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Neither?
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 31 Dec 2008 05:42:58 Share Post by Email
In Reply to: Pre-pump or Main Pump?, EverettDave [Profile/Gallery] , Tue, 30 Dec 2008 22:58:26
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How is the boost in lower gears? How does it feel at 3000 rpm, in say, 2nd or 3rd?

If the car boost strongly and pulls well at 3000 or 3500 in 2nd and 3rd, then you've got all the fuel flow and pressure you need. Under boost at those speeds, the engine is sucking down lots of fuel.

From memory, 3K in 5th would be about 70 mph. Is the problem that from a cruising condition (light throttle) at 3K, you hit the throttle and the car doesn't respond?

I'm guessing that the problem isn't the fuel pump. My first thought would be the Air Mass Meter. In 5th gear, you've got no torque multiplication from the tranny and at those speeds, lots of drag. Any bogging by the engine would be very noticeable in higher gears. The AMM senses airflow and decides how much fuel to add. Hesitation is one sign of a bad AMM - yours may be on the way out. It's tough to troubleshoot an AMM without a known good one to swap in, especially when it is just a little flaky.

Other things to check would be the timing - make sure it is spot-on. How old are the plugs, wires, rotor and cap? Plugs gapped right? How do they look? If you had a fuel pump issue, you'd expect to see very lean running - white spark plugs.

As always, check for vacuum leaks. But if you get good boost and can run up the rpm in lower gears, the fuel pump delivery is not an issue.

posted by 76.221.218...

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