It's more of a clacking sound than a tick. It doesn't seem to come from either side of the motor in particular. In fact it sounds like it's coming from the water pump/timing chain area, but I already replaced the water pump.

When I start the car there's no sound out of the ordinary at all until I go closed loop and the idle slightly drops, then it's a steady "clack" sound. Every now and then it will be accompanied by a slight rattle.

Oil pressure is good. It's about 70 on cold start and 30-40 after it's been running. The car is an 88 L98 with 117k miles and an auto transmission.

 

Have you got a stethoscope? You know-so you can locate exactly where the noise is comming from-I've used a short piece of garden hose before. I'm kinda wondering if the timing chain could be on its last legs, Any missing or poping noises?

 

Put your finger a fuel injector. Does the noise coincide with the pulses you feel through the injector? If so, maybe a problem with the cold-start injector. Just a WAG here, but easy enough to check.

 

The only things I can think of in the area of the waterpump that might make noise are the tensioner or air pump solenoid. I would think that the tensioner would make noise hot or cold, but if the noise only occurs at lower rpms, then it might not appear until the engine is warmed up.

The air pump solenoid should be directing air to the converter once it's in closed loop. A bad check valve on the converter line or broken solenoid will divert the air in the area of the water pump. It sounds somewhat like an exhaust leak and wouldn't be noticable until the engine is warmed up or until the valve switched the air flow from headers to the converter.

Having a good seal on the solenoid valve is important too, so if you removed it to replace the water pump and didn't replace any of the gaskets, this may be the source of the noise.

If you do suspect something from the air pump or tensioner or any accessory, remove the belt and then run it briefly to see if the noise is gone.

 

 

Thanks for the responses guys.

I tried the stethoscope trick with no luck. I could definitely hear the noise through the stethoscope but no matter where I placed it, there was no "sure spot".

I've thought about the timing chain as well. There are no pops or misses, only a rattle every now and then that sounds almost like a heat shield. Everything looks secure unless there's something hidden down there that I can't see.

I hadn't even thought about the diverter solenoid. I have no catalytic converter, diverter valve, or smog pump now. I've been toying with the idea of removing the line that goes over the passenger side valve cover, removing the solenoid, and removing the pertinent vacuum lines. It would certainly clean things up but I'm sure I'll start getting some codes. Is there anything I can do as far as a quick disconnect so I can rule out the solenoid?

I wouldn't say the sound coincides directly with the injector pulses. The rhythm is definitely about the same but the sounds aren't simultaneous. I assume that to check this I simply have to disconnect the cold start injector? In the past when I've done this (even when it's really warm outside), my car cranks for about 10 seconds, might catch, then immediately dies. I've asked on the forum if this is indicative of a bad injector but didn't get any response.

As long as it's nothing internal to the motor and I can single out where the problem is, I'm confident I can fix it myself. I just hate throwing money to fix things that aren't broken in an attempt to figure out the cause.