DanielRicany

Hello. I'm having a problem where while I am in open loop on a cold start, the car will idle about 18:1 when I come to a stop light. It will not return to it's usual AFR unless I restart it. However, if I continue to drive it will be fine when driving and when it returns to idle it will be lean again.

If I start the car and do not move at all, the idle will be fine all the way to closed loop.

Anyone know why this is happening?

It's annoying because I am getting some surging occasionally and it runs slightly rough.

1985 Corvette

Thank you.

Cliff Harris

What do your data logs show for coolant temperature while this is going on?

bjankuski

Take a look at the two tables I attached, one adjusts the amount of extra fuel added in open look based on temperature only and the other adjusts it by load. Find out what your temperature and load are in the problem area and tweak those areas.

DanielRicany

How do I find out what my load is?

bjankuski

Use a scanner, it will give the load number. Assume decel is 16 to 32 load, idle could be 32 to 80 but your best way to know is use the scanner.

DanielRicany

Okay well, I plugged my Snap on scan tool in, I didn't see a data stream for Load. Here's a video of what's displayed on my scanner.


And on Tuner Pro RT, there is a thing called "Load Variable". This is what I assume I need to look a for this situation? Problem is, it's fixed at 59 no matter if the MAF, Engine Speed, Vehicle speed, or TPS changes. It's always at 59.

I'm using the ADX file from Tuner Pro's website if that matters.

Thanks!

bjankuski

Use a different scanner to get load values. I believe my Autoxray shows them or the scanner in tunerpro.

I have attached the tunerpro tables, thay are named the same as in cats.

DanielRicany

A little update on the situation:

I plugged my laptop in today. I watched the AFR gauge when it returned to idle. Mostly averaging 16-17 and sometimes spiking to 19:1 at a few times.

The MAF sensor never moved out of 11.xx gm/sec while idling the whole time.

This was all in open loop mode. BLM was fixed at 128 and INT was fixed at 128.

Here is the important part, Injector BPW was about 2.1 - 2.2.

When it switched to closed loop, the integrator started moving, and the BLM finally settled at 142.

This is where it gets strange, the Injector BPW now was at 1.9 and the AFR gauge was at 14.7:1. MAF was still in 11.xx gm/sec.

Why would injecting less fuel in the engine cause the AFR to richen up?

bjankuski

Your BLM added in 10% more fuel by the math but your pulse width went down, that does not make sense. The bottom line is more fuel was added by the BLM and the car ended up richer.

DanielRicany

That's exactly why I'm confused. That's what was displayed on the computer screen. What do I make of it?

DanielRicany

Also it seems as if the BLMs are higher when the engines is colder running in closed loop. I guess because the air entering is denser from less engine heat?

bjankuski

It could be that the fuel on a cold engine was not vaporizing as well so the engine requires more fuel to operate at a specific AFR since some of the fuel does not burn and goes out the exhaust. Once the gets into closed loop it is at least 120 degrees and the extra heat is causing the fuel to vaporize better so less fuel is required to run at stoic.

DanielRicany

On my lean return to idle issue, could it be caused by having a very small exhaust leak at the collector gasket? Maybe there is a pressure change in the exhaust when it returns to idle causing it to suck in outside air? Is that possible?

bjankuski

Yes, that is possible.

DanielRicany

I think that's what the problem is because it doesn't run any different when the AFR changes.

DanielRicany

Would it affect the AFR when the engine is running at a higher RPM?

bjankuski

At high RPM with exhaust backpressure it will not effect the AFR readings.