How to test for a leaking fuel injector

Adam Vinnicombe

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Hi all my fuel trims on my new edge are slowing getting more negative day by day. Some history, back in September it took the garage two days to get the mustang to pass the U.K. emissions test and when it finally passed it only just passed. Anyway at the time I wasn’t that bothered about it but I did but my scanner on and noticed that the STFTs were -4 and LTFT were -2 at idle only as soon as I increase the rpm the fuel trims all went slightly over zero. So day by day the fuel trims are going more negative. Yesterday the LTFT are at -6 and STFT are at -4 on both banks. The O2 sensors have been replaced but that did nothing. Today I did a 70 mile drive got home hooked up the scanner and saw that bank one was looking normal, STFT were -3 and LTFT were 0 to -1 BUT bank twos STFT were at -5 and LTFT was now at -10. The car drive just fine, the idle is steady, the only small problem that has just started is that once in a blue moon when I dip the clutch at a red light the idle will drop down lower than normal for a second or two before returning to the normal idle speed of 850 rpm. what is going on?
Is this indicating a leaking fuel injector or some thing else?
Cheers all
 

Adam Vinnicombe

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Fair enough I will give it a sniff. All so she has one again become mega hard to start when warm like when you have stop to get some fuel and then try and re start her she just cranks over fast but just never bloody fires up
 

ttocs

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are your trims supposed to stay at 0? I would think that depending on weather/pressure that the would go +/- to keep the afr happy. Is your afr off?
 

Adam Vinnicombe

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I was told back in September that the old girl was running rich and since September the fuel trims have been going more and more negative at idle which I believe means she is getting more and more richer
 

Adam Vinnicombe

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14.25:1 on bank two and 14.5 on bank one just went out and checked for you mate. LTFT are at -6 and -4 and STFT are at -3 and -5. I am slowly starting to understand fuel trims now but not sure why mine are in the negatives? all I know is that they are having to pull by fuel to get the correct A/F ratio.
 

ttocs

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I am not a tuning expert by any means so if someone else knows more please correct me. The ability to change those trims to adjust to keep the afr happy is the advantage of efi over carb. Stoic for gas is 14.7:1 so its pretty close. If you really want to find out if its running rich, pull a plug and check it. It doesn't take long to pull it out and that will tell you what is really going on.
 

miscreant

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I know of a couple of methods off the top of my head.

There are noid lights that can test to make sure the injector isn't just holding open or closed.

Another method requires you to hook up a fuel pressure gauge and fire each injector individually and watch to see how much fuel pressure drops as you pulse each injector. An injector that causes more pressure to drop than its counterparts would be the one leaking.
 

Adam Vinnicombe

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Poo looks like I’ve found my issue. Front bank one O2 sensor must of been playing up and now it’s got stuck. The first and third photo are of revenging at idle and the second and fourth photo are of the engine at at 2,500 rpm and the fifth photo is of a code that set the service engine light on this morning not sure what it means as yet 7F1409CF-7FA6-4BA6-9A9A-D4D754E7FA98.jpegE1AEDAE5-CE72-47B8-A0E5-BA958A2CECC6.jpegED5981F5-60A4-4EDB-AD74-2BCF7557E0B0.jpeg2631084B-8B89-4790-9CE5-FA36BEFD9132.jpeg2D3436A6-1815-4401-86D1-C2A078C310B2.jpeg
 

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