Can timing control cause a surge at idle

[djmac]

I have a GM based Multi Port EFI controlling my Ford 460 engine (controls ignition timing too) . I got it thru CUSTOMEFIS about 5 years ago and it has been very reliable. I have been chasing down a surging idle for the last bit. I have changed the intake and T body gasket, checked all the vacuum lines and changed MAP sensor and the IAC valve with no improvement. It occurred to me that that maybe the timing might be causing the issue so I disconnected the timing wire and sure enough the idle sucked but it was steady. I forgot to mention the idle is good until the motor warms up. So is it possible that the timing is somehow surging impacting the idle speed and if so what would cause it.

[Bill USN-1]

The timing can do it if the timing table around your idle speed is not smooth.

But if it has not done this since you owned it and it only recently started then the timing table has not changed.

You are probably lean and it causes a lean roll at idle.

Vacuum leaks and an old O2 sensor are the normal causes.

The system may need tuned to your engine.

Log data and post it up.
If your not sure how just hit the FAQ's in the injection forum on binderplanet.com.

[mdcptman]

Are u still running the AIR smog system with the CTO valves? IIRC, custom efis tbi recommendded keeping all th smog stuff. If so, then one of th CTO valves may be bad, and could leak, or not shunt th vaccum where u need it.

[djmac]

Are u still running the AIR smog system with the CTO valves? IIRC, custom efis tbi recommendded keeping all th smog stuff. If so, then one of th CTO valves may be bad, and could leak, or not shunt th vaccum where u need it.

No smog at all, I will take her for a ride Friday and post a log
Thank guys

[djmac]

The timing can do it if the timing table around your idle speed is not smooth.

But if it has not done this since you owned it and it only recently started then the timing table has not changed.

You are probably lean and it causes a lean roll at idle.

Vacuum leaks and an old O2 sensor are the normal causes.

The system may need tuned to your engine.

Log data and post it up.
If your not sure how just hit the FAQ's in the injection forum on binderplanet.com.

I noticed in a post about a Howell system not idling well you mentioned to make sure the map sensor vac line is going to the right port on the TBI? Is there a right or wrong port on the throttle body of a multi-port system? I assumed as long as there is vacuum present I was good.

[Bill USN-1]

First, are you sure of the multiport and not TBI.
If the throttle body has 2 injectors mounted on top it is a throttle body system.
If you have 2 fuel rails and an individual injector on each intake runner then it's multiport.
I didn't remember john at Custom EFI selling MPFI but I'm sure he could have.
just want to make sure were on the same page.

But for either system the map reference does matter.
The map needs to be a full manifold vacuum and not a ported or single runner vacuum like where the vacuum brakes are normally connected.

Even with MPFI you will have a throttle body. It should have vacuum ports on it. most have one opposit of the others to isolate it from them so they won't interfere in the vacuum signal.
For TBI the map port is on the back between the fuel lines and there are a port and a manifold vacuum connection on the front.







Here is a MPFI and you can see a ported(above the throttle plate) and the manifold port (below the throttle plate.

The port you want will have full vacuum on it at idle. A ported vacuum source will only have vacuum on it as you open the throttle blades.

[djmac]

Ok, I checked out my vacuum connections and they seem to be fine and I started going thru the check list for initial startup from binder planet. I found that my throttle plate setting wrong and was not allowing the IAC to control the throttle. I actually got the throttle to level out reasonably well and the motor was idling for about 10 minutes and then suddenly stalled and then it did it again shortly after. I noticed that it idles well and then for some reason the ECU is going into open loop and then the truck stalls? Any ideas what is going on with the open loop? My understanding is that is should be in open loop when the o2 is cold or at WOT but should it be going to open loop on a warm idle?

[JeepsAndGuns]

Mabey the 02 sensor is cooling off at idle?
Is it a 1 wire sensor?

[Bill USN-1]

With a cam OL idle is preferred.
If the fuel table is tuned for your engine then OL idle is better.
A lot of our older designed engines will maintain a more stable idle without the "lean roll" that can sometimes occur in closed loop idle.

So if your engine is dieing then I would look at logging data and adjusting the fuel table for a proper tune.

There is nothing wrong with having an OL idle.
Like you mentioned, it is OL at startup.
there is also a timer and rpm limit that must be met (and can be adjusted) before dropping into OL idle.

I also reviewed your log with 8d351 but didn't hear back from you.
The long and short fuel trim is off based on the histogram.

I know you use Datamaster Not sure how 4.0 displays data. but a switch to the super8D adx in tunerpro5 may help you with more useable data.

http://www.tunerpro.net/downloadBinDefs.htm

You will need to import the ecu file to convert for the xdf to tune with and import the ads to an adx to log data.
I have them already converted if you need me to email them to you.

[djmac]

Mabey the 02 sensor is cooling off at idle?
Is it a 1 wire sensor?

Yes it is a one wire sensor but I do have an aftermarket cam so I am going to take Bill's advise on using the Open Loop to help smooth out the idle.