martin1975chester

Hi, hopefully someone can help as I am running out of ideas. I have a 2005 rx8 231 normally aspirated, I bought the car 6 months ago and it's never run as it should. Now the prob I have is that the car runs really well and starts first time every time hot or cold but as soon as I hit about 4500rpm, the car bogs down and my afr jumps to about 19. I new the car needed work when I bought it and the plan was to fix it up and learn as I go which so far I have learnt a lot and tinkered lots (lots of cuts and scratches and swearing). since I bought it I have put new air filter, plugs and leads, coils, maf, New cat, full exhaust and new front and rear lambda sensors, New fuel pump. i have also checked the ssv which is clean and does not stick. also checked the vacuum to the ssv and it holds vacuum. I changed the ssv solenoid just to be on safe side to try to fix my issue which didn't make any difference. has anyone had a similar problem and have any ideas where I should look next? I know some might think I was mental for buying it if it needed work on it but I have done this with every car I have ever bought and have always found working on my cars to be the best way to learn about the car and I enjoy tinkering. any help would be gratefully appreciated. don't want to give in and take it to a specialist until I have no other options.

paimon.soror

iTrader: (15)

double check your plugs. Make sure you tighten them properly and they haven't backed out. As stupid as it sounds, it is a fairly common mistake.

martin1975chester

Hi, thanks for the quick response. I have had this issue since I bought the car and I changed the plugs as one of the possible fixes for this issue. I have already double checked the plugs and are still secure. thanks again

RIWWP

iTrader: (2)

One thing I don't see mentioned is an ESS cleaning and then ESS profile reset.

martin1975chester

haven't done ess clean yet, would this affect it only after engine passes 4500rpm? Will do it tomorrow though to rule it out. Will post how I get on. thanks

jasonrxeight

fuel pump?

RIWWP

iTrader: (2)

Specifically that RPM? Not necessarily. However if the profile is a bit off and as the RPMs increase it gets more and more out wack from where it should be, then at some point you will run into a situation where the fuel and spark are being cut because the ECU doesn't know what position the engine is in. This would show the huge lean values you see, just like you let off the gas.

It's not common that an ESS fouling or profile problem manifests this way, but it is entirely possible. Just an idea, it may not be the source of your problem. Just an easy thing to clean and reset and wasn't on your list yet.

RIWWP

iTrader: (2)

In general, it sounds like fuel is being cut. The possible ways that this can occur:
- Fuel pump pressure problems (possible, but unlikely, and would include other symptoms that you haven't mentioned yet)
- Fuel pump failure itself (highly unlikely given the symptoms and known history of failure methods for the fuel pump)
- ECU cutting the fuel deliberately (could be ESS not knowing when to inject or a commanded limp mode)
- ECU cutting the fuel mistakenly (a sensor fault that confuses the ECU, either MAF or front O2)
- ECU not knowing that it needs to add more fuel (a sensor fault, likely at the MAF, like it if is only injecting fuel for 20g/s of airflow, and the engine is clearly using more, HIGHLY DANGEROUS to the engine if this is happening)

If this cut is happening while parked in neutral and not under load, you can also hook up a timing light to see if you are also losing spark at the same time.

martin1975chester

Hi and thanks.for the responses so far. I've ruled out fuel pump as I have already replaced it. I will do the ess clean in the morning and see if that helps. when the car is in neutral I can rev it up past 4500,without any issue so it's only when driving under load. not a maf or o2 fault either as I have replaced them all. once again I really appreciate your replies in trying to help me so many thanks

martin1975chester

as for specifically bogging at 4500rpm Its exactly at that rpm that it happens. one thing I forgot to.mention is that if I let of the throttle when it bogs down so that I am only just touching the accelerator pedel, the bogging goes and then the measured afr matches commanded afr but It comes back as soon as I press the pedal any more than 5 or 10 mm down

RIWWP

iTrader: (2)

Ok, this is a load based problem them. Still clean and reset the ESS, but I doubt that's your problem.

I'd go back and look at the MAF. Ignore that you already replaced it. Go back to it again. Clean the connector, make sure the wiring is clean and intact, no kinks or splits or exposed wires. Make sure that the MAF is an OEM MAF (aftermarket ones do not work well at all for the RX-8).

If everything checks out, then get an OBD2 logging device and run a log of the behavior and post it up for us to look at. Log RPM, throttle position, MAF g/s, commanded AFR, measured AFR, STFT, LTFT, ignition timing, and fuel duty cycles.

martin1975chester

I have a Bluetooth obd and I'm running torque so I'll do a log tomorrow and post. thanks

Phil Bate

Also check the fuel pump high speed relay.

Phil