Megasquirt running Ignition only - Erratic Idle

[Woznaldo]

OK, I've finally got the car started with MS running the ignition only but, the engine won't idle without 1/2 choke. AFRs are 14-15 which would seem like I'm not getting enough fuel but, the exhaust is spitting out black soot!

I'm going to take the O2 sensor out to do a free air calibration but my datalogs show a lot of jumping about for AFR and Ignition advance but MAP seems fairly stable?

I'm not running resistor spark plugs and I'm wondering if this could be the problem?

[Dave Reed]

Check the timing with a timing light.. Sounds like its most likely out quite far..

Can u adjust the timing trim megasqurit? If you can have a play with that, I know when I do e mine I was miles out and it still ran, but badly.

[Scoff]

puffs of black mean misfire, maybe intermittent spark or ignition not staying in sync or timing a country mile out as dave says. misfires show as lean on a A/F gauge but it won't actually be lean.

[Woznaldo]

If I'm not running resistor spark plugs, could this also be a symptom?

[Scoff]

Most standalone ask you to use resistor plugs but I really don't know how it affects megasquirt. There is the potential of HT interfering with a line in to the ECU.

[SCHWARTZ]

Saw your thread on msextra woz. If it helps I'm using standard b18ft plugs with my ms1v3 and it seems to idle ok. I did notice that the datalogs were a bit jumpy but think that was due to the dog**** spark map at the time.

[Woznaldo]

I'm using the std GTT spark map so that shouldn't be the problem. I've gone ahead and ordered some resistor spark plugs just to take that out of the equation.

On my spark map I don't have a load site at 0 RPM (first is at 500 RPM). Could this be an issue with the idle?

[Woznaldo]

Here's my Spark MAP.

[SCHWARTZ]

i have mine the same 500rpm then 900rpm.

[Tutuur]

It probably doesn't affect the idle but that map should be looked over by someone who knows what he's doing.

You only have 3 vacum bins... Also you'd want more cruise rom bins. Unless it's a drag only car?

[Jimmy_GTT]

Here is my map:


Idle is around 1000rpm @35-40kPa and 10 degrees
If rpm gets lower than that ignition is a bit more advanced to get the rpm back higher. -> idle will be more stable

[Woznaldo]

Jimmy, I tried to throw in some extra advance up to 80kPa and it worked a treat. The car now idles with no choke at 900 RPM at around 40-42 kPa.

The engine still won't accelerate up through the RPM range. It just gets bogged down and dies. If I let off the throttle as it starts to die, it will drop down to a steady idle again?

I'm not sure if it's a Carb or ignition issue?

[Woznaldo]

Here's a datalog for my last run in MSword format that you can just save as .msl to view in a datalog viewer program, like MegaLog Viewer, or save as an excel doc to view the raw figures.

[Woznaldo]

When I say "save as" I mean, change the name of the file type, as in delete .doc and insert .xls or .msl

[Woznaldo]

One of the guys on MSExtra forums has had a look at my datalog and said that my RPM signal is noisy which maybe why I'm getting problems.

I'm going to change the earth for my EDIS set up (direct to the battery (-)) and see if that improves matters. All my RPM signal wires are shielded twisted pair from the aircraft world so top quality.

I'll report back after the earth change...

[Woznaldo]

OK, got the earth changed to the Bat (-) terminal and the idle seemed to be a lot more stable but when I tried to give the engine a little rev, the idle got lumpy again and didn't want to rev at all after that.

The MAP seems stable but the AFR is very jumpy, like the revs. This really has me foxed at the moment?...

[Woznaldo]

I've made some more changes including the addition of R type Spark Plugs and the addition of a Capacitor between 2 of the pins on my MS Processor (in an attempt to prevent resets) but the erratic idle persists!

The engine seems to idle really well at the moment (probably the R type plugs) but, when I try to press the accelerator, the AFR goes really lean (18s) and the engine dies unless I let off.

I can pump the throttle to get the revs up but when trying to hold it (at 3000 rpm) the engine hunts between 2000-3000 rpm? It's like fuel is cutting out and coming back in again?

I'm going to short the fuel pump out to eliminate MS cutting the fuel pump?.....

[Woznaldo]

Shorted the Fuel Pump so it was on constantly, but no change? Could something wrong with the Carb produce these symptoms (the hunting)?

[Tony Walker]

Air leak on the carb, perhaps accelerator pump needs adjustment or diaphragm split.

[Woznaldo]

Thanks Tony, I'll take a look.

[Woznaldo]

I've just rebuilt the carb so there shouldn't be any issues with diaphragms but, I'll have a look anyway.

I tried spraying carb cleaner to detect an air leak but nothing found?

[Woznaldo]

I've had the Carb off and all the diaphragms are in good condition and the accel pump is still set up correctly.

The engine idles beautifully and will rev cleanly if accelerated slowly with no misfires. It's just the quick revs that seem to make it stumble?

I might have to put the AEI back on just to confirm whether it's Carb or MS at fault?.....

[SCHWARTZ]

Woz mine does this from idle but when over about 2k you can rev it as quick as you like its just the initial stab from idle. I have to look at the fuel map and accelerator enrichments so if you're in the same boat it may just be carb setup. I still think it could be my tdc sensor and or signal to it at fault. What are you using?

[Woznaldo]

I'm using one of Scoff's VR Sensors and it's wired up using aircraft quality twisted wire shielded pair.

I'll try to do some quick revs when the engine is already at 2000 rpm and see how it responds.

[Woznaldo]

Fired up the engine again today and although not perfect, it did seem to respond to quick rev pulses above 2000 rpm quite well?

I might just leave it at that until the suspension is back on and take it for a road test.

Thanks for the help so far.