USA 2012 CNG weird whistling noise

[AccApp1]

2.0 l 4 cylinder gasoline engine with BAF CNG conversion installed by Knapheide when new. 71,000 miles. Starts with difficulty when cold and stalls easily until warms up. Lacks power even then. Makes a weird vibrating whistle noise. Video attached. Would appreciate any help in resolving this issue.

Link to video on Imgur
https://imgur.com/gallery/2012-ford-tra ... se-K2ehKrm

[metalworker0]

Squeal could be a manifold leak or turbo pipe work and intercooler

https://www.youtube.com/watch?v=wCm3pB1c3FU

My experience is with LPG not CNG: for a start all LPG systems are "dual fuel", don't know about CNG --- reflected in this answer

My experience with LPG says, turn it off ...switch to gasoline and see how it runs on that ...if runs good then the problem is with the CNG

Don't quite know how CNG works ... but according to google ...after the vaporiser and pressure regulator its the same as LPG..
it gets injected into the inlet manifold.... from here on it can be:

1. injectors worn out
or
2. injectors contaminated with tarry gunge
or
3. there are vac pipes to a sensor type devices and the vaporiser . they can perish

Try the switch to gasoline ...if it runs well you know it's the CNG

CNG and LPG require a perfect ignition system to work, this is because the gas is an insulator and it's hard for the spark to jump the gap at the plug ..it would rather go anywhere but across the gap.
so needs perfect plugs and perfect plug leads or coils.

it can run perfectly on petrol but run badly on CNG /LPG because of insulating proprieties. and LPG / CNG, will show up, worn out plugs / and faulty coil overs many 1000's of miles before gasoline does.

if your system is set up to run on CNG ONLY --- then its a lot harder to diagnose ...as without the comparison of gasoline ...then it could be anything!.

all the best.mark

[AccApp1]

It’s a dedicated CNG fuel vehicle. Only gasoline ever ran through it when driven off the line and until it reached the upfitter who converted it.

Update: as of today. Replaced injectors with OEM Bosch parts, installed remanufactured brake booster from O’Reilly and changed spark plugs. One of the spark plugs broke in the head and I was lucky enough to drill out the broken stub and chase the threads without needing to pull the head. Still getting the weird whistle/rattle noise and drove it for a week without an engine code appearing until yesterday. Same PO171, bank too lean.The little wrench light came on as well but didn’t have a readable code for my Zurich diagnostic reader. Seems to have a bit more power than before the spark plug change but stalls when cold coming off of acceleration. Once warm responds better to throttle but still seems to lack pep. Brake boost remains good after sitting idle. I can reset the wrench light by pushing brake and accelerator pedals down with key on and engine off but it comes back on with the check engine light.

[metalworker0]

An air leak from any one of the many rubber tubes that go,: here, there and everywhere,would possibly make it whistle .. also .. it would run higher rpm at idle, if any of the rubber or plastic pipes that are connected to the inlet manifold are cracked, split, broken or disconnected.
Some of these are vac pipes and are independent from the brake vac line system.
i wouldn't know if its had the evaporative emission control removed from it, this is the system that included charcoal canister and was used to vent the gasoline tank and consume fuel vapours from it, in the engine..
Other rubber pipes may go to the ECU, well they used to do a few years ago (Vacuum advance information , manifold pressure information)

Any leak into the manifold down wind of the throttle body will make the revs increase and make it run lean .

They usually test these systems with a smoke tester machine .

My last lpg system had vacuum pipes that went from the manifold to the vapouriser and to a sensor device ... i noticed that the lpg deteriorated rubber if it wasn't of the correct rubber.

all the best.mark