test what power was coming out of the harness during the post glow period or while I put my foot down to get above 2500 rpm but I've read about post glow being suspended at engine seeds above 2500 and the change in glow plug bits at these speeds points to this being the case.

I guess this is part of the reason why Elsbett tell you to keep rpm between 2000 and 2500 when possible...



"Hope you have your Durotherms, ( slow glow ) g.p.'s ;-)"

The GPs are standard (I think ?)

I might add a pressure sensor to get a crank case pressure signal. I could add this to the range of signals I'm going to send to the data logger I'm in the process of fitting
(see posts on using glow plugs as combustion sensors at http://biodiesel.infopop.cc/eve/forums/a/tpc/f/159605551/m/1071029711 )
I have an oil pressure sensor (engine oil pressure sender) that I intended to us to monitor fuel pressure on my Mercedes truck (pressure side of the lift pump) I played with it attached to a air pump and pressure regulator and was getting a change in signal within a range of pressures. I have yet to convice myself that it is the right tool for the job - not sure if the sensor range or sensitivity is suitable also if using air was giving an accurate picture of what would happpen on engine - I might try and rig it up for crankcase pressure.

Best

Darren

"I didn't test what power was coming out of the harness during the post glow period or while I put my foot down to get above 2500 rpm but I've read about post glow being suspended at engine seeds above 2500 and the change in glow plug bits at these speeds points to this being the case."

Drawing 40 - 70 amps to heat 7 g.p.s will put a sinifican tload on the alternator. That might effect the load on the engine, the fuel necessary to maintain constant RPM and your readings. I don'y know a way to easily disable the voltage regulator.

Hello BD

My car has not got the three coolant glow plugs.
Also I'm testing without any ECU controlled glow plug action.
Interestingly I'm getting no fault codes with the GPs not plugged in....
(on my car there are two wires going into the glow plugs rather than the later models which have four and flash codes for dodgy GPs or wire connections)

I'm doing the initial testing on diesel fuel (what I have in my tank) and expect to notice some difference after cold starts (otherwise VW would not bother with the afterglow period?)

I should have some more results to post soon....

Best

Darren

Darren,

"My car has not got the three coolant glow plugs."
Ok. So maybe 40 Amps battery draw max instead of 70.

"Also I'm testing without any ECU controlled glow plug action."
But you posted the g.p. bits, so that was ECU controlled. (???)
IN any case, whether manual or ECU controlled, turning on the g.p.'s
might cause the alternator to charge the battery, loading the engine.
I'm assuming your fuel readings would be higher for a loaded engine.

"Interestingly I'm getting no fault codes with the GPs not plugged in...."
I think they work by measuring the current difference between plug pairs,
not the absolute current draw ( or lack of one ).
1&2 and 3&4 maybe?
Try plugging just 1 in. I bet you get a g.p. CEL.





"(on my car there are two wires going into the glow plugs rather than the later models which have four and flash codes for dodgy GPs or wire connections)."
Hmmm. I have 4 g.p. wires in my AHU.
They could still do a differential measurement with only 2 wires, but thats a pure guess.


I'm doing the initial testing on diesel fuel (what I have in my tank) and expect to notice some difference after cold starts (otherwise VW would not bother with the afterglow period?)

DarrenUK said:

A quick test running on diesel after a coldish start (I had run the car a few hours before this) showed the post glow running for three minutes with a coolant temp of 15deg C. glow plug bits show 10110000 when after glowing or 11010000 if rpm is above 2500

Click to expand...

Darren, I'm under the impression that the data show in Group 13 is semi-meaningless unless the engine is fully warmed up. I've seen erratic readings when the engine is cool or cold. Have you noticed this?

Biodiesel ,
the glow plug loom is not plugged in so the ecu bits report what should be happening

with the 2 wire loom both wires go to the same screw terminal on the relay board - i dont think there is a current comparison.

Dieseldorf
i did some more testing today and was getting meaningfull readings at idle after cold start. Activating the gp made a noticeable reduction to the fuel sent to

That cylinder.

Ill post some data and graphs soon.

Best
darren

I just stumbled on this thread yesterday and think this is very interesting. I was clearing some codes last night so I thought I would check out measuring block 013.

My question is, why is cylinder 4 showing no reading at all? This is for a 98 AHU. The engine was at operating temp. and was idling on diesel.

Stark see the first post. With some ecu s the other cylinders are compared to cyl 3.

Best darren

I have put some graphs and data online.

http://vegburner.co.uk/logs/ISSR_GP_timing_cold_idle2.htm

shows the effect of igniting the glow plug in cyl4 after a cold start with no ECU controlled post glow period.

http://vegburner.co.uk/logs/TickOver-LJ-VAG-GP.htm

shows the same but with a mV signal back from the glow plug when not powered (in effect a temperature reading of the glow plug) - when the blue line is visable on the graph the glow plug is not powered.

You can click on the tabs at the bottom of these pages to see the data or view other graphs I made from the data.

There is a definate trend to a lower smooth idle adjustment value when the glow plug is powered which rises again when power is cut.

I am getting simialr results with a hot engine at tick over.

When driving the ISSR does not appear to change when the glow plug is powered - engine cold or hot.

All these tests on diesel fuel 180,000 on a (apparently) reasonably well maintained AGR engine. As far as I know injectors (and nozzles) still original - which I consider to be less than ideal.

What I'm apparently seeing is combustion at idle that could be improved.

Which leads to this recent discussion which I think could be of interest
http://biodiesel.infopop.cc/eve/forums/a/tpc/f/159605551/m/4571057022

Best

Darren

http://vegburner.co.uk/logs/ISSR_GP_timing_cold_idle2.htm

In this, first graph, it looks like the change is less and less as the car gets a bit warmer. That first change is dramatic, so I'm guessing that was right after start-up with a stone cold engine?

Also, note that Cylinder #3 changes each time as well, again, going a bit towards zero. Interesting data, thanks.

Hello whitedog,

Yes the first graph shows a cold start with a cold engine.
If you click on the tab in the bottom left corner 'LOG-01-012-004-013' you can view the full data set engine start tem was 13.5 the car had sat overnight.

Best

Darren