CharlieS
GOLD Star
This is going to be tricky because it is an audible clue.
I've finally had a chance to do as much deferred maintenance as I'd hoped to and got the 80 out for a long drive and some trails. I have a sound that I can't diagnose, and am wondering if I could get some thoughts from the group?
I first thought it was the water pump, so I replaced that and the belts. Nope. Then I thought it was the alternator, so I replaced that and the tensioner. Nope. Maybe the AC, so I removed that belt, and nope. Hmm, starting to get stumped.
The noise occurs when I'm not moving, idling in the garage, so I am going to focus on what I've done in the engine bay that are in that area:
The prior owner replaced the following recently:
Timing is at 3 deg BTDC at idle, with DLC pins jumped.
Belts tensioned per FSM with a Kriket tool (3 different times now). Using the new belt spec initially and the used belt spec after that. Given how they work, there is always a possibility that I could have over-tensioned the belts, but I think I got in in the right range.
I've removed:
I removed the AC drive belt, and the sound remained, so I put it back on. With the AC belt installed, AC on or AC off, no difference.
The only component I haven't changed in the drive belt area is the fan clutch and fan blade. I have replacements on order (and I plan to modify the fan clutch with the Landtank mod, I already have the 10k silicone oil).
The sound happens when idling in the garage, raising the idle by hand with the intake cam, driving down the road idling along. BUT... if I apply the tiniest amount of accelerator pedal (not even enough to register an RPM change) it goes away. If I let back off the pedal, it comes right back.
The sound pitch changes with changes in RPM, increasing with more RPM.
I tried an electronic stethoscope thing, that wasn't super helpful. I used a length of poly hose and think I have narrowed it down to somewhere above the alternator, near the coolant neck that comes out of the head.
The fan clutch resistance stops the fan immediately and doesn't make any noises when rotated by hand. The engine isn't overheating. But, I'm going to replace the fan clutch, fan blade, and FPR to eliminate possible causes, and more generally as preventative maintenance. (save the old ones for spares).
I am not saying this is it, but it has the kind of high pitch sound like a helical gear whine, where it is quiet on the drive side, and too much lash on the coast side. The sound goes away when it is under acceleration (drive) and comes back when idling (coast). My tiny animal brain wants to blame the gear driven alternator, but I don't see how they could get out of lash spec. They only install one way as far as I can see. And I don't experience the same gear like behavior/sounds in the shop, only when driving.
I have serviced the diffs with the proper amount of synthetic gear oil, and this sound happens when stopped, and is isolated to the front of the engine, so I don't think driveline gears come into play.
I think I've traced down and plugged any vacuum leaks.
Any thoughts? Fan clutch? Distributor gears? Belt tension? Timing belt tensioner? Something else?
I've finally had a chance to do as much deferred maintenance as I'd hoped to and got the 80 out for a long drive and some trails. I have a sound that I can't diagnose, and am wondering if I could get some thoughts from the group?
I first thought it was the water pump, so I replaced that and the belts. Nope. Then I thought it was the alternator, so I replaced that and the tensioner. Nope. Maybe the AC, so I removed that belt, and nope. Hmm, starting to get stumped.
The noise occurs when I'm not moving, idling in the garage, so I am going to focus on what I've done in the engine bay that are in that area:
- three belts
- alternator (rebuilt)
- idler puller
- water pump
- air conditioning compressor (done by prior owner just before me buying it)
The prior owner replaced the following recently:
- AC compressor
- Aisin blue fan clutch (no knowledge of whether it was modded)
- oil change
- oil filter
- valve cover gasket
- spark plug gaskets
- plugs
- cap
- rotor
- distributor-o-ring
- all coolant hoses
- all vacuum hoses
- radiator (Koyorad)
- Coolant sensor ECT (the ECM one)
Timing is at 3 deg BTDC at idle, with DLC pins jumped.
Belts tensioned per FSM with a Kriket tool (3 different times now). Using the new belt spec initially and the used belt spec after that. Given how they work, there is always a possibility that I could have over-tensioned the belts, but I think I got in in the right range.
I've removed:
- EGR, with block off plates
- PAIR system
- VSV assemblies and related hoses (open vacuum ports looped or blocked off)
- Second row heat
I removed the AC drive belt, and the sound remained, so I put it back on. With the AC belt installed, AC on or AC off, no difference.
The only component I haven't changed in the drive belt area is the fan clutch and fan blade. I have replacements on order (and I plan to modify the fan clutch with the Landtank mod, I already have the 10k silicone oil).
The sound happens when idling in the garage, raising the idle by hand with the intake cam, driving down the road idling along. BUT... if I apply the tiniest amount of accelerator pedal (not even enough to register an RPM change) it goes away. If I let back off the pedal, it comes right back.
The sound pitch changes with changes in RPM, increasing with more RPM.
I tried an electronic stethoscope thing, that wasn't super helpful. I used a length of poly hose and think I have narrowed it down to somewhere above the alternator, near the coolant neck that comes out of the head.
The fan clutch resistance stops the fan immediately and doesn't make any noises when rotated by hand. The engine isn't overheating. But, I'm going to replace the fan clutch, fan blade, and FPR to eliminate possible causes, and more generally as preventative maintenance. (save the old ones for spares).
I am not saying this is it, but it has the kind of high pitch sound like a helical gear whine, where it is quiet on the drive side, and too much lash on the coast side. The sound goes away when it is under acceleration (drive) and comes back when idling (coast). My tiny animal brain wants to blame the gear driven alternator, but I don't see how they could get out of lash spec. They only install one way as far as I can see. And I don't experience the same gear like behavior/sounds in the shop, only when driving.
I have serviced the diffs with the proper amount of synthetic gear oil, and this sound happens when stopped, and is isolated to the front of the engine, so I don't think driveline gears come into play.
I think I've traced down and plugged any vacuum leaks.
Any thoughts? Fan clutch? Distributor gears? Belt tension? Timing belt tensioner? Something else?
lol
