Whistle and cough after servicing

[HutchoUk]

Hi everyone. I'm a long time fiesta owner, but new to the forum and would really appreciate some advice.

We've had our current Fiesta (1.25l, 2016, mk7, ~38k miles) for over a few years, and now the extended warranty is expired, I convince my wife to let me service it myself rather than pay a small fortune to the main stealer.

So over the weekend I self-serviced my Fiesta (1.25l, 2016, mk7, ~38k miles), changing the air filter, spark plugs, oil and oil filter. I've serviced other cars before, but still followed my Haynes manual to be sure. I fitted all Bosch parts with the recommended Magnatec oil and all seemed straightforward, apart from a peculiarity when adding the oil (I'll go into that later as I don't think it's related).

We went for its first long drive today and I started to hear an intermittent high pitch whistle which went up and down with the engine revs. When we got home I had a look under the bonnet to investigate whilst my wife was revving the engine. It wasn't whistling when revved on the driveway, but I noticed that if the engine was revved suddenly, a single popping noise was made and the whole airbox would jump.

I inspected the airbox and air intake pipes - I could not see any issues and the screws where all tight. I undid the airbox to check the filter was sitting properly, which it was. With the lid sat loosely on top of the air box I started the engine and gave it a rev to see if the problem went away. However, the popping noise occurred and the lid (with the air pipes to the engine) pushed off away from the airbox, suggesting that air was being expelled rather than being sucked from the inlet manifold.

I'm guessing I've either fooked up somewhere or I've fitted faulty parts, but I can't see how this could cause the popping problem.

Has anybody else experienced this popping noise and whistle after a plug and/or filter change?

Also, regarding the oil issue I mentioned above: The owners manual, haynes and every reference I cold find online says the engine takes 4.1 litres of oil, however I've only put around 3.6 litres of oil (measured using the marks on the bottle) in and the oil is right at the upper limit on the dip stick. I've checked the level again after letting the engine run for 5 minutes whilst parked on flat ground, and it's still saying it's full. Is that normal?

 

[econoboxrocks]

Make sure that all the emissions lines are properly connected. A loose or disconnected one can cause weird sounds.
The 4.1 liter figure is probably a total. There is usually some oil left after a change. Did you change the filter, too?

 

[HutchoUk]

Thanks - I didn't think to check the connectors. I'll have a look later.

I fitted a new oil filter, so that wouldn't account for the capacity shortfall. But if some oil is normally left over I won't worry too much.

 

[Handy Andy]

You said you changed the plugs, recheck your plugs and wires, make sure the plugs are tight to the seat (don't overtighten, just backout and reseat them) them to make sure they didn't jump out - then also re-check your boots.

To help, on my car (2018 Fiesta) - the firing order is 1 - 3 - 2 - 4 - so remember this when you work on these - that you don't pull all the wires completely off the engine unless you know and or at least took a picture of what the motor looked like before you did this.


But locating Pin 1 to Plug 1....

​

The jumping of the airbox is a clue that it may not have jumped time, but it is thinking of backfiring. This means a timing or plug firing issue - make sure you have the wires to the right plugs - and that all the plug wires are checked good, you use an ohmmeter to do this - one lead to one end, other lead to other end and set for 2K resistance - should show ohmic reading - and any open ones got broke when they got pulled or otherwise twisted. They're pretty durable, but not unbreakable.

IF you think you have it right - and still have this condition - the plugs might be bad, as in a fouled out or cracked plug - making a vacuum leak into the cylinder it's mounted to.

You said you did an oil change - make sure you're not overfilled - 3.8 to 3.9 Quarts NO MORE - else that PCV valve will suck that excess oil in and it'll try to reburn it - that can cause this "bucking" issue too - it's not a Bronco, but similar to the Pinto - and thats' close enough - enuff said...

 

[HutchoUk]

Thank you both so much for your really helpful replies.

Econoboxrocks - after reading your post, I checked the wiring with no issues. I also had another look at the spark plugs. I retightened them, possibly over tightening them a little but it didn't make a difference. (annoyingly the only torque wrench I have capable of measuring 15Nm is a 1/4" drive, and my spark plug socket is 1/2" drive). I also put the original spark plugs back in and it made no difference.

I would put the original air filter back in too, but I binned it and it's now covered in dust and oil.

Handy Andy - I suspect you may have hit the nail on the head with the oil being overfilled. The oil mark is on/slightly over the line when the car is on flat ground. However, I'm testing the car whilst it's sloping downwards on my driveway pushing the dip-stick oil level even further up.

