High EGT mystery

[GTSBoy]

Gentlemen,

I present for you a mystery.  The short version is;

• The tank of Shell 98 that I used last week, pretty much right from the beginning of the tank, until I filled it back up on Wednesday, ran really high EGT and in a really odd way.  About 450km of this behaviour.
• I have EGT probe installed through a hole in the top of the turbine housing.  Has been there for years.  I'm very familiar with what sort of EGTs the car makes.  It will settle to <400°C at idle.  It will run at ~500-600°C just driving around.  It will run >800°C when stomping it hard or driving it fastish up a steep hill.  All normal.  When it has had a problem in the past (like a bad batch of fuel I had once that caused it to detonate), the temperatures would go spastically high under load, as you'd expect when it's detonating.
• Last week, it would run up to 900-1000°C at odd times.  Sitting at the lights it would continually climb until it got up there.  Driving around it would do it.  Stomp on it a bit and it would sometimes stay high, sometimes it would settle back to the ~600-700°C territory you might expect.  It would also sometimes run normal EGT and sometimes idle down to the <400°C I like to shut it down at.  Other times after pulling up to park it, the EGT would just continue to rise through 800°C.
• I must stress that I did not hear it ping at all.  It also felt very normal.  It drove the same, it idled at 600rpm, it was just as fast.  It wasn't as if it was running a blocked injector and missing some of its fuel, etc etc.
• As soon as I put 50+ litres of fresh fuel in it, the car went 100% back to normal.

So, theories on what would cause it to happen on a single tank of fuel?  What could possibly be wrong with the fuel that would make the car seem normal in all other respects but run such high and odd EGTs?

Back story on the fuel.  I pretty much only use Shell 98, in Adelaide.  Occasionally it gets BP98, but I can tell there is a tiny difference in how well it runs, so choose Shell.  I use a number of Shell stations and maybe 10-20% of the time I use the one at Golden Grove.  This tankful came from GG.  The replacement tankful came from the Shell on Churchill Rd.  I have occasionally been suspicious of the operation of the engine after fills at GG.  Some fluffiness at idle, maybe some pinging (in fact, I think the tank that caused it to ping like a meth addict last year came from there).  That sort of stuff.  But only vague suspicions, nothing quite as convincing as last week.  Has anyone else had a weird result from there, or any other servo in particular?

[KiwiRS4T]

Adulterated fuel...water seeping into the inground tank?

Or take a sample for testing...maybe you are being ripped off getting 91 fuel for 98 price.

[GTSBoy]

Yuh, well, my initial thought was low octane.  But it didn't ping at all.  I've seen what happens when it gets a dose of fuel that is clearly not high enough octane.  It pings like crazy on load.  This lot didn't.  And the car should fairly happily run 91 at idle and low load, but in this case would get really hot out the exhaust.  Makes sense, it does not.

[Dose Pipe Sutututu]

Was it a hot day? Does your car have a Nistune and or some form of idle management strategy that retards timing to keep the idle at its set point?

I put in a Nistune into a S13 last week and because his idle screw is cooked the idle was quite high however would settle after 10 seconds or so.

Went to check timing and guess what? Was idling at 4 degrees... I thought something was not right but had a feeling the ECU was pulling timing on idle and yep it was. Changed the TPS voltage threshold and boom, base timing back to 15 degree.

[GTSBoy]

Hi Johnny,

The answers to your questions are yes and yes.  However, it wasn't always hot weather.  Air temps on the road varied from well below 30 to nearly 40 last week.  The normal idle control works very well to keep the idle at 600 since I cleaned and properly adjusted the valve some (long) time ago.  In fact it was the previous occurrence of fuel related weirdness that prompted me to check the operation of the IAC when I found it idling at 5° back then.  I didn't get a chance to put the laptop onto the car while it was doing it because I was invariably too rushed to do it.  Kind of wish I had though, to be sure.

 

[Dose Pipe Sutututu]

Maybe bad batch, another reason I always tell people to run BP Ultimate and nothing else. I'm sure other tuners would say the same as well.

Wonder of the batch was overloaded with detergents and addictive which could be causing it

[GTSBoy]

Yuh, I wonder a lot of things about additives etc, too.  Here in Adelaide, my car runs better on Shell98, but I used to stick to BP/Mobil (same stuff here).

[Lithium]

A quite relevant detail which seems missing here unless I missed it - what were AFRS doing?  Tracking as normal? 

Did you ever stop and check the exhaust manifold by eye to see if it was glowing like could be expected under those conditions?

[GTSBoy]

I would have needed the laptop hooked up to see any AFR info.  I don't have a wideband and my cute little 0-1v meter hasn't been hooked up since I had to replace the O2 sensor.  Times like these I wish I wasn't so lazy!

I did stop and pop the bonnet once when I was driving at ~80km/h (which is not really a high load) with 800°C indicated but nothing was glowing, nor did the amount of heat near the exhaust feel outrageous.  I looked under there a couple of times when I pulled up at home with high temps at idle, with same non-result.  I can imagine hot gas inside the manifold/turbine/dump not having enough mass flow to heat the metal bits up enough to make them glow if it's only at idle/cruise loads, so this probably isn't really useful data anyway.  I would probably have needed to put it on the dyno - give it some moderate load and both see the manifold and watch the AFRs.

