[T3] Temp sensor and MPS problems on new motor

[Jessica Chase]

Thanks for all the input so far. You guys are beyond kind!!

Keith, we rented a place on Airbnb in Keene off exit 30. We passed through Clifton Park on 87 and got off to get some food at the Colonie Center. Is that your ‘hood?

Here’s where we are now:

In general, we use the AFR sensor to diagnose trends rather than moments or instances. That’s because of the lack of data about what’s appropriate under what circumstances, etc. If we pay too much attention to it, it drives us crazy and gives us numbers that may or may not mean anything. The only hard number we have is that AFR at warm idle should be 13.1 and that info comes from factory trained D-jet meister George aka Tram. The other numbers we think of are based on this list.

AFR Values & Characteristics in Four Stroke Engines

 6.0 AFR - Rich Burn Limit (engine fully warm)
 9.0 AFR - Black Smoke / Low Power
11.5 AFR - Best Rich Torque at Wide Open Throttle
12.2 AFR - Safe Best Power at Wide Open Throttle
13.3 AFR - Lean Best Torque
14.6 AFR - Stoichiometric AFR (Stoich)
15.5 AFR - Lean Cruise
16.5 AFR - Usual Best Economy
18.0 AFR - Carbureted Lean Burn Limit
22.0+ AFR - EEC / EFI Lean Burn Limit

So if we’re accelerating and bucking/lurching with an AFR of 18.5 (as happened today), we know we’re definitely too lean because the numbers on our gauge reflect more or less what should be happening at that AFR.

We were able to get to the magic 13.1 first with our adjustable but then also ultimately (after a year or 2) erratic MPS. We also got that number with the MPS we made our long drive out of town with though only on the previous motor.

In other words, things have changed since the new motor! Apart from the motor and the distributor, every single FI part we’re using is exactly what we used on the other motor and it all worked fine! Now, it doesn’t. It seems like maybe everything was quite close to okay on the way out of town the other day but then the situation deteriorated. Suddenly, we were going up small hills and the AFR was 16.5 which clearly isn’t that good for a poor air-cooled motor climbing a moderate hill!

FWIW, the new motor is using a stock cam, compression ratio, rockers, etc. It’s all stock!

The AFR sensor we’re using is this one

http://www.innovatemotorsports.com/xcart/product.php?productid=16321 <http://www.innovatemotorsports.com/xcart/product.php?productid=16321>

It has a Bosch 02 sensor but I can’t find the part number right now. 

While we were able to remove the epoxy from the sensor that got us out of town and make it adjustable, we couldn’t get the motor to start with it hooked up. We counted the turns it took to remove the screw and put it back in accordingly but no dice. We haven’t checked the resistance but maybe the sensor has failed for some reason?

What got us home in the end was a NOS pressure sensor we bought from Jim a year or so ago. In order to use it though, we had to unplug the intake air temp sensor. With it plugged in, we were idling really lean (15.5) and while driving it’d spike even leaner (18-20) and we were underpowered and bucking while trying to accelerate. Not fun. Unplugging the temp sensor was the only thing that made the car drivable. The exhaust stank like hell and we had to refill the tank twice when once would have done but we got home. We only got about 17 mpg  :(

Jim…your recollection about our brains is correct. After we “fried” one during a bad electrical test, we’ve been running one that has worked fine (apart from not grounding the fuel pump) since 11/25/15. This one is still in the car. We also have another B brain that doesn’t ground the pump as well as an A brain which we’ve never tried to use.  
We can try our current setup with those 2 brains tomorrow and see if we have any luck with sane AFRs.  Also, just before we left town, we finally acquired USPS priority boxes so we can ship you the collection of ECUs we have…we’ll do our best to ship them tomorrow or Monday.
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