exhaust wrap

What is an exhaust wrap? Why would a hot tailpipe help? I suppose a pre-heated catalytic converter would help with reducing emissions the first five minutes you drive the car...

 

As mentioned, the tailpipe really doesn't matter, but if you wrapped from exhaust manifold to the cat, it might help a bit, but I would worry about moisture getting trapped between the wrap and the exhaust components and rusting out the pipes prematurely..

What I did is line the hood with a layer of that foil+bubblewrap insulation and blocked off the radiator except for a small hole over just the small hybrid radiator. When it really starts to get cold, I'll probably close off the hole as there will be enough losses without the extra air flow.. In any case, what this has accomplished is that the car warms up slightly faster, seems to have a bit more power as the warm air stays in the engine compartment- intake air is 15-20C above ambient, and after even a short drive, although the outside of the hood is cold, the engine compartment is nice and warm (without the radiator block and hood insulation, in cold or cool weather, the engine would barely be warm, even after a lengthy drive)..

The one caution would be to to get watch the temperatures closely- a Miniscanner, Scangauge or similar diagnostic device should be attached to watch engine temperature readings until the real cold weather arrives..

The hack/mod I'd love to see is something to disable the "warm-up" mode- the concensus seems to be that the fastest way to warm up a car is to simply drive it, so a mode that forces idling in a fuel-and-power inefficient valve-timing mode is IMO rather useless.. I'd rather have the car start and stop the engine even when cold and let us "just drive".. I'd bet that you'd get *fewer* overall emissions when cold by not doing this warm-up, allowing the ICE to proceed normally under load and to allow normal shut down at stops instead of wasteful idling in a rather futile attempt to try to keep the tiny little engine hot (indeed, most people in cold climates report that the ICE seldom stops in the winter, preferring instead to idle away like regular cars)..

Unfortunately, my first attempt at this hack (fake a 70C reading on the coolant temperature sensor) failed (got a MIL and P3191 and P3101 codes) probably due to some other cross-checks that the computer does.. Strange because the service manual implies that even if the coolant temp. sensor fails, it's supposed to assume a fail-safe value of 80C.. Anyone have any insights?? Maybe just disconnecting the sensor vs. fooling it??

 

with the CANVIEW scanner I see that the coolant flush from the thermous gets the temp to about 55C for the time it takes the ICE to start then it almost immeadiatly drops to low 30's C (OAT 15C) then the ICE runs till the temp gets back up to 70C for S4. It's also my understanding that the Prius ICE runs from a cold state, in retarded timing mode with a slightly rich mixture to get the cat's up to temp fast. On the MiniScanner in my Classic the output from the O2 sensors starts to rise almost upon starting. I doubt that wrapping the manifold would have much of an effect, also wrapping the Cat's would probably cause the monolith inside of them to melt, as the heat would probably get to high. If you had a cat failure because of he wrap I doubt that you'd get warranty on it. There are likley more sensors that tell the computers what state the temps are and what has all happened since the last time the car was started. There are thermistor buried in the MG's and in the Inverter. This is pretty well protecting the car from you by the sounds of it.

 

C4 have you considered a rheostat that you could adjust over a period of say 20 seconds that would tell the computer that the ICE has reached 70+C. By disconnecting the temp sender the computer probably thinks the system has a problem and sets the MIL. This would also give the computer some time to see things like the O2 sensors working etc. Possibly a 555 that latches a resistor to trick the computer then when the temp sensor sends a value higher than whats going to the computer the 555 shuts off till the next start. Just a thought.

 

You probably don't want to mess with the cats, and just consider
that heat loss as protecting them. [Cats get really unhappy when
you try to wrap them up, right??]
.
I've been playing with a warm-air intake redirect, but I won't really
know its effect on mileage until the weather gets colder. It's just
a piece of cheap NAPA heat-riser hose [probably to replace those ol'
lines running up to air cleaners atop chevy big-blocks..] sent back
over the engine and into a piece of larger tubing [dryer hose],
whose end tucks around under the edge of the heat shield over the
exhaust header. Seems to collect fairly warm air from back there
and effectively recycle it -- heck, I've already generated those
BTUs, why not try to re-use them, right? May play with radiator
blockoffs later. But retention of heat in various ways has plenty
of merit as an efficiency idea, as long as it doesn't present risk
to components.
.
_H*

 

Hello,

I would really like to be able to monitor coolant temp on my '05. It is really the only way I would feel comfortable about playing with limiting air flow throught the radiator, or other more exotic attempts to increase the speed of warm up.

I am not a real auto tech, but I used to do my own valves on my '67 VW. I also replaced the muffler on that sucker a couple times, which was a solid afternoon of work!

Is there a simple way to make this monitoring happen?


storm petrol

 

Frank- based on the schematics, my first attempt at the cold-start defeat mod was hooking up a potentiometer in parallel to the temp sensor (the idea was the lowest temp the ECM would see would be 70C, but if it rose above that, the proper reading would be reflected), but what I did was to switch the car to Ig-On where I adjusted the potentiometer up and down and monitored the reported temperature readings to figure out the range of adjustment, and then I set it to a reading of 70C. I then proceeded to start the car (without first switching it off). The engine started, ran about 5 seconds, and shut off, then a second later, the MIL came on.

