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Rough Idling During Cold Start - Trigger Related


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Well I was going to email this to Link Support but I cant find an email address so here it is.

Can anyone help me?


Subaru Impreza STI V4 with Link G4 Plug-In ECU


Vehicle Details

1998 Subaru Impreza WRX STI V4

ECU: Link G4 Plugin for V3-4 STI

Engine: EJ20K with 3.5Bar Map, Bosch IAT sensor, top mount intercooler

Fuel: E85 fuel, ID1000 Injectors running stock fuel pressure

Turbo: TD05-18G

Problem description

Car is very hard to start and when it does eventually start it runs very rough for a few minutes. It eventually runs correctly and then has no further problems until it is started next time. The rough running lasts the longest when the car is cold.

While the car is running rough the rev counter is jumping up and down and generally giving erroneous values. This can be seen in the logging data.


Car ran fine with the Link G4 for a number of years. It was converted to run on E85 with larger injectors etc and then ran fine for a few weeks after being tuned at E&H Motors. The starting problem seemed to occur out of the blue.


·       The ignition circuit and fuel circuits seem to be working correctly. The problem seems to be coming from the ECU.

·       While the car is running rough the ignition angle is constantly changing darastically. It sometimes reaches the ignition advance limit.

·       While running rough the indicated revs are occasionally reaching extremely high values and causing the rev limiter to activate.

·       While running rough the Trig1 Err counter sometimes counts but only small values up to 30-40.

·       The problem seems to be related to the Trigger 2 input.

·       The Trigger 2 Arming voltage indicates a constant voltage of 0.17V while the car is running rough. As soon as this increases to 1.8-3.2V the car begins to idle/run correctly.

·       Sometimes a Hardware Block 3 Error occurs while the car is running rough and this will often correct itself after the car is running normally for a while.


·       What is the Trigger 2 Arming Voltage and what could cause this to misbehave?

·       What is the Hardware Block 3 error status indicating and what could cause this? What does Hardware Block 3 do?

·       If the Trigger 2 Arming Voltage is incorrect how come the Trig1 Err counter is not reaching much higher values? I understand this is comparing signals from Trigger 1 and Trigger 2.


Attached Log File

Please review the attached log file. This is logging two cycles where the engine starts up and idles very roughly for a while before returning to a normal idle and then I turn it off and start again.

Note the rough idle between 4s and 16s and then the idle smooths out and returns to normal. This perfectly aligns with the Trigger 2 Arming Voltage being 0.17V. The same rough idle happens between 44s and 68s. Also note the Hardware Block 3 Error occurring at 54s.




As at 3-07-2016.pcl

Log 4-07-17 4;38;58 pm.llg

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You definitely have a trigger error, I dont think the HW block error 3 means much but I will have to confirm what that means with Engineering tomorrow.  I also think the Trigger 2 arming voltage not following its table is probably a symptom of the trigger error rather than the cause.

The trigger pattern on these engines can be a bit troublesome, especially as they get older.  The alignment of the teeth on the cam in reference to the crank position is quite critical.  On my simulator I get trigger errors for instance if I advance the trigger 2 position more than about 12degs from the normal stock location. 

The subaru engine due to its very long cam belt weaving across the whole width of the engine and the aluminium crankcase/heads means the cam position changes a lot from cold engine to hot engine.  As the engine warms up the camshafts get further away from the crankshaft which takes slack out of the tensioner system and rotates the cam position.  When your engine is cold your cam must be just moving into a zone where one of the cam sync edges crosses over one of the edges on the crank.

There could be many reasons but it will pay to check all the related mechanical bits first.  Is the cambelt tight, is the tensioner working, any loose or worn pulleys or keyways/dowels etc.  Other common causes are excessively "decked" crank cases, skimmed cylinder heads, aftermarket pulleys, stretched belt, cam timing wrong, etc.   

I will report back tomorrow if the HW block error and trigger arming voltage are anything we need to investigate but my feeling right now is these are probably just symptoms.  However I would say hold off pulling the engine apart until I report back...

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Hi Cods4,

Well I was wrong.  Talking to Engineering this morning they tell me HW Block error 3 is something to do with one of the DACs on the trigger circuit, and the arming voltage will be affected by that so there is likely a hardware issue causing this.

You will have to get the ECU back to us for inspection.  Please fill out/submit the service request form here:  http://www.linkecu.com/contact/ecu-service-requests/

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Hi Adam

Thanks very much for the replies. I'm on holiday now so I'll have to send it back in a couple of weeks when I get back. Is this sort of thing covered under a warranty? Or what would it cost to replace the DAC module?


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Hi being a G4 and not a + series the warranty is only 1 year, However we wont wound you too much to fix it generally around $150

Of course a lot depends on what we find damaged and possible causes for it.

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