Yesterday I went out on my favorite stretch of highway and got up to about 120 mph in fifth. I was monitoring EGT, and I got nervous and backed off at about 1500F. I was surprised it got that high, since I was at partial throttle and not boosting. At least I think I was not boosting - I never looked at the boost gauge, being fixated on the EGT. I was definitely at partial throttle though, so the ECU was in closed loop mode. This makes me wonder what temperature the ECU will allow when in closed loop operation.

For you guys that have checked, what EGT are you seeing at partial throttle, high speed?

On a side note, I did a compression check yesterday and my compression is unchanged from the last time I checked it, before I installed the SC. Plugs looked great, except the number two plug showed very slight indications of high temperature (tiny slivery deposits).

I have never gotten up that high...even going WOT up a 35% GRADE I get about 1450 max, not boosting mind you...milking it to stay down on temps and not boost uphill...

if I partial throttle to enter a freeway from 30mph to 80mph, it will hit my 780C limit. so that's 1430F. If I boost, from 65 to 100mph @ 10psi, it will go up to 720c....which is 1328F.

regarding the plugs.....where did you see the silver deposits? I thought high temperature usually mean white and melted insulators.

When boosting I only get as high as you do, about 1430-1450F. But then the afr is being controlled by the fmu. It's only at partial throttle and at high speed that I see it go higher.

The deposits are on the insulator and electrode.

I remembered that I had this discussed with you....did we every figure out why partial throttle will increase EGT faster than boosting? I initially thought it was the FMU that's not able to detect small amount of boost (1 - 2 psi) but after I installed the fuel pressure gauge...seems a little tap of the gas pedal will push the fuel pressure. @ 1 - 2psi, my fuel pressure is about 49psi. either the FMU reacts to it....or it is just factory FPR.

same here...when I partial throttle it to 80mph....it hits my EGT limit.

I think the answer is that we generally try to calibrate the fmu so that the afr is pretty rich in order to prevent detonation - much richer than the ECU tries to achieve when in closed loop (partial throttle)operation. So we see a higher EGT and EGT rise rate under partial throttle operation. That makes me wonder what the EGT will stabilise at when cruising at 135 mph or so, or if the Maxima ECU is even programmed for safe continuous operation at that speed.

Wow...I never get above 1250 - ever.

Maybe I can lean that AFC out a little safely, eh?

i see about 700 C at 130 ish, but I am very rich... 11:1 at that point

Thanks, Ian and Bags for the input. Keep in mind I'm talking about EGT at partial throttle, i.e. not boosting. Are you seeing 700C at WOT or partial throttle?

hmmm....super rich here, AFR under 10:1 after 3000 rpm. nice EGT though. mine's really hot I guess.

Stephen - where's your EGT probe located?

In the y-pipe, just below the front bank O2 sensor, i.e. a couple of inches below the front header.

EGT's at part throttle are going to be higher because the efficiency of the blower and the fact that above atmospheric pressures are inside the intake manifold giving more power without boosting enough for the fpr to come into the play with higher fuel pressure. As the throttle is applied boost will be sensed by the fpr and you will see a richer condition = lower egts. I was on a trip just last week to Destin with 4 passengers and 400lbs of luggage and my egts on a long uphill grade cruising at 85 with the a/c on would hit 790c. It would only get that high up a long constant uphill. I got a little nervous when I saw that but it mostly stayed around 720 cruising at 85. Stock injectors suck I wish we had an option for some side fed 320cc without having to get dramatic with 370cc and use an aftermarker regulator.

hmmm....but my fuel pressure gauge reads 49psi (39@idle) when I part-throttle the car.


going uphill kicks the EGT up to 800c..same here.

Did you dyno-tune and watch the EGTs with the probe there? The absolute value can vary drastically. Someone seeing 1400F with the EGT probe near the junction in the Y would probably notice more like 1500-1500+ in the location you're at. I'm up real close to rear header with my EGT and have my fields checking the front bank - not perfect but it'll do for now. I haven't dynotuned but would expect my temps to be higher than the standards set by people who have their probes further downstream when I do.

That's a good point, I've always just assumed without thinking about it that everybody puts their probe the same place I do.

I havent't dyno-tuned yet. My daughter enters UT in the fall, so there are all kinds of expenses that need to be taken care of first.

that much of differences? mine is tapped on the ypipe between the front and rear bank. I thought it should be around 50 - 70F diff. If the ypipe is wrapped with exhuast wrap, it should be even more accurate.