'90 Mazdaspeed Miata Rallycross Project

I'll check the exhaust, maybe the outlet cracked...that would be awesome.

EvanB wrote: I just need to let it sit for a few days so I set it on fire.

I hope you forgot the ''don't'' in this sentence.

maybe...

EvanB wrote: The O2 sensor is right on the turbo outlet, it may need recalibrating. At idle it is reading fine but cruising AFRs are 15.5-16.5 and they aren't going below 14 going into boost, I didn't go too far into boost. I still can't believe the IAT is above 200...that just doesn't seem right. I just need to let it sit for a few days so I set it on fire.

That's about the cruising AFRs i run on my car... Leaner than "normal" AFRs as you're spooling up is somewhat common depending on what sort of load you presented. See what happens if you just quickly go WOT at a low-ish RPM in a high gear, and be prepared to get out of it quick if it spikes. Just gradually rolling into the gas because you're afraid of what's going to happen will give you leaner readings than full boost WOT.

The IAT is something you need to figure out. I doubt it's that high. Sounds like a voltage offset issue with Megasquirt. We fought this issue for weeks on a buddy's turbo Miata. There's a value you have to change to account for the voltage difference at different points in the harness. (IAT vs. main power for MS in this case.)

Or the IAT itself is bad. Are the readings actually changing? Let the car cool down all the way, and see if you can get a reading out of it before you even start the car. If it's not reading ambient, then you need to do what you need to do to get it to read ambient.

Well I was worried because the AFRs are higher than they used to be...or I could just be crazy because I'm worrying about other things.

It could be the IAT sensor went bad...it was reading fine a month or two ago last time I checked.

The readings are changing, I'll have to check if it reads ambient with the engine off.

I checked the IAT with the engine off and cold...219F. It didn't seem that hot out so there must be something wrong.

The only thing I can think of is the connection to the IAT. The wires pulled out of the weatherpack connector a couple weeks ago while I was working on the radiator. I crimped the pins back on then soldered them for good measure, maybe they aren't making a good connection? I'll have to get another connector to put on.

That makes more sense than the IAT sensor going bad after ~2k miles.

Basically all temp sensors used in the modern era are negative temp coefficient, resistance goes down as temp goes up.

Unplugged, the sensor will be baselined and shorted it will be pegged. It's been a little while, but IIRC, MegaSquirt can only work with 255 degrees, so if it baselines at -40f, then it can't read any higher than 215f.

You have yourself a short to ground on the IAT circuit.

It COULD possibly theoretically be conductive gunk on the sensor, though. When I was new to MS and paranoid about failures, I used to keep resistors in the car that would give me ~70f on the CTS or IAT if plugged into the connector. I don't have 'em anymore, but YOU can grab a resistor of some value (I'd like to say it was either 1k or 4k, but consulting a chart is best) and plug it in to the connector and see if you get the expected reading.

Could that be caused by a poor connection in the weatherpack connector? I just resoldered the wires from the IAT to the harness and made sure those were good. Soldering the pins in the connector is the only thing I have done to the IAT between it working and not.

DIY Auto Tune says the resistance is 1930 ohms at 87F, so a 2k resistor should get close to that.

It could be gunk on the sensor since it was reading 200F on the way home from the rallyx and is now reading even higher. I'll have to pull it out and check.

Are you using a GM IAT or a Mazda one?

GM

I have the IAT in the intercooler piping right before the throttle body since I don't have an AFM anymore.

I just doublechecked, high temperature is low resistance. You don't have a bad connection, you have a short to ground somewhere.

The temperature SHOULD baseline when the sensor is unplugged.

The sensor's resistance SHOULD be about 3400 ohms at 70f, 1800 ohms at 100f. 210f is about 185 ohms.

Whichever one isn't right is where the true problem lies.

PS - Tire still has 30psi in it.

You're right...I just remembered I tried unplugging it a couple days ago and the display was at 0, plug it back in and it goes to 220ish.

I guess every tire repair kit should have iced tea and rubber cement.

Three reasons not to burn the thing to the ground... Suspension is about as good as it can get for the cost!

LSD and rally tires!

Spreading the RWD disease!

I've calmed down a bit, I think I might hold off a bit on burning it to the ground.

I checked all the wiring for the IAT sensor, it looks in good shape. I think the problem may lie with the impromptu connector repair I performed. I'll have to check it out after I finish my take home exams that I put off until today.

I took the connector off the IAT and put a resistor between the two wires. I'm not sure what size resistor it was (I think 3ohm maybe) and the temp display went to 435F.

So maybe the sensor is bad?

EvanB wrote: I took the connector off the IAT and put a resistor between the two wires. I'm not sure what size resistor it was (I think 3ohm maybe) and the temp display went to 435F. So maybe the sensor is bad?

Don't sensors like that usually go the other way? More resistance = higher value?

The sensor might very well be bad, but you mention a potential wiring issue. I'd take a long hard look at that first.

Then look into the voltage offset thing with megasquirt and IATs. There's tons and tons of posts about it on Miataturbo.net. If you lost a ground somewhere, that could absolutely cause what you're seeing.

With the GM IAT lower resistance = higher value.

I went over all the wiring and connections again and they look fine.

I'll have to do some more searching on miataturbo, I couldn't find much discussion on IAT problems last time I looked.

I posted the question on miataturbo and someone mentioned checking the resistance of the sensor at ambient temp, can't believe I didn't think of that myself. Anyway, it measured 170 ohms at ~85F, spec at 87F is 1930 ohms.

Looks like the sensor is bad.

New IAT sensor in and all is well again. Intake temps are now only about 5-10F over ambient while cruising.

Bump for movement to the new forum.

I didn't have much to do today so I decided to put the Mazdaspeed decals on to hopefully receive some contingency money in the upcoming national events. I also cleaned up the car a bit and it does look quite nice.

Looks awesome!

Your vinyl guy needs to make me some meatballs. And some big stripes.

He would probably ship you some from Columbus if you want.

http://artifexgarage.com/ - That is his website, pretty much just an email and phone number listing.