rickeo

iTrader: (1)

Alright everyone, i've been holding off on making this thread as I've wanted to spend as much time trying to come up with what would be causing this on my own, and waiting for all different weather conditions to see how the car reacts.

• '04 GT 6spd
• ~70,000 miles
• Always WAWA 93 fuel
• BHR Ignition
• BHR Midpipe
• Cobb AP w/ MM Tune
• AEM CAI
• 1000 miles on current spark plugs
• Sufficient oil level
• Pre-mix 8oz of Idemitsu with every fill up
• REmedy water pump & thermostat
• Clean MAF sensor
• No CEL's

About a month ago, I began noticing a severe loss of power when:

1. Water temp over 190f
2. Ambient temp over 85f
3. Relatively high humidity

This is with the AC OFF. This got so bad that at stop lights that are on a hill, its almost hard to get moving due to such a loss of power. Oddly, if I go WOT, I feel what feels like a valve opening and suddenly my power is back somewhere between 3500 and 5500RPM, however it doesn't seem consistent and its been hard to track down.

Things that I haven't done just due to lack of time:

• Compression test...
• Pull spark plugs

I'm at a loss guys. The car turns into such pain in the *** when its hot at humid recently.. It can't get out of its own way.

Given the fact that when I go WOT, I can feel the power return abruptly somewhere between 3500 and 5500RPM, I want to think there is an intake valve issue going on but troubleshooting that without pulling the LIM and UIM is a lot of work without being sure the issue lies there.

I almost wish I had a CEL to at least point me in the right direction!

Help?

fallafalla

Just a shot in the dark but the SSV? opens up in that range so perhaps its sticking open, easy to check at the very least and can be done with the UIM still in place.

tpb7463

iTrader: (1)

MSP-16 status?

If you put fresh fuel (cold, straight from the pump) and wait 5-10 minutes does that get any better?
(Possible fuel pump)

rickeo

iTrader: (1)

Couple more facts regarding the issue.

• Yes, the car had the MSP-16 flash years ago. Has a MM Tune on it now.
• Happens regardless of fuel temperature. Fresh tank or 1/3 of a tank that's been sitting.
• The SSV moves properly when pushed on with a socket extension and cycles once like it should when turning off the engine
• At WOT, power seems to return abruptly at 4500RPM give or take.

Also, I have a data log from my Cobb AP that I took today. Would that help anyone? I can't for the life of me find the post I saw ages ago show exactly what valve opens at what RPM.

I was getting so pissed off today. Car barely had enough power to take off from a stoplight on a slight incline.. I thought it would stall. Ambient was 92f and water temp was 191f.

9krpmrx8

iTrader: (46)

Well first things first. How many miles are on the plugs and BHR kit?

rickeo

iTrader: (1)

Plugs are about 1000 miles as stated in the OP. The BHR kit has about 4000 miles.

9krpmrx8

iTrader: (46)

Oh missed that, sorry. So have you checked to make sure your plug wires are snapped on correctly? Also check to make sure you BHR ground wire is secure. If all that is in order then you need to vacuum test the engine. Do it while hot, hook it up to the VFAD nipple behind the throttle body.

rickeo

iTrader: (1)

Hmm, ok, they sell the genuine Mityvac at the local Harborfreight. I'll have to pick one up.. I've been eyeing it ever since I saw the valve testing videos i've seen on here (can't remember the user who made them but i'm sure you know). Thanks man, at least i have a direction to go in.

You obviously deal with high ambient temps all the time living in Texas. It's crazy that this doesn't happen at all in cool temperatures. Without a compression test I can't be certain my motor is on its way out but hell, hot starts are still not a problem at all!

Emery_

iTrader: (8)

I would say check if your wires are properly secured to your plugs and coils like 9k said, clean your ess sensor, and try reinstalling your MM tune that way your fuel trims are reset also maybe try the stock tune .

rickeo

iTrader: (1)

Ok, its been a few weeks and honestly, just coming on this forum gets me depressed recently because of the state of my car which is why I've been avoiding updating this thread...

Recap on the issue:

• Significant power loss at low RPM when hot/humid out
• Car can barely get moving, especially on a hill at a stop light
• Only seems to start when ambient temp is over 85f and water temp is over 185f.
• ~75f degree weather and low humidity, car screams and performs great
• At WOT @ ~4500RPM, there is a noticeable surge in power
• No CEL's
• Definite "rough" exhaust note change when this power loss is occuring

What i've done so far:

• Checked plugs, wires and BHR coils. All appear fine.
• Cleaned ESS / Reset NVRAM
• Reloaded the current MM tune.
• Cleaned MAF (wasn't dirty).

What I haven't done:

• Compression test (NO hot start issues but who knows...)
• Replaced fuel pump /cleaned sock
• Had you guys look over some datalogging of a WOT run from idle through redline in second gear.
• Comprehensive test of all intake valves... kinda hard with everything in the car.
• Loaded factory tune.

