4cu small throttle opening poor running

jikovron · Post by **jikovron** » Mon Jan 21, 2013 9:24 pm

hello all not much of a poster more of a lurker type but certainly enjoy reading up the experiences people have with various projects on here

just looking tap into other peoples v8 knowledge to see if anyone has had similar experience of a 4cu rover 3500 intermittently running badly and what caused that

the intermittent problem is limited to idle speed and small cruise throttle openings ie up to 45mph (snatchs and jerks really quite violently @ 30mph) , above 50 the roughness isnt felt unacceptably badly but i notice the vac gauge shows it needs 5in/hg more to maintain the cruise speed than when its running normaly at most cruise speeds

when i come to a stop and allow it to idle it starts to hunt up and down (400-900rpm) in a pulsing sine wave idle (at around maybe 0.75hertz ish) and will normally stall despite the idle screw and co setting being correct(vacuum rises and falls in time)

usually after 40mins driving the engine will inexplicably chime into normal running and idle properly

the engine is in a triumph dolomite,,but the installation is all as stock
overrun vac cuttoff has been bypassed
3 ecus all do the same thing (some make the engine feel less responsive but i guess thats variable mapping)
throttle over 10% is strong and smooth
cold running is smooth as silk (fast idle 1100rpm)
3 dizzys didnt affect it,,opus one,,the latest one and a points dizzy
fuel pressure is good and constant

not sure if the air flow meter could be the cause, or a temp sender having a duff reading at certain temp ranges

ive also tried a 14cux system but had if anything much less success running wise massively lean,,and its idle valve created a slowly hunting idle

anyones opinions and tips as to fixing the efi,,or alternative fueling will be greatly valued so i can hopefully drive around enjoying 8 cylinder flexibility rather than it being akin to a lister single diesel in a washing machine

cheers
Ron

DaveEFI · Post by **DaveEFI** » Mon Jan 21, 2013 11:26 pm

Does unplugging the TPS make any difference?

ramon alban · Post by **ramon alban** » Tue Jan 22, 2013 11:23 pm

Hello Ron, Working through all your reported symptoms I think the rythmic hot idle/low rpm problem is most likely caused by a minor air leak masked when cold by the CTS created enrichment occuring at low temperatures.

The eventual stalling is because the uncontrolled (ie: not monitored by the AFM) rogue air leak reduces the available torque caused by the weakened idle mixture to an unacceptably low level.

It does not occur straight away because some fuel vapours hang around in the plenum

You should use the dynamic leak detection process, to the letter, as specified in my Plenum Chamber essay PDF as found in my Efi component archive.

http://www.vintagemodelairplane.com/pag ... nts01.html

the process is also detailed in my Efi ops manual.

The reason for the inexplicable reversion after 40 minute, is, er, "inexplicable" and does not fit my above analysis.

So there may be two fault conditions or the air leak mysteriously closes when engine bay reaches a high temperature. ????

There are other unmentioned potential air leak locations at the air intake hose, plenum hot spot bolts, inlet manifold gasket seals and the rocker gaskets.

While dealing with the Plenum, check the idle and breather galleries and system are clear, also the 40 thou hole in the breather located on the LH rocker cover.

Finally, dont overlook the possibility of an electrical connection problem with the Efi wiring loom usually to be found with strategic cable wriggling.

A hot engine bay can also affect local wiring/connections.

Good luck and happy new year.

ChrisJC · Post by **ChrisJC** » Wed Jan 23, 2013 8:52 pm

The other thing to try is to alter the timing significantly (don't forget to mark the original position).

Chris.

jikovron · Post by **jikovron** » Wed Jan 23, 2013 10:01 pm

may i say thankyou all very much for your replies, i shall have a drive with the tps disconnected to see what happens as a cheeky easy test but it does change voltage smoothly over its operation

the timing is ok and stable ,advanced till it pinked,then backed back as an interim ,it doesnt have a pointer so had to take out a spark plug and time it off btdc both valves shut haha then do the above

the air leaks hypothesis could indeed be a valid factor for definate i agree and i have been reading up on your pdf link in prior times for greater understanding of various parts of the 4cu system, a really impressive piece of reading i must say and will have a look again for the section mentioned
one thing i note, i removed the hot spot plate due to corrosion of the steel fittings and left out the bolts, does the tapped hole run right into the throttle plate bore
also i plugged up the hole for the crankcase vent system and did away with it and adjusted the afm to suite, although huge co screw adjustments make little change (pressing the flap in though makes it stall which i imagine is through increased richness)

many thanks again for the thoughts on the matter

ramon alban · Post by **ramon alban** » Wed Jan 23, 2013 11:51 pm

Oops! You have probably induced three faults as a result of redesigning your Efi system.

