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QDM-B error and secondary injectors not activating?

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  • Gold FFM

Took an Espritmon log on a friend's S4s that had a permanent CEL.

It's showing a QDM-B error and it looks like the secondary injectors aren't activating when TPS is at max. 


The Espritmon manual indicates that secondary injectors could be a source of the QDM-B error (among others). 

I'm far from an expert in analysing these logs. I was hoping that someone might have time to cast their eye over the attached log to see if they can find anything else untoward?

If it is the secondary injectors, any pointers as to why and how to further diagnose and fix?

Does the MAT look a little on the high side as well?

Many thanks in advance! :)


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  • Gold FFM

You need to see if there’s continuity to the injectors, the injector resistance and then finally stick the injector on a test jig. There’s a flow chart for diagnosing this error in the manual.

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Hi Robin,

Your tps is showing that the throttle was only fully open for brief moments x3.

Also you barely hit the critical 4800rpm target (once) required to activate the secondary injectors.

On the one occasion you did hit 5000rpm, the tps was only at circa 80%.

So, you may not have actually triggered the secondary injectors during that particular drive.

Boost needs to be 0.7bar minimum, tps over 95% and rpm over 4800 according to the EMH manual.

Your MAT does look high so I would suggest checking the charge-cooler pump impeller at some point.

I assume you're seeing a code 26 error. Can you confirm?

I would make the first check similar to Barry's advice and look at the secondary injector ballast resistor for continuity. The resistor can break off from its terminals inside its case. Should be 3.3ohms from memory.



Edited by AndyPG
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Hi Robin,

One of our most knowledgeable forum members (Sailorbob) has kindly pm'd me some corrections to my previous post.

The use of the secondary injectors is not dependent on the throttle position and, on the S4S, the minimum MAP is 1.61 for the injectors to come into play.

I wrongly assumed the '95 S4 operated the same as my  '90 SE.

Regards, Andy.

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  • Gold FFM

@AndyPG (and @sailorbob :) ) Many thanks for your comments. 

(By the way, this S4s isn't mine, just a friends I connected my laptop+Espritmon up to.)

Using Espritmon, it's showing a QDB (QDM-B) error (this is an error 26 I believe).

I don't have access to the car (and actually don't have the experience or competence to attempt the diagnostic checks recommended). He was just looking for confirmation of what the CEL might be indicating and whether he should drive it at all for the time being.

Ironically, looking at the Espritmon log he took whilst taking it out for a spin with my laptop attached, the MAP only got up to about 1.59, not the 1.6 indicted as being required to activate the secondary injectors. So no proof there as to whether the secondary injectors are actually active or not.

One other thing I've noticed, the wastegate solenoid doesn't get activated at all under driving conditions I would have expected it should have: 


Compare that to my S4 where similar MAP, tps and MAT conditions did activate the wastegate solenoid:


That, coupled with the comparatively high MAT temperature on the S4s (and the higher coolant temp, would that be any different to an S4 log?), might indicate another underlying cause?

I've asked my mate to check whether the wastegate arm is movable, also to touch test the temp of the charge cooler next time he drives it. Beyond that, just looking for a possible diagnostic that would indicate whether he shouldn't drive it all, or could.


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