Dumps too much fuel after warmup-closed loop issue? - Page 2 - RX8Club.com



Series I Trouble Shooting This is the place to learn more about or discuss any issues you're having with your RX-8

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Old 08-25-2017, 02:58 PM   #26
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If you are flooding your engine when it's warm, the excessive fuel will just wash away oil that makes a perfect seal between faces. Additionally, carbon buildup can cause compression loss. Seafoaming has improved compression with many, and even water decarbonizing has increased the pressure of RIWWP (forum admin) by 2 full bars and he has numbers to back that claim up.

Also, there is much more going on in the ECU of your car than you may think. Don't think that Short Term Fuel Trims can fix anything. They are just there to catch the extra temporary load, like the radiator fans, your A/C, braking, or turning your steering wheel on idle or low load in general. If your MAF is completely out of whack and reading erratically, the short term fuel trims won't be able to keep up and correct every single misreading and misfueling that the MAF causes. Before the o2 sensor can even read the damage that the erratic MAF has done, it can't correct it because it can't go back in time.

Long Term Fuel Trims take roughly, I don't know exactly, say the average minimum value of your Short Term Fuel Trims. If your fuel trims is always atleast at 3%, then LTFT will become 3% and take away those 3% from the Short Term Fuel Trim, and trim this number permanently.

It's just so you get a feeling that fuel trims rather point at a consistent mechanical problem, while fuel trims will never show whether your MAF has turned in a piece of useless garbage. Look on videos of ScannerDanner and he will never ever tell you that fuel trims can indicate a bad MAF as far as I can recall.


It would help if you could get the fuel injection timing data besides the MAF and RPM reading. But you can't do that with a simple OBD2 reader from eBay, that requires a decent device as far as I know. I just happen to be able to read them because of my LPG controller that's hooked up directly to the wires of my injectors.

Last edited by TomX8; 08-25-2017 at 03:00 PM.
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Old 08-25-2017, 08:21 PM   #27
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Please be careful about which advise you follow. Without calling them specifically out, there are people on here who can barely tie their own shoes let alone have any comprehension about automotive engines in general and the Renesis in particular or are in some cases posting information that is either misleading or even completely wrong. It's best to pay attention and differentiate between members with low post counts and/or a couple years or less experience here and those who have owned and dealt with this this particular vehicle extensively. Frankly, it seems like the least experienced if not outright clueless people are the first to rush in and demonstate what an "expert" they are.
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Old 08-26-2017, 09:56 AM   #28
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Please be careful about which advise you follow. Without calling them specifically out, there are people on here who can barely tie their own shoes let alone have any comprehension about automotive engines in general and the Renesis in particular or are in some cases posting information that is either misleading or even completely wrong. It's best to pay attention and differentiate between members with low post counts and/or a couple years or less experience here and those who have owned and dealt with this this particular vehicle extensively. Frankly, it seems like the least experienced if not outright clueless people are the first to rush in and demonstate what an "expert" they are.
I don't think that a high post count correlates to knowledge. Alot of the solutions are just copypasta without any diagnosis through video, obd2 data or other information like sensor readouts with a picometer. It's just a blind shooting range in most cases.

Last edited by TomX8; 08-26-2017 at 10:06 AM.
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Old 09-07-2017, 04:21 PM   #29
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OK. So, I finally got the car back from the 'mechanic'. That debacle is a whole other thread on its' own, but I won't get into that here.
Anyways, now that I've got the car back, I can give some more specific information.
The car starts right up. Runs as it should with a steady idle for the first couple of minutes. Then the idle starts hunting.
I took some readings on my odb2 app..
Once the idle started hunting, the afr(commanded) stayed in the 14.3 - 14.7 range, but the afr(measured) swung from a low of 11.x to a high of 17.x. The swing would happen every 2 seconds.
I let it idle this way for maybe 2 minutes or so. Coolant temp went up to 120 F. Cat temp went up to 833.9F.
I also tried to track the ltft and stft. The ltft stayed at 0%, the stft 1.6%--tho I have no idea what that percentage is.
Any idea what could cause the swing in afr every 2 seconds?
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Old 09-07-2017, 04:26 PM   #30
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A faulty Baro sensor can cause similar symptoms .... try unplugging it and see what happens
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Old 09-07-2017, 06:27 PM   #31
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Is it in neutral? Does it stop if it in gear with the clutch pushed in?
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Old 09-08-2017, 05:21 PM   #32
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Is it in neutral? Does it stop if it in gear with the clutch pushed in?
I took those readings with it in neutral. I'll try the above.
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Old 09-11-2017, 03:35 PM   #33
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Is it in neutral? Does it stop if it in gear with the clutch pushed in?
If I push the clutch in, the idle evens out immediately, then if I let it run for another minute or so with the clutch in, it starts hunting again.

