diesel injectors - what does T4 balance actually do?

[pondweed]

spoken to Lynx about balancing my injectors should Millers not clear any obstruction that is giving the occasional flutter on idle. He said they will overhaul the 2 old ones and balance all 4 on a test rig (with the two new ones removed) Thus, they wont need any T4 action when they are put back.

So what does a T4 actually do, and what settings will be on my car as a result of the last balancing after the replacement of the second new injector? Will this have any bad effect with the four now in perfect balance?

[ColinW]

spoken to Lynx about balancing my injectors should Millers not clear any obstruction that is giving the occasional flutter on idle. He said they will overhaul the 2 old ones and balance all 4 on a test rig (with the two new ones removed) Thus, they wont need any T4 action when they are put back.

So what does a T4 actually do, and what settings will be on my car as a result of the last balancing after the replacement of the second new injector? Will this have any bad effect with the four now in perfect balance?


This question I discussed on the "Dark side" back in Dec '07. Keith thought initialy T4 could be used to adjust individual injectors. As it happens it cannot.

Here is the link to that discussion.

http://forums.mg-rover.org/showthread.php?t=215069&highlight=injectors.

So as I, & many others have found, there is no substitute for good mechanical balance of all four, as Allan at Lynx does so well.

Colin

[pondweed]

colin - that is very useful but the screen dumps arent further discussed so its a little ambiguous.

I presume that the rpm correction will mean the ecu automatically adjusts to the new circumstances (in the cylinders) to the best of its ability, each and every time.

Thus when I re-introduce 4 balanced injectors, the ecu will sigh "aaaaah" and not have to work quite as hard to perform this adjustment?

So the only adjustment I may need to make is to lower the idle (on T4) back to the lowest available level... or do you/Keith think this will be done automatically where it detects its stepping-up is further unrequired?

This process sounds like it is going to result in an engine that will be better than the original - I cant believe that balancing to this degree would be possible in conditions of non-bespoke engine build. Although I suppose there is an analogy to 'cars that topple over' - computers maintain perfect stablility in chassis designs that would otherwise be classed as unsafe.... in this case we are just lessening the need for so much computer input?

[ColinW]

I wouldn't read too much into those screen dumps. If you read Keith's remarks, they are more pertinent."I was wrong you can't tweak individual injectors on T4 the engine ECU does all that to maintain smooth running only thing you can change is the tickover in 10rpm steps I have just turned mine up 10 rpm and it now ticking over much more smoothly"

As pointed out to him, if it was that easy, service centres with T4 would have been making hay long ago by correcting uneven idling, which by all accounts they cannot. Certainly on T4, the injection volume per stroke at idle is readable, as I have seen that for myself. However to store bespoke settings into a none volatile memory in the ECU, is perhaps something that may have been thought about, but not implemented.

By contrast, Delphi injectors unlike the Bosch, cannot be adjusted. So they have to be adjusted by their respective ECU. It sounds better, but there has to be a limit of adjustment, so in the end, one might have to throw a Delphi injector away.

According to Allan at Lynx, the same Bosch injectors have the same problems in BMW engines. So it would seem that even they have decided not to go down this software re-adjustment route.

Certainly, when I put in nicley balanced injectors, it was quite dramatic, apart from the noise of the crankshaft pulley, which subsequently got sorted. In fact, I do believe an uneven tickover contributed to the failure of the rubber in the pulley. So if nothing else, an even idle puts less strain on many things, not the least of which is ones ear.

Colin

[pondweed]

ok. I can see that as the idle gets higher, the capacity to handle greater variation increases. And that is all they are inferring in T4-speak.

And I presume the reference to Delphi is for comparison only - ours are all Bosch, right?

[ColinW]

ok.
And I presume the reference to Delphi is for comparison only - ours are all Bosch, right?


Yes indeed. Ours are Bosch, who have designed the injector, such that manufacturing tolerances can be taken up by the aid of shims. Allan at Lynx had a box with at least 20 different shims of varying thicknesses. It is a reiterative process, in which the injector is tested for flow at the idle fuel pressure, then a shim is replaced by a thicker or thinner one to get the flow to the specified rate. Each time the injector must be stripped down & reassembled.

