Lean Behaviour, Possible Heat Soak?

[edizio]

Hey,

I'm finding that after an hour or so of driving on a motorway at a steady 100km/h, the fuel ratios start leaning out from where I set them when at normal operating temperature after driving for 10miles (14.7), all the way up to 16+. This is the same behaviour that happens if I leave the car and get back in it again after it being switched on which leads me to believe it has something to do with the crappy air temperature sensor that is on the standard car. I am running twin map sensors but with the standard nissan temp sensor which I think I'm going to be changing. I'll write this up like I did with my AAC post.

Is this behaviour happening because of heat soak or is it possible that there is something else happening? i.e. fuel temperature rising? I don't have a fuel temp sensor and it's not showing an option for specifying values in datalogit. I am thinking it is heat soak because I have a single turbo conversion with no turbo blanket.. yet, in combination with the crappy sensor.

Any thoughts?

[Scott Black]

What ecu are you using, what engine, does it have intake temp.correction, is the injector pulsewidth changing significantly, have you checked to ensure its not an issue with the afr gauge. Have you.checked the signal from the temp sensor to ensure its correct and giving the ecu the correct signal

Edited January 26, 2015 by Scott Black

[edizio]

Hi Scott,

• It is a 2.6 rb26 with a fairly large turbo!
• The ECU is an apexi powerFC, I use datalogit to manage this (I tune it myself and turn off O2 feedback as I can get fairly decent values myself)
• There is temp correction but the temp reading stays around the same which is weird; I think it's reading hotter than it actually is though.
• The AFR gauge aligns with the value that is being read from the laptop
• The air temp sensor is reading the correct voltages within the standard parameters
• The injectors are 1000cc which made idle tuning a bit tricky but that's all fine and she boosts/drives just fine. It's only after a long drive that it starts getting lean, similar to starting the engine again after leaving it off for maybe 15 minutes although not so bad as this.

I do suspect it's just a heat soak issue which is why my latest project is to replace the sensor with a more appropriate one and fudge the resistance with some DIY.

Thanks!

[Scott Black]

Simple test is to put a multimeter on the temp sensor or just read the value from the ecu and get a hair dryer and blow air from that over it. If the reading doesn't change then you know that the sensors stuffed, wait so you mean the air manifold temp sensor, if so on the rb26 there really shithouse as there really a water temp sensor fitted as a air temp, so the element is surrounded with brass and very susceptible to heat soak, I'd get one the same sort of style as a vp commodore and install it on the ic piping before the manifold or the manifold itself if it fits

[edizio]

Yes, that's the temp sensor I'm on about!

Do you think the issue is just that? I was thinking it was but wanted a second opinion.

[GTSBoy]

If this Power FC is a MAP sensed one, then you really shouldn't be using the Nissan IAT sensor. Nissan provide that sensor to the original ECU only for the purposes of dealing with extreme high temperature situations. The ECU doesn't routinely use it to calculate fuelling. That's why they can get away with a huge slow reacting sensor that looks like it should be in the cooling circuit.

If you're going to be doing MAP sensed fuelling calcs, then you really want an accurate and fast responding IAT sensor. So regardless of whether you were having the problem that you report or not, you would not want to be using the slug that Nissan provided.

[edizio]

Hey GTSBoy,

Yeah, I've ordered the GM IAT and the resistors to bring it inline with the nissan one so it 'tricks' it into thinking it's the real one. It's apparently fast reacting and accurate but unfortunately not waterproof so it has to go behind the watermeth nozzle.

I run water meth injection too which injects just before the manifold but I was thinking of placing the new IAT just after the intercooler and then compensating the fuelling using my wideband and datalogit. Do you think that it's ok to place the sensor elsewhere?

[Scott Black]

Providing its after the ic it should be ok. Closer to the engine is better as it's the air entering the engine, yet there shouldn't be a huge change in air temps between the ic outlet and the throttles

[GTSBoy]

Tough call. The water-meth will, strictly speaking, change the temperature of the air. So you realistically will need to use the "hotter" temperature that you read at the IAT but tune as if it were "cooler". Know what I mean? Pretty much the same as anyone who is probably running water-meth or E85 on any engine, regardless of MAF or MAP, you can lean on the timing more than the IAT would lead you to believe.

From another point of view, having an IAT that was waterproof and could be located after the spray would allow you to tune truly at the indicated temperature. If no spray is on, therefore hotter air, then IAT sees hot and your ECU pulls some timing. If spray is on, then cooler temps, IAT sees it and advances accordingly. It might not be completely representative of the real air T going into the inlet runners, but closer than the other option.

[edizio]

Yes, well hopefully this will fix the heat soak issues of going lean on long drives without boost. Funnily enough though, the fuel ratios on boost are perfect, even when in this state.

Going to order a DEi turbo blanket and some wrapping for my gt4294R. Thinking a T4 size will do!

