Single injector injecting too much fuel
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Joined: Mon Jun 16, 2014 9:00 am

Single injector injecting too much fuel

Post by event » Mon Jun 16, 2014 9:16 am

I have a DIYPNP w/ the P&H board running my 1.6L Miata. an Issue developed where my 4th cylinder started running VERY rich and eventually flooded the cylinder, with raw fuel entering the exhaust. I immediately figured that the transistor heat sink must be grounding to the case like with the issue I had twice before, but I took the ECU out and checked. They were not shorted to the case. However, injectors 1 & 3's resistances were on the MegaOhm scale while injectors 2 & 4 were on the kiloOhm scale, if I remember correctly. Only cylinder 4 was flooding. I put the megasquirt into batch injection & swapped 2 & 4 which caused cylinder 2 to then flood, so it's not an injector hardware issue. It must lay in the drivers.

It doesn't seem like the injector is being held at 100% because when the car is hot it will run ok. Idle is a bit rough and I get a bit of a misfire just above idle. I am going to hook up to an oscilloscope once I get a hold of one so hopefully I can see what is happening, but are there any common failures on the components during normal operation? The issue occurred suddenly, I hadn't touched the ECU or tuning in weeks before it started happening at AutoX.

Also, while I'm in there, is there a more robust solution to mounting the TIP122's to the case? I was thinking of picking up some Nylon nuts and bolts but I worry that they might loosen over time with heat & vibration. I'm going to try to jiggle the TIP122 while checking resistances to see if maybe it's intermittently touching the case.

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Joined: Sat Oct 03, 2009 12:24 pm
Location: Quebec, Canada

Re: Single injector injecting too much fuel

Post by jbelanger » Mon Jun 16, 2014 11:41 pm

Make sure there isn't any metal swarf left from drilling the mounting holes. That can short the tab to the case and it can also be intermittent. Also make sure that the shoulder washer is correctly seated and straight. One other thing that has been mentioned is that some heat sink compound are conductive but that would not really fit your symptoms with a single driver.

Finally, do not use nylon bolts and nuts. They will stretch and that will lead to heat build up and likely heat-related failures.


P.S. Please note that I'm still in the moving process so my replies may be delayed.

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