Misfires Disappeared with Cold Weather

Posted By: Chris Browning

Misfires Disappeared with Cold Weather - October 17, 2016 10:31 pm UTC

So I was attempting to cure the small misfires that I was getting at idle this summer, I installed new exhaust gaskets, a new O2 sensor, and sealed the engine up tight for vacuum / boost leaks but I still had a misfire that would show up after the car had been running for awhile. By that I mean not just after it got up to temperature but after drives longer than half an hour or so. The only thing that seemed to help was reducing my plug gap from 0.28 to 0.24 on BR7ES plugs, but even that wasn't a huge improvement.

Well fast forward to the fall and my misfires have gotten better and better as the outside temperature has dropped, then today with the temperatures back up close to 20 degrees the car was missing again. So with all that evidence I'm thinking that either the PTU or coil packs must be getting heat soaked with the higher under hood temperatures in the summer (coolant temps have remained the same in the colder weather).

Does this make sense or is there something else here I'm overlooking? I'd like to try to diagnose this without swapping in alternate parts so if anyone can think of a method of testing the components other than trying to get the multimeter on them when they're roasting I'd like to hear it.

Posted By: Bryan Lawrence

Re: Misfires Disappeared with Cold Weather - October 17, 2016 10:55 pm UTC

Based on what I am reading it looks like you might be right, posts on tuners seem to think it's probably the coil pack or transistor.
I would try and replace those and see how it goes.
Posted By: Stephen Richardson

Re: Misfires Disappeared with Cold Weather - October 17, 2016 11:38 pm UTC

Is the misfire only at idle? Do you have a log of said event?
Posted By: Chris Browning

Re: Misfires Disappeared with Cold Weather - October 18, 2016 02:25 am UTC

It's generally only at idle, although I do get occasional blips of power loss during some WOT pulls, they are very minor but could also be ignition related. I'll try to get a log.
Posted By: Chris Browning

Re: Misfires Disappeared with Cold Weather - October 27, 2016 11:28 pm UTC

Hey guys,

Here are some logs from today, it was cold out but I was still getting some misses after my 45 minute drive home. The first log is after 10 minutes of driving around with the coolant temps just coming up to 190+, the car wasn't missing at all at this point. The second log was taken at my place after the 45 minute drive home, the misses appears in the log as rich spots in the O2 signal after which the ecu seems to pull a bit of fuel (probably making the situation worse). I'll try to get another hot log next week, it looks like the temperatures will be a little higher so I can get a more erratic idle.

Idle After 10 Minutes

Idle After 45 Minutes
Posted By: Stephen Richardson

Re: Misfires Disappeared with Cold Weather - October 28, 2016 12:42 am UTC

Your global is set for 720cc injectors. Is there a reason why?
Posted By: Chris Browning

Re: Misfires Disappeared with Cold Weather - October 28, 2016 12:06 pm UTC

That global value along with my current MAFcomp settings result in my Boost gauge, BoostEst, AFREst, and Wideband aligning at 5000-5500 rpm during third gear pulls, along with 0.25g/rev at idle. I used dead time adjustments to dial in my idle fuel trims after that.
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