What I think the issue could be:

• Dirty fuel sock or failing pump? This is first on my list of things to be replaced. Will the recorded fuel trims in the datalog help us figure that out?
• Possible bad front 02 sensor? I dont' have any CEL's so this is doubtful.

I've attached a datalog from my AP of a WOT run up to redline in second gear. This was from a stoplight and it was like the car wasn't going to get moving in first... its horrible. Would a datalog of the idle when this is occurring help at all?

Keep in mind the ambient temps were about 93f with about 85% humidity. Its was atrocious outside. Windows down and A/C off.

Help?

9krpmrx8

iTrader: (46)

The log looks ok. But you really need to test things properly if you want to figure it out. Post up an idle log with the engine warm, check engine vacuum with the engine warm, and test your fuel pressure to rule out the pump using the FSM procedure. Then we can go from there.

Don't assume anything, plenty of what seem to be obvious low compression symptoms turn out to be something stupid simple. I have seen a lot of people assume their engines are toast only to find a simple vacuum leak, faulty starter, etc. I had hot start issues with a brand new S1 Denso starter and assumed my engine was toast after a poor compression test (but with low cranking RPM) and then I installed a brand new S2 starter (expensive but worth every penny) to get my cranking RPM to normal and my hot start issues disappeared and my next compression test showed great numbers.

tpb7463

iTrader: (1)

I wouldn't completely rule out the front O2 sensor--you don't necessarily need a CEL to have a failing one. The caveat for your particular case is that your symptoms only arise in extreme conditions.

(Beating a dead horse) Check stupid things first, if you're really at a loss then try the front O2 sensor. The car is old enough that, in my opinion, could warrant a replacement as preventative maintenance.

9krpmrx8

iTrader: (46)

Diagnosis by parts replacement is stupid. His AFR's are fine so his front O2 is working fine.

EviLStewie

9k would you review the log file again paying close attention to the RPM's
There is quite a few spots where they go done and instead of continuing to go up.

Enough so that it's something not right to me, imo
It starts at line 167 then again at 185, 188, 194, 199 and 213

So maybe ignition?

Doesn't the Calculated load seem a bit low as well? Unless OP took log going over a cliff lol

Other thoughts
Dirty ESS with 20 brake stomp
Maf?
ECT
Fuel pump
?????????

9krpmrx8

iTrader: (46)

You need more experience viewing RX-8 datalogs. Those lines of data are but brief snapshots in the sampling. What you see as a stall or drop in the RPMS is snapshot of data within hundredths of a second.

EviLStewie

Hmmmm gotcha
I was more considering how many times it was occurring but ok.

rickeo

iTrader: (1)

Thanks all, I just need to keep at it instead of assuming the worst and sulking lol. Let me get some of these things done and i'll get back to you. Driving back from the company picnic today in 103f ambient temps was killer... I had to stop on a hill for a left turn... didn't think i was going to be able to get moving again!

C-PHLAT

I'm having a similar issue.. I have stutters in the power btw 3k-5ishk particularly in 4th-6th gear. 04 6sp 130k New motor has 2k, plugs, coils, wires fairly new, bhr midpipe, gladiator rad, exedy clutch w 2k... was going to replace fuel pump but haven't done that yet..was about to order one then saw this thread.. thoughts?

rickeo

iTrader: (1)

You've got the same info I have. I haven't gotten a chance to do any additional testing the 9K suggested but I'll update this thread once I have. I DO know that temps dropped in my area last night to 73F and once my coolant temps dropped below 180F the car ran great. So freaking weird.

9krpmrx8

iTrader: (46)

You should trouble shoot properly, but keep in mind that your Coolant Temp Sensor is a very important sensor to the ECU and it is only $20.00 or so at Autozone.

rickeo

iTrader: (1)

Are you suggesting that it could be faulty? Never thought of that but I don't see how that could have a direct impact on the driveability issues i'm having.

Unless you're just pointing out its importance, which of course I understand.

9krpmrx8

iTrader: (46)

Just pointing out it's importance to the ECU in determining fuel delivery, etc.

rickeo

iTrader: (1)

Well then, its on my list of things to replace because.. well why the hell not. Thanks.

I sat in my car last night when I got home thinking it would be a time when i could pull an idle data log but of course it was cool out and the car was running great... figures.

C-PHLAT

Well I just ordered an Airtex pump cartridge assembly. if that don't solve my problem i'll go to temp sensor next. I'm leaning towards my problem being the pump or sock. It's the original and has 132k, even if that's not the problem, it's something I'll have peace of mind knowing it's new.

rickeo

iTrader: (1)

Ok so I grabbed a ~15 second datalog after I got home from work and parked. I let the car settle at idle for about a minute before taking this log.

Ambient temps were at only 86f but with 81% humidity. Hopefully I'll get a proper vacuum test and fuel pressure test done this weekend.

Honestly I feel like if someone could just drive the car and feel and hear whats happening it would make a lot more sense. I feel like i'm just not accurately describing this as its really something that I feel and hear, not just "power loss".

You can feel the power come and go abruptly and the exhaust note clearly changes. Ok sorry, mini rant over.