Engine loading up at long idle (FAST)

[carbuff]

Hi guys,

Here's my second question, and it might be related to the first that I just posted. When I let the engine sit for a long time idling, it seems to load up and then wanted to backfire when I start driving again. After it backfires, it runs fine.

Since I've set my IDLE area VE numbers to be fairly rich (the O2 correction is -14.9% at IDLE), I figure I might be dumping too much fuel in while I'm idling causing this problem. Does that make sense? If so, I will go back and lean out the Idle VE's and see if it helps. I just want to make certain I'm on the right track here ...

Also, I get a lot of pops in the exhaust when I decelerate. Is that a sign of being too rich during deceleration? ie: too much unburnt fuel in the exhaust?

Thanx!
Bryan

 

[Streetracer00]

Well

It sounds like you are running closed loop at idle, which I thought was a no-no. I think your closed loop low RPM should be higher than your idle speed. Look in the FAST FAQ on the website - it explains it in detail. http://www.fuelairspark.com/information/support/c-comhelp/v1-00/

 

[Craig Smith]

If you CAN idle well in closed loop, no problem. Many cars can't, so I generally recommend idling in open loop. If it works, though, there;s no reason not to if you are happy with the results.

You should reduce the VE numbers in the bottom of the map where you are decelerating. Seeing the A/F ratio pegged at 15.94:1 on decel is normal. There is virtually no air flowing through the motor on decel so you need next to no fuel to keep it going.

 

[bruce]

Originally posted by carbuff
Hi guys,
Here's my second question, and it might be related to the first that I just posted. When I let the engine sit for a long time idling, it seems to load up and then wanted to backfire when I start driving again. After it backfires, it runs fine.
Since I've set my IDLE area VE numbers to be fairly rich (the O2 correction is -14.9% at IDLE), I figure I might be dumping too much fuel in while I'm idling causing this problem. Does that make sense? If so, I will go back and lean out the Idle VE's and see if it helps. I just want to make certain I'm on the right track here ...
Also, I get a lot of pops in the exhaust when I decelerate. Is that a sign of being too rich during deceleration? ie: too much unburnt fuel in the exhaust?

Since your mentioning what your working on, on vaque general answers are possible.

I'm going to assume you have more cam then a stock engine.
Which means the engine will be more self egr'ing at low engine speeds, which means you'll need to add some timing and fuel compared to a stock engine. 30d of timing and a AFR of 13.5 aren't at all out of line. 24 at 14.7 is more like what a stock motor will like.

Real lean or real retarded timing will make a motor cackle on overrun. If a turbo motor real retarded timing will help keep the EGTs up, and make for better spooling when you get back on it. Real lean N/A will keep the engine from loading up and be crsip when you get back in it.

YMMV,
not to be attempted without adult supervision.
you get what you pay for hahaha

 

[carbuff]

Hi guys,

I've been out of town, but I did see the replies before I left. I leaned out the idle VE entries as well as the decel locations, and things seem much happier now. I probably haven't leaned out the decel areas quite enough, but it's popping less in the exhaust now. Any suggestions on timing during decel? Somehow I'm thinking a lot of advance in these areas is preferable, but I'm not an expert on timing...

Thanx again!
Bryan

 

[bruce]

Originally posted by carbuff
Any suggestions on timing during decel? Somehow I'm thinking a lot of advance in these areas is preferable, but I'm not an expert on timing...

Running lots of retard on overrun will keep your EGT up so respooling after a coast down will be quicker. or just shut off all the fuel, and then it doesn't matter what the timing is. Lots of advance with any fuel lenghtens the roll down.

 

[carbuff]

Bruce,

Thanx for the info... Guess I should have stated that I'm running a SBC with no turbo. It's a 377, solid roller cam (252/268, .672/.672, 110), and all the associated goodies. I have a Holley throttle body sitting on top of a modified Edelbrock Victor Jr. manifold with 36# injectors, FAST ECU, etc.

I will plan to lean out the decel areas some more once I have things up and running again (stupid timing cover leak), as well as look at the timing some more. I really don't know exactly where all the timing should be set on the decel areas.

Bryan