Piston Slap: Tapping and Clicking Fuel Injectors?

Sajeev Mehta
by Sajeev Mehta
piston slap tapping and clicking fuel injectors

Walt writes:


I wrote to you five years ago about a frozen Ranger parking brake, and later on about the incredibly dumb idea of purchasing a vintage Mustang with a loan. Thankfully, the former resolved itself, and the latter remained a pipe dream. What I did do, however, was buy a ’14 Mustang GT with a 5.0-liter Coyote V8 and six-speed manual. It now has around 9,800 miles.

At around 3,000 miles it developed a clicking noise at idle, audible with the driver side window rolled down and a curb or jersey barrier to bounce the sound back at me. The frequency of this click increases with engine revs. Existence of this issue with the 5.0-liter Coyote is well documented on F-150 and Mustang forums alike.

Theories range from “don’t worry about it,” to noisy fuel injectors, to normal operation of the variable valve timing system, or camshaft problems.

I haven’t noted any power loss or additional malfunctions, just the click. The only thing I have seen is oil consumption; about 3/4 of a quart over the last 5,000 miles or so. With forum posts that report anything from zero oil consumption to rates similar to my own, I don’t know what to make of it.

There doesn’t seem to be any technical service bulletins for such a problem. I am somewhat hesitant to take it in for unnecessary diagnostics and tear-downs if it’s a non-issue. However, if it truly is a ticking time bomb, I want to take care of it while the warranty is still in effect.

I would appreciate any insights you or the Best and Brightest may have to offer.

Sajeev answers:

Yeah, my 2011 Ford Ranger makes that fuel injector clicking sound too. It comes from the disc design (?) of newer fuel injectors, combined with the fact that computers normally dump extra fuel to keep a cold motor running. It’s the only logical reason I’ve seen for this phenomena, as it does cover a variety of makes and models over the last decade-ish.

I reckon you could disconnect a fuel injector when idling to see if the sound changes. It won’t hurt anything, as the old school EFI cylinder balance test has done this for years.

Speaking of old school, I was worried my 1988 Mercury Cougar would start that late-model tick after ditching the old pintle injectors for the discs (?) from a 2004 Mustang GT. Thankfully, they are silent — or perhaps Sanjeev got lucky after getting an old Cougar drunk late one night?

(BTW, this is what happens when you can’t find your roll of painter’s tape.)

[Images: Ford, © 2016 Sajeev Mehta/The Truth About Cars]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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  • on May 04, 2016

    I'm not a mechanic but I've been doing IT work for a small chain of auto repair shops for 20 years or so. I'm out in the shops very very often keeping the Tech 2's, IDS's, DRB 3's and Can scan tool stuff working. I see a lot of cars. Mostly broken cars. Seems to me that almost all modern engines, regardless of make, have injector noise. The quieter ones all have some miles on them. 80k or so. There's a sweet spot in there mileage wise when most engines seem quiet. I own two Town Cars. One has 147K on it and the other has 54k on the odo. The low mileage car has a fair amount of injector noise. Nothing overly objectionable but it's there. The 147k car is quiet as a mouse. You can hardly hear it idle at all. Never had the injectors serviced. They seem to "wear in" for lack of a better term. I don't know the how or whys but that's the casual observer take for what it's worth.

  • Compaq Deskpro Compaq Deskpro on May 04, 2016

    My Pentastar Challenger did this since brand new on the dealer's lot. I don't think much of it because my Crown Vic did it a lot louder.

  • MrIcky I would like to compare the answers here against the answers in the recent civil forfeiture article- but I won't because research is hard. It's true though that currently a ticket has no punitive value on those with means and maybe an outsized punitive value on those without. That's not communism, that's just the way it is. Speeding tickets are too arbitrary anyway though: officer discretion, speed trap towns, excessively low speed zones in areas to increase ticket revenue instead of safety, etc. I could clearly see a case where expensive cars are selectively enforced over cheap cars because you only have so much time in a day to up the revenue. It's a gray rainy crap morning and I'm sure the government will do it wrong.
  • 28-Cars-Later Feels a bit high but then again... forget it Jake, its Clown World.In 2021 someone in Sewickley had an MY01 soft top in a manual with 54K otc which I am fairly certain was a 996 and not a Boxster - $20K. I already had my C70 at the shop being reborn and could have done the $20K but it would have been tight and just didn't make sense. Still...
  • SCE to AUX Q: Should Speeding Fines Be Based on Income?A: Yes. Rich people (the guy with $1 more than you) should pay less, because giving his income to the government means he has to lay off a worker at his business.Laws are for poor people./s
  • SCE to AUX "Volvo has suggested it’s capable of yielding 275 miles of range"Every non-US car's range estimate is based on WLTP - worth mentioning.EPA range never 'backs up' WLTP; it's always about 15% lower - so figure maybe 234 miles. Not great, except as a commuter.As for the interior - it's obviously a Model 3 clone, but the screen is substantially smaller. Incidentally, I suspect Tesla made the Model 3/Y interior so minimalist to save money - not just to be different. When you're trying to become profitable on EVs, every dollar counts.
  • SCE to AUX "there haven’t been a lot of good examples hitting the market recently. Most models are aimed at the affluent, resulting in 9,000-pound behemoths with six-figure price tags"I hope you were joking, because that is blatantly false.