Irregular ticking sound loudest between engine and firewall at 193K miles.Solved

[prince402]

A recent development with my 193K miles 94 Eddie Bauer is an irregular ticking sound loudest between engine and firewall that sounds identical to an engine knock (ping or pre-ignition or detonation or dieseling) and is observable at idle and highway speeds. It increases sometimes when accelerating however it is irregular and sometimes non-existent. It also sounds like a pebble inside a hub cap and also like a wire coat hanger hanging down, bouncing on the highway.

My mechanic went around with his stethoscope and came up with nothing definite. I specifically asked him to check the catalytic converter and he ruled that out, but I'm still suspecting it. He is a good mechanic so it's likely something else.

Any ideas?

 

[410Fortune]

Could it be a simple exhaust leak or from your description sounds more like its inside the engine?
Suspect: Cam synchronizer on back of engine

So if I determine I have an engine noise with a ohv 4.0 first thing I do is remove the serp belt and start it let it run briefly. Noise still there? Okay then its not in the belt or accessories
Next time to see if we can sort what part of the engine
Oil pan, valve cover or elsewhere
Oil pan = lower end knock, crank bearing, rod bearing,etc
Valve cover, lifter or push rod issue, oiling issue
If it does not sound like oil pan or valve cover the next thing that rotates in teh area you describe is the cam synchronizer
In 1994 there is a cam sensor and synchro on the back of the block, with your miles it would make sense that it is time to replace
This device helps to determine ignition timing for the computer (Like a distributor)
It drives the oil pump off of the camshaft
It has a hall effect sensor on top
It rotates with engine RPM When they fail you can lose oil pressure worst case, they usually make a chirp chirp noise when the bearings run dry but knocking noise can be metal on metal contact also

Other things to consider (Your mech probably already did)
Any loss of coolant with this engine? (detonation from water in combustion chamber)
Any check engine light?
Does it use oil? have steady oil pressure?
Is it an automatic? With 193K your torque converter can begin to make noise as well

 

[mgmgmg]

+2

 

[prince402]

Thank you for your thorough reply. It looks like I've got some looking to do. Will let you know.

 

[prince402]

Solved.
The third shop put it up on a lift and found the problem in a few minutes. It was a defective return spring on the starter almost but not fully returning the starter gear fully away from the flywheel gear. So in that not-fully-retracted position, the gear teeth of the flywheel and the starter were ever so slightly touching sometimes.

They installed a rebuilt starter and no more tingling sound. Fortunately there was no visible damage to the flywheel gear teeth.

 

[410Fortune]

I love it when there is a solution! thank you for posting it!

 

[Centaurious]

410Fortune, the cam synchronizer is there to control the fuel injector timing. The crank sensor is for the ignition timing. 94's were the first year with sequential fuel injection instead of the earlier batch fuel injection.

 

[RustyMacintosh]

I had (have) a 99 Suburban 5.7 with a new motor in 6/17... 8/17 it started to misfire...it got worse and worse...I went thru 4 shops EVERYTHING was changed multiple times...except the rear brakes and a door handles.

I was ready to donate it. On the way to the Rescue Mission, it was on a flatbed behind an 80 F100--I stopped at a shop 3 businesses away from the RM.

The owner and I had a long talk. He was very hesitant to take this Suburban. He did not need to. He had Vipers, AMG's and other toys in the service bays. One of his techs said he wanted to try his hand on the Suburban, the max they could charge was 5 hours per BAR.

24 hours later I get a call. Its repaired. Plug that goes tot he dizzy was mashed, one wire was intermittently connected. They put all Delco Remy parts on. $1300 later, it hauls ass. Today it tows a Uhaul car carrier to get to Yosemite to bring back a V-8 Mountaineer.

Moral? None I guess but never give up. Keep at it until you find a tech who actually is talented.