Very high EGTs but rich?
 

Hi All,

I had a search for similar issues but could not see anything looking like this. In short, my EGTs appear to climb very quickly, just a 5 second 2nd and 3rd gear pull will almost reach 900C (1650F) yet my AFRs at WOT (15-16psi) are mid 11s.

Pertinent setup details (Build thread soon!)
94 with built VVT.
GTX2860 Gen 1 (12psi spring with EBC) with FM2 manifold and 2.5" DP and 2.5" exhaust, no cat.
Rev Built MS3 Basic with inbuilt EGT module and Zeitronix EGT sensor, AEM WBO2 via CAN,
99 RON gasoline (probably similar to US spec 93 R+M/2?)

My only thoughts could be that
1. The spark map is sufficiently retarded that EGTs rise very quickly, but 5s from ~550C to 880C seems too quick?
2. The EGT reading isn't correct.

Does anyone have any comparable data to shed some light on this? Log attached for anyone wanting to go into detail, screenshot for people that don't.

Thanks,

Tim

Whoops, uploaded the wrong spark map.

Spark doesnt look retarded to me. Dunno. verify your timing, check yoour crank pickup isnt on wrong, the plate that is. Make certain that the ecu actually see TDC.

Dann

Thanks for the response. I checked the timing with a light this week so I don't think it is that. Could it be anything with the timing if the timing light is OK and I do not get any sync errors?

If its a VVT chassis and a plug and play ecu, no.

If the crank pulley has been disassembled then it may be on wrong and someone diddled with the trigger settings until it worked... if that happened maybe it could be.

But yeah on a stock VVT car with a plug in its not likely.

Dann

Whoops! I uploaded the wrong spark map by accident. I've updated it now. This one does look a bit retarded...

that's still not bad

Thanks. I'll try a 3rd gear log with +2 spark and another with baseline spark but +0.5 point fuel and another with -0.5 point fuel and see what I can gather from that.

One point just to add, the EGT probe is mounted in the turbine housing, shortly after the inlet flange.

How do you know 1650F is high? Are you detecting detonation? Do you have data from a Dyno that shows the EGT with respect to peak torque to help guide your decisions about EGT?

On 2-stroke engines I would exclusively use EGT to tune (tuning fuel) and you'd see EGTs increase as you reduced fuel. You'd know it was time to stop decreasing fuel when the EGT would start dropping. Then you'd back off a jet size or two. But this is a really dangerous way to tune (spark or fuel), you are pushing the settings until it fails (detonates) and then are backing off. Not a good plan.

I based 1650F as being high based on Emilio's engine building post giving that as the limit for OEM exhaust valves. I know modern turbocharged direct injection engines run higher pre-turbine temperatures, but they have suitable exhaust (and turbine) materials to deal with that.

I have not detected any detonation with this setup. I think it is too far retarded rather than advanced.

Interesting note about the 2-stroke engines, though I think the mechanisms for EGT related melty issues are very different.

BTDT- you can't look at the EGT as an indicator like the coolant/oil temps. I spent some time reading aeronautical info regarding EGTs and TITs and didn't bother installing an EGT on my current build. Here's a good summary on EGTs from an aeronautical view: http://www.alcorinc.com/PDF/EGT_Myth...n_Oct_2010.pdf

That link was an interesting read, however I'm not sure we are/were trying to avoid the same failure mode. The failure mode I am trying to avoid is purely melting the exhaust valves. (And of course avoiding melting the turbine, but the stock exhaust valves on this car are likely to melt first) so I think what I'm trying to do is valid. Were you trying to use EGTs to avoid engine "stress"?

The sensor is ~1" after the turbine flange so I don't think error caused by exhaust pulses will be as large as a cylinder by cylinder one, but even so, that error only adds to the temperature that my valves are seeing!

Yes, my original intent was to avoid engine stress. The read over and over that a 1600f TiT was normal in aeronautical applications and quit worrying about. My EGT probe was 1" before the turbine flange and my EGTs peaked at ~1600. That was roughly 5k miles of street use with the EGT and I've put over 2k on it this time around with the EGT.

I also read that too rich can also cause higher EGTs - along with other stuff like cam overlap. Basically anything that's going to create or allow combustion past the exhaust valves.

There are settings in megasquirt that will retard the actual timing away from the map timing if your IATs start to rise. Make sure that is turned off.

I can't recall which tab it is under

At one point in time, both 18 and Hustler suggested using this function. Are you suggesting never use it, or turn it off in helping OP diagnose his possible issue?

I think the concept was to use it above the AIT at which the car was dyno'd as this could be uncharted territory on the track.

I turned it on after Hustler's thread on it. It cooked the fuck out of two turbos before I figured out to turn it off.

Thanks, I don't think that is an issue though, the IATs look to be well controlled. I have taken some logs on the road, aiming for 2000-6500 full throttle 3rd gear pulls. I have 3 results to compare.
1. Baseline tune
2. Baseline tune but advanced 3 deg in the 180-220kPa cells
2. Baseline tune but added ~half a point of fuel.

I have made two plots. One comparing the baseline to the advanced spark run and one comparing it to the richened run. In both plots, the solid/bold lines are the baseline.

In the plot looking at 3 degree advanced spark, the rate of increase of EGT is definitely lower with the advanced spark, however it still pretty much hits 900C in a single 3rd gear pull and doesn't appear to have plateau'd.

In the plot looking at the effect of adding fuel, it looks like it may have helped with EGTs slightly, but it's not definitive like the advanced spark run.

One note though, there appears to be some kind of weird instability with my boost control despite having all boost control set to no duty above 3500rpm so the baseline run did get more boost at the than the others, perhaps this could be due to it being the first run and so no heat soak in the manifold? I don't know, it doesn't look right to me, but think it does not greatly affect my EGT conclusions here.


I'm at a bit of a loss with this really. I've checked the timing with a light and it's correct. I've also checked the spool as a way of verifying I don't have some big exhaust restriction and this looked pretty healthy, with the wastegate spring pressure of 12psi being reached at 2860rpm in the 1:1 gear (3.6 diff)

Thanks. I had wondered if that could happen. Help prevent detonation, but shoot up EGR. Will fix. The knowledge does grow over time.

-- My bad, misread something. Ignore this post.

Do you suggest just letting the fuel enrichment at high IATs solve that?

I wish the MS3 had a closed loop boost target that instead (or perhaps in addition to) adding fuel near the EGT limit, reduced the target boost. I really want to take this car to the Nurburgring, and the Kesselchen back straight really is an EGT torture test. ~40s WOT up a hill so steep that you'll reach terminal velocity.

Off topic, but I've just seen you're in Tampa. I'm heading to Orlando tomorrow for 2 weeks, is there any Miata related stuff happening round there in the next two weeks?

really? it's almost 10° retarded below stock timing at 100kPa, and the same in boost... thing is hitting single digit spark angle at 7psi?! i'd be running 20° there...