engine and drivetrain Odd Running Behavior.

[eurotrash]

So, last week, I had something start to creep in..  I haven't had time to do a thorough trouble shoot since, only a quick jiggle of the electronic ignition power wires, coil power wires, and that's about it. I haven't had time to work with it, and the issue is burning my brain as I sit here at work.  Thought maybe it would be good for discussion.

 

Here's the scenario.. 

 

M10 (fresh rebuild)

Dellorto side draft carbs (accelerator pumps)

Electric fuel pump (4 psi)

Electronic ignition distributor (123ignition)

 

First instance and evidence of a problem:  When I was coming off a cloverleaf and hit the gas, it rev'd to go and then just cut out. Died. Idiot lights lit up, etc. Restarted after a couple tries, no problems immediately after..

 

The next time I drove it, it began to stumble/misfire hard at about 3k rpm, unless I approached 3k gradually..but if I needed to GO, it would miss fire hard. Always at 3k.

 

Next drive, when going over a rough-ish rail road crossing at about 30 mph, it cut out as it had the very first time. Died immediately. Restarted just as immediately.

 

Now, it revs fine when sitting still, to 6k.  But when I try to take off in first, it cuts out,stumbles... unless I take off very slowly and smoothly.  Runs fine beyond that.

 

What ever it is, its seems to be across the board.  As if electrical.  I thought maybe it was happening when the engine was torquing, and maybe a wire was getting pulled.  (That is when I messed on the wires while it was idling, kind of in the middle of the problem as described above.)  I couldn't replicate the problem.  By neither revving, nor by manually moving wires that looked like they might get tensioned under load.

 

Not sure if the pump could be the culprit?  Doesn't seem likely.

 

Internal problem with the ignition??
 

Discussion welcomed.

Edited June 4, 2014 by eurotrash

[Mike87]

I'm thinking something floating around in the fuel tank not allowing adequate fuel to flow. Not knowing the car and all it's little nuances, it is just a guess.

[Arizona02]

ignition problem,  the spark is weak on acceleration when more spark voltage  is needed to fire the plugs.

[KFunk]

It sure sounds like a fuel problem to me, as I've had my share.  Cloverleafs tend fling fuel side to side in carb bowls, and what little you had in the bowl doesn't make it to the engine. 

You can rev it just fine in neutral because it takes very little fuel to do that.  But as soon as you put a load on it like heavy acceleration, it cuts out because not enough fuel.  Smoother throttle alleviates this, by requiring less fuel. 

 

The first place I'd look is the fuel level in the carbs.  I'm not sure how the Dellortos work, but that's been my problem with my webers a couple times.  Fuel level has to be perfect (and not just float height, as that's not a reliable way of measuring it, cuz shit gets old and bent). 

Beyond that, yeah check any fuel filters, fuel inlet screens, and screen in the tank. 

I've also had problems with the o-rings on accelerator pumps on my webers.  If they're not sealed right, it'll stumble bad when you really hit the gas.  Once again, not sure how that works on dellortos, but I'd check those accelerator pumps. 

Edited June 4, 2014 by KFunk

[Parkertii]

I had a simular but slightly different scenario a week or so ago on a freshly built engine. Mine ended up originating from a ballast resistor wire that was not needed with the electric ignition i am using. The previous owner had wired in a older style ballast resistor and i had missed the old one and accidentally reconnected it when i installed my new motor. 

The car would run great when it worked but then would completely die, sometimes after a half hour of driving fine and other times after just several minutes. 

im not familiar with the version of electronic ignition you have as i am using the Crane system but if your coil does not need a ballast resistor check to see if you have the "sneaky wire" type which is what was causing my intermittent problems.    

here is the link to the thread regarding my issues

http://www.bmw2002faq.com/topic/154311-tii-dies-under-load/

[eurotrash]

Thanks for all the input guys. I'm going to try every suggestion in some logical order.

I also found this during a search about the distributor...

"..If your engine develops an intermittent misfire under load, you should replace the ignition coil. A weak coil that just barely functions with points will fail when pushed by the electronics in the 123 distributor which switches the coil on and off much faster."

I am still running a stock coil.

Edited June 5, 2014 by eurotrash

[Emyers]

If the coil does not do the trick, maybe reinstall the "steam driven" distributor (If you still have it) to see if the 123 item is at fault.

