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g4 atom idle tuning

Hamish Sheldon

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Hi all

ive been chasing poor idle issues with my engine round in circles for some time now and have finally got to the point im going to ask for help. 

I get a miss fire at idle where ive got it set at 1200rpm which is manageable but annoying and if i try to set it down below 1000rpm its not manageable which i think it should be happy at 900rpm. the engine is a ford 2000ohc from a sierra with a uk assembled oem multipoint fuel injection manifold running bosch 320cc injectors in sequential fuelling. im triggering from the orignal distributor drive with a nissan 360 opto from a ca18det,  and using a 2ch ignitor running evo 2 post coils running waste spark. internaly its got 10.5 to 1 compression ratio, gp1 valves, porting, a kent fr34 cam and a lightened flywheel .

Ive tryed closed loop idle and ive tryed open loop idle, ive tryed all kinds of different frequencys for running the iac valve, ive tryed 8 degrees all the way up to 25 degrees btdc ignition timing at idle and it strangely prefers lots of timing at idle hence where ive got it set at the moment. Ive built this map up over the last 3 odd years and it preforms well and has ok drive ability. This is the first link ive ever owned and tuned and im not expert by any standards so dont take the piss out of me to much with my base map. Any help to get to the bottom of this would be much appreciated.

escort latest.pcl

Log 26-06-18 10;46;16 am idle issue.llg

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We received a similar email in Tech support from Hamish so Im going to post my email reply here also - just so we dont get too many conflicting comments.  Based on the slightly different info we were given (misfires at idle) my thought is it is more fuel or ignition related problem rather than idle valve control (idle valve is not moving in log).  So here are my thoughts or ideas to look at:

I dont see anything glaringly obvious but I have a couple of thoughts & questions I will list...

  • What is the injector resistance?  Have you got a part number?
  • Its pretty odd to use BAP as the load equation when you are using MAP/MGP on the fuel table.  Typically it is only used with TP on the fuel table.  Load = MAP looks like it would be the preferable option for this engine but would require completely re-tuning the fuel table.
  • It is not common to have CLL active at idle so you should set up the RPM low lockout above normal Idle to prevent that acting
  • Not many older modified engines with poor port velocity and non-ideal injector placement/spray pattern will idle at stoich, I wouldnt be surprised if it is happiest around 13-14:1. I know you say you have already experimented with that but I just wanted to mention, try to keep a stoich target out of your mind and just give it what its happiest with.
  • If you lock timing at idle and check it with a timing light, is it stable?
  • Since you are wasted spark your offset could be 360deg out and it will still run - just injection will be squirting in 360deg too early/late.  To test this you can either just try adding/subtracting 360 from your current offset to see if it runs any better, or turn on individual cylinder trim and add a negative -50% trim to cylinder 1.  Then pull cyl 1 and 4 plug leads off alternatively to check if that killed #1 or # 4 cyl.
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