EMAP Sensors - choosing the right sensor

[Ben-S]

I am having failure issues using two of the Honeywell 100psi sensors for EMAP sensors on my race car. I have used the sensors in the past with success but I'll list a few reasons I think they might be failing:

Peak pressures from cylinder pulses are obviously over 100psi although very brief could this cause a failure. My EMAP is usually around 26psig

"backfires" - rarely happen but maybe it doesn't take much.

EGTs in the 1500*F range - although I have run close to 3ft of stainless tube from the source and the tube is mounted to a heat sink that is bolted to the chassis with heat dissipation paste (like on a ignitor). Ambient temps around the sensor are in the 150* range.

I custom blend my own fuel, it is a mixture of ethanol and toluene, my turbine wheel looks brand new so obviously it is fairly caustic.

There are a few things I could try, the easiest of which I am thinking is the 500psi TI "Nitro" sensor. It would allow me to just swap sensors without changing anything other than the sensor cal table, resolution might suffer though. What is everyone else doing? If it makes any difference one sensor still works, the other failed slowly. It would start reading lower than the other (causing me at first to look for mechanical issues) but it quickly started to get lower and lower without any difference the power output so I knew it was the sensor. It has now completely failed and I have noticed that the "good one" now reads 95kpa at atmospheric (usually reads 100.x around here) which makes me think it's on its way out.

[sam@tdi]

I've found good reliability using these,

http://www.omega.co.uk/ppt/pptsc.asp?ref=PXM209_PXM219&Nav=preb03

the stainless internals cope well with the exhaust gas fall out acids, I tend to use them for emap combined with one of these

http://www.omega.co.uk/ppt/pptsc.asp?ref=PS_SNUBBERS

I've got a couple of these now ending there 2nd full season of motorsport with no problems at all.

[Ben-S]

Awesome thanks for the link, I will definitely change over to those.

[Scott@FP]

The Honeywells seem to be more failure prone, especially when subjected to vibration from mounting directly on engine.

[Ben-S]

So I finally switched over to those sensors with the pressure snubbers. Using a 0-60psi sensor and running about 13psi EMAP they lasted about 6 dyno pulls. I can confirm it is not heat as the sensors were still cold to the touch. I guess I'm going to try and completely isolate the sensor from the exhaust gasses. I'm certain it's the fuel I'm using that is the culprit for shortening the life of these sensors so drastically.

[sam@tdi]

Are you running this thing on Plutonium?

Frankly I'm astonished you managed to knacker those sensors at all, let alone that quick.

[Ben-S]

55% ethanol, 38% toluene, 5% methanol, 1% methyl isobutyl ketone, and something called "rubber solvent" with a CAS of 647742-89-8 which I can find no information on at all (can't buy pure ethanol so they mix in some random chemical that keeps changing every time i buy a drum). I also add a few ounces of benol (castor oil).

My gm map sensor is still fine so I'm thinking its some chemical forming during combustion but i'm no chemist...

so far the tally is

(2) 100psi honeywell
(2) 100psi kalvico
(2) 60psi omega (with snubbers)

[fivebob]

At a guess I would say it's most likely to be the castor oil. When it burns the byproduct is a soft sticky varnish which might be what is stopping the sensors from functioning. See this article for a techicnal view on how castor oil behaves in an engine.

If it is the castor oil that is causing the problem then you should be able to clean the residue from the sensors by soaking them in methanol, but I'm not sure how the sensor would handle that, and I'm pretty sure it wouldn't like some of the other methods for removing the stubborn varnish deposits like boiling in a crockpot of antifreeze for 24hours

[Ben-S]

It's definitely worse a shot, it can't make them any worse. I would be more inclined to think that was the case if it weren't for the omega sensors which failed almost instantly.

Could be that it clogged the snubbers.

[Ben-S]

Turned out to be the snubbers clogged up, I will switch to a piston type snubber and see what happens