Jump to content

Limit Ign Trim

Andy Drummond

Recommended Posts


While working to improve starting on my G4 silver extreme latest firmware etc.

On my last start run during cranking found the ign angle retarded by 5 degrees (ie -5), showed up as 'Limit Ign Trim' parameter. Once the engine was cranking the Limit Ign Trim started to decrease by 0.5 deg steps until its was -3.5 deg and rpm > (619 to 1033) then went to zero. Engine running.

The ECT Ign Trim = 0,  IAT Ign Trim = 0, Only Ign Table 1 active.

'Transient Ign Trim' = 0  , Decay Rate = 0.5 Degrees/Cycle

'Cyl (1 to 4) Knk I-Trim' = 0

'Knk Sys Status Lockout' < 500 rpm , Knock 'Advance Rate' = 0.5 degrees/sec, Knock Ign Retard Limit = 5.0

The question is where did this -5 limit ign trim come from?

One possibility is that the first crank did not fire (Don't have log) and on stopping caused a limit?, then the second crank fired as above. Please note that sometimes when you stop cranking and/or turn off  the engine ign the PC log records a very high rpm.

As multiple start attempts do happen, should there be a software condition that if zero rpm then set 'Limit Ign Trim' to zero.

Your thoughts, questions.



Link to comment
Share on other sites

Sounds like the ECU is seeing a false RPM reading causing the RPM limit to activate and the ignition trim is coming in due to the limit being hit.

In a good set up the RPM reading should not be doing this at cranking or engine stop.

What trigger set up are you using?

Link to comment
Share on other sites


My setup, sequential Trigger2 is cam reluctor, Trigger1 crank reluctor 60 - 2 tooth.

Then key off turns off power to injectors & coils etc, the ECU remains powered up.

Was able to do the fault again today.

Engine started and running at idle speed (1060rpm) all good & stable. Then turned off the key (Dig Input2), revs dropping until 516rpm within 350 msec. Then the next reading (90msec later) the rpm jumped to 33,967 rpm. the following reading at 33967rpm and the Limit Ign Trim set to -5 deg. PC log finished and engine stopped.

Now the Limit Ign Trim will remain during cranking until the Knock Control over writes it, at rpm > 500.

So to solve this problem, lets look the cause. Very high high rpm at the end of engine stopping.

Possible noise/interference, 12 volt power for the injectors, coils and fuel pumps is removed it lease 2 engine cycles before the very high rpm reading. The only possible external running item is the electric PWM water pump and actually was not running at the time (engine cold). So as the trigger system runs very good and smooth over the rev range and there is no external devices running. Leads to state that noise/ interference is NOT causing the very high reading.

 Another possibility? It is noted that the crank stopped about 90 degrees after the missing 2 teeth position. To get such a very large rpm number leads to a divide by very small number. So during the stopping the rpm is dropping very quickly and the crank trigger is passing through missing 2 teeth with very low rpm and/or rapid decreasing engine speed.

Your thoughts

Cheers  Andy

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...