My car makes a fairly soft and somewhat rapid ticking sound at idle, after the engine settles into its idle rpm a few moments after starting. A slight increase in revs and the noise seems to go away, but then resumes once it settles back to idle rpm's. It also seems to go away once the engine has warmed up a bit. I have a cheap mechanic's stethoscope, and the noise definitely seems to be loudest right at the injectors.....pretty much all of them. It's been making this soft ticking sound for a long time, maybe a couple years or longer.

I have tried BG 44K a few different times, but it doesn't seem to help much. I have never checked compression, valve clearance, or oil pressure, but since it's been making the soft ticking sound for so long, I'm sure it's not a more serious issue or the engine would have failed long ago! I've used the stethoscope several different times, and I've been convinced that it's the injectors each time I checked. So I've never worried too much that the engine was about to fail. The sound has been about the same noise level ever since it started.

Researching the issue (and using the stethoscope) always led me to believe that it's the injectors. I still think it is, but I'm curious what experience any of you have that would either confirm or refute this assumption. I suppose I'll have to remove the supercharger if I want to replace the injectors. Years ago I removed the supercharger, serviced it, and replace the coolant hoses underneath.

If it is the injectors, is there any risk by not replacing them right away? The engine runs fine, no other issues that I can tell. I'd call it a mild annoyance rather than a serious problem right now.

Thanks!

Edited to add: The car has about 190,000 miles on it, and I have no reason to think that the injectors were ever replaced. I have done a ton of peripheral engine work to the car over time, but I believe that it's the original nikasil engine, heads, and original injectors.

 

That particular sound isn't at all alarming, like a sewing machine, I've been used to it since before EFI with Bosch mechanical units making louder noises.
If it was getting worse I would be suggesting whipping valve covers off to check valve clearance, but no these engines are that quiet you can hear fuel delivery.

 

I checked the injectors with the stethoscope last night just for fun. It’s about 3-4 of them that are the noisiest, but the one at the front left is the loudest. It almost looks possible to replace that one without removing the sc. Two questions:

1. Does anyone know if it is possible to replace the front left one without removing the sc?
2. Is it advisable/ok to replace one injector but not the other 7?

Thanks all!

 

Injectors only have one job so it does not look like there would be a problem and it could
provide some insight as to whether it is a valve clearance issue or not.

 

OK it definitely looks like I can replace the front two injectors without removing the supercharger. The front left one is the noisiest by far, but the front right one is second noisiest. If I end up learning that I was wrong and the sc has to be removed, then I'll probably live with it for now because it definitely doesn't rise to the level of "urgent". More of a mild annoyance at this point.

That said, the Jaguar Classic Parts site says that the injectors are no longer available. Google would seem to agree. I did find a couple of sources for remanufactured injectors. Does anyone have experience with a particular source that you would recommend? Is it more advisable to have my injectors rebuilt by someone vs buying remanufactured ones? If so, who would you recommend to rebuild them?

I think I'll figure out how to depressurize the fuel rail, but if you have a quick suggestion for doing that, feel free to share it!

Thanks again!

 

1998 JAGUAR XJR 4.0L V8 Supercharged Fuel Injector | RockAuto

 

Thank you Randy. I ordered two! Looking at it again, I would say that the front right one can be swapped with minimal effort. The front left one, which is the more noisy one, looks to be a little bit more challenging because of the coolant hoses, but I think it’s doable. We’ll see! I will post my findings here when I get them replaced.

 

FWIW, Rock Auto canceled my order saying that they are out of stock. I tried partsgeek, and they are out of stock too. I ordered two "rebuilt" injectors from a place called Five-O Motorsport, which is the only other place I found online that supposedly had them in stock. I did learn from all-knowing google that you apparently can't really 'rebuild' an injector. You can have them cleaned and replace the O-rings, but you can't replace the mechanism inside. Some of them have microfilters and tips that are replaceable, but that doesn't seem to be the case with the Jag injectors. So the ones I get might not be any quieter than my old ones, but I'll chalk it up to education expense and move on! I will post a follow up report here if I learn anything.

 

Ok here are some updates and another question. It is quite easy to replace the front left and right injectors without removing the supercharger. In my case these two are the noisiest. I ordered two injectors from Five O Motorsport because they were the only ones I could find in stock online. One injector seemed fine but on the other one the micro screen had a tear in it. I’ll sort that out with the company.

The left front injector (definitely the noisiest one) had some black buildup on the nozzle. Not sure what that means. Thoughts?

 

I think I have a slight injector noise, too. My car is an ‘02 XJR with 90,000 miles. I don’t hear the noise when it’s cold. I only hear it at idle after it’s warmed up. Like yours, it sounds like it’s coming from under the supercharger. I haven’t used a stethoscope.

I’ve had my car 9 years and maybe it’s always made that noise. I know I noticed it a good two years ago and like your car, it hasn’t gotten worse, so I haven’t worried too much about it. Maybe I’m just being paranoid. A friend (who isn’t a mechanic) said it just sounds like a normal car running.

I’ll be watching this post for any updates. Thank you for posting it.

Regarding the coolant hoses under the supercharger, I’ve never changed them. I’ve changed all the other hoses. Do they fail often? Is this a routine service issue I should be doing? I haven’t serviced the supercharger either.

 

I don't know how often they fail, but they will fail eventually and you'll see a mysterious coolant leak. If you ever have reason to remove the supercharger, you'll want to replace those hoses even if they're not leaking, but it's not what I would call routine maintenance like an oil change. The part load breather tube is under the supercharger too, which you'll need to replace while you're there because it becomes extremely brittle over time, and you'll probably break it anyway. The knock sensors are under there too. Might want to replace those if the supercharger is out. None of this stuff is what I would call routine, but if the supercharger needs to come off for any reason, you'd do these things as preventive maintenance. I didn't replace the knock sensors in my car at the time, mainly out of ignorance, but I'm not having any problems with them. Still, I should have replaced them "while I was there".

 

Thank you for this helpful information. I appreciate it!

I have never serviced the supercharger. I don’t think servicing the supercharger is a recommended service. I’ve read some people recommend replacing the oil in the supercharger. I’ll have to research it. I do want to get those coolant hoses replaced that are underneath the supercharger. If I do remove the supercharger, I will replace everything you recommend. Thanks again!

 

Injector noise is usually associated with the injector nozzle being clogged however that is not
always the case. Soaking the injector in brake fluid overnight will loosen the deposits however
you also need to use compressed air to blow out any loosened debris. They should quieten
down considerably after that.

 

OK, just to button up this thread for anyone doing a search in the future. I got both refurbished injectors installed, and the car runs great. Definitely less ticking now. The left front one was the main culprit, as I had mentioned. One thing you need to know if you ever mess with the injectors: exact OEM replacement pintle caps are an extinct species. You’ll need to be super careful removing them, because you may have to reuse them if the replacement Denso injectors you buy do not have the original Jag caps. You can’t buy the correct OEM’s separately - not that I found anyway. The replacement caps that you CAN find will fit correctly, but they are 4mm shorter than the OEM’s.