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JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
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Will not idle below 1500 - Megasquirt

I am at the end of my rope with trying to get this motor to settle into a ~900 rpm idle. I would love some help from some of the Megasquirters here. I did a live teamsession with a tuner but he got stumped too.

The motor:

bottom end is a 3.2 on a 3.0 crank with 10.5:1 compression pistons.
Twin plug with 2xMSD cdi boxes driving 2 vibration coils.
DR20 cams
Carrera aluminum intake
Stock carrera throttlebody, refurbished and functioning properly. Adapted for Mustang TPS.
Carrera idle valve. It passes a little bit of vacuum when fully closed, and opens fully properly. It closes on default when disconnected.
Throttle bypass screw cover removed.
Bursch headers, mk muffler.
Rising rate fuel pressure regulator baseline at 43psi.
JB racing 12-plug distributor

What is is doing:

The motor starts up no problem. It idles at 1500 steady and even. Temperatures settle in normally and megasquirt is responding and logging normally. AFRs are ~12-13 when idling.

When I try and get the idle down the RPMs go into an oscillating cycle between 800 and 2000 and eventually dies.

What I have tried;

I set the throttleplate to a small opening where it will idle steady, and adjusting the bypass screw directly effects the engine speed and MAP.

Open loop idle.
Set timing locked to 14 degrees. Have tried 10 to 16 with no difference in the results.

Disconnected the idle valve and checked it is closed (through it does draw a small vacuum. Not enough to effect the idle speed when blocking and unblocking it.

Looked all over for vacuum leaks. Double-checked torque on the intake. All the gaskets are new. Sprayed some brake cleaner around them while it was running and no change in idle. Sprayed around the injectors, throttlebody, idle valve connections, regulator and MAP sensor connection. No change in idle. No brake booster so thats not leaking.

It seems crazy to me that the idle oscillates and then falls on its face even with timing locked, no change in throttlposition and no change in idle valve. I dont think it is lean-surging, the AFRs are ~12-13.

Any helpful hints to diagnose why this is happening?
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 02:52 PM
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What happens if you add fuel in the table at low rpm? What's your dwell?

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Old 06-09-2017, 02:56 PM
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If I set my timing to 14 BTDC it would idle at 1500 RPM too. Surely it needs to be down at 5 degrees BTDC or less?
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Old 06-09-2017, 03:08 PM
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I would try to set your warm base idle with the idle valve completely closed and use your base throttle blade position to get you your desired idle speed. From my experience with the Carrera idle valve, with the electrical connector disconnected, the valve is open about 25%. I have my base idle set using the blade base position (you can use the bleed screw to fine tune), and even with the idle valve completely unplugged, it will settle into a rock steady idle at 950 RPM every time.

Also make sure that there is no Idle Ignition PID active when setting the base idle (not sure if MS has this functionality), or any idle ignition modifier active. It sounds like there might be an Idle Ignition modifier going on in the background that, when it becomes active, starts chasing its tail and might be causing your oscillations and stalling.

And FWIW, my idle ignition timing is 10 degrees BTDC.

Last edited by '76 911S 3.0; 06-09-2017 at 05:01 PM..
Old 06-09-2017, 04:57 PM
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Quote:
Originally Posted by kenikh View Post
What happens if you add fuel in the table at low rpm? What's your dwell?

Sent from my Nexus 6P using Tapatalk

Hi, thanks for helping. If I add fuel it just richens up. I can keep adding fuel all the way down to 9 and then it dies right away. Dwell is 3.3-3.5.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 05:23 PM
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Quote:
Originally Posted by Jonny H View Post
If I set my timing to 14 BTDC it would idle at 1500 RPM too. Surely it needs to be down at 5 degrees BTDC or less?
Quote:
Originally Posted by '76 911S 3.0 View Post
I would try to set your warm base idle with the idle valve completely closed and use your base throttle blade position to get you your desired idle speed. From my experience with the Carrera idle valve, with the electrical connector disconnected, the valve is open about 25%. I have my base idle set using the blade base position (you can use the bleed screw to fine tune), and even with the idle valve completely unplugged, it will settle into a rock steady idle at 950 RPM every time.

Also make sure that there is no Idle Ignition PID active when setting the base idle (not sure if MS has this functionality), or any idle ignition modifier active. It sounds like there might be an Idle Ignition modifier going on in the background that, when it becomes active, starts chasing its tail and might be causing your oscillations and stalling.

And FWIW, my idle ignition timing is 10 degrees BTDC.

Thanks guys. I just went through another cycle of trying some adjustments and logging.

I dialed the ignition back to 7.5, then 5, then back to 7.5. Not a huge change.

Once warm, I closed the throttlebody bypass all the way. Then I closed off the idle valve (Anything below 20 is closed on this idle valve, i locked it at lucky 13.) Then I backed off the throttle stop until the idle went into its usual surging up to 2000 rpm and down to 600. If I back off further it just dies. If I screw it in to 2.2% throttle it will idle smoothly there at 1500 but anything below that is just cycles between 600 and 2000.

I richened up the fuel map there too and even when its cycling the AFRs are 12 to 13.

I eliminated the idle valve by closing it, and closed off the throttle bypass almost all the way (just a 1/4 turn open so I have some downward-adjustment) and locked in the timing to 5, 7.5 and 10. I adjusted down the idle with the throttleplate screw but still I get this cycling.

