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How to guess a failing fuel pump on the RCZ - hints

Engine, gearbox, exhaust and other drivetrain issues

RCZ-R User avatar

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Location: Germany
Hi guys!

After I went through the struggle of a failing high pressure fuel pump on my RCZ I might give you some hints on how to anticipate a failing (but not yet failed) fuel pump.

There is a simple test each of you can do:
- Start the engine and warm it up. It doesn't matter if you do that test after a cold start or after you have been visiting your fav retail store. Just ensure the engine is properly warmed up.
- Now, let the engine idle and rev it up like you'd challenge someone to a street race. You don't need to rev it up higher than 2000 rpms but what is important, you need to slam the accelerator very quickly and release it very quickly too. So basically you kick the accelerator by about 30% of its range and release it immediately. Do a sequence of 2 or 3 those revs up in a row. Means, for one test you do those 2 or 3 slams one after the other. It is like, bam bam bam and you see the revs go up for the first kick, you release it, you kick it again while the revs are already dropping a bit (slowly due to the flywheel mass) and you rev it up again and release it and so on for 2 or 3 of those accelerator kicks for a single test row.
- Then release the pedal and watch the rev counter dropping to idle. It shall remain there, and be steady. No drops, no choking up, nothing shall happen. Just a steady idling at close below 1000 rpms.

Now what is the difference between a failing fuel pump and a good one?

When the pump is failing the revs at idle will drop a bit lower for a moment, the engine will not run smoothly, it will almost choke and stall.
This very procedure forces a quick pressure rise and fall on the fuel rail. It put strain on the fuel pump as it has to follow those accelerator slams quickly but it cannot when failing to build proper fuel pressure. As a consequence the revs will drop at idle and the ECU will kick in and try to rise them.

Unfortunately I have no video clip of this faulty behavior but I did experience that effect a lot while waiting at red lights. I often played with the revs just to listen to the engine sound and the exhaust banging in the rear. And with time I recorded this strange rev irregularity as described here. First I did not pay to much attention to it but with time I got worried. Apparently it was the fuel pump slowly failing.

Now as there is a new fuel pump on my RCZ, it is gone. I can kick the accelerator and the revs always return perfectly to idle without any hesitation and there is no choking or stalling.

I hope I described it properly. Please feel free to ask questions.

cheers :greetings-wavingblue:
RCZ R in red. driven daily. and driven hard.
Dyno results here:

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