Still breaking up after 3,000rpm...what else to check? - MustangForums.com



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Old 04-28-2013, 06:22 PM   #1
StalkerGT
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Default Still breaking up after 3,000rpm...what else to check?

I have replaced my tfi module and ignition coil...when I hit 3,000-3,500rpm's it breaks up and the tach kinda bounces around. If I full throttle it it seems ok but if I hold it steady around 3,500 that's when starts to bounce around and break up....if the car is just sitting and I rev it up to that it doesn't do it. Seems to be only when driving. What else should I check? I'm stumped
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Old 04-28-2013, 09:36 PM   #2
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EGR related vacuum lines would be a good start.
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Old 04-29-2013, 07:10 AM   #3
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Ok I will check out the vacum lines today
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Old 04-29-2013, 09:13 AM   #4
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coil, the pick inside the distributor and the shaft in the distributor check it for wear from side to side I have seen a few wear out. Then you might want to start looking at valve springs
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Old 04-29-2013, 10:09 AM   #5
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to me it sounds like a fuel pump...have you checked the pressure?
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Old 04-29-2013, 10:55 AM   #6
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Good voltage?
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Old 04-29-2013, 12:07 PM   #7
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The tack jumping around kind of say electrical to me But I could be wrong that's for sure
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Old 04-29-2013, 02:24 PM   #8
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All vacum lines checked out ok...my fuel pressure is about 36-37psi with vacum on at idle. The regulator is new...fuel pump is Walbro 255 that was put in last summer. Now it's just doing it around 4,000 and when I let off the gas as the rpm's drop the tach still jumps around without hitting the gas pedal...but when the rpm's get under 3k it's fine and stops jumping. If the car is sitting and I rev it up to around 3,500 and hold it there it breaks up pretty bad...it doesn't really do it when the car is cold...just when it gets around 180 or higher. Sometimes cranks for a few seconds before it starts too. That's also when it is warmed up

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Old 04-29-2013, 03:42 PM   #9
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Fuel pressure is at 42 with vacum off...also realized today that when I slowly press the throttle the fuel pressure goes down a few psi. But if I hit it fast it goes up like it should. I stopped by a garage today and they suggested maybe the distributor but almost seems fuel related now? When the car is cold fuel pressure is around 37 at idle but when fully warmed up its at 34 at idle

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Old 04-29-2013, 05:26 PM   #10
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The tach is exclusively controlled by the negative wire of the coil, so if it's acting weird in any way it's either the wiring, the coil, or the tach. The breakup can be explained by anything else mentioned here, but it would be rare that they aren't connected.
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