robrecht

What are normal EGTs? What would be considered significantly too high?

Harlan

iTrader: (3)

Ok, let me get some things straight.

This is your third engine.
The problem started with similar symptoms on a previous engine.
Cat was previously replaced.
Coils/plugs have been replaced multiple times.
Fuel tank empty vs full has no difference.


If that about sums it up, then there must be a common thread, possibly the cause of all the problems, which is not the engine block, not the ignition, not the fuel pump, and not the cat.

I've seen the SSV stick closed and drop a lot of power top end. Never seen it stick open, but it's possible. I remember a forum member who messed around with AP settings and got the secondaries to begin fueling with the SSV closed and that caused some interesting effects. So I guess it all could come down to the SSV sticking, but I've never seen it do what you describe. Might be good to reach in there with a long handled tool and see if it strokes easily.

EGTs as measured from the front o2 sensor are around 1600-1650F in cruise at 65-70mph. They will drop below 1600 after the plugs self clean with a strong engine. If EGT is >1650 and stays there during cruise it's an indication of a problem. It could be from a clogged cat, or retarded timing, or a lean mix.

Oh.... One more thing to log. IAT. If your IAT sensor is bad it could cause all sorts of issues. I've never heard of one going bad on an 8, but there's always a first.

robrecht

All correct.

Why do you say its not the fuel pump?

Will do this. As soon as I have time to search and figure out how to do this. Edit: Hear's the cleaning procedure. Think I'll the the dealer do this: https://www.rx8club.com/australia-ne...closed-182041/

Oops. Maybe I can't measure EGTs and IAT. I thought I could but that might just be options of my OBD Torque smartphone program that do not actually correspond to the RX8 sensors. Thanks for your help.

Harlan

iTrader: (3)

IAt and EGT both work in torque. Its what I use.

logalinipoo

Harlan, what about a bad injector that gets sticky when its hot?

robrecht

It doesn't seem like I can measure EGT (2006 MT), but I can measure the temperature at the Cat Bank 1 Sensor 1. Cruising temperature is around 1650. On a modest hill climb in 3rd gear at 5k rpms it went up to 1788.

I measured fuel flow while the engine was cutting out under load at higher rpms. When the engine would cut out it was around .32 gal/min and would not go higher. When it was not cutting out, I occasionally saw it spike to around .45 gal/min. So, the fact that it would not go above .32 gal/min when it engine was cutting out, could that be because of fuel starvation?

Tomorrow I will try to measure AFT and voltage when the engine cuts out.

Harlan

iTrader: (3)

Yeah the Bank 1 sensor 1 is the wideband and it indicates EGT. The high end EGT is pretty darn high, like I would be worried high, but we don't yet know why. I have seen 1740ish at high rpm and load, but I don't think I've ever seen it that high.

Your fuel flow indication is probably from injector pulse width. That sounds like fuel starvation, but your injectors are responsible. Definitely log MAF and IAT. Something is wrong, probably feeding load calc and it appears to be making you go lean.

The other option is that your fuel flow calc is only using P1 injectors. Then it could be the right indication, but it would show fuel flow problems when your P2s/secondaries kick in. Lemme see what I can find out.

robrecht

Thanks!

robrecht

I also measured AFR (commanded) vs AFR (measured). When the engine cut out at higher rpms under load, the AFR (c) stayed about the same, around 9ish, but the AFR (m) would jump from around 9ish to 13ish, which seems to confirm the lean issue.

I did not see anything unusual with AIT or voltage.

Thanks again, everyone.

logalinipoo

13 is not too lean. Thats about target when tuning n/a. The 9 command is to give cooling to protect the cat. You should have more power at 12-13 than at 9 but not enough to notice only a few hp.

robrecht

But if 9 is commanded by the computer and 13 is what is being measured, isn't that a problem. Shouldn't commanded and measured be closer? I'm not trying to tune for a little more power but trying to diagnose why I'm getting no power at that point.

logalinipoo

I agree that it is out of spec, what I'm saying is 13afr is not your cause of power loss. You are getting plenty of fuel.

robrecht

Gotcha, thanks.

logalinipoo

Did you ever check your cat?

robrecht

Dealer has the car for the next week while I'm on vacation. If they can't figure it out, I will take over, and that's pretty scary!

Razz1

Your AFR chart that is posted shows the car running in the 10's.

That is too rich.

robrecht

Could that be an indication that the Cat is clogged, limiting the amount of air that can be pulled through the system?

logalinipoo

The car commands as low as 9 if looking at atr maps. And i don't think it would indicate anything with the cat. Fuel is added based on air in. If you slow down air out through a bad cat you'll slow down air in.

Wide band sensors don't read correct when in a pressurized environment like a turbo manifold or maybe behind a clogged cat.

robrecht

That's how I thought carburetors worked (yes, I'm that old). I didn't think fuel injection worked that way.

That's why I'm still thinking it could be a clogged cat. Provided a cat which tests OK and which looks fine from the front can in fact be clogged.

robrecht

Dealer says the problem is the fuel pump. It tests fine when just started but over time the presure drops to the 40s and sometimes as low as 10 psi.

Free beers to logalinipoo (no lean code) and Tonik (fuel pump) and to everyone else for their help!