I'm just waiting for a downpour of rain to pass and then I'll try draining off some of the oil to see if that helps. I'll also double check the wiring and ht lead impedance whilst I'm at it.

 

[Handy Andy]

When you hear a whine - is it in the radio speakers or the "outside" as in from the engine compartment?

IT could be alternator whine - the alternator charges the system, if charging issues were to come up this is one part that is suspect.

IF you have and know how to use - a Digital Volt/Ohm meter then I highly recommend you check the battery and voltage at the battery posts while the engine is running and not - you may have discovered, by that noise, a wiring problem.

You'd see or should see 14.4V max at the battery as the engine runs - means it's charging the battery.

When you shut off the engine and keep the doors shut, the battery floats down to about 12.3 to 12.4V - which is normal after about 1/2 hour to an hour after it's been shut off.

IF the voltage is low even while running - then something is causing this whine and it needs to be checked.

 

[HutchoUk]

I've now checked the ht lead impedance and order and all is fine. The battery voltage is comfortably above 14v when running and I've drained off ~1/2 litre of oil so the oil mark is half way between top and bottom on the dipstick (when parked on a flat road).

I managed to take it for a long drive today and the whistling noise didn't return. I'm guessing the air filter was poorly seated and it's been rectified whilst I've been investigating. However it still hiccups when I suddenly rev the engine. I'm actually starting to wonder whether I'm overthinking things and this is actually normal behaviour.

This is only happening when I slam the accelerator peddle down, which I've only been doing whilst troubleshooting but never actually do when driving the vehicle. It hiccups only once with each rpm spike and does not do it continuously when the revs are maintained.

 

[HutchoUk]

Here's a video of the issue. You can hear the hiccup as a chopping sound before the engine note goes up. The air box jolts when it happens, but you can't quite see it in the video.

 

[Handy Andy]

This is the differences in the years this engine is made.

In previous years, this (the Fiesta) and others (Focus Fusion - Think Duratorqu) before 2013~2014 they had MAF sensors in the intake - the subsequent years they used MAP - so the MAF was on the air flow INTO the throttle - then the MAP was AFTER the throttle when they swapped noses on the Fiesta from the old, sloped aerodynamics to the "Aston Martin" look in 2014.

So, since this, the "AFTER" years - the MAP sensor and the headaches along with it are part of this.

Do you have access to a dealer that can help you with the Ford Customer (ed.- Experience) Assistance program that allows you to modify the vehicle to make it more like you? They can change the profile of how the system responds to your driving - it isn't cheap but throttle response and ability to drive the vehicle comes to mind.

The "gulp" of air is that intake - which is part of the noise and "loss" of power. Not as in the older days, where the dry throttle intake and the injectors mimicked the carbureted "accelerator pump" thru the use of an anticipation of throttle action when the sampling the PCM uses, suddenly sees one value to another - and how quickly the change - signaled acceleration.

What you're experiencing is this change in loading as the engine is trying to figure out its next move or the 4-cycle action.

If you can't, get them to help you make the lag time less - then join the club - not much forgiveness from my local dealerships in help on this - else just get rid of the car - and tell Ford they don't know how to make cars accelerate anymore - good luck at NASCAR (which they backed out of - by less funding) - this may be a negative statement - but it is a reality for many new car buyers.

 

[HutchoUk]

So is this a design flaw rather than me breaking something? If so, I can live with it.

I don't floor the throttle like this when driving normally so if it's just how the car is, that's fine. I was more concerned that it might have been a signal to a much bigger problem that I needed to sort.

 

[Handy Andy]

After a breaking in period, I encountered the same effect - a type of lag-time between the throttle and the increase - so by investigation I found specific instances in operating a Manual Transmission - that they used a switch that told the system to have a little more sensitivity and or idle-up during a shift in gears moment allowing the takeoff (as I put it) sense it "sees" to help with throttle and timing advance.

When you "speed shift" this sensing is not happening - so it "drags" itself - you can fix it somewhat by allowing a higher shift RPM point to let the next gear fall into place and that lag time in seconds versus the RPM - is somewhat offset but the throttle is indeed affected by this.

The Automatic transmission side - uses this switch to tell the system it's out of Park or Brake - so the transmission then is ready for acceleration - if it's not completed past a given level of time - the transmission goes into a neutral state and if not restored will let the vehicle roll. And if you're not careful to pay attention you'll find yourself rolling in whatever direction the tilt in pavement is - hence the "Hill Assist" function

 

[HutchoUk]

It sounds like something I can live with then. I'm just glad it's not a sign of anything more serious.

Thanks to both of you for your help. It's much appreciated.