Significantly higher EGT (50-60C) in one cylinder

Taken my Toyota MR2 back out after a few years of storage, after sorting out many issues (including a rusted fuel tank) everything appears to be in working order.

However, when running on the dyno, I noted EGT for cylinder 3 was running 50-60 degrees C hotter than the others under WOT pulls on the dyno (I have individual EGT probe installed roughly 1 inch from the cylinder head in the exhaust header). Giving it an additional 5%+ fuel did not seem to help either. Cylinder 3 does appear to be more knock prone and I had to retard timing 2-3 degrees specifically for Cylinder 3 around the 6500 rpm area for it to not knock. Even at steady state, EGT for cylinder 3 will be much higher when under load for various RPM.

This is a Gen 3 3S-GTE engine which is known to have heat issues with cylinder 3 but 50C is way too much. I am hitting 920C at the end of a dyno pull on cyl 3! I am also using a side feed intake manifold instead of the stock centre feed.

Since the fuel tank was full of rust when the car was first taken out of storage, I initially suspected the injectors but I have tried swapping them between cylinder 3 and 4 but nothing changed (unless maybe I have messed up and mixed up the injectors?). I also tried swapping the EGT sensors around thinking it might be a faulty sensor but it was all the same.

I am taking the car onto the track next month and the EGT issue have me very concerned. What could possibly be the cause of the significantly higher EGT in one cylinder? Thank you!

EDIT:

Compression test was all good. I do have some miss-fire issues above 1.3bar of boost but it is still happening when there was no miss-fire and at much lower boost levels. The spark plug themselves looks good and I have swapped in a few new sets already (due to the miss-firing issue).

First thought was the injector was slightly compromised on flow/blocked, but as you've both swapped around the injectors and adjusted fuel trim, to no improvement, it may be down to the manifold(s) design - some exhaust designs, in particular, can cause variations due to gas flow and "heat sink" affects.

Have you tried moving the thermo-couples around, just in case there's a issue there?

I'll be interested in others' thoughts?

By moving the thermo-couples around do you mean swapping them between cylinders? If yes, I've already tried and ruled out sensor giving wrong readings.

Since the olive is stuck pretty tight on the probe, I couldn't really loosen it and shift the probe higher or lower without damaging the olive and I do not have any spares. Attaching a photo to show where the probes are located on the exhaust manifold to see whether that would shed any light. Have also included a plot of the exhaust temperatures too.

It's well documented and you've mentioned that cylinder 3 is troublesome, this is due to the OE manifold. The only true cure is to ditch it and install a good aftermarket one.

As a workaround you've already started down the right road, the retarded timing to remove knock will likely, unfortunately, generate heat so I'd just add fuel until the cylinder temperature came under control, especially for a track session where everything will be getting hotter.

Out of interest, what fuel are you running?

I always thought the cylinder 3 issue was due to the stock intake manifold which favoured additional air into the middle cylinders causing it to run lean. With a side feed manifold it should've solved the issue or at least it would be the front/rear cylinders having not enough/too much air rather than the middle.

But I agree, exhaust manifold design might have a great impact too. Especially when it is usually just cylinder 3 having issues and not also cylinder 2.

However a very reputable MR2 builder/tuner also did a test with individual EGT similar to my setup here:

www.koracing.net/mr2modproject/mod/4egtmod/4egtmod.htm

Results showed very consistent EGT temperatures between the cylinders with cylinder 2 and 3 being just marginally hotter by maybe 20-30F. I would have ignored by EGT issues and attributed to the exhaust manifold design if not for his findings.

Update:

Did a few more runs on the dyno today. Added as much as 9% to cylinder 3, no significant change in EGT. After a few back to back runs, EGT reached as high as 939C for cylinder 3. Decided to richen the overall AFR target by ~3% (from 0.76/0.75 lambda to 0.73/0.72) and EGT dropped for all cylinders including cylinder 3 by 10-20C. Cyl 3 is still reading much higher than the others though.

From the picture of it, it looks like the part ofthe manifold that will run hottest, because of the way the exhaust gases look like they're directed, would be the region around #3.

If it was a lean/fuelling issue, at the very least adding fuel should have dropped it compared to the others, that the result was negligible would suggest that isn't the issue.

I would strongly suspect it was just down to the exhaust manifold - what was the other chap using, that you used for the comparison? - and/or a variation in probe depth, as the placement can have a significant affect on the reading, as the cross-sectional gas temperatures will vary.