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My Mirage (1994, 4G13 (carb), ~95,000km) shudders whenever I accelerate. This is largely a recent problem. This generally occurs after ~2min of driving and persists for ~20 minutes. Depressing the throttle does accelerate the car, albeit very slowly in phases of no power and power. It judders about like a clutch would if it wasn't engaged very well. After it stops the car runs fine. This only occurs when the pedal is further depressed, it can handle static loads fine. The first time this occurred it stalled on takeoff from an intersection (but not the initial start). Here are more probably related (but more historic) problems:

  • On first run to more than crawling speed depressing the pedal doesn't do much until it quickly speeds up

  • Car doesn't start (or takes a long time to) if it is parked pointing uphill or with the left side higher than the right (the fuel pump + carb is on the left)

  • Burns oil on start-up (enough to need to refill it after ~4 months)

  • Driving up a steep hill (~12%) I could sustain speed (~70Km/h) until I caught up to a bus, so I slowed down and as the road flattened out the bus pulled away and with my foot on the floor I wasn't accelerating at all (similar to point 1)

  • When low on fuel on two occasions the car has run for ~3 seconds after turning it off

I just replaced the fuel filter and oil, those are not the problems, nor is the air filter, that is reasonably new. Looking down the carb reveals grime but nothing excessive, just thin grease or a thin baked on layer.

What is wrong, I'm 99% sure it's fuel related so carb or fuel pump?

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Sounds like a fuel pump issue. It's possible that that the fuel sending unit itself is just going out. Few questions. Is your fuel pump internal to the tank or external? Have you recently ran it out of gas, or ran it much lower than you normally would? I recently had a very similar issue. I replaced the coil pack and it eliminated the issue completely. Though it does sound like a fuel pump issue, possibly a bad motor or a lack of proper power disbursal to power the pump. If all other avenues are exhausted it may be something to look into.

  • The fuel pump is bolted onto the engine – Alan. Q Jones Jun 27 '18 at 9:45
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There are multiple posible errors causing theis problem:

  1. f̶̶u̶̶e̶̶l̶̶ ̶̶f̶̶i̶̶l̶̶t̶̶e̶̶r̶̶:̶̶ ̶̶t̶̶h̶̶e̶̶ ̶̶f̶̶u̶̶e̶̶l̶̶ ̶̶f̶̶i̶̶l̶̶t̶̶e̶̶r̶̶ ̶̶c̶̶o̶̶u̶̶l̶̶d̶̶ ̶̶b̶̶e̶̶ ̶̶c̶̶l̶̶o̶̶g̶̶g̶̶e̶̶d̶̶ ̶̶u̶̶p̶̶ ̶ (already replaced)
  2. Fuel Cap: The air valve of you fuel cap could be clogged too. This can prevent fuel flow because you need air replacing the the fuel beeing used. (Sometimes it can be cleaned - sometimes it has to be replaced)
  3. Fuel lines: A Fuel line could be buckled or narrowed. Try to check all fuel lines for irregularities and if you find any replace the corresponding fuel line
  4. Fuel pump: The fuel pump can also cause this problem but i would check the other points first since they are cheaper to replace

Another posibility would be to messure the fuel rail pressure. This should probably be done first to make sure that it isn't a problem caused by the Engine control or a blocked exhaust system - Although it is most likely something fuel related as you have mentioned.

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