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Old 11-25-2010, 10:38 PM   #1
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Default Higher RPM cruise misfire?

So today I was heading to my inlaws for dinner and figured I try and tweak my tune at higher RPM cruise around 4000 to 4500 rpm. The cars seems to misfire pretty bad. My wife pulled out the laptop to see what was going on and AFR's are like 11:1 to 9:1. I checked my VE table and numbers in that area of the table seem to be ok and should'nt produce an AFR like this. I'm guessing a misfire would cause very rich readings like I am seeing. Map reading is rock solid and stays consistent and my AE is off while I tune. I should have had my wife record a log but she is afraid to touch anything cause she recently messed up a nice VE table from VE analize live.

I'm gonna check

1. plugs
2. wires
3. Coils
4. grounds?

Is there anything else I should be checking. I'm just kinda stumped because it runs great around town and feels really smooth.

BTW I did plugs, wires and fuel filter about 3k ago.
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Old 11-26-2010, 04:49 AM   #2
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A missfire would cause a lean reading.

If you're actually seeing 9:1 during high rpm cruise, you're getting missfires as it's too rich.

I'm not sure how you 'know' the VE numbers look right, it may only require a few points drop to cure the AFR's. the actual VE numbers are pretty irellevant really as they're only a part of the entire calculation.

Just tune the VE table leaner/to your desired AFR in the problem area and be happy, don't throw money at the problem
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Old 11-26-2010, 09:36 AM   #3
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I hope your right rich. when I say my VE numbers look right they dont make a huge jump in that area. They are only 2-3 points higher than the cells around. Going back out with some lower numbers to see if this helps. what else could make it run super rich. Can an injector be sticking?
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Old 11-26-2010, 10:00 AM   #4
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I think you might be putting the car in front of the horse a bit man. 9:1 (or even 11:1) is too rich for cruising. You're likely just washing your spark out. Tune for 14.7:1 at cruise and I bet your problem goes away.
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Old 11-26-2010, 11:00 AM   #5
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I think you might be putting the car in front of the horse a bit man. 9:1 (or even 11:1) is too rich for cruising. You're likely just washing your spark out. Tune for 14.7:1 at cruise and I bet your problem goes away.
Around town I am running about 15:1 for anywhere between 2000 and 3000 rpms. My target is in that range in the higher rpm cruise thats why I was thinking my VE table looks ok. My targets are 15:1 up to 40kpa then 14.5:1 at 60kpa then 14:1 at 80kpa and the 13:1 at 100kpa. My targets are right on at lower rpms and the table doesnt make a huge jump in VE numbers from 3000 to 4000 rpms.

I gonna take it for another ride sometime this morning.

I guess I was wrong thinking it would look rich for a misfire. Can someone please explain why it would look lean.
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Old 11-26-2010, 12:26 PM   #6
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Ok so I leaned out the VE table in that area to lower than my idle setting. Once I got on the highway the afrs just kept droping and went down below 10:1 WTF? I get off the highway and head home, runs mint the whole time. I pulled the plugs and they look pretty good to me. Checked my wires and the resistence is getting a little high. I found my old set of Belden and they read less so I will put those back in. Next I checked the Coils. Primary is speced at .78 to .94 and I'm getting 2.0 and 1.1 so I hope this is it. Secondary coils read within spec.

I am confused why so rich if missfires should be lean?
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Old 11-26-2010, 01:54 PM   #7
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Quote:
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I am confused why so rich if missfires should be lean?
If you're missing on a cylinder, the fuel in the cylinder is unburnt, and thus, the oxygen is unused. The higher mass of unused oxygen passes the o2 sensor, and causes a false "lean" reading because there is more unused oxygen in the exhaust stream than there should be.

If you're running rich, and all 4 cylinders were firing, you'd see rich AFRs, if one or two of the cylinders started missing here and there at higher RPMs (does the coil have less time to build up spark voltage at higher RPM?) then your ratios might lean out.

You have a coil dying? Let us know how the wire swap works for you.
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Old 11-26-2010, 02:21 PM   #8
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Quote:
Originally Posted by urabus View Post
Ok so I leaned out the VE table in that area to lower than my idle setting. Once I got on the highway the afrs just kept droping and went down below 10:1 WTF? I get off the highway and head home, runs mint the whole time. I pulled the plugs and they look pretty good to me. Checked my wires and the resistence is getting a little high. I found my old set of Belden and they read less so I will put those back in. Next I checked the Coils. Primary is speced at .78 to .94 and I'm getting 2.0 and 1.1 so I hope this is it. Secondary coils read within spec.

I am confused why so rich if missfires should be lean?
You want 14:1 or leaner, your chasing your tail, pull more fuel!!!

Or just use VEAL in TunerStudio to do it for you.
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Old 11-26-2010, 04:15 PM   #9
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Wire swap did nothing. It seems to be getting worse though. My wife just drove me around for a while and the mis seems to be creeping down the rpm band. Its starting to get rough at 3k sometimes. I leaned out the map like crazy to satisfy Rich and that did nothing so I am not chasing my tail. I reved it slowly at a stop with no load and it starts to mis pretty bad. Funny thing is my wife hammered it from 2k to 7k and felt no mis under full throttle. I have been using VEAL for a while and no help. Parking it till my new coils come in.
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Old 11-26-2010, 06:04 PM   #10
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If it doesn't miss under load, then I would not suspect the coils, plugs or wires. What's your air/fuel when it misses? If it's too rich or too lean, it will miss. "leaning it out like crazy" will miss. You wan to shoot for 14.7:1.

Does the tach needle bounce with the miss? Do your datalogs show 0 rpm with the miss?

Do you have really good grounding?
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Old 11-26-2010, 06:47 PM   #11
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I should not have said leaned out like crazy. I reduced my VE numbers big time and it still misses with crazy low AFR's. Please stop telling me what I need to shoot for with AFR's. I know this, it is not getting there. I leaned the VE table out about 10 points with no change in what it was doing. Tach is perfect. My coil resistence is bad, why do you guys think this is not the problem.
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Old 12-04-2010, 09:30 PM   #12
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So I replaced my coils yesturday and took it for a ride last night. Seemed good so parked it satisfied. Woke up this morning and took another ride. All was good nice afr's until i got on the highway. Started with about 14:1 but still felt a little mis in the engine so turned on VEAL to fine tune my afr's. Then the car felt worse and worse and afr's went lower and lower. I look at the table and VEAL keeps pulling fuel lower and lower and car seems to be getting worse and worse.

So i get to thinking and notice every time I seem to use VEAL it will change higher ve numbers then lower ve numbers the next day. Injector must be sticking open every once in a while. I get the mis feeling more and more and seems worse the longer the car runs. Is there anyway to test for a sticking injector. It seems it doesnt happen all the time.
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Old 12-04-2010, 09:48 PM   #13
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lol, something's adjusting your fuel backwards :P
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Old 12-07-2010, 11:25 PM   #14
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Problem solved!!!!!!!!!! Misfires due to running LEAN. Injector was sticking and causing me to pull fuel for target AFR's. Added fuel and car is running awesome but still too rich. Its funny because the injector starts out fine and then sticks after about 20 minutes. I took it for a cruise with no problems then all of sudden afr goes crazy but car still feels good. Pulled over and unplugged 1 injector at a time and found 1 stuck open because car did'nt want to stall out like the other 3.
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