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Old 01-14-2014, 02:05 PM   #1
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Default 1990 20V 90 fuel pump - Real Time alternatives?

So I'm getting a flat spot/hesitation on the freeway as I tip into the throttle, and the fuel pump started making noise a couple months back. I put in a new filter immediately but suspect it's the pump unable to keep up with 3500rpm. Though when I press deeper into the throttle it does not hesitate - so open to anyones input on that.

Was thinking of putting a new fuel pump on and looking for cheaper alternatives. I read somewhere that an ordinary Ford pump available anywhere is a perfect substitute to the $200 Bosch usually spec'd. Any input? Kinda under pressure because wanted to drive the Audi Thursday on a 300 mile trip but have another car. Perfect Quattro roads, so help me if you have a minute.

DougM
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Old 01-14-2014, 02:17 PM   #2
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How certain are you about it being the fuel pump? it doesn't sound like it to me. I'd suspect either a vacuum leak, or bad injectors before the fuel pump.
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Old 01-14-2014, 07:55 PM   #3
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Yeah, I'm not convinced of the fuel pump either, with only item pointing to it being mere noise. Since it's one of the few key components I have not upgraded in the year since getting the car thought it would be a good time, and some chance it is the issue.

Injectors are all new (034's nice conversion kit) last spring, general major tuneup items as well. Everything save plug wires that you would think of doing to make a 23 year old car reliable for daily driver use has been done. Didn't do plug wires simply because of the shocking cost for the 20 valve set - my little protest...

Full throttle acceleration seems down a bit as well sometimes, other times it's normal. Fuel consumption slightly off, but not tracked precisely enough to say that definitevly. It's been going on for a month or more so not bad fuel.

I notice it when steady state driving at freeway speeds. In making those tiny pedal adjustments to match speed with traffic. Apply a tiny bit of gas and a faint falter occurs - not bucking or anything , just faintly felt hesitation. Sometimes I have also felt as I let up barely on the gas it will actually accelerate faintly. So behavior I would typically call a flat spot in the carburetor days. Thoughts?
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Old 01-15-2014, 07:19 AM   #4
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sounds like you might be getting flooded... but on the pump, if its making more noise then usual, it usually indicates that its reaching the end of its life and i would have one just in case yours fails and leaves you stranded in the middle of nowhere.
on the other problem, i don't think these two are related aether. look for a vac leak, i also assume no codes?
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Old 01-15-2014, 12:10 PM   #5
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So a bit more info you may find useful. I realized this morning that the engine has for a long time exhibited a tendancy toward abrupt responses to the throttle at higher rpms, so this may be all that is happening at fwy speeds is what I'm about to describe. It's most obvious when the engine is cold, which is why I tolerated it figuring its a 23 year old engine and has some aged sensors that don't play well when the engine is cold up here in Idaho winter. Here's what its like.

Pulling away from the house with a cold engine, the throttle is very abrupt. A small accelerator movement pressing down makes the car lurch forward, and an equally small letup makes the engine instantly feel like it's been shut off completely from fuel and lurches the car slower. This hyper sensitivity goes on until the engine is warm. But even when warm, it tends toward this behavior such that at times it is hard to shift smoothly because the engine has this on/off feeling that makes clutch engagement tricky.

Thought I'd add that as I realized how bad that cold behavior had gotten while leaving the house this morning and it seemed logical the touchy throttle may simply be all that is happening on the freeway. Years ago I had a new K Jetronic Jetta that had that annoying throttle "tip in/tip out" behavior and the dealership and research confirmed was simply a part of the software that shut off fuel for fuel economy on coast that was a little aggressive and they could not adjust it. This feels like that only stronger.

So I guess this hyper throttle response would be the thing I'm wondering about - sorry for changing course a little and embarassed I didn't think this post through a bit before typing.

Doug
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Old 01-15-2014, 12:10 PM
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