Scope for a leaky injector?

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Scope for a leaky injector?

Postby blakestreet » Fri Aug 12, 2016 3:08 am

Hey everyone, I am suspecting 1 or more leaking fuel injectors on a 1997 Mercury villager 3.0 (this is a Nissan Quest platform). This has a consistent miss at idle and off idle, with total fuel trims at -20 to -25% and has failed emissions for HC and CO. It seems to clear out under heavy acceleration and fuel trims get closer to 0%. Its too old and stupid to set a specific cylinder misfire code. My lamda PID is 83, so this thing is really rich. Ignition components are testing normal and relative compression looks good. Using the Firstlook sensor and the ACE misfire detective software, #2 and #6 are showing misfires. I wanted to swap the #6 and #4 injector and retest, but someone already has stripped out the screws holding the injectors into the rail, so I will need to pull the upper intake manifold off and fuel rail and extract to swap injectors. I would rather not do that. I did an injector fuel pressure drop test and #6 drops from 42psi to 25psi. #4 drops to 26. #2 drops to 27. Tough to call an injector off of a 1-2 psi difference. Passes resistance test 13 ohms, spec is 10-14. Can a leaky injector be spotted on scope voltage or current? If so does anyone have an example waveform? Any help would be awesome.

Blake
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Re: Scope for a leaky injector?

Postby victor2k » Fri Aug 12, 2016 8:24 pm

Hello,
If you have HC and CO issue on your car then try to retest with some injectors unplugged(2 and 6 -must decrease content of HC and CO ).
With clamp meter I see only the lazy injectors(need higher curent for open needle than other) but leaking injectors ...indirect injection will not use corection for every injector.
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Re: Scope for a leaky injector?

Postby blakestreet » Sat Aug 13, 2016 3:26 am

I had some more time with this Villager this morning and was able to do a current ramp of all the injectors from the fuse box, with a voltage synch to use the firing order. I found that all the injectors had bad current waveforms especially 2 and 5. I recommended, with confidence, to replace all 6 injectors in order to pass Colorado emissions. 5 was almost completely shorting which makes me question the ACE misfire detective software a bit. Although, on this vehicle the firing order is 123456, which would indicate that 5 and 6 are companion cylinders, for the money that I spent on the tool I am disappointed that it led me to focus on 6. Just like anything else, you have to get familiar with the tool, which I admit, I haven't. I need to practice on my car and create failures and see what the Firstlook and ACE waveforms say.
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