On a clean plenum one of the empty hot spot bolt holes is open to atmosphere making for a rogue air leak.

Also you may be lacking any perceived hot spot benefits.

http://www.vintagemodelairplane.com/pag ... ety01.html

Then there is the problem of blocked off or modified crankcase ventilation.

Have you made alternative arrangements for relieving crankcase pressure, or perhaps the gasses have simply blown an exit path through one of the engine gaskets/seals?

Did you compensate for the missing breather by adjusting the AFM innards?

CO AFM control will return after you correct any rogue air leaks.

Owner/enthusiast modifications do tend to make remote analyses (hypothesis?) more difficult. Perhaps more akin to guessing!

jikovron · Post by **jikovron** » Thu Jan 24, 2013 11:20 pm

i tried removing the tps plug and it basically ran the same but with a sluggish throttle response but if power was fed in gradually it had the same torque

i checked the hot spot and it is fitted, but i omitted to run coolant via it hence me thinking i had removed it
the breather from the rocker covers basically vents into the engine bay but i'm looking at fitting a catch tank rather than oiling up the bonnet
and its the inlet to the throttle i blocked up

i didnt adjust anything inside the afm just wound the co screw out to take into account the slight increase of flow through the afm due to the blocked breather vent

i fitted yet another ecu and it idles smoothly now and is much improved slow speed running but it does have a very slight hiccup on top gear overrun which i imagine is possibly just the age of all the components and the points dizzy,, i shall carry on tinkering with it following the laid down tune up instructions and thank you all for the most helpfull insight on the matter

ramon alban · Post by **ramon alban** » Fri Jan 25, 2013 5:14 pm

jikovron wrote:i tried removing the tps plug and it basically ran the same but with a sluggish throttle response but if power was fed in gradually it had the same torque

That's normal behaviour because the acceleration and full load enrichment circuits are not being engaged with the TPS being disconnected. So the TPS is probably OK

jikovron wrote:the breather from the rocker covers basically vents into the engine bay but i'm looking at fitting a catch tank rather than oiling up the bonnet and its the inlet to the throttle i blocked up

OK! Lots of folk do that and can usually get away with it by accepting the change in performance because with the rocker cover being open to atmosphere, then it acts like an air leak into the inlet system. But that area is also subject to complicated pressure changes due to the crankcase gasses behaviour.

As a demonstration I often show owners how, on a properly set-up breather system with the car idling smoothly at (say) 800 rpm, removing the oil filler cap immediately induces an unacceptable lumpy idle.

Ergo, its the same as having a rocker cover gasket breached or the breather system open to atmosphere.

If one temporarily leaves the oil filler cap off and try to adjust the CO or Idle speed control screws it is not possible to get back to an acceptably smooth idle.

Unlike the carb breather system, the Efi gubbins have to ensure a leak free environment for the slight suction always present in the inlet tunnel to consume the crankcase gasses via a fixed orifice and to compensate that function, there is a very small inlet hole on the LH rocker cover.

By upsetting the system, one has no option other than to fiddle and tweak other controls to compensate still further.

I've been there and tried all the alternatives, but to no avail.

Unfortunately, all this fiddle and tweak can only happen at idle, whereas one has no idea how to make any compensations to a wide open breather, at normal motoring speeds, unless on a rolling road - which I never tried and without which - to make the system behave, therefore, would be down to luck, methinks.

On the other hand, if you are a religious person, praying might help!

i didnt adjust anything inside the afm just wound the co screw out to take into account the slight increase of flow through the afm due to the blocked breather vent

From the above, I think this qualifies as fiddling or tinkering, as you predict?

!

i fitted yet another ecu and it idles smoothly now and is much improved slow speed running but it does have a very slight hiccup on top gear overrun

So the former ECU comes under suspicion also, plus, anything that happens on overrun will be compromised due to the disconnected overrun control system.

Dont get me wrong, I'm happy to be analysing what might be a solution to your compromised system problems, it sure stretches the old grey cells, but I am reminded of a jokey tale told by a totally lost person looking for the main thoroughfare of O'Connell street in uptown Dublin, to which a local resident offered this advice:

"If I were you Sir, I wouldn't start from here!" (add your own Irish Accent!