Strange CL Misfire - Tuning Forum

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Strange CL Misfire
Saturday, February 06, 2016 1:27 PM
Quick context
2003 Sunfire (pcm doesn't have the cranking table)
Turbocharged it 2 weeks ago
BOV and IAT right before the TB, BOV is open at idle and is after the IAT
42 lb green tops, stock fpr and pump
ngk iridiums (I think the 1 step colder ones) gapped at 040
stock internals
Injector pulsewidth at idle is around 2.6 ms
Ran a wire to the AC pressure connector for wideband signal. Don't know if AC pressure sensor being disconnected is a problem
Key on engine off fuel pressure is 56 psi, running it was in the 40s

Current flash is all stock tables with DFCO disabled, adjusted for earlier PE, and 0.10171 injector constant (also tried 0.0869 calculated from a spreadsheet I found on the hpt forums).

The Problem:
I can't really tell in open loop because on cold start it seems to run great. Once it goes into closed loop I get a steady misfire on 2 cylinders (logging current shows cylinders 1 and 3, the code is P0300). The car also stalls without throttle input when coming to stop lights. If I give it throttle input while coming to a stop and slowly let off it can usually find idle fine. If it stalls it will need throttle input when I try to restart it before it will idle again. Also the car stumbles heavily when electrical load is introduced, particularly when the cooling fans turn on, sometimes it will die; will happen with rear defrost, and reverse lamps as well. Headlights seem to have less of an impact. The voltage is 14 at idle and the alternator's current is strong.

Before I started hunting the problem the current misfires counter showed them on cylinders 1 and 2. When I put new plugs in and it still missed at idle I took them out and cylinders 1 and 2 still looked brand new where cylinders 3 and 4 were slightly darkened.

What I've tried:
Battery to engine ground seems fine. I can see bare wire where it passes the battery tray, not sure if this is normal or not, I think its grounded on it on the way to the engine.
Smoke tested and fixed vacuum leaks
Cleaned TB and IAC
Replaced whole IDI cover with a junkyard unit (was told that they tested it and it worked fine)
Re-gapped spark plugs to .035 and cleaned
Replaced spark plugs
Listened to injectors for clicking sound through screwdriver and they were all working fine
Removed and cleaned injectors
Replaced battery

I've run out of ideas for what could be causing this and would really appreciate it if anyone could chime in. Is there anything in the tune file I need to change to make it idle normally with the new constant? The only think can think to try is rewiring in the stock injector connectors and re-flashing back to stock to see if it will idle again. One other thing: pre-turbocharger my idle vacuum was 20 inches, and its come down to 17-18 now.

Re: Strange CL Misfire
Sunday, February 07, 2016 1:47 PM
What are your AFR's while misfiring?

Staling coming to a stop is in the tune. I have ran into this many times.

Is your primary O2 sensor reading correctly?



FU Tuning



Re: Strange CL Misfire
Sunday, February 07, 2016 2:03 PM
I haven't logged O2 readings, but the fuel trims are being adjusted.

The wideband fluctuates with the rpms (as its misfiring) between 14 and 16 while idling and cruising in closed loop. Commanded afr is 14.6.

The spark advance also jumps around between 0 and 20 but I read that this is normal as the car tries to maintain steady idle. 0 knock retard.
Re: Strange CL Misfire
Monday, February 08, 2016 3:59 AM
I would log the O2 sensor and see what it is doing.

16 is on the high side at idle. for AFR's.

My car not a eco idles between 14.1-15.1



FU Tuning



Re: Strange CL Misfire
Monday, February 08, 2016 3:11 PM
Primary o2 fluctuates between .1 and .9v like one might expect but it doesnt match my wideband readings. At one point the wideband reads 13.6 and the o2 readys .9v, another time its 15.4 afr and .8v, 15.3 and .15v.

