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Old 01-17-2006, 11:06 AM   #1
tmarcel
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Default Misfires + UTEC + new engine

Recently I built an engine and since it went back in I've got misfires on a nearly regular basis. The misfires happen primarily in lower rpms and most of the time in 1st, then a little less in 2nd, and rarely in 3rd. Never in 4th or 5th Anyway, I've gone over the car and all mounting points are tight for the engine and trans. I was getting a CEL for the cam position sensor so I replaced that. That CEL didn't come back on but I keep getting the misfires in all 4 cyls still. The only other thing is that the front O2 was bent slightly (put it in by accident before dropping the engine in) and so occasionally I get a CEL for slow response from the front O2.

Some other important data to think about. This is the second engine that I built in the last 6 months. The first engine which was nearly identical had the same UTEC, same sensors (crank and knock w/the exception of the new cam sensor), same coil packs etc. It did the same thing too (misfires in all 4 cyls in low gears and rpms). That engine cam out after it suffered a broken rod bearing. The only diff with the UTEC is that it had the 4.2 firmware and is now flashed to ver 5.0.

As for the plugs, it has NGK iridiums range 7 now. On the last engine it had 8's (colder). The maps on the two cars are completely different. I started this one from scratch where the last one I recycled from the previous set up. Either way, both misfire(d) so the maps don't seem to be the culprit. BTW, this UTEC is a toggle version (I think ver 5 IIRC), no dip switches.

Thoughts...ideas what is causing this?
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Last edited by tmarcel; 01-17-2006 at 11:13 AM.
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Old 01-17-2006, 11:45 AM   #2
LiquidForce
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I had misfires when I lost my engine. I did a compression check and #4 was at 70. I put in a new short block and continued to get misfires. Turns out my coil packs were bad. I have always wondered if the coil packs caused my block to go.
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Old 01-17-2006, 12:45 PM   #3
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Is the car misfiring (you can feel/hear it) or are you just getting misfire codes?
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Old 01-17-2006, 01:10 PM   #4
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LiquidForce,

Is there a way to test coils? Mine seem to be okay as it runs LOL! I hate to just throw money at it without knowing why.


Harman Motive, Inc.,

Well the codes is the only thing I see (flashing CEL via UTEC) and I can't feel it through the car. When the light flashes it's not knock since the UTEC isn't pulling timing. It doesn't show up as knock either when logging.

Would the crank angle sensor be suspect? There hasn't been any codes for that though.
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Old 01-17-2006, 03:01 PM   #5
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I too get misfires on all 4 every day or two. It's a 2.5 hybrid with modded injectors. I checked compression and everything was fine. I am also running 7 series plugs (NGK).
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Old 01-17-2006, 03:09 PM   #6
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Quote:
Originally Posted by TypeC
I too get misfires on all 4 every day or two. It's a 2.5 hybrid with modded injectors. I checked compression and everything was fine. I am also running 7 series plugs (NGK).
Everyday or two? My thoughts would be first that it might be tuning related but....On mine, we're talking frequency of misfires is many times a day. Not every single time but most of the time in "no" boost and lower rpms at part throttle.
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Old 01-17-2006, 03:58 PM   #7
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try this-

put key in ignition
turn key to 'on'
wait 5 seconds
start car

this cured my misfire CELs....and i would usually get misfires within the first minute of driving the car (no boost, < 3k rpms).
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Old 01-17-2006, 03:59 PM   #8
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You mean every time you get in the car?
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Old 01-17-2006, 04:02 PM   #9
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about every other time....ie- if i ever saw the CEL go away, it would come back the next time i drive the car when cold.
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Old 01-17-2006, 05:00 PM   #10
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I get misfire codes (only after i installed my fmic) only if all these conditions are met,
-the car has been sitting for 2-3 days
-it's cold out (40 or less)
-It idles for 2-3 minutes (if i just get in and drive it doesnt do it)


sti, stock plugs, walbro, aps fmic, sz55, perrin injectors, typhoon (yeah, no bigmaf)
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Old 01-17-2006, 11:06 PM   #11
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Update...I was doing a little reading earlier and came across one of those "grounding threads" I always thought those grounding mods were for the guys who put in air filters and lower their cars 'cause it looks or sounds cool. Anyway, I must say that after installing some quality 8G wire that I purchased from Tweeter (and I didn't hit all the points) that it's not as bad. Now it is only doing it in first gear and and only when I get to 3-4k rpms and/or shift. Strange because now it's gone in 2nd gear. Remember, this is no boost and slight throttle when the misfires happen. What the hell is this?...Arggg....
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Old 01-18-2006, 09:01 AM   #12
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To determine if it was the coil packs I borrowed some off another wrx. I don't know a good way to bench test them.
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Old 01-18-2006, 09:11 AM   #13
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Same problem here. Misfires below 3k rpm under light throttle conditions on all cylinders. Runs great when flooring it. I noticed that if I lightly revved the motor when not in gear, the motor would rev then hesitate for a moment and then continue reving.

The problem was that I was not pulling enough fuel in the 0% column (offset to ECU fueling). I'd suggest looking at your long-term fuel trims. They should be +/- 5%, but mine were at -15%, which means that the ECU was trying to pull alot of fuel to make me idle properly.

