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Hi everyone, new member here and before I get flammed I did do a research on this topic and found several cases similar to mine but not exact and some of the cases are left without resolve so heres my issue.
I have 2005 RX8 and have 200 miles on a new rebuild. I used brand new rotor housings and OEM apex seals and side seals and all o-rings. I have built many rotary engines as I drag raced an RX2 for 10 years- actually ran world record at one time. I did a conservative Racing beat street port on the rebuild. Engine starts right up hot or cold and runs really good, no smoke. The issue I have is when I start the engine up it will idle like a bridgeport- between 500-1100rpms back and forth and after 10 seconds then it will idle smooth and normal at 800-900rpm. When I blip the throttle the rpms will go up like normal and then drop really low and then most of the time will go back up to normal idle but sometimes it will stall the engine- same when taking out of gear and coasting. Throttle response seems a little slower than normal too. Things that I have checked and done. No check engine light is on, during rebuild I replaced all the coils with the brand new OEM Mazda coils, spark plugs and wires, has high speed starter. Racing beat header and cat back muffler, still have OEM cat, Racing Beat ram air, and I have the REV 3 Racing beat flash tune for streetport. I have checked for vacuum leaks, no leaks found, compression front and rear is 110psi, I have done the 20foot brake stomp and reset ESS, ESS has been cleaned off, Airmass sensor has been cleaned, All the injectors are plugged into the correct harness connectors. I don't know if it just needs to be driven more to learn the fuel trims or I have an issue? Like I said it has 200 miles on it and doing the same thing, although it seems to not be stalling out as often but still the idle drops really low to almost stalling then goes back up. Higher rpms the engine runs like a raped ape. I know one thread I found a guy had a similar issue and he said it was a fuel injector but didn't explain which one or how he diagnosed it. I assume one of the primary injectors as the engine idles on those? What do you guys think?
My first guess would be to do a once over of the vac tubes, cuz free. One in particular that people miss/forget is the one that goes into the lower intake near the exhaust manifold. A smoke test would be easiest just to be sure.
EDIT: I see now that you already checked for vac leaks. Checking fuel trims and maf values may be helpful
Trims are in live data, I would think any scanner should be able to read them, including the smartphone based ones. LTFT and STFT are the values you're looking for. You could also check what your airflow rate (grams/sec) on a warm, stable idle is, if you can get it there. It should be 5.7g/sec. Under 5 would indicate unmetered air coming in.
Trims are in live data, I would think any scanner should be able to read them, including the smartphone based ones. LTFT and STFT are the values you're looking for. You could also check what your airflow rate (grams/sec) on a warm, stable idle is, if you can get it there. It should be 5.7g/sec. Under 5 would indicate unmetered air coming in.
Ok thanks, I will check that and what is a normal fuel trim at idle?
Nevermind, fuel time close to zero. Been 10+ years since I tuned anything and most of that was at WOT. I'll check when I get home today and let you know. thanks
I'm still at work but my son who is now driving the car said the check engine light came on and code p0171 for system too lean bank 1. So back to checking for vacuum leaks, air mass sensor and possible cat or injectors? I do have a cat delete pipe I can throw on
ok, here are the results-
Short term fuel trim is 24.2%
Long term fuel trim is 0%
Air flow from mass air flow is 5.63g/s
I checked all the vacuum lines and nothing found. I sprayed the intake all over with carb cleaner and no change in idle. What do you think I should check next? I'm starting to think I may have a bad fuel injector(s). Primary injectors are original that I know of, secondary injectors I got from a friends intake with very low mileage. Original engine had 135k miles before rebuild. Air mass sensor is also original that I know of.