Is this discrepancy to be expected? Or do you think this means the o2 is going out the door. There is no o2 code but I've heard that they go silently if its not a sudden death.
Re: Strange CL Misfire
Tuesday, February 09, 2016 3:44 AM
Ryan DaCunha wrote:

Primary o2 fluctuates between .1 and .9v like one might expect but it doesnt match my wideband readings. At one point the wideband reads 13.6 and the o2 readys .9v, another time its 15.4 afr and .8v, 15.3 and .15v.

Is this discrepancy to be expected? Or do you think this means the o2 is going out the door. There is no o2 code but I've heard that they go silently if its not a sudden death.


I have never paid attention to the wideband and O2 matching, as the factory O2 is only accurate at stoich. If it is sweeping back and forth then it seems to be working properly.

I would work on richen it up at idle so it is a tighter sweep that is more in the 14-15 range.



FU Tuning



Re: Strange CL Misfire
Tuesday, February 09, 2016 9:21 AM
Does the pcm use the tables in closed loop? I was under the impression that it was completely independent from what we see in HP tuners.
Re: Strange CL Misfire
Tuesday, February 09, 2016 4:29 PM
Ryan DaCunha wrote:

Does the pcm use the tables in closed loop? I was under the impression that it was completely independent from what we see in HP tuners.


It uses the sensor's mostly, but uses the table as a base.



FU Tuning



Re: Strange CL Misfire
Tuesday, February 09, 2016 5:10 PM
Okay I'll give it a shot. It seems to be improving itself over time too, isn't idling as rough but still missing. Thanks a lot for the help.
Re: Strange CL Misfire
Monday, March 14, 2016 2:26 PM
Bumping this thread because I'm stuck again.

I've tried a bunch of different adjustments without any luck and today decided to revert back to stock injectors to make see if it was a mechanical issue. Flashed back to stock, disconnected intake from turbo, with stock injectors back in the car runs like brand new.

So all I can think of as the issue is potentially bad injectors (cylinders 1 and 3 were misfiring, but the 42s were all brand new), or my constant was way off. I assumed that the car should run well with just the proper constant at idle, and my constant came from the spreadsheet calculator on hptuners forum.

These are the injectors that I bought: http://www.ebay.com/itm/FUEL-INJECTOR-For-Bosch-EV1-style-injectors-0280150558-440cc-min-TURBO-42-LB-HR-/281769898863?fits=Make%3AFord

Any ideas? Thanks for all the help.
Re: Strange CL Misfire
Monday, March 14, 2016 2:27 PM
Forgot to ask too if the 42s are just too big to idle without an afpr.

Re: Strange CL Misfire
Monday, March 14, 2016 5:33 PM
42's are not too big.

what was your constant?



FU Tuning



Re: Strange CL Misfire
Monday, March 14, 2016 5:50 PM
I tried 0.10171 calculated from the scaling formula on this forum, and 0.0869 calculated using that calculator I was talking about from the hptuners forum,
Re: Strange CL Misfire
Thursday, March 17, 2016 3:18 PM
Updating for people with similar problems in the future.

Was playing around today, put the injectors back in with a stock tune and 0.10171 constant but swapped injectors around and the miss followed them so ya. Two of my cheap injectors aren't working properly even though they click and have expected resistance.

Thanks for the help Addicted even though it was a way simpler issue than expected.
Re: Strange CL Misfire
Thursday, March 17, 2016 3:24 PM
Ryan DaCunha wrote:

Updating for people with similar problems in the future.

Was playing around today, put the injectors back in with a stock tune and 0.10171 constant but swapped injectors around and the miss followed them so ya. Two of my cheap injectors aren't working properly even though they click and have expected resistance.

Thanks for the help Addicted even though it was a way simpler issue than expected.


Good job and diagnosing



FU Tuning



Re: Strange CL Misfire
Wednesday, April 06, 2016 2:48 PM
Final update for those with similar problems in the future. I ordered 2 more ebay cheap injectors to try and solve the problem. It didnt, drivability was worse. Ended up buying a set of Lucas 42# from ZZP and they fit perfectly (03 with the injector cups) and it runs and drives just like it did before turbo except with boost! Good luck people.
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