Not sure what your exact setup is, but I am stage 4 w/ UTEC and UR 680cc injectors. The other thing to remember is that the UTEC does not compensate for low impedance injectors and their dead time.
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Old 01-18-2006, 10:32 AM   #14
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Thanks for the input everyone. I would bet that the fuel trims might play a role in the misfire diagnosis too. I'm kind of at a loss right now until I can grab up another laptop as I'm having to borrow one here and there. Also, I've got modded stock injectors that were cleaned and tested recently when the engine was being assembled. They flow 810cc and the report showed that the spray pattern was fair due to the fact that they had been modded from the original design. Otherwise, they said that it was acceptable but not ideal as the caps being in place.

However, all of this seems weird that it only happened in 1st and 2nd gears but now from adding the extra grounds only in 1st gear!!! Of course that was only driving after I reset the ECU and taking it for a 3 mile test drive. I'll have to see what's happening after a few more miles today to know if the grounds really helped.
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Old 01-18-2006, 12:00 PM   #15
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Quote:
Originally Posted by tmarcel
Also, I've got modded stock injectors
This is likely your problem.

I too had 0 misfire dtc’s ever on OEM injectors, then immediatly after installing modded stock injectors I get a misfire code every few days now, either individual cylinders or a combination. Everything is running fine and with a professional tune. I inquired with TXS about the issue and was told it’s a pretty common problem when running modded stockers, and is really nothing more than an annoyance…

PS: Mine were flow and spray-pattern tested too, same results...
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Old 01-18-2006, 12:49 PM   #16
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Misfires are common on modded stockers. Its hard to get them to flow right at low RPMs and low load. Its uneven at those levels and creates (in my experience) a rich misfire. I've learned to live with it until I can afford to get properly sized injectors. Uping my idle helped a lot.
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Old 01-18-2006, 12:54 PM   #17
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Quote:
Originally Posted by xcntrk75
I too had 0 misfire dtc’s ever on OEM injectors, then immediatly after installing modded stock injectors I get a misfire code every few days now, either individual cylinders or a combination.
Same here. Zero misfires on stockers, then it started with the modded ones.

Quote:
Originally Posted by cdvma
Uping my idle helped a lot.
What did you set it to?
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Old 01-18-2006, 12:54 PM   #18
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Quote:
Originally Posted by cdvma
Misfires are common on modded stockers. Its hard to get them to flow right at low RPMs and low load. Its uneven at those levels and creates (in my experience) a rich misfire. I've learned to live with it until I can afford to get properly sized injectors. Uping my idle helped a lot.
same here guys, modded stockers and a ton of misfire's. Sucks, but I guess they're worth it for now.
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Old 01-18-2006, 02:21 PM   #19
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Boo modded stockers... then again, $650 is a lot to stomach for a "real" set of injectors
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Old 01-18-2006, 03:26 PM   #20
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Is there any evidence that people with PE injectors are having fewer misfires at the same/similar power levels?
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Old 01-18-2006, 05:00 PM   #21
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Quote:
Originally Posted by bboy
Is there any evidence that people with PE injectors are having fewer misfires at the same/similar power levels?
According to posts here, the PE's don't idle nearly as well.
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Old 01-18-2006, 05:11 PM   #22
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I've heard many PE trouble stories, not just around idling. I'd be rather surprised that removing the screen leads to misfires, but it's possible.

Did the people that switched to mod'd stock injectors and picked up misfires all use UTEC.

I have not had trouble with lean misfires and the Hydra. I do have some rich misfires under boost and I've not worked hard to tune those out.
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Old 01-18-2006, 06:09 PM   #23
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id like to say that i was fine (no misfires) when i was modded stockers (perrin sti), sz55, typhoon intake, oem tmic.

It wasnt untill I installed the aps dr725 that my afrs started wandering between 14.6-15.2 at idle and the misfires. Before the fmic my idle afrs on the same injectors were a consistent 14.6-14.9.
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Old 01-18-2006, 09:22 PM   #24
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Quote:
Originally Posted by AaronWRX
id like to say that i was fine (no misfires) when i was modded stockers (perrin sti), sz55, typhoon intake, oem tmic.

It wasnt untill I installed the aps dr725 that my afrs started wandering between 14.6-15.2 at idle and the misfires. Before the fmic my idle afrs on the same injectors were a consistent 14.6-14.9.
That sounds like a tuning problem.
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Old 01-19-2006, 08:58 AM   #25
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Yes, I am running a UTEC, which is a more crude tool with respect to EM and larger injectors. You guys running modded stockers should not be having an issue with injector dead time on a UTEC since the dead time is, well, stock. Other EM can compensate for dead time. We just have to live with it.

You guys might want to search for some threads by RiftsWRX. He, for those who do not know, is a well-respected tuner who has some interesting opinions about modded stockers.

I had my LT fuel trim adjustment scanned last night. It was at -4%, which is at the edge of acceptable. I could lean them out a bit more, but you are better off slightly negative than slightly positive, they say. My misfire/hesitation problem is severely reduced now to the point where it rarely happens. Not sure if this will change with the temperature, though. Just remember, tune your 0% fuel column by LT Fuel trim adjustment, not AFR. The adjustment represents what you ECU is trying to do to get things at the proper AFR.
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