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Old 08-26-2010, 03:21 PM   #1
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Default Misfire? Won't hold steady RPM.

So I went to do emissions, besides failing (miserable and I'll address that later) I noticed my car would not hold a steady rpm. The test was at a steady 2500 rpm and every full cycle the engine would droop to about 2200 rpm and then back up to 2500. I went home and tried the same test at a few different rpms between 2k-3500 and it did the same every time.

Any ideas what could be causing this?

It's a very brief cutoff and according to TunerStudio the fuel load seems to spike slightly at the same time (from about 30% to 35% load).



Not sure if this is related, but when I start the car it idles perfect right around 1000 rpm however when I drive for a short period of time it idles at 1500rpm. Still smooth, but it won't go beneath 1500. A few times it will idle closer to 2k rpm, but I can touch the throttle once or twice and it will come back down to 1500.


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Old 08-26-2010, 03:34 PM   #2
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log\msq of said happening?
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Old 08-26-2010, 03:57 PM   #3
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Perhaps something in your car is creating a load. Is your fan kicking on and off?

What do you mean "every cycle"? Every RPM? Every Minute?

If you had an on/off load kick on while holding the throttle constant, your RPMs would quickly drop. To compensate, you would have to increase manifold pressure, which would cause a "fuel spike" in order to return the car to the previous operating RPMs.
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Old 08-26-2010, 04:07 PM   #4
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post your msq, it could be a number of things, idle could be idle settings, the weird surge could be an untuned VE cell
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Old 08-27-2010, 02:33 AM   #5
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Quote:
Originally Posted by fooger03 View Post
Perhaps something in your car is creating a load. Is your fan kicking on and off?

What do you mean "every cycle"? Every RPM? Every Minute?

If you had an on/off load kick on while holding the throttle constant, your RPMs would quickly drop. To compensate, you would have to increase manifold pressure, which would cause a "fuel spike" in order to return the car to the previous operating RPMs.
The fan is on constant, both of them. The original owner had them wired that way and I haven't bothered fixing it yet. So no extra load is being put on the car past that, which is why I assume the idle hangs around 1k normally.


I should have been more specific with the description, it isn't every engine cycle but it is timed exactly. It's approximately every three seconds, but constant and like clockwork.

I will try to post up an msq tomorrow.
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