[TransAm400]

Working on fine tuning my base timing table. Any advice on where I can make some improvements? Specs: Sniper EFI with Hyperspark ignition, 455, 10:1, 87CC E-heads, 242/248 on 112. Just a street car.

[JLMounce]

Can you post a .csv file? Your picture is too small to really read accurately.

[TransAm400]

See if this PDF is better. I exported to excel but I can't attach it here.

[JLMounce]

I think as a base starting point this is pretty decent. Your car probably idles around 45kPa and you may find that you want a bit more timing in that zone. I run about 24 degrees there and have a full 10 degrees less duration on my cam.

I also think you can stack some timing at 100+kPA in the higher rpms. Again I push in another 2 degrees between 4000 and 6000 myself. I would also experiment with a bit more than 10 degrees additional advance in your cruise zone.

You may want to watch your half to 3/4 throttle timing around your engine peak torque. at around 60-70kPa you might be a little hot there.

[TransAm400]

It idles around 65 kpa. Seems like it should make more vacuum. That's why I started playing with the table.

[JLMounce]

Adding some timing at idle may help vacuum a bit. I'm surprise it's load at idle is that high.

Don't forget about your fueling as well. That will also have a slight effect on engine vacuum at idle. With the 21 degrees of overlap in your cam, you may need to lean the idle (and cruise) mixture a bit more than you would think.

[TransAm400]

I'm having an issue with AFR at idle also. Target AFR is all the way up to 14.5 at idle but it is usually reading around 12.9-13.0 at idle. I did have the timing at 24 degrees at idle. When I pulled it back to 18 degrees in this new table the AFR at idle started reading closer to 14.0. Still not at the target but it seemed to help.

[JLMounce]

I would suggest starting with some basics here. The first thing I would do is check your IAC. You should have around 10-15 counts at warm idle in park/neutral. If the IAC is closed too much, that could effect the system's ability to fuel properly at idle and may also contribute to the amount of load you're seeing at idle.

Second thing I would check is your fuel pressure at idle. Warm idle is actually the point at which the return portion of the fuel system is taxed the most, as you are passing the most fuel through it. If you're building pressure in the return, you may be seeing pressure creep at the regulator, that could cause a rich fueling issue.

I would also try and read the plugs. I would specifically be wanting to see if they are showing rich or even fuel fowled.

If you could post your VE table that would be helpful. I'm not entirely familiar with the setup wizard on the Sniper, but some of these symptoms indicate that the VE table may be built in such a way that it believe the engine has a smaller cam in it. If you're up against the limits of your short and long term trims, the system may not be able to pull enough fuel out at idle and low load cruise.

[TransAm400]

Here's the VE table.

[JLMounce]

I don't see anything really glaringly wrong with the VE table, but you're idle loads are almost exceeding the idle "zone."

Timing will have an effect on load at idle. If you've seen the engine lean out be reducing the timing, I would continue to go in that direction in small increments. You've got enough cubes and enough compression to soak up the cam you're running. It seems like the timing values you're currently working with aren't making the engine happy. I'd go to 16 degrees and see what that does to both your fueling and measured load. You may also consider bumping the idle rpm up in 100 rpm increments. Both of those things should decrease idle load and may help fuel the engine better.

[HWYSTR455]

Any updates on this?

[TransAm400]

It's been awhile since I messed with it but I did get it running better. I think reducing the idle timing helped. I believe I ended up around 16 degrees. The AFR at idle is close to the target and it is going into closed loop learn now.

I do still have an issue with the RPM's hanging up when I let off the throttle. TPS and IAC are at 0% but RPM will hang around 2,000 until I blip the throttle and then it will return to normal idle. That has been pretty annoying. I only drove the car a couple times in the past months since it was 100+ degrees all summer here in Houston. Looking forward to getting it out more now that it has cooled off.

[JLMounce]

Originally Posted by TransAm400

It's been awhile since I messed with it but I did get it running better. I think reducing the idle timing helped. I believe I ended up around 16 degrees. The AFR at idle is close to the target and it is going into closed loop learn now.

I do still have an issue with the RPM's hanging up when I let off the throttle. TPS and IAC are at 0% but RPM will hang around 2,000 until I blip the throttle and then it will return to normal idle. That has been pretty annoying. I only drove the car a couple times in the past months since it was 100+ degrees all summer here in Houston. Looking forward to getting it out more now that it has cooled off.

Something is going on with that. Throttle blade adjustment, issue with the IAC, vacuum leak or all of the above.

If your throttle is closed and the IAC is closed, the engine should darn near stall.

[HWYSTR455]

Or the throttle blades are hanging up. Is the throttle return spring too weak? Is the throttle cable hanging? If it's not fully closed when you turn the key on it will use whatever position it's at as 0% (TPS autoset occurs at every key-on)

If the IAC AND the TPS are at zero, sounds to me that the throttle blades aren't closing all the way, and it's referencing the open position as 0%. Maybe take the throttle body off and check to see if there's any witness marks on the gasket etc, and that they are near closed.
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Any exhaust leaks?



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[JLMounce]

Originally Posted by HWYSTR455

Or the throttle blades are hanging up. Is the throttle return spring too weak? Is the throttle cable hanging? If it's not fully closed when you turn the key on it will use whatever position it's at as 0% (TPS autoset occurs at every key-on)

If the IAC AND the TPS are at zero, sounds to me that the throttle blades aren't closing all the way, and it's referencing the open position as 0%. Maybe take the throttle body off and check to see if there's any witness marks on the gasket etc, and that they are near closed.
*
Any exhaust leaks?



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Good call on the throttle hanging up. My system did the same thing when my throttle cable started binding in its sheath.

[Formulajones]

On the holley it's pretty common to have the rear blades hang up. Sometimes after they are run a while and go through some heat cycles things move around. Sometimes it's apparent right away.

It's an easy fix. You can have a look at the blades and make sure they are centered but most just give the rear throttle blade spring another wrap around the shaft.

https://youtu.be/avRqQZBOxP0

[TransAm400]

Interesting. I'll check out the secondaries first. I also have an extra IAC on hand I can swap out if needed.

[TransAm400]

Update: another wrap on the secondary spring seemed to cure the hanging idle. Just need to put some miles on it now and keep fine tuning but it seems to get better every time I get it out.

[HWYSTR455]

Just keep in mind, any 'auto tuning' is only to the base fuel table, and other changes, such as ignition curve, will impact that.


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