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V6 (1994-2004) Mustangs Technical discussions on the 3.8L and 3.9L V6 torque monsters
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Old 05-22-2013, 06:31 PM   #1
JC316
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Default Bucking under load.

Hey guys, long time member of the 4.6l section, but I picked up an 00 mustang with the 3.8L engine. I know these motors fairly well from owning a 92 super coupe. I am having an issue with this car, it's bucking during acceleration. Doesn't matter how much gas I give it, it still bucks, once I am up to speed though, it stops. No bucking or misfire at idle or revving in park, only when it's under load.


No active codes and the only past code was for the PATS system, which I cleared and it never returned.

Checked the plugs, they are new. Gap was off, so I set it at .056. Wires are also new. I had a known working coil pack off from my old t-bird and tried it, no effect. Compression test was 165 PSI on every cylinder. Just picked up a new camshaft position sensor, no effect. When I changed it, I checked for play in the synchronizer and there was very little. MAF was clean. No vacuum leake

Next on my hit list is checking fuel pressure and making sure that the injectors are firing. Any other ideas?
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Old 05-22-2013, 06:49 PM   #2
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What kind of plugs do you have in? If they are Platinum, you never gap them, regardless what auto zone or anyone of them says. Aside that, you're having the same type of problem I'm having, and I have no idea aside a new coil pack.
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Old 05-22-2013, 06:51 PM   #3
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our coil pack 'worked' but replacing it got rid of the hesitation - see my post
http://mustangforums.com/forum/v6-19...ast-night.html
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Old 05-22-2013, 06:59 PM   #4
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Quote:
Originally Posted by 3.8Cobra View Post
What kind of plugs do you have in? If they are Platinum, you never gap them, regardless what auto zone or anyone of them says. Aside that, you're having the same type of problem I'm having, and I have no idea aside a new coil pack.
Champion copper plugs.
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Old 05-22-2013, 08:57 PM   #5
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Think I found the source. Hooked up a fuel pressure gauge to the valve. Key on, engine off, 40PSI. Engine running, it does this creepy little dance. Goes down to nearly 20 PSI and then jumps back up to 30PSI in rhythm, just like the rhythm of the engine bucking. Now, I have never dealt with an electronic FPR, but I can't see any situation where that would be normal. Unplug the FPR and it drops, blip the throttle wide open and it jumps to 60PSI, but at idle and part throttle, it dances.
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Old 05-25-2013, 03:59 PM   #6
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Got it. The fuel filter was badly clogged, not allowing enough pressure. That is what caused the dancing gauge and the misfire.
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Old 05-25-2013, 11:01 PM   #7
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Glad to see you found it!!!
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Old 05-25-2013, 11:01 PM
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