Metallic rattle/grinding in Z20 (mech fuel pump?)

Hi everyone,

I took my '91 4x2 Z20 to the mechanic the other day; confirmed that my alternator was dead, said that my fuel pump was on the way out. I wanted a lookover cause I had a tinny rattle on deceleration and high revs.


Just finished the alternator swap today and tightened the new belt, she's chugging along like a champion. My battery's charging and all is well. I ended up discarding the earth from the back of the alternator because the existing bolt that I had for it didn't fit the reconditioned alternator (swapped from a Mitsu to something else). Is it okay to ditch the earth? The fella from The Battery Terminal (Steve) said that it'd just ground through the main battery ground.


On to the important question. My mechanic (Peter at Harry's in Belconnen) said that the mechanical fuel pump on my Z20 is probably going to be the next thing to go.

Compression is good in the motor, but I badly need to change my oil.


When I get to high revs (highway speed in fourth) there's a tinny rattle or metallic noise from the motor... The best way I could describe it is waving a light marble around the edge of a can at high speed... Or a bike bell without the cover, but at very high speed... Does that make sense?


I was wondering if that'd be the mechanical fuel pump, or a sign that I need to change oil pronto, or noisy cams/lifters/valves? Could it be the timing chain?


Compression is good, the mech said, and she doesn't blow any smoke (unlike the pollies around here).


Any help is very much appreciated!

Good way to identify where the noise is coming from is tO use a bit fuel hose or similar like a stethoscope. While the engine is running, stick one end near your ear and the other end near the sus bits like the fuel pump or rocker cover. Once we know where the sound is coming from you can look a bit closer at that part.

Change oil and filter if it's due. Always first thing.

Crossroads said:

On to the important question. My mechanic (Peter at Harry's in Belconnen) said that the mechanical fuel pump on my Z20 is probably going to be the next thing to go.

When I get to high revs (highway speed in fourth) there's a tinny rattle or metallic noise from the motor... The best way I could describe it is waving a light marble around the edge of a can at high speed... Or a bike bell without the cover, but at very high speed... Does that make sense?

I was wondering if that'd be the mechanical fuel pump, or a sign that I need to change oil pronto, or noisy cams/lifters/valves? Could it be the timing chain?

Click to expand...

Change the oil anyway and get into a pattern, it needs to happen regularly. Could be any of those things you listed, if the mechanic thinks the pump is on its way out, just replace it. It's relatively cheap in the scheme of things.

Thanks Pinelli, thanks Dion. I'll get onto the oil change ASAP.

I was having a listen tonight at idle and it sounds like it could be either the dizzy, or a part on top of the air intake (out past carburettor, past filter, past filter housing, on the pipe between the housing and the intake point).

The enging seems to 'cough' every so often at idle, and that's pretty freaky... But it didn't seem to cough as loud when I put my hand on top of that doohickey (what is the thing?) on top of the intake.

I used a screwdriver as a stethoscope and the fuel pump has a very distinct clicking noise; the valve cover sounds fine (just the vibration you'd expect).

I need to get a length of fuel line and a friend to rev, like Pinelli suggested. : )

But yes... Oil definitely, definitely is due.

Thanks fellas. Hopefully I'll update tomorrow.

Final question: Repco quoted me $200 for a mechanical fuel pump... Which seems very expensive. Is that about what they should cost?

Other option for a fuel pump is to go to the wreckers and get any old electric online fuel pump they have lying around and bypass the mechanical one. Make sure it's a crab low pressure one though. I did this on my old 74 galant many years ago and worked a treat. The fuel pump will click though. Are you sure it's stuffed?

You can rev the engine yourself from the engine bay using the throttle cable on the carby although that might mean three hands if you are using a fuel hose to listen
If you have to buy a length of hose you might find supercheap sells mechanics stethoscopes for not much more. Like a doctors but with a metal stick like a screwdriver on the end. I just use fuel hose because I'm cheap and it's lying around at home