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2002 WRX 6000+RPM exhaust poping

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On really hot days (36deg+) while WOT @ 6200rpm + I get loud "back firing" or poping and a puff of black smoke from the exhaust.

Im guessing its too rich up top and high exhaust temp causes excess fuel to ignite.

What could be causing this issue?

I have a link g4 ecu installed and was wondering what I should be looking at adjusting. IAT fuel table perhaps?

Sounds like a missed ignition event, what modifications and boost levels are you running?

What you should do before you do anything is take a datalog of how the engine is running when the pop's happen, I usually set up automatic datalogging on G4+'s so that if anything happens I can pull the data without customers needing to try and re-create the events.

Here's a link to a guide I made on setting up the on-board datalogging:


If you hook a laptop up to the ECU to datalog it can record all parameters at the same time, which is useful sometimes but the sample rate suffers compared to the on-board logging.

What you'll need to record as a minimum is RPM, IAT's, AFR's, injection duration or duty cycle, Coolant temps, global knock count and manifold pressures. After you've done this you'll be able to see a broad picture of what's going on and narrow down the areas you need more data from.


565 sti injectors

vf48 running @ 20psi


and the link g4

it is a little rich up top 11.5

It may be a week before I can get a log.

It's likely to be an ignition issue. Start by changing your spark plugs and setting the gap to whatever is recommended for your application.

The 11.5 AFR you are running wouldn't cause the issue.

Are you getting any trigger errors?

If this is the V7-10 WRX they have a trigger lockout rpm under trigger setup. If you're getting errors and this has not been setup correctly then you could be suffering from erratic timing/scatter causing misfires etc in higher rpm.

Chris, I think you are right. It does look like a triggering issue, RPM is all over the place up top.

Here is a log of a short run and the setup file.

Please note the wideband needs a recal as its way off.

Attached Files

Bring your Trigger 2 Lockout down to 6000rpm and try that. I can see in the log you have a trigger error counter of 255 which is the limit. After you make the change carry out a log and monitor "trigger error counter" if there is still an issue in the higher rpm you will see the error counter start counting up when the error occurs. You might need to adjust the lockout.

Hi Chris,

I noticed that too however it is constantly 255 even at idle... it does not change at all. Im not sure we can use that indicator.

I am think Im going to re-ground the engine with a grounding kit and keep an eye on the IAT and AFR when I fix the wideband to see what is actually happening are 6k RPM.

If you think of anything else I can try let me know.

Thank you.

The trigger error can't start at 255 so it must be counting up as soon as you start the car. I would try this, turn ignition on and connect to ECU press 'R' or F12 to open your run time values and scroll along to "Triggers/limits" the counter should be at 0. Start the engine and see if the counter starts counting up. If it does at idle then it could be any of the following, faulty cam or crank sensor, incorrect polarity, incorrect arming thresholds or filtering level, interference into the signal causing noise.

If it doesn't start counting up then drive the car and see when it does start counting up.

Good idea with doing the grounds, also check you ecu to engine ground which should be on the intake manifold, I have seen these cause issues many times.

Good luck and let me know how you get on.

Issues all fixed, trigger threshold was incorrectly set which caused the issues.

Revs freely now all the way to red line.

Thanks for the help and apologies for late reply.

We usually reply within 12hrs (often sooner)

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