Violent Bucking M20

[PeterCip]

OK, so the car had been running fine under boost for two years with the megasquirt stand-alone fuel, and a boost/timing retard by MSG.

All of a sudden, the car started acting up, and would "cut out" under random load conditions.. Some times it would happen at cruising speeds, sometimes under acceleration. I have recently replaced the plugs, and the Relay cable(thought there might have been a short somewhere in the cable) and cleaned all the contacts in the system.
I'm pretty sure that it has nothing to do with the MS, because after all, I haven't touched it in quite sometime.
I'm gonna get the laptop hooked up on my way home from work, and see if i can't see a lean or rich condition at the time of cut off.. It really feels like a fuel cutoff of some kind. But if it goes rich, it may be that i am losing spark.

So, when i am moving, accelerating, whatever.. The car will lose all power, for a second, and then return.. The lights in the dash, and all electronics stay on, so i think it may lie in the fuel system/ignition only.

Can't be the AFM, because i don't have one..
Any ideas what else would be causing such a harsh hesitation?
Oh and it happens under boost, and non boost condiditions..

Thanks in advance,
pete

[Addissimo]

Have you replaced your o2 sensor lately?

If you're running boost, and ms is getting bogus o2 readings it could be supplying too much fuel, or not enough.

Wideband o2 sensors are alot more fragile than closed loop- if you're running your daily with a wbo2, i'd suggest your replace it at least once a year.

-Addis

[PeterCip]

Thanks, but let me clarify a few things:

Ok, the wideband sensor doesn't come into play with megasquirt, since i have the EGO turned off. Also, its a wideband sensor, and its about 2 months old, and is giving accurate readings as far as i can tell.. I use it mainly for diagnostic, tuning purposes. I should really get a data log of the event.

I wonder if this type of behaviour would be related to the fuel pump or filter?? the filter is 2-3 years old, and the pump is less than one.. any ideas?

And remember, its happening boosted or not.

[Addissimo]

Under flat line acceleration, or cornering?

Always at the same rpm?

Have you checked the connector on the fuel pump? Mine went bad and I just streight soldered the wires to the fuel pump.

Also check to make sure that you have a solid connection for switched 12v coming from your ignition switch. I also had a problem with this, when I cornered, it'd tweak a bit and cut the switched 12v long enough to stop supply fuel, and turn my ecu off- then as soon as I got out of the corner it'd act perfectly normal.

-Addis

[PeterCip]

I'll check the 12 volt source in a few.. the weird thing is, it happens under all conditions, randomly. Some times it happen cruising at 70, 2500 rpm.. Sometimes hard acceleration.. Sometimes it happens a whole lot(cutting in and out the whole drive) sometimes its only once.. I can seem to make it happen if I pull through the whole RPM band, and stress the engine.

And I think that the ecu stays on. I'll know for sure when I do some data logging during a road trip this weekend, and on my way home today at lunch.

As far as the fuel pump connections, they're new. I figured I might as well replace them out when i had the gas tank out.

Could a filter cause this? or maybe the Crank angle sensor? Perhaps there is an angry midget in cylinder 2?

seems urrebody else is scared of this one ;)..

thanks for your interest Addissimo!

[Addissimo]

haha- i'm fitting sds on my m50- so i realize the time it takes to get a standalone figured out.

I think the midget is probably your best bet.

You can check the fuel filter- just remove it and put the fuel inlet side down into a jar and shake it a bit. all the fuel will dump out- if its really dirty, try replacing it.

I dont know why a crank angle sensor would all of a sudden start this madness- unless you lost a magnet or something, or there is thick thick grime over the sensor...

[PeterCip]

Yah i'm stumped.. hense the post.

I don't think its the stand alone, but will verify that in about 10 minutes on my way home.. as for a thick grime on the CAS. There might be.. i'll wipe it down when i leave today.

Damn midgets always hitching rides.

[nando]

check the following for corrosion: fuel injection wiring harnes, throttle postion switch and harness, and check the throttle body coolant lines for signs of leaks. Also test the crank posistion sensor, and your coolant temp sensor.

you can also try unplugging the TPS (with the car OFF), and run without it. I had a very similar problem that turned out to be corroded wires because of a coolant leak at the throttle body. coolant got into the injector harness, I believe the car was simply cutting fuel (all electrical systems kept working, and the check engine light would flash momemtarily). my idle was off but it didn't buck anymore. I did that for 2 months until it warmed up enough for me to fix it (autocrossed it that way too, boy was it slow).

[PeterCip]

Ok, so I just changed the fuel injection harness last night, with the relay cable.. i unplugged the idle portion of my "TPS".. which is now two seperate contact switches.. i thought maybe the idle contact switch was shorting, cutting fuel and spark (idle condition) but it didn't help.

Coolant temp sensor is working, and MS see's the appropriate warm up times..
I'll check to see if its cutting fuel.. i'll know when i watch the logger on the way home.. cut fuel = crazy lean..

I'll repost after my drive with a data log.

[PeterCip]

I found 'loose" injector wire that provides power to one of the banks after my drive home today.. i'm gonna tighten it up, and see if it helps. I wasn't able to get the car to buck at all on my way home today (30 minutes, even with the loose wire). I tried every scenerio!

Hopefully in my 5 hour drive, i'll find something. I did notice some odd instantanious lean spikes, which i am gonna attribute to my loose wire.. so, i'm gonna tighten it up, and see if it helps.

I'll keep y'all posted...