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Old 09-11-2017, 03:38 PM   #34
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A faulty Baro sensor can cause similar symptoms .... try unplugging it and see what happens
I tried unplugging the Baro sensor. Same problem.
The vacuum line connected to it was cut. Going to investigate that.
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Old 09-11-2017, 03:43 PM   #35
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I tried unplugging the Baro sensor. Same problem.
The vacuum line connected to it was cut. Going to investigate that.
Scratch that-looks like the vac line is not supposed to plug into anything.
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Old 09-11-2017, 03:46 PM   #36
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Check the neutral safety switch on the transmission. It can cause a hunting idle like that

Also check the switch on the clutch pedal...
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Old 09-11-2017, 06:37 PM   #37
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Is it hunting or is it revving up and down? Not sure you understand the difference ... 50 rpm change is hunting, several hundred rpm is revving
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Old 09-11-2017, 06:41 PM   #38
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LOL.....you can call it what you want.....the neutral safety switch issue will make the RPM fluctuate rhythmically up and down around 800RPM..
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Old 09-11-2017, 06:53 PM   #39
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That typically results in a P0850 code though ...
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Old 09-11-2017, 07:40 PM   #40
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Is it hunting or is it revving up and down? Not sure you understand the difference ... 50 rpm change is hunting, several hundred rpm is revving
Sorry, didn't know there was a difference, but yes, it is revving (several hundred rpm). Going to check the clutch switch and neutral safety switch tomorrow.
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Old 09-11-2017, 08:05 PM   #41
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if it is indeed the neutral switch causing this , you should go back and kick your "mechanic" in the nuts !
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Old 09-11-2017, 08:17 PM   #42
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if it is indeed the neutral switch causing this , you should go back and kick your "mechanic" in the nuts !
You have no idea. I had to get it towed out of there because he had it for well over a month, couldn't fix it and was trying to get me to let him rebuild the engine.

Be glad you don't live in Boston. Mechanics around here are **totally clueless**.
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Old 09-12-2017, 06:20 PM   #43
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While checking out the neutral safety switch, I noticed that one of the wires in the harness was broken. I repaired it, then started the car -- no more rpm fluctuation. AFR's are solid at or around 14.x or so. There's a CEL for Network communication, but nothing other than that. Thanks you guys, for pointing me in the right direction!!

Now, it starts up the way it should, idles without fluctuating, but then the idle drops after several minutes and the car shuts off. It literally has 0 miles on the rebuild so I'm wondering if it just needs to be broken in for a bit or if the 'mechanic' screwed something up. He installed a new cat, but I'm wondering if he possibly damaged it when it was running rich.
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Old 09-13-2017, 06:07 AM   #44
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Old 09-18-2017, 06:29 AM   #45
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I spent the last several days researching the above and trying the different methods found to force the pcm to relearn how to idle with no success.

Some of what I tried ..
3500 rpm for 15s, then 5000 rpm for 15s.

Multiple drive cycles.

1000 thru 6000 rpm for 15sec's at 1000 rpm increments.

NVRAM reset in between each method. NVRAM and KAM reset after the first method.

Current symptoms--start it cold, even idle for about a minute, then starts fluctuating/bouncing. Eventually bounces too low, then dies.

Start it cold, drive it until warm. Will stall if foot is not on the gas.
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Old 09-18-2017, 08:18 AM   #46
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What are your coolant temps when it dies after letting it idle?
(Don't go by the gauge in the cluster, you need an OBD-II adapter and phone or computer to get a real reading.)

Fluctuating idle makes me wonder if you have a vacuum leak. You should probably have it smoke tested.
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Old 09-18-2017, 08:59 AM   #47
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What are your coolant temps when it dies after letting it idle?
(Don't go by the gauge in the cluster, you need an OBD-II adapter and phone or computer to get a real reading.)

Fluctuating idle makes me wonder if you have a vacuum leak. You should probably have it smoke tested.
Around 180 to 185F.
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Old 09-18-2017, 11:30 AM   #48
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Does the ecu take coolant temp as a factor in the idle learning procedure?
I ask because I believe normal coolant temps for the RX8 may be above 185 and I have an external fan controller that turns the fans on at 185.
If it's expecting a coolant temp of, for eg 195f, before it starts its' learning procedure, possibly that may be why my ecu doesn't seem to be going thru the procedure?
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Old 09-18-2017, 12:34 PM   #49
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I don't know about re-learn but the ECU uses coolant temp to decide how it deals with O2 sensor data (open vs closed loop).
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Old 09-19-2017, 01:24 PM   #50
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Anyone know if the ecu take coolant temp as a factor in the idle learning procedure?
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