Hmmm that's a little weird. You'd expect the car to have learned a high long term trim given the massive short term. Trims end at 25% so you're at the limit of error that the computer can compensate for. Air mass rate is correct for 800rpm though, so it's not an oversupply of air, it's undersupply of fuel. This only happens at idle? I would look into fuel pump pressure. The fuel pump has 2 speeds governed by a resistor module. Low speed at idle, high speed basically everywhere else. If the low speed is having difficulty maintaining pressure, this would be what you see. If the fuel pump is original, you probably want to refresh it as well. With minor modifications a series 2 pump is a bit of an upgrade.
Hmmm that's a little weird. You'd expect the car to have learned a high long term trim given the massive short term. Trims end at 25% so you're at the limit of error that the computer can compensate for. Air mass rate is correct for 800rpm though, so it's not an oversupply of air, it's undersupply of fuel. This only happens at idle? I would look into fuel pump pressure. The fuel pump has 2 speeds governed by a resistor module. Low speed at idle, high speed basically everywhere else. If the low speed is having difficulty maintaining pressure, this would be what you see. If the fuel pump is original, you probably want to refresh it as well. With minor modifications a series 2 pump is a bit of an upgrade.
The engine runs fine and has good power after idle, it's just the idle that acts up. If you blip the throttle at idle when it comes down it will drop down to 500rpms and when it does that the short term fuel trim goes to 0%, then the rpm goes back up from the 500 to 800-900rpm and as soon as this happens the STFT goes back to 18-20%. You don't think a bad primary fuel injector could cause this? If one is clogged it would make the idle mixture lean? If I'm not mistaken I took my car into the dealership many years ago for the fuel tank recall. I think they replaced the fuel pump but I don't remember..
It could be an injector but my first guess is fuel pressure because an injector doesn't clog on and off, and it would still be clogged at higher rpm. And it would only affect one injector, so one rotor at a time which would give you misfires and other symptoms. Fuel pressure at low pump speed would affect all injectors at the same time and look more like this, IMO. How does the STFT look before the rpm drops? Does it ramp down slowly or drop back to 0 instantly?
The recall, if done correctly, replaces the bump housing but not the pump. Plus the issue might be the resistor pack.
It could be an injector but my first guess is fuel pressure because an injector doesn't clog on and off, and it would still be clogged at higher rpm. And it would only affect one injector, so one rotor at a time which would give you misfires and other symptoms. Fuel pressure at low pump speed would affect all injectors at the same time and look more like this, IMO. How does the STFT look before the rpm drops? Does it ramp down slowly or drop back to 0 instantly?
The recall, if done correctly, replaces the bump housing but not the pump. Plus the issue might be the resistor pack.
The STFT stays pretty constant around 18-22% and as soon as the rpm drops below 800 down to 500 it instantly goes to zero, then the ECU notices the rpm is too low, adds fuel to bring it back to 800rpm and then the STFT goes back to 18-22%, this all happens in a second.
Where is this fuel pump resistor pack?
The STFT stays pretty constant around 18-22% and as soon as the rpm drops below 800 down to 500 it instantly goes to zero, then the ECU notices the rpm is too low, adds fuel to bring it back to 800rpm and then the STFT goes back to 18-22%, this all happens in a second.
Where is this fuel pump resistor pack?
https://www.rx8club.com/series-i-tec...equest-220470/
Diagram in this post.
I'm not sure how to test the pack itself, but what I would do is measure fuel pressure at idle, and see if it jumps around, to confirm that's the direction to dig.
https://www.rx8club.com/series-i-tec...equest-220470/
Diagram in this post.
I'm not sure how to test the pack itself, but what I would do is measure fuel pressure at idle, and see if it jumps around, to confirm that's the direction to dig.
When at idle isnt the engine only running on the two primary fuel injectors? At what rpm/input does the secondary injectors kick in?
Also, there is no fuel service ports, how are you checking fuel pressure while engine running?
You can put a tee fitting in line ahead of the injectors with a gauge. Some universal fuel pressure kits have the right fitting. I wouldn't drive with it, but for idle with the hood open, sure.