However, and this where the likes of Allan are so good, it is possible to match each injector to the others, to a degree which is closer than the specified flow tolerance that Bosch put on it. On mine, he got the spread to better than 10% across all four. Theoretically, this could be improved, if enough time and enough different shims were available.

By contrast Delphi do not bother, ie there are no shims, so there could be large variations, which are taken out with the ECU.

So that's it.

Colin

[BT@Home]

All seems rather labour intensive, is this balancing etc a costly experience?

[ColinW]

All seems rather labour intensive, is this balancing etc a costly experience?


Yes it would normaly be from a major refurbisher, but Allan from Lynx diesels has lower overheads, so quite cost effective. Also, I suspect some of the big boys wouldn't bother.

He does 2 types of service, with and without the injector tip replacement. At the moment I believe he charges £90 each, which inludes the tip replacement.
Others charge between £130 & £150 for this. New ones cost around £230+, and, as one forumite can confirm, they can be out of spec when new.

Colin

[Keith]

As I said in the org thread at first I had been given the impression you could adjust the balance but once I got my T4 I realised that was wrong.

The only option is to increase rpm at 10 rpm steps which may help with a rough idle once it has been proven nothing else is causing the rough idle.

Nothing to do with injector balancing but last year as my car was doing very short school type runs I was having trouble keeping the battery (read that as swmbo was probably turning everything on including the seat heaters) charged so I whacked the idle up to 800 rpm which meant the alternator was chucking out a bit more whilst idling in traffic especially with the HRW and rad fan whiring away and that worked fine!

The ecu compensates for subtle variations in injectors using a cylinder balancing algorithm to maintain a near identicla rpm per cylinder this is automated and not adjustable so you can replace a single injector and the ECU adjusts the injector timing to maintain balanced running.

What the T4 screen shows is just by how much the ECU is having to compensate the output from a given injector and that with experience (and it is the experience you are paying for with this type of work) allows a good mechanic to identify what may or may not be a problem, for example a leaking injector may show up quite markedly on T4


No doubt dedicated Bosch DDC15 ECU diag tools are more advanced but do a similar thing

my pics below

What you need to remember is the info is real time and very much a result of other factors on any given day the before and after pics below show once I upped the tickover the compensation on two of the injectors reduced slightly on the day I did the work.


http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDEidleadjust.jpg

http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDEidleadjustb.jpg

This is the resultant cylinder balancing after knocking the tickover up 10 rpm

http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDECylinderbalancing3.jpg

http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDECylinderbalancing2.jpg

And this is the before shot

http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDECylinderbalancing1.jpg

Info screens

http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDECylinderbalancingstatus1.jpg

http://i102.photobucket.com/albums/m91/alexank/Projects/Testbook/DDECylinderbalancingstatus.jpg

[podge]

I paid another trip to Alan and had a long talk about injectors and how he overhauls and balances them, a very, very experienced guy and very methodical, should mine ever need work doing to them, thats where they are going.In fact I allmost pulled them just to get them perfectly balanced and yes you can via shims on the Bosch ones but replacment Delphi ones no.

[Jules]

Just found an invoice in our car's history for £1400 for "maintenance & fault finding" to the injectors!!! (main agent in Bristol)

Glad we didn't have to foot the bill for that;)

[oddsocks]

As per my post before Christmas, Alan serviced all 4 of my injectors including 2 that were factory exchange units 3 months earlier (the other two had leakback). From door to door it took 4 days (3 of which was post) and was £90 per 2 x injector to fix plus £20 for a new nozzle on one of the 'exchange' items. Alan insisted on me shipping all 4 so he could balance them and only charged for parts on the factory ones - the intention being to get the repaired ones to match them.

When I refitted them the engine was rock steady - no vibration at all. Seeing as this was my first diesel I had assumed that engine vibration at idle was normal.
Looking back at Keith's screen shots and last comments, when I had my car on the T4 the two cylinders that subsequently I confirmed with leakback were showing 30RPM higher than the cylinders that had the exchange injectors - the T4 op did not interpret this as any problem but i suspect it was indicating the root cause (he did try to tell me i needed a new in tank pump - I had just had one fitted and fuel was plentiful out of the filter).