3.4 and what I think is a misfire... - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-18-2007, 02:06 AM   #11
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Well, I didn't really want to dive into rockers or headers right now. I was sort of trying to slowly build my car to imitate the intense stage 1 package. The only thing I don't have from that is the PCM. I havn't heard back from DHP yet so a PCM might be a lost cause anyway.

Next day off I am going to eliminate that misfire and see where my KR stands at from there. If I still have the huge KR issues I will step up to a 3.5" for the time being.
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Old 07-18-2007, 02:09 AM   #12
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Some stock S2'* can handle a 3.4, and some can't. This is why we caution people to be prepared with a 3.5, and why you must have a scantool. You're doing it right, and you found what is to be expected in some cases. This is a good thing.
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Old 07-18-2007, 02:12 AM   #13
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A popping from the exhaust is a pretty serious misfire. You didn't wire the plugs wrong, did you? I'd check that, pull the plugs out and check them and check your wire resistances.
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Old 07-18-2007, 09:44 AM   #14
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I doubt the misfire is KR.

Check the plugs and wires as mentioned. Remove one wire at a time to try and determine which cylinder is missing.
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Old 07-18-2007, 09:48 AM   #15
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A week or missing fuel injector could cause you to run lean on one cylinder causing KR, but I doubt an ignition misfire could cause it also.

Is it always the same cylinder?
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Old 07-18-2007, 09:02 PM   #16
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I don't know what cylinder it is...it has not thrown a code. All I can say is I get a pop from the exhaust and a stumble. My scantool is my aeroforce so I am limited to the capabilities of that.
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Old 07-19-2007, 03:02 AM   #17
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I'm so confused now...

So on my way home tonight I go from a 30km/h roll...mash it. 1 degree of KR, no misfire, and lots of power. This was AT operating temperature.

Then I was cruising in third gear, mashed it, and it ony dropped to second gear, and I had huge KR in the mid-range RPM...again, no mis-fire.

Blah.
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Old 07-19-2007, 08:28 AM   #18
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The difference is the gearing and how much the engine works. The more load...typically the higher KR.

let'* back track..you've done plugs, wires, got fuel pressure numbers?
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Old 07-19-2007, 02:06 PM   #19
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I had three runs today. The first was only a drop into second at mid-range RPM. Lots of KR. I think this kind of acceleration applies to your load theory. The car could have gone to first but didn't since I wasn't coasting. So increased load to get the car going, in a tougher gear then first, means more KR.

I did a 30km/h roll, then to the floor (drop to first). I had ZERO KR almost the entire run to 160 km/h.

I then did a drop to second from about 70 km/h. Pretty much nil on the KR.

The really strange thing is, no misfire the entire time....and I havn't changed anything.

Plugs were changed to Autolite 104'* @ 0.55 with the 3.4 install. Wires are my old ones which are only about 6 months old (belden premiums). I still need to get a fuel pressure gauge.

It seems both the KR and the misfire are totally intermittant, which is making trouble shooting difficult.
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Old 07-26-2007, 09:27 PM   #20
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MMMmmk...so with the misfire all sorted out...

I had an ideal test today. 90* F outside, very humid. The most KR I saw was 4* spikes. It was usually hanging around 1-2.5*. This is on 94 octane, however it is a 10% ethanol blend...not race gas...

Too much KR? (aka pulley up or keep modding...)
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