Ok guys.. Some of you folks know that I have been testing the new Firmware for the past 2 weeks or so..

Well, 2 days ago I discovered I had a CEL P0107... Turns out the problem is likely my MAF sensor (the error is a BARO/MAP sensor value to low) in the MAF sensor, there are two additional sensors, a 1 bar atmospheric sensor, and a intake air temp sensor.. The combination of the data with the shedder bar (Vortex sensor) is what calculates air density and therefore fuel control.. Turns out either the connector or the sensor is defective (I need to swap it into someones car to be sure its the sensor and not my wiring, but thats neither here nor there)

Anyway, because of the weather I have not had the time to refine my tunes while testing open loop operation, and since its a little lean with my mods, I switched to passthrough (Map 0).....

So, I get into my car, start it up and it starts fine.. hit the gas and it cuts out.. Turns out the factory ECU gets confused and cannot grab a fuel trim or load cell without the Baro input (even though Karmann frequency is there) So basically my car is undrivable..

I figure, ok, I have a base map with just timing installed in my MAP1 location, (the map I'm working with is MAP2) so I switch it to 1.. Car runs fine, even though this is an issue that would render **ANY CAR RUNNING A FLASH OR PIGGYBACK** UNDRIVABLE!!!

So, what does this mean? That the engine control features of this new firmware are so complete, that the car still ran correctly, running off the UTEC when the factory ECU was in a state where it could not possibly run..

Guys.. We are not dealing with a fuel computer, or a piggyback, we're talking features and tunability only available with a FULL STANDALONE in this unit.. And this is just the most notable of several new features available.. Open loop Fueling saved the day!

This is what got me home, where I otherwise would have had to get the car towed...

 

 

BTW, I'm going to test my MAF sensor in a friends EVO today.. But I think I figured out what happened..

I hit a giant pothole the other day (I already had a CEL light on, but it was the same one that is triggered by my MAF pipe every so often) I think it caused my MAF sensor to bounce around severely because I didn't have it adequately anchored.. It either pulled on the wiring harness and damged it, or the bounce "broke" the sensor itself..

Its a good excuse to finally finish the blowthrough setup.. In this case, if my sensor is definitely damaged, I'm going to cut it up and use the harness connector off it on the new blowthrough wiring harness..

 

Its weird.. because without the UTEC, (in bypass mode) if I were to start the car, it would kick over, but not keep running, since the car starts in open loop it makes sense..

If I start the car with the UTEC in Map 1 using the new Open loop Fuel control.. the car starts and runs no problem.. then the stock ECU can take over in closed loop (Closed loop fuel control relies on the front O2 sensor to maintain 14.7:1 AFR)

After the car is running, and I switch it back to Map0, the car will idle (in closed loop) but when I try to rev the engine, it dies..

This is definitely something that went out recently because I had been running map0 to get the passthrough when I'm not working on tuning anything until I get my boost control resolved.

I really hope its not something like the wiring or in the harness simply because of the troubleshooting involved to find the problem.

But the lesson learned here is its **VERY** important to anchor the MAF sensor if you put an aftermarket air filter assembly on the car. I got a very early Buschur filter which was missing anything to use as an anchor. If you have an aftermarket cone filter that doesnt have an anchor, pick up an aluminum strip from home depot and make a bracket to anchor it.. Although this is an obvious statement, the MAF sensor is VERY VERY vibration sensitive and should be protected. (if you don't have it anchored, something as simple as slamming the hood can affect the idle either the air pressure change can trick the baro sensor, or the vibration can startle the Vortex sensor)

Just a quick word of advice, I suspect that if there's a few MAF sensor failures, its likely due to excessive vibration or it becoming damaged by ingesting water..

 

My theory about why the engine doesnt run is, in closed loop, it can maintain an AFR with the O2 sensor.. But in open loop, it relies on several inputs.. Airflow (vortex) Air Temp (IAT) and Air Pressure (Baro/Map)

Since the error I am getting is saying Baro Sensor low (the baro sensor is in the MAF assembly according to the EVO manual, someone tell me if thats actually correct and there isn't a second MAP sensor on the intake manifold??) its like being in a low pressure environment (low air pressure like being up in very high altitude) Ok.. so the engine thinks your in the vacuum of space so it cuts fuel to try to match it.. Normally air pressure will hover at something over 0.. and airflow through the sensor will affect the pressure slightly..

Here's the rub.. there's no direct output of the air pressure in that sensor in the OBD-II diagnostics.. But it is used by the VAF (correct term for the MAF sensor) as a reference to calculate air volume and then air density..

So how does this affect the ECU?? Well, the sensor is still producing a karmann frequency, but it must rely on the air pressure value in some way since the engine won't stay running except at idle... Zero or very little registering air pressure no matter what IAT and Vortex frequency means it thinks very little fuel would in theory be required to keep running however thats not the case, and the engine just cuts due to no fuel..

 

You are a brain man and I cant understand what the heck you are talking about but it sounds real good. =)

 

you are right...i have noticed that when i slam the hood down to shut it, and if the car is running, the idle takes a huge dip and then pops back up again.

Malibu, you just sold me on the UTEC. Since I have had Al flash my car 3x's it is time for me to move on. But the only thing that makes me a little nervous is that I dont KNOW **** about tuning, but I am learning.

 

Yep.. the issue turned out to be relatively minor.. But it was nice to get myself home..

 

MalibuJack, do you have a wideband on the car? What is it reading right before the engine dies?

Your theory sounds good, but at idle isn't the ECU still in closed loop? The UTEC doesn't go into open loop until you hit a certain TPS point. I know the UTEC has corrections at idle, but the ECU technically isn't in open loop. but that still makes sense on why your car is still idling, because the UTEC will see the signal before it even reaches the ECU. The ECU doesn't stand a chance with the UTEC

So what did you find out the problem to be?

 

The engine starts in OPEN loop, then depending on engine temperature will switch to closed loop once the O2 sensors are up to temp and "Responding" to the mixture.

Since the UTEC intercepts signals, it continued to run even though it wasn't getting the correct signals. FWIW it was a minor issue, I had a broken wire on the MAF sensor connector.

I can't tell you what the AFR's were because it wasn't "Trapping" it in time to be able to answer, what I can tell is the signal for the MAP sensor was fouled up and basically the engine thought it was operating in the vacuum of space.. :LOL:

This thread really is informational and not intended to diagnose a problem since I already knew the circumstances and solution to the problem when I posted it.