Earl

74 02Lux

02 M roadster

72 Volvo 1800ES

[eurotrash]

     I drove the car in to work today.  But first, I swapped in another black coil from some ole' parts car.  No change.  I still had to milk it off the line, as it would stumble if if revved it at all when letting the clutch out in first gear...  Once lunch rolled around, I picked up the (123ign. recommended) Bosch blue coil up the street and promptly installed it.  The immediate difference was that the misfire when taking off went away.  And with the short drive I had back to the shop, I saw some stumbling when running through the gears to get up to speed on the entrance ramp. But the 3k cruising/toe in hesitation I was getting before (which was also new with this issue, the car ram silky smooth before) seems to have been remedied with the coil.  In the end, the drive wasn't long enough to burn off any build up from fouling over the last week.  I will report back later once I get through the 25 mile drive home, and really put it through its paces.    

 

Tonight I will go through the carbs as needed. Sync them, adjust idle, etc.  

[KFunk]

Imagine you're sucking the milk out of a bowl with a straw, while someone else pours some in at a constant speed.  If you suddenly suck it at high speed, faster than it gets poured in, then you're gonna empty that bowl out quickly and suck in some air and start coughing.  If you just ease into at a similar rate as what the person is pouring, then its smooth sailing.  If the bowl is tipping side to side (from cornering or acceleration), then it's gonna be harder to get that little bit of milk at the bottom. 

Improving ignition will help with burning what little fuel you do get, but you may be masking the issue.  Ya gotta have a nice steady fuel level in that carb no matter how hard you hammer on it.

My Datsun even has a little glass window on the front of the carb with a 'Fuel level' line, because it's so important to have right. 

[eurotrash]

I hear you Kevin.  I'm just starting with the simple, and very over due, coil swap first.  I have been down the road of jumping straight to the big stuff, and being wrong. IE, both brake lights being out in my DD.  bought a 100$ brake light switch, put it in, and it didn't fix it.  turned out to be both bulbs had failed at the same time..  who'd a thunk it. 

 

OH, yeah. Coil didn't fix it.

 

I have a small, cheap, fuel pressure gauge in line, before the regulator.  The electric pump is supposed to be 4 psi, and is only showing a bit more than 3, when it used to hold 4 solid.  But then, 3.5-4psi is the target,  and the regulator was set to 3.5 anyway.. not sure if this is an indication of anything.  I bumped the regulator to 4 and it make no change..

 

I am trying to get my brain wrapped around how normal toe in, off idle, can cause a car to immediately starve for fuel.  If it misses off idle, it misses all the way through the rpm range.  If it doesn't miss at idle, its fine to about 3.5k before missing. Other times its fine..

I ran it up to 6k yesterday, a few times, with NO stumble at all.  Did I mention I can hand rev it like mad with no stumble???

 

So weird.

 

Could it be that a float is sporadically sticking when the motor angle changes under load??

 

I'm going to pull off and inspect the cap and rotor, look at the plugs, etc. before I move on to fuel delivery.  That would be the last of the easy stuff.  I will research how to confirm fuel level on Dellortos today.

[eurotrash]

http://sideways-technologies.co.uk/forums/index.php/topic/1048-setting-dhla-dellorto-dellorto-float-fuel-level/

[KFunk]

Our E30/M20 Lemons car would rev like hell in neutral, with NO fuel pump running at all.  No fuel pressure whatsoever, and you can still rev it up by hand with no stumble.  Just siphon action alone is enough.  Under load, you need way, way more fuel.

Acceleration does tip the float bowls as well.  With the webers, if the fuel level is too high, then straight line acceleration will tip the float bowls, and make the fuel spill into the barrels, essentially flooding the engine and making it stumble.  It acts like there's not enough fuel, but its actually too much!  That's just the nature of the webers.  That link looks like the right track for dellortos, no time to read it myself now, though.

Edited June 6, 2014 by KFunk

[eurotrash]

here's some afr data when this happens..  its interesting. not sure what it means. 

 

 

http://www.youtube.com/watch?v=gNle_opeOAg

 

 

Edit:  in scrolling through the video slowly on the phone, I see 13.8 at idle.  12.3 as a low (high?) during first gear revs and then it  goes lean to the 19s when shifting. Second gear hits 11.4 at 4 grand, and then in third it hangs at 13 to high 14s for the whole range..which is awesome.

 

You can't really hear the misfires that well, but in first it staggered pretty hard in the beginning, the tach needle shows it.

 

ideas?  Still fuel level you think?

Edited June 6, 2014 by eurotrash

[eurotrash]

Got it. Scraped the posts in the distributor cap clean. All good.

Good new is, the bowls are both at proper fuel level, the accelerator pumps are balanced and the AFR read out is installed into the pod. And I test drove after each one. Nothing helped until I scraped the posts clean.

Ha!!

[peterschop]

Good, you should be able to make it to Arni's tomorrow.