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Very high negative fuel trim at idle

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Very high negative fuel trim at idle

 
Old 03-12-2019, 05:55 PM
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Is this a stock ecu?

Aftermarket fuel pump?

Any one or several coil packs starting to go out? Spark plug gap?

obstruction in the cat or cat back?
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Old 03-12-2019, 06:15 PM
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ECU is stock. Never messed with the pump. Don't know for sure if it's stock but I assume it is. The car appeared completely stock when I purchased it. I replaced all the coil packs with Denso units when the engine was rebuilt. Berk highflow cat flow freely. New exhaust installed by Inline Pro. Q300
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Old 03-12-2019, 06:32 PM
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I thought my Berk was fine too, then I took it off a few weeks ago and found that the catalyst element had become loose to the point that it was able to rotate diagonally in the chamber relative to flow. I'm not saying it is the problem, but I will say to keep an eye out for it.

Does the car run better with the upstream o2 unplugged? As far as I know, the downstream is just used to indicate that the cat is working correctly.
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Old 03-12-2019, 06:49 PM
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The car starts cold insanely rich and that's well before the Primary O2 is doing anything. You can hear the exhaust gurgle and pop with a very strong smell of fuel. I haven't tried running with the O2 unplugged. I actually bought the Berk HFC trying to resolve this issue long before the engine was rebuilt. It's easy to take off so I'll have a look. If it's toast then I'll just gut it. Thanks for the ideas.
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Old 03-12-2019, 06:56 PM
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Rich running is normal on cold starts, its programmed into the stock ecu, however the air injection system if operating properly levels this out. Is your air injection working on cold starts? Once the car is warmed up, is it still just as rich?
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Old 03-12-2019, 07:30 PM
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I understand that cold start up normally runs rich. But this is actually ridiculously rich. The air injection system is working fine to my knowledge. Sounds just like before the rebuild. You can hear the pump on cold start. I wouldn't know if it were malfunctioning unless it threw a code which it never does. I have a scan tool in my car 24/7 now trying to diagnose this issue. -12 STFT to - 24 STFT at idle. I don't let it idle long enough to let the LTFT get up high enough to cause a CEL. I read some where that our Hondas only throw a code if the LTFT is at -/+ 20. Once I start moving everything seems to level out. I've made it a habit now to stab the gas a bit to get the fuel trims somewhere near normal then I pull away. It usually has less hesitation doing this. I'm worried that I may be washing the cylinders out and may ruin my freshly rebuilt engine. I don't drive it much anymore other than trying to fix the issue. I avoid stop lights and traffic at all costs. Trying a different set of injectors tomorrow. Crossing my fingers.... Please throw any more ideas at me now matter how far fetched they may seem. I'm at a loss.

Thought I'd add a pic of my new Fortune Auto 500 series coil-overs. 12/12k. I won't install them till this thing is running right.

Last edited by kikkomon; 03-12-2019 at 07:47 PM. Reason: Adding pictures
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Old 03-12-2019, 07:42 PM
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Originally Posted by kikkomon View Post
I understand that cold start up normally runs rich. But this is actually ridiculously rich. The air injection system is working fine to my knowledge. Sounds just like before the rebuild. You can hear the pump on cold start. I wouldn't know if it were malfunctioning unless it threw a code which it never does. I have a scan tool in my car 24/7 now trying to diagnose this issue. -12 STFT to - 24 STFT at idle. I don't let it idle long enough to let the LTFT get up high enough to cause a CEL. I read some where that our Hondas only throw a code if the LTFT is at -/+ 20. Once I start moving everything seems to level out. I've made it a habit now to stab the gas a bit to get the fuel trims somewhere near normal then I pull away. It usually has less hesitation doing this. I'm worried that I may be washing the cylinders out and may ruin my freshly rebuilt engine. I don't drive it much anymore other than trying to fix the issue. I avoid stop lights and traffic at all costs. Trying a different set of injectors tomorrow. Crossing my fingers.... Please throw any more ideas at me now matter how far fetched they may seem. I'm at a loss.
The fuel trims are keeping the car running at stoich so in reality the ecu is doing its job keeping the car from running rich. However that doesn't address why exactly the eu is pulling so much fuel to keep the afr on target at idle. My fuel trims are running about where yours are as well up to -19ish max LT/ST, but thats because im running a stage 1 supercharger with the fuel pressure jacked up intentionally. If you are worried about fuel wash, pull your plugs on cold start and see if they are wet. I doubt they are. But -24 is off the charts a bit and not ideal. The ECU is likely struggling a bit there to keep on stoich target. But even at 11-12afr you wont get fuel wash. You might be seeing around there but probably leaner.

Last edited by s2000Junky; 03-12-2019 at 07:47 PM.
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Old 03-12-2019, 08:20 PM
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Thanks Junky for that reassurance. I'm trying to post a video of my car at cold start although it wasn't completely cold on this start. I posted a picture on the previous post with all the soot on the ground behind my car. After pulling the O2's out today they were completely black. I cleaned the primary yesterday and stuck it back in. I'm sure the inside of my combustion chambers probably are looking just like the old sensors. Black and covered in soot. Along with my new spark plugs.
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Old 03-12-2019, 08:37 PM
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You Tube finally decided to publish my video. Here it is. Note the professional editing by yours truly.
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Old 03-13-2019, 04:19 AM
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What's that darth vader sucking sound that happens at 7, 16 and 38 seconds in? Is that also part of the issue? That sounds awful!

I'm chasing a very similar issue as you (read down a few posts where I resurrect the thread):

https://www.s2ki.com/forums/s2000-un...aning-1168151/

In terms of the popping sound I had my injectors cleaned and it resolved it, (that's actually a misfire), but I think one of my injectors is leaking causing a high negative fuel trim.

This weekend I will finally be able to test the Fuel pressure using the Honda Fuel Pressure gauge and adapter, so I will be able to determine if I have a Fuel Pump issue as well.

Afterwards you can see the laundry list of items I'm going to replace (Regulator, Dampner, Coil Packs, Injectors, Spark Plugs, and O2 sensor). If none of those fixes the issue then I have no clue what else is causing the fuel pressure issues.

I will report back...
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