Any more help? I suspected a vacuum leak but I cant find anything.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 05:53 PM
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How's your idle switch?
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Old 06-09-2017, 05:58 PM
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Gotta be a leak.

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Old 06-09-2017, 06:07 PM
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Quote:
Originally Posted by steely View Post
How's your idle switch?
No idle switch. Running Megasquirt and a TPS. The TPS has no contol over the idle valve when its locked like I have it.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 06:39 PM
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Quote:
Originally Posted by kenikh View Post
Gotta be a leak.

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Thats what I was thinking but I've hit each intake gasket, the central joining gasket across the two intake halves, the throttle body base, the injectors, regulator, MS vacuum lines and the idle valve plumbing with starter fluid...no sign of a leak.

And if it was a vacuum leak, wouldnt I see the AFRs rising up?

I am going crazy!
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 06:42 PM
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Check your VE table. I have a partly similar set up - 3.0. SSI, Carrera intake. My MS 2 oscillates between 800 to 110 rpm too before fully warm still. Fully warm is not bad at around 1000 rpm. It oscillated all the time at Idle until I messed around with the VE table. I set a block of 6 cells at about the same value (about 45) and this improved the warm situation immensely.

If anyone has some killer advice on the idea oscillation thing both John and I suspect others would be quite happy!
Old 06-09-2017, 06:57 PM
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Block off the idle valve completely. Block of the intake completely. If it doesn't die...leak.

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Old 06-09-2017, 07:28 PM
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You've checked joints for leaks, but have you checked for cracks or something that could be causing a vacuum leak Elsewhere?

This is well beyond my Megasquirt level, but there is a very good Facebook group that might be of help.
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Old 06-09-2017, 07:32 PM
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JohnJL: MS standard or MS Extra? Have you posted the MSQ in the appropriate forum for whichever firmware and ECU you are running? There are folks there that can read the MSQ that you post. Regretably, I cannot do it.

But I see that you have tried a host of possible corrections and gotten lots of advice from folks who know. But there are lots of other items you have not mentioned that the MSQ will tell the smart folks -- including one or two that form the basis for your problem, but that you have not thought about yet.
Old 06-09-2017, 07:51 PM
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Quote:
Originally Posted by Marwil View Post
Check your VE table. I have a partly similar set up - 3.0. SSI, Carrera intake. My MS 2 oscillates between 800 to 110 rpm too before fully warm still. Fully warm is not bad at around 1000 rpm. It oscillated all the time at Idle until I messed around with the VE table. I set a block of 6 cells at about the same value (about 45) and this improved the warm situation immensely.

If anyone has some killer advice on the idea oscillation thing both John and I suspect others would be quite happy!
I will try this tomorrow. Thanks.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 08:01 PM
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Quote:
Originally Posted by kenikh View Post
Block off the idle valve completely. Block of the intake completely. If it doesn't die...leak.

Sent from my Nexus 6P using Tapatalk
Thumb over the idle valve makes no change in idle speed or AFRs. Hand over the intake trumpet kills it immediately.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 08:02 PM
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Try this.

1. Get the settings to the same state as above. I.E. close the idle valve, set the throttle to 2.2%. You should now be idling at 1500 RPM...
2. Adjust the throttle stop to lower the idle, but stop just as it starts to surge.
3. Instead of richening the mix......lean out the fuel map in the idle cells a bit and see if the surging is reduced.
Don't go too far, too fast....just lean it out a bit and see if the surging issue improves.

Are you logging?
regards,
al
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Old 06-09-2017, 08:03 PM
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Quote:
Originally Posted by cmonref View Post
JohnJL: MS standard or MS Extra? Have you posted the MSQ in the appropriate forum for whichever firmware and ECU you are running? There are folks there that can read the MSQ that you post. Regretably, I cannot do it.

But I see that you have tried a host of possible corrections and gotten lots of advice from folks who know. But there are lots of other items you have not mentioned that the MSQ will tell the smart folks -- including one or two that form the basis for your problem, but that you have not thought about yet.

Hi, thanks. I havent posted a recent file up to the MS forum. I was, then one tuner started helping and we took it offline, I gave him some $ to make some upgrades to my MS box to MS3 and dual-ignition. He helped with some tuning but we seem to have hit a wall.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 08:06 PM
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Quote:
Originally Posted by al lkosmal View Post
Try this.

1. Get the settings to the same state as above. I.E. close the idle valve, set the throttle to 2.2%. You should now be idling at 1500 RPM...
2. Adjust the throttle stop to lower the idle, but stop just as it starts to surge.
3. Instead of richening the mix......lean out the fuel map in the idle cells a bit and see if the surging is reduced.
Don't go too far, too fast....just lean it out a bit and see if the surging issue improves.

Are you logging?
regards,
al
Hi Al,
Thanks for coming in. Yes, at 2.2% throttle on the stop I idle at 1500. i will try out our suggestion of leaning out then instead. What ignition advance do you typically see at idle, and and what MAP at around 900 rpm typically? I am running DR20 cams. More aggressive than 964 but not crazy. My tuning experience is on a supercharged and a turbo car so I am having difficulty mapping over what worked in those situations.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 06-09-2017, 08:09 PM
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Injector dead time is very important along with voltage correction.
Old 06-09-2017, 08:12 PM
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