Idle issue after CTS hits 150°F.

[RockinRobin]

Trying to tweak idle settings and I noticed that as soon as CTS hits 150°F, MAP goes higher and idle becomes rough. I don't know what's changing the MAP reading suddenly.

[GPatrick]

What cam are you running that requires a 1600 RPM idle speed? You have Closed Loop disabled below 150°F, so it probably runs differently when it goes into Closed Loop.

Your IAC Position does not appear to be set properly, but aside from that it starts to rise the longer it idles which means that the engine is not happy with your Closed Loop parameters. Once it goes into Closed Loop instead of running off of base fuel it now attempts to meet your Target AFR setting. The AFR selected may not be appropriate for the engine.

Throughout the AFR reading is very noisy. Are you running a full exhaust behind the WBO2 sensor. There's enough noise that if you are running a full exhaust you may have a leak at a collector flange, the WBO2 sensor bung, or the header gasket.

Please describe in detail your engine specs, cam, timing (since the Sniper isn't controlling timing), compression, etc.

You may need the help of an experienced tuner if this engine is "wild" to ensure that the system is setup properly.

The learn table is showing very large numbers in the idle region - in the order of + 40% or higher. Check your fuel pressure and confirm that all four injector are firing. Low fuel pressure or a missing injector will cause the Sniper to add more fuel which is reflected in high learn and/or closed loop values.

[RockinRobin]

This is a Gen 3 Mopar race engine. 13.5:1 compression, high lift race cam, Mopar drag pak intake manifold and a Sniper 4500 on top. Timing is controlled by an MSD 6-Hemi box. Timing is basically ramped up to 26° at 1400 RPM and is flat from there.
There's about 20" of pipe behind the WBO2 sensor. This is a race car only, not street legal.

The 1600 idle speed is for drag racing purposes. Some classes I race in do not allow a 2-Step so I have the idle set where I want to leave at.
Thanks, and please point me in the direction of a tutorial on how to set IAC Position.

[GPatrick]

I readily admit when the application exceeds my level of experience. I think the 20" of pipe may not be long enough given the noisy WBO2 sensor reading. In your application you may need to disable Closed Loop below 1800 RPM (or higher) and manually tune the Base Fuel Table in the idle region. Hopefully some of the people with much more experience on race applications can give you further guidance, I don't want to lead you astray.

[RockinRobin]

Thanks. Was told I needed 18" of pipe past the WBO2 sensor to prevent scavenging, so I went with 20" to make sure. Disabling Closed Loop down low sounds like a good idea.

[GPatrick]

I think it's a combo of length and diameter. A large diameter pipe may need more length, the data seems to show this. It's easy to test turning off Closed Loop. Check the box Enable RPM to enter Closed Loop and set it to 2000. Test it and see it's better or worse. If you take a look at your datalog notice how hashy the WBO2 reading is at idle. When you take it up in RPM at about 165 seconds in the datalog you can see that the WBO2 reading is much cleaner. I'd be tempted to add some pipe while also checking for and correcting any leaks and let Closed Loop work for you. It's probably easier to tune by changing some AFR Targets rather than manually tuning the Base Fuel Table when dealing with temperature and elevation changes. It's easy to see if the increase in exhaust length is working, look at the AFR trace on the datalogs.

[dcs13]

Just a spitball here. Are your cooling fans coming on at that temperature by chance? We had a car that had the intake in close enough proximity to the fans, it would through a bunch of extra air into the intake and cause a similar issue. Just a thought.

[RockinRobin]

Just a spitball here. Are your cooling fans coming on at that temperature by chance? We had a car that had the intake in close enough proximity to the fans, it would through a bunch of extra air into the intake and cause a similar issue. Just a thought.

In my case, no. Fan is controlled manually by toggle switch.

[GPatrick]

I was looking over the data again and when it hits 150°F and goes into Closed Loop, your fuel flow increases from 17 to 31 lbs/hr. Several things are happening. The RPM drops, the vacuum drops, and you end up in an area on the Base Fuel Table with a lot more fuel. On top of that your Closed Loop Compensation is 40% on top of a Learn Table with 40%. Part of this is explained by the fuel map, but another part of it may be corrupt data in the Learn Table and over compensation in Closed Loop due to the exhaust effects on the WBO2 sensor. Another contribution is that your target idle AFR is a little rich. Some engines with aggressive cams need a higher Target AFR. If you're into testing, I'd clear the Learn Table and set a higher AFR by about one point in the idle region and see if it behaves a little better in Closed Loop. But, if you intend to stick with the 18" extensions then disabling Closed Loop below 2000 or so may be the best course.

Noisy WBO2 sensor readings can lead to over fueling in closed loop but high Closed Loop & Learn values can also be a sign of fuel flow problems such as low fuel pressure or an injector that isn't firing. The likely culprit is the AFR signal, but I'd verify pressure and injectors to make sure.

[RockinRobin]

Just ran a test. Cleared the bad part of the Learn Table and disabled learn below 2000 RPM. this seems to help. What should my Closed Loop Compensation & Learn% be? Like 10% at this point, since the car runs great down the track idle is just iffy. I would think at this point I just want it to compensate for weather changes on race day. Also at operating temperature the IAC Position is 30% or higher. How do I lower it? Sniper is not controlling timing and control type is "Sniper TBI". Should I try a different control type and see how it responds? Thanks!

[GPatrick]

To lower the IAC turn the idle screw in 1/4 to 1/2 turn to open the throttle blades a little. You can do this while the engine is running but watch your TPS. If it goes over 2% the system will invoke the IAC Hold Position. I like to turn it in 1/2 before starting. When you turn on the ignition the Sniper will auto-zero the TPS. Getting the IAC down to 2 to 5% gives the Sniper more ability to add air when necessary to maintain idle speed. Set the IAC Position when the engine is fully warm.

[RockinRobin]

OK I did that and IAC Position is now between 5-10% and the giant sucking sound is gone. Raised Idle AFR by .4, it's liking that too. Noticed that the secondaries stick when trying to return to idle. Probably need to re-center the butterflies.

[Danny Cabral]

https://forums.holley.com/showthread...7846#post97846 (Throttle Blade Misaligned/Centering & Secondary Shaft Coiled Spring Tightness)

[RockinRobin]

https://forums.holley.com/showthread...7846#post97846 (Throttle Blade Misaligned/Centering & Secondary Shaft Coiled Spring Tightness)

Thanks! Fiddled with it some and it doesn't hang when engine is off. I had noticed at the track that sometimes the RPM would not come all the way down and I'd have to blip the throttle to get it to come down. Maybe adjusting idle screws to fix the high IAC helped. At any rate I don't want to remove the unit unless I have to, I'm afraid that might cause other issues such as a vacuum leak, so I'll leave it alone for now. There's a slight slack in the linkage to the secondaries. It's very minor, but they don't open exactly when the primaries open. I don't know whether I should adjust the linkage or just leave it alone.

[GPatrick]

All four injectors increase flow when the TPS on the front shaft opens, so correcting the link (by bending) can help with some off-idle stumbles. The coil spring on the secondary shaft can be given one more turn to help it close. I'm not sure if this can be done with the Sniper mounted or not since I've never had to do it. Sounds like you're making progress.