1HZ noise at higher rpms - rattle / buzzing (1 Viewer)

[CHILLCAT]

I've got a 92 HZJ73 with the 1HZ ---- I've noticed some rattle / buzzing noise when I reach around 1.9-2k rpms and higher. Best I can tell it seems to be coming from near the engine.

It happens whether I'm driving or sitting in neutral and rev the engine. Its much easier to hear in the low gears (2nd / 3rd) but that might be due to more road/traffic noise when in the higher gears.

If anyone has suggestions for some basic things I could/should check before looking for a shop to take it to, I'm all ears!

*Edit: I'll be crawling under the truck this evening to make sure skid plates, heat shields etc are all tight. Will report back.

Cheers

 

[JDM Journeys]

Any progress?

I might be fighting the same battle by the sounds of it? Mine (hzj77 w/H55f) starts to rattle around 2000 rpm, only under load. Lessens once it's fully warmed up but doesn't entirely go away. It's really noticeable under acceleration if you pass a guardrail with the window down. It's harsh and changes with rpm...

My frequent forays with my stethoscope have been inconclusive. If you come up with some possibilities, I'm all ears.

 

[lowtideride]

Belly of air in your injection pump. Something is leaking air into the system (lines, fuel filter, primer pump etc). Every time I hear it I know air is in the system.

 

[PBcuiser]

I was having some sounds/rattling with mine and once I started using a fuel additive they have all gone away.

 

[CHILLCAT]

Any progress?

I might be fighting the same battle by the sounds of it? Mine (hzj77 w/H55f) starts to rattle around 2000 rpm, only under load. Lessens once it's fully warmed up but doesn't entirely go away. It's really noticeable under acceleration if you pass a guardrail with the window down. It's harsh and changes with rpm...

My frequent forays with my stethoscope have been inconclusive. If you come up with some possibilities, I'm all ears.

It sounds like we have a similar issue.. The clatter/noise does seem to lessen when fully warm. Very similar symptoms.

I don't have a clear answer yet. My troubleshooting knowledge is limited here.. I don't have a stethoscope but tried the ol "put your ear to the end of a screwdriver" but haven't been able to track down the noise.

I have a local LC specialist shop that is going to fit me in early next month. They know the 1hz much better than I so hopefully we can get to the bottom of it. I'll let you know what they come up with.

 

[CHILLCAT]

Belly of air in your injection pump. Something is leaking air into the system (lines, fuel filter, primer pump etc). Every time I hear it I know air is in the system.

Interesting. I'll do some poking around and tighten up anything I can in the fuel system. That would be a relief if it was just a bit of air sneaking in..

 

[JDM Journeys]

Hmmm. I've got brand new injectors. Rebuilt pump. New rubber fuel lines. And I've run clear lines to check for air. I can't discount anything for sure, but I'd be doubtful of the fuel system being problematic at this point. Starts perfectly, runs with zero smoke. I'm suspecting something in the clutch/transmission, but have't been in there yet... Untouched H55F with 280k, clutch is unknown...

 

[JDM Journeys]

Here's a blast from the past which possibly addresses same: 1HZ ticking in certain RPM range - https://forum.ih8mud.com/threads/1hz-ticking-in-certain-rpm-range.281027/

Also, the spectre of "crank flex" comes up. I've read about it in other places as well, but I'm not sure its a thing or not... sounds a lot like "Crankwalk" from my Mitsubishi 4G63 days...

 

[JDM Journeys]

@CHILLCAT it is time for me to follow up since I've effectively solved my issue.

@lowtideride wasn't far off the mark. It seems it was indeed the fuel system although not air in the system. I diiscovered some old threads that mentioned rattles from poorly adjusted dynamic timing. I knew of course about setting the ip timing but dynamic timing was new to me. Turns out the adjustment is the spring tension on the load sensing timer... that locked Allen head bolt below where the ACSD sits (or used to if you've removed it). I needed to add some tension to the spring inside which governs the pump pressure under load. I slowly added tension on many short test drives until suddenly? No more rattle under load! This truck has rattled the whole time I had it and even a full pump teardown by a reputable shop didn't make a difference. I assume they set the dynamic timing the exact same?

In any event I get some normal rattle when cold but now it quickly fades away as I reach operating temperature! Job done!