Engine stuttering and drop in AF

dylans · Post by **dylans** » Sun May 17, 2009 8:12 pm

Occasionally when I am driving around, especially when the car is hot and I have been driving around for a while, I have an issue where for a few seconds the engine starts stuttering and the AF ratio drop to the minimum on the gauge (10.0). It usually only happens at low MAP, low enough that it should be in closed loop. Although the car has been driven for a good amount of time, the water temps and IAT are not high enough that it should be an issue.

Here is a 14 second datalog I took last time it occurred. The problem can be seen at about 3.5 seconds and then again at about 10.5 seconds. The AF ratio drops even though the injectors do not change, both instances occur around 400mbar of MAP. When looking at the datalog, the AF ratio drop to 10 and then goes straight up to 19.9, however, the 19.9 is not correct because the ELD voltage stays down at nearly 0 V, which corresponds to an AF ratio of 10. If you need to see the calibration I am using just let me know

Thank you!

Oh and here is car info:

'96 Civic DX
Stock B18B1

k_boi · Post by **k_boi** » Sun May 17, 2009 9:39 pm

thats what happens to me too, on my 00 civic si stock b16a2 with just bolt ons.. anyways, mine does it when Im about to leave in first or when just crusing in idle. Its werid man I know how you feel. NEED SUGGESTIONS..

Post by **Spunkster** » Mon May 18, 2009 11:19 am

without the calibration it is hard to see what is actually happeneing or driving the actions.

dylans · Post by **dylans** » Mon May 18, 2009 11:31 am

Touche.

Post by **Spunkster** » Mon May 18, 2009 12:03 pm

You have 8% long term fuel trim so it looks like you need to do some more part throttle tuning to get this so that it stays as close to 0 as possible.

dylans · Post by **dylans** » Mon May 18, 2009 4:46 pm

Doesn't that mean it is adding 8% more fuel? It is adding so much fuel because I already leaned out the lower end (below 500 mBar) a ton. That didn't fix it at all.

It doesn't seem like it is actually adding too much fuel. There is a huge jump in AF ratio with almost no change in injector pulse width. I can keep trying to lean out the bottom end but when I am not in closed loop it is already running 16.0+ AF ratio so it seems like it is lean enough, Plus, it only occurs when it is hot outside and the car has been driven for a decent chunk of time.

Post by **Spunkster** » Tue May 19, 2009 9:17 am

By leaning it out more you are making the problem worse. If you have an 8% long term trim it is running 8% too lean and needs to be richened up.

dylans · Post by **dylans** » Tue May 19, 2009 12:43 pm

You're the boss Spunkster. I will richen up the lower end and post up a new datalog and calibration if it happens again.