If this bullshit behaviour had continued onto the next tank of fuel I would have gone out of my way to do that.  Because then it would have been clear that the car had something odd going on.  But the instant change on the fresh tank made it dead clear that it was the fuel.

[Guilt-Toy]

try another egt sensor and gauge.

[GTSBoy]

38 minutes ago, Guilt-Toy said:

try another egt sensor and gauge.

I think you miss the point.  EGT was weird for 1 tank of fuel.  Then back to normal.

[niZmO_Man]

That's why I only use Mobil's finest 98RON petrol

The fact that 7/11 is a minute from my house is a bonus

[GTSBoy]

Yuh, me too, except substitute Shell for Mobil, because that's what works better here.  You have to keep in mind that different cities get the various branded fuels from different sources.  Many are the same, but they're not all.

I might have to do a number of tanks of BP or Mobil to see how it goes.  It's been some time since I switched to near 100% Shell.

[niZmO_Man]

It's been a while since I've done back to back testing. About 10 years ago, I did a long coast drive in my R31, home to a rented holiday house (end of year uni gathering) + home. 1 full tank of Caltex 91, 1 full tank of Shell. Got 50 km extra from Shell. The dirty30 also liked the Shell better, but ran best with Mobil 91/95 (back when Mobil stations were still around). Bonus was the Mobil was closest to my old house haha. I found that BP ran well but didn't do as well mileage wise, Caltex was consistently the "worst" but there wasn't much difference. Once Caltex dropped regular 91, I avoided it like a plague (E10 stalled my R31 during cold starts).

But yeah, 100% agree it varies between stations and varies between tanks (the underground tanks under the servos). A friend of mine full-tanked her old Cruze with 7 Eleven 95RON (different servo from my local), there was water in the petrol and it stalled her car. 7 Eleven paid for the mechanic's costs though (why I always get a receipt if I fill up elsewhere).

Although, these days, my boat/best gen Liberty doesn't care what it drinks, as long as it's 95RON or better.

[Chris32]

Sounds stupid but my car doesn’t like the fuel from shell at GG much at all

I’ve always put it down to fuel quality, particularly storage. It’s a old servo, with old tanks. It’s in a odd spot too, so I don’t think they have the fuel turnover of some others in the area

I’m finding the Mogas on golden grove road pretty good, the tanks there are only a few years old and there’s always cars buying 98 there

The other option is the liberty at sunnybrook with there premium 100 blend with a dash of ethanol

[GTSBoy]

It seems as though one confirmation of GG's oddness will do.  I shall blacklist them immediately (backdated to 2 weeks ago).

[GTSBoy]

On 1/2/2018 at 4:25 PM, Guilt-Toy said:

try another egt sensor and gauge.

 

On 1/2/2018 at 5:05 PM, GTSBoy said:

I think you miss the point.  EGT was weird for 1 tank of fuel.  Then back to normal.

 

On 1/5/2018 at 8:03 AM, GTSBoy said:

It seems as though one confirmation of GG's oddness will do.  I shall blacklist them immediately (backdated to 2 weeks ago).

 

OK, so a month later (but only 1.5 tanks of fuel later, because I've been overseas half the time).....and it appears as if it is not dodgy fuel.  I haven't put Shell in since then.  Just 2 fills with BP98.  First one was normal operation.  The most recent tank, the EGTs have been high again.  But, properly intermittently.

I finally got the shits up enough with it to put the laptop on it while it was playing up.  Timing was exactly as commanded by the map, so not retarded.  Fuelling looked fine (pulse widths were as expected, narrow band was flicking back and forth from 0-1v as normal). 

Got the shits up even more and took the IR pyrometer along for a drive.  Drove up a big hill and parked it with the EGT indicating 800°C idling.  Turbo flange was only 400°C. which is exactly the sort of temperature I'd expect it to be based on old normal operation where the EGT would sit on about 550°C after that drive.

Suspicion is now nearly 100% on a dodgy EGT probe, or more likely, gauge.

[Lithium]

That makes a lot of sense.  Cheers for updating

[burn4005]

yea gauge likely. it's difficult for a thermocouple to generate more voltage differential than the junction could produce.

either cold junction comp is stuffed or your gauge/wiring is generating an signal offset.

[GTSBoy]

I figured the CJ compensation is #1 suspect, but given that these things are little microprocessors with an analogue input and stepper motor driver etc etc, I figured that a whole lot of things could go wrong inside them.

These are the relatively cheap Taiwanese made (but decent brand) stepper motor style things that, in my case, had some of the illumination LEDs inside die after only a short period of use, forcing me to choose the other colour LEDS to use.  Lucky none of that colour have died.  Short version, they are built down to a price.  They have been surprisingly accurate for that though, up until this misbehaviour.

Edited February 7, 2018 by GTSBoy