Thread: V8 - Load stalling driving me crazy

Is the throttle plate adjusted properly? When the throttle is closed there should still be an airgap where the throttle plate doesn't quite touch the throttle body bore.

This behaviour is a characteristic of a 14CUX and I still have it a little even after changing the whole inlet manifold to a Thor. LOL. So my conclusion is it is not mechanical but electronic in nature.

I believe that it is caused by the stepper( ie the ECU confirming the revs) not being able to react quickly enough to the change in load. With mine I find if I let the idle stabilise for about 10 seconds ( which seems an eternity at the petrol pump) that it minimises the issue. This is after start in neutral where mine revs because of the Unichip aligning, then it steps down and may fall to 500 then up to 650-700RPM. Then wait 10 seconds then into drive. My theory is that the stepper closes right up which cause s the revs to drop but the time delay in the ECU recognising the lower revs causes the revs to drop below 500 and the ECU then to shut off fuel.

Also mine got MUCH worse when after I had a dyno tune where they advanced the timing at idle by adding 5degrees to my Unichip. I had the tune reversed to have nil additional advance under 1000RPM and it became much better.
So if you have a lot of static advance , you should back off to 7-8 degrees.

It should IMHO have got a bit better when you set the base idle up a bit . How did you do it? Did you block the hoses to the stepper on both sides?Then set the base/curb at say 600RPM. Also mine seemed to get better after I cleaned all the gunk from around the throttle butterfly.

It is only a minor problem for me now and mainly happens in reverse, where I think the load is higher from the trans.

But to repeat it stayed the same with a different complete manifold, stepper, temp sensor, TPS, adding o2 sensors, richening the MAF to 1.5 Volts ( recommended with 02 sensors). I think it may have got a tiny bit better after I fitted Iridum plugs also.

Not much left but the ECU. But they do not all do it.

I have another ECU at home and they changed the part numbers several times. probably trying to fix glitches like this. I really cannot be bothered to fit it to see as now it is only a minor prob.
Regards Philip A

Mine was doing this when my coil was failing. I would try to back up over a lip into my shed and it would stall when I took by foot of the accelerator. I replaced the coil and it's all good now. Very responsive and doesn't stall. I was also getting a bit of a miss when warm as well. Might be worth a look.

Hi Guys,

thanks for your answers.

I will have a look at cleaning the throttle plate... I have checked it as per the manual, where it says the difference between top and bottom with a depth vernier should be less than 0.5 mm which is ok on mine... but I am not sure about the remaining airgap... maybe it is too much sealed at now ??
BigJon, can this gap be seen/checked/adjusted easily ?

Philip :-) I have been looking at going Megasquirt for a while, to forget the 14CUX, but have not found the energy to go this way yet... mainly because of the tuning involved.
I did the base idle as you say, and set static idle advance with no vac at 6 deg BTDC.

Landover, one of the few things left unchanged by now on the ignition side was the coil... your description is similar to my problems, so maybe I should try a new coil... the only thing is, if it was the coil (ignition related), why would it behave perfectly with additionnal air entering the plenum ??

Thanks again... any other ideas welcome :-)

Cheers

Erik.

I usually use a piece of paper to check the air gap. Slide a slip of paper into the intake and let the throttle close on it. You should be able to pull it back out without the throttle plate jamming it in place.

if it was the coil (ignition related), why would it behave perfectly with additionnal air entering the plenum ??

Because you are speeding up the idle, there is just more headroom above the ECU cutoff point. Even though it is unmetered the difference in leanness is not enough to matter.
You could do the same by increasing the base idle to 800 RPM or so.
Regards Philip A

BigJon,
Thanks for the tip, I will try that.

Philip,
this is where it becomes crazy... with everything plugged as it should, I even nearly completely unscrewed the base idle once, taking it to about 1000 rpm... and it will still make the same trouble, with an irritating then high idle !

On another hand, if I unplug the fuel regulator vacuum line and let the plenum suck air by this port, even if I set back the base idle just at about 600/700 rpm, it never make the stall problem !!! crazy.

I have also tried something else. I plugged everything as it should and tried giving the plenum some air by using the charcoal canister port on the plenum... guess what, the problem is still here !!!
The only way by now to get rid of it, is to let air get into the plenum by the fuel regulator vacuum port on the stepper housing... you still say crazy ?!?

Last try... I ran a hose from the pressure regulator vacuum port on the stepper housing to a nipple on the side of the air filter box (which normally takes a breather hose from the LHS rocker cover)... and the problem is still present. Unplug the hose from the air filter box, and no stalling then !!! not enought air when plugged there maybe... more and more crazy I say :-)

Thanks again

Cheers

Erik.

On another hand, if I unplug the fuel regulator vacuum line and let the plenum suck air by this port

If you unplug the fuel regulator then you are richening the mixture which also will give a more stable idle.


<LI id=jsArticleStep1 itxtvisited="1">

<LI id=jsArticleStep1 itxtvisited="1">When the engine is suddenly under heavy acceleration, the vacuum drops off momentarily and then recovers within a very short period of time. This sudden drop in pressure during acceleration also affects the fuel pressure, as the injectors are suddenly opened longer. The fuel pump takes a second to catch up with the pressure, so the fuel pressure regulator reacts to the drop in vacuum by closing the fuel return line momentarily. This gives a momentary boost in fuel pressure. <LI id=jsArticleStep1 itxtvisited="1">

Read more: How Do Fuel Pressure Regulators Work? | eHow.com How Do Fuel Pressure Regulators Work? | eHow.com<LI itxtvisited="1"><LI itxtvisited="1">Regards Philip A

PS hmmmm, i wonder if it is the fuel pressure regulator not increasing the pressure quickly enough when teh load comes on? I have a new one that I have been meaning to fit but haven't yetr got around to it.