[JustinP]

I'm going to have the same problem regarding the IAT sensor with WMI (if I ever finish putting my car together). I'm tempted to just run the IAT sensor downstream of the WMI nozzle and see what happens!

Tough call. The water-meth will, strictly speaking, change the temperature of the air. So you realistically will need to use the "hotter" temperature that you read at the IAT but tune as if it were "cooler". Know what I mean? Pretty much the same as anyone who is probably running water-meth or E85 on any engine, regardless of MAF or MAP, you can lean on the timing more than the IAT would lead you to believe.

From another point of view, having an IAT that was waterproof and could be located after the spray would allow you to tune truly at the indicated temperature. If no spray is on, therefore hotter air, then IAT sees hot and your ECU pulls some timing. If spray is on, then cooler temps, IAT sees it and advances accordingly. It might not be completely representative of the real air T going into the inlet runners, but closer than the other option.

[edizio]

So tonight I had heat soak because I left the car for 30 minutes; got back and the AFR was around 18 when starting.. traditional heatsoak due to the sensor. After a few miles everything was normal again.

This is strange and leads me to believe that the issue with driving on the motorway and gradually getting leaner after an hour or so is not the same problem.

Any thoughts?

[Scott Black]

airflow over the engine bay might of cooled down everything again after the car sat for a while, yet on the motorway the engine running for longer periods of time warms everything right up again, or it might be seperate, yet id start by changing the temp sensor then go from there

[edizio]

That makes sense to me Scott. I'll make a walk through as I do it, just waiting on the parts now. I ordered the sensor/resistor/electric box with some silicon to make a nice job of it.

I don't suppose it could be fuel getting hot? I do have twin bosch 044 fuel pumps to a sard pressure regulator feeding my id1000 injectors. The car is capable of running to around 750hp+ with this setup but for road safety, I've got the wastegate opening at 0.8bar as opposed to 2.2nar which would be somewhat around 850 at close to 100% duty cycle.

[crashsvg]

ok.. i had this problem also..straight to the point the stock air temp sensor is garbage..it would hover between 60 and climb to 70c regardless of if your running 20 psi (which is when it should be climbing) n off boost when is where it should be low.. remember dense air need more fuel , less dense (hot) needs less....

so when the air sensor is stick at 70c while the actual temp is only 45c its gonna send less fuel to the moto which is gonna cause u to lean out.....

quick fix...simply put all the compensation for the air temp sensor to +10 in your compensation map for 50-80c ..in that way it wouldn't lean out but u may end up getting a few richer spots than desired..

if your running afm remember the afm don't need a air intake temp sensor ( that's why the stock is junk )because essentially its able to tell the amount of air and temp of the air coming in ..

what i sad to u above is only applicable if your using a map sensor..

so if you believe you have heat soak issues you can bet your ass those afm are reacting to the hot air inside the engine bay..

just allow your car to warm up ,take a hair dryer and direct the blower not inside the afm but around it , just enough so it can suck in the hot air and watch your afr ratio lean out at idle

[edizio]

I am using map sensors to acquire the volume as opposed to measuring air flow with a MAF so yes, it does apply to me; thanks!

Funnily enough, I have never seen the air temp actually go above 45 when monitoring with datalogit, even when this issue is occurring. Anyway, the new temp sensor should be here soon so I'll fit that and report back.

I can confirm that when I go onto boost the temps drop considerably though!

Edited February 1, 2015 by edizio

[crashsvg]

temp is suppose to raise when you go into boost not fall off. higher the boost more it should heat up ... but yr as i said the stock one is crap. its actually a water temp style Nissan stuck in there so its reaction time is awful . at start up mine would be 50c at warm up 20 min later its at 65c off boost.it basically just measured the heat in the intake..even if i shut off with with ignition on only it would retain the same degree for bout 30min

[edizio]

Yeah so it seems like this is the issue, just out here in England the air temps never get high enough to go over 50 lol. But definitely notice that the temps drop on boost! Quite excited to get this new tmo sensor set up.

Actually going to drop it in just after the intercooler and tune the delta so that I measure the true temperature coming from the turbo. The delta should be constant though I believe so shouldn't cause a problem :-)

[GTSBoy]

The heavy Nissan IAT sensor could actually read lower on boost because assuming;

• the plenum is heated by coolant and/or contact with the head, which is pretty hot (like at least 80°C),
• the boost isn't too high and the intercooler is doing its job, then

all the cooler air rushing past the IAT sensor will suck heat from it and you get a decrease. Get off the boost and the heat will flow back in from the plenum alloy.

[edizio]

GTSBoy, where would you be inclined to place the new sensor? I was hoping to get it away from the plennum as that is getting hot. I was thinking just after the intercooler on one of the connecting pipes. This would give a true indication of the air temp coming from the turbo and wouldn't get any heat soak what so ever but would this give inaccurate results when off boost?