Little update- Since I did so many things at once during the rebuild I went back and checked a few things. Did the smoke test on the intake for leaks- no leaks. When I did the rebuild I also took the Racing beat K&N filter out and cleaned and lightly re oiled it so I thought to myself maybe some oil got on the air mass sensor I just cleaned so I re cleaned the airmass sensor again. I did notice the screen that is before the airmass sensor was starting to come apart at one edge, but very little. I don't know if this would have an effect? I put everything back together and re learned ECU and let it idle- still have the idle issue. I then removed my cat and checked it- cat is fine but my son wanted the test pipe I had so we installed it and then I also added some seafoam in the fuel tank to see If it would clean out any stuck injectors I may have. Didn't put many miles on it as its 105degrees the last few days here. I also ordered the aeromotive fuel pressure adaptor so I'm going to installl that with a gauge so I can monitor the fuel pressures, at least at idle. I'm also planning on replacing the fuel pump as I haven't replaced it and I have no history of the previous owner did. I bought the car over 10 years ago and it had 60k miles and I put another 76k miles on it before the engine let go. So its probably a good idea to replace the fuel pump for sure. The injectors are probably not the best either but after idle it seems to run really good. Also, it idles much better with the A/C on most likely due to the higher idle. Still idles like a bridgeport on start up- so weird. I also found the SSV that I painstakenly cleaned spotless is now ticking at idle, I can press lightly on the lever arm and it goes away. That shouldn't effect idle should it?
Last edited by 25BAHIAMAN; 09-08-2024 at 10:15 PM.
. I did notice the screen that is before the airmass sensor was starting to come apart at one edge, but very little. I don't know if this would have an effect?
A lot ...if it's moving at all.
Also ... was that 24% trim negative or positive? ..... If it's negative and air flow is normal (around 5- 5.5g/s)your injectors are wired wrong. If it's positive, could be erratic readings from maf due to above screen issue.
The ecu wont tend to build a long term trim if it sees things are too far away from normal.
Also ... was that 24% trim negative or positive? ..... If it's negative and air flow is normal (around 5- 5.5g/s)your injectors are wired wrong. If it's positive, could be erratic readings from maf due to above screen issue.
The ecu wont tend to build a long term trim if it sees things are too far away from normal.
STFT is+18-22%, long is zero, Air mass 5.63g/s. I double checked fuel injector wiring and its correct, also verified both primary fuel injectors are clicking at idle.
Can I just remove the screen?
Last edited by 25BAHIAMAN; 09-09-2024 at 09:47 AM.
Removing the screen risks unstable MAF readings which will give you one more problem to chase. I suppose you could remove it and put back if it's worse. Picture of the damage? There should be 2 screens, maybe put the healthier one closer to the MAF. IMO a little tear isn't a big deal, not enough for +20% perceived airflow. But pictures will tell.
Removing the screen risks unstable MAF readings which will give you one more problem to chase. I suppose you could remove it and put back if it's worse. Picture of the damage? There should be 2 screens, maybe put the healthier one closer to the MAF. IMO a little tear isn't a big deal, not enough for +20% perceived airflow. But pictures will tell.
I have the Racing beat Revi intake combo system. It only uses one screen. Never had any problems for over 10 years with this system. I will take pics of the screen tonight. thanks
I think I saved all my old parts. The factory intake came with two screens. I will take the other good screen and swap it with the bad one.
Last edited by 25BAHIAMAN; 09-09-2024 at 11:16 AM.
If mass flow is normal and not jumping around and AFR is normal (14.7ish at idle) but STFT is high and positive, I'd be suspecting a blocked injector. One of the reds. A good check might be to let it idle (fast idle if you have to) for several mins then pull the plugs.
Also: does it act differently when the clutch is depressed or put into gear?
Here is pic of mesh screen. I found my stock intake and removed the other mint condition screen and installed it- no change still doing same thing. Im going to upload two vids too
09-05-2024, 09:53 AM
