Does an injector make noise when it is failing?

I'm ******* down a intermittent but recurring ticking sound that accompanies rough running - like it is dropping a cylinder. No codes thrown.

A few weeks ago I had the same situation but it seemed to be fixed with a new coil. There were codes associated with that event pointing to the A4 coil. It ran fine for 1,000 miles in some really cold Minnesota weather - minus 10 degrees or more. Stout little car!

Anyway, on the way back home it started clicking and acting like it was intermittently missing on one cylinder.

I'm out of ideas. About the only thing that isn't fresh is the injectors...

 

I would generally expect that a solenoid would stop making noise when it failed, especially if it was stuck closed.

If an injector quits spraying fuel, you should see it in the fuel trims. The L or R side would suddenly go 25% lean.

Anything like that accompany the rough running?

 

One question first; did you replace ALL 8 coils? or just the one for #4 cyl.? I would think the ticking is one of the coils firing to ground inside the spark plug "tube"... it would explain the temporary miss as well. I might suggest replacing the spark plugs and checking the condition of the insulator boots on the coils. I have had this happen to me on two vehicles.

 

I just replaced one coil, A4. Interestingly, I have replaced that coil before.

Yes, the fuel trims rise when it misfires and return to normal when it's not having a fit.

I like the notion of a short in the spark plug tube, it fit the facts pretty well. I could replace all the plugs and take the opportunity to inspect the boots. I haven't looked at them in 30,000 miles or so. I had a split boot on my Corvette give me trouble some time ago...

Thanks, I'll report back.

 

I got some spark plugs had the hood up and was getting ready to do a coil check. I got in to move the car, turned the key on but didn't start the engine and...the engine starts clicking like mad.

I was able to get to it before the clicking stopped and it is clearly coming from the throttle body. You could feel it on the TB itself and up through the intake hose. I presume the butterfly is clacking open and shut.

I called ASI (who did my rebuild in 2011) and they said they would check it at no charge under my lifetime warranty. Better yet, since mine was one of the early rebuilds and they have learned a lot in the intervening 4 years I'll get a re-rebuild which includes the refurbishment of more internals and a bead blasting, too. Two hoses and four bolts later it was in the mail to them.

I hope it is something internal to the TB and not some errant signal from upstream.

 

Keep us posted.

 

As promised, ASI re-rebuilt my throttle body after I found it rapidly cycling the butterfly - that was my ticking sound I think. The technician, Will, that did my first rebuild told me that they have expanded and upgraded their XK8 rebuild process since I had mine originally done. There was no charge.

It came back in 2 days - professionally cleaned (looks like soda blast) and with evidence of the motor being worked on along with the TPS and other work. All the OEM screw seals were broken which is a good sign.

I made sure the TPS was in it's correct position (using the witness marks I made beforehand) and had it installed in about 15 minutes. (I have, unfortunately, become an expert at XK8 TB installing...) It looks great, if you are into that sort of thing.

After an initial high rev (about 3,000 RPM for 3 seconds) it settled right down into cool, then warm idle. I took it out for a 20 mile spin, works perfectly.

Interestingly, the car starts a bit better than before - just a tap of the key now. It took a second or two of turnover prior....

We'll see if this resolves my issue or if there is more sleuthing in store for me.