Two possible explanations come to mind: 1) because I twiddled the potentiometer and made the temperature range go up and down quickly while the ECM was powered up, and then proceeded to start the car without first powering off, the ECM saw the apparent temperature fluctuations and got intself into a strange mode and this is what caused the MIL.. 2) There's additional logic in the ECM that tries to cross-check the temperature reading with timers and other sensors, and something about an instantaneous 70C reading was inconsistent with these other readings..

I can easily see if explanation #1 is the reason by setting the temp, then turning the system off before attempting to start and seeing if it still triggers an MIL.. The reason I wanted to pull the sensor input entirely is to see the behaviour of the system in the event of a sensor failure... Again, the repair manual says that it's supposed to assume a fail-safe value of 80C for coolant temperature if the sensor fails.. There's a specific code for coolant temperature sensor malfunction, but I did *NOT* get this code, instead, I got the generic hybrid failure codes (P3101 and P3191). I basically want to know if pulling the sensor gets the desired result when spoofing the reading does not..

In terms of explanation #2, if there's a consistency check, I'm somewhat at a loss because as far as I can tell from looking at the vehicle schematics, there's only two ICE temperature sensors: 1) the coolant temperature sensor and 2) the intake air temperature sensor. The IAT is simply used to control the mixture,so the coolant temperature should be the only sensor responsible for measuring engine temperature.. The hybrid portion has its own temperature sensors and cooling system but these should be independent of the ICE cold-start function (and indeed, the thermos only collects ICE coolant, so it's very much possible for the ICE to get rewarmed by the thermos while the hybrid is cold).. Setting a fixed coolant temperature of 70C should theoretically be fine as it basically reflect the following real-world scenaro: you've been driving around and the system is at temperature, then you stop and shut the system down and then come back shortly- the coolant temperature should still be quite high and the system should use it's "abbreviated" cold start sequence (ie, engine runs for about 30 seconds and then shutdown is allowed). The cat may or may not have cooled in this situation but this shouldn't affect the function either: I believe the O2 sensors are narrow band, so the ECM should only be able to derive a binary reading (cat hot or cat cold)..

I'm definitely going to try again- the last time, I had an appointment to go to, so I didn't spend a whole lot of time attempting other things after the initial failure (instead, I concentrated on getting the car back to normal, but this really should be a doable mod- I can't see why it shouldn't work as intended..

Lather- I'm of the opinion that the computer spoof is the most effective solution.. The amount of environmental change you can implement is rather limited: it's difficult to control Mother Nature, but a computer behaves in a well-defined manner based on its inputs, so if you can just figure out which inputs to change, you can change the behaviour of the system.. You might improve the cat warm-up by a minute by wrapping the exhaust, but in comparison, if you ca figure out the right sensor(s) to spoof, you can completely eliminate the wasteful "cold start" procedure..

 

C4 it might be possible to spoof the computer to think that the ICE is still at 70+C and bypass the cold start routine. You might be on to something with leaving the rheostat in the circuit set to whatever gives 70C. I wonder if the hybrid computer on the battery side which has a circuit to determine the time off and time on is not the culpret that's triggering the MIL by saying it's been off for X hours and the ICE should be cold. I doubt that the intake air temp is the problem here, it's probably used to get the fuel ratio right for the temp and amount of oxygen in it for combustion. Cold air=more dense ie: more O2 warm/hot air less dense=less O2 so it trims the fuel flow to get the best mixture. The inverter temp and the battey temps are probably also a contributing factor in the computer logic to get the car warmed up as quick as possible. Another thought if the PTC heaters are triggured would that have an effect on it as well. Better question is can anyone reverse engineer the codes in all the computers and tell us what is happening and when?

 

Yes.
You can check the THW(coolant temparature signal) voltage at the Pin 19 of A connecter of engine ECU by volt meter.

It is not a linear conversion. The conversion table is shown at...
http://priuschat.com/index.php?showtopic=7494&st=21

Ken@Japan

 

Ken,

Thank you for that info.

Now, can you direct me to any instructions as to where pin 19 is physically located? Would I use any voltmeter that I would pick up at my local auto parts place? Could I leave this in place for continuous monitoring as I drive?

Sorry about the endless questions, but do you know why Toyota did not put a temp gauge into an option package?

Thanks,

storm petrol

 

The engine ECU is located behind the globe box.
You can refer to the following EV button installation article about the location.
http://www.priuschat.com/forums/kb.php?mode=article&k=5

The article is for the Hybrid ECU, but you'll find the engine ECU next to the Hybrid ECU at the procedure (6).

The THW signal is pin-19 of E4 connector.
Please refer to the attaced picture.

You can get a voltmeter any place you want, such as Radio Shack.
Sure, you can monitor the voltage during driving, no problem.

I think the reason is a cost.
A normal driver does not care about the coolant temp.

Ken@Japan