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PeteMck

Rover 4.6 V lumpy idle then revs by itself

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Hi guys. After some ideas. So finally got the engine running all be it badly. It sits there on a horrendous lumpy idle nearly stalling and then I'll rev itself and runs quite nicely but quickly goes back to nearly stalling. I've put a pressure gauge on the fuel rail and the pressure actually drops when it revs itself. So wondering if its trying to over fuel, which eventually causes the pressure to drop which reduces the fuel and so it then revs, and then the fuel pump recovers the pressure and it goes back to over fueling. Pulled a spark plug out and it's pretty sooted up after a very short period of time. Going to stick a laptop on it tomorrow to see what the values are but just wondering if my logic makes sense or if anyone has experienced this before?? 

Edited by PeteMck

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yer i think its running too rich. ive had a bit of a fiddle but cant get it to idle properly. Its now either revving too high and has the odd pop or bang, or if i drop the amount of fuel then it will start nicely but instantly rev itself up to 1600/1700rpm and back then cuts out instantly. I had the truck in pieces for a quite a while so its been since it was all apart. After getting a laptop on it the VE table and spark table had changed the pressure to 100kpa and revs to 5000 rpm for each row / column with fuel values all at 50. cant remember what the spark table value was but it had done the same thing. If anyone has a msq file for MS1 for a 4.6 GEMS rover v8 that would be great. 😄😄 ive tried googling it but ill be damned if i can find one. Have lost my original map as the laptop that i had all that on has died and i cant find Niges original disk. Also if anyone has any ideas what could have caused it?

Edited by PeteMck

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Have you set the base idle? It shouldn't stall after a warm start then.

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How do you set the base idle? I've basically just guessed (using other rover v8 maps) to try and get my ve and spark tables back to something that look vaguely correct. It's got a Bosch pwm valve in it as well. Whether that could be causing problems? 

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4 hours ago, PeteMck said:

How do you set the base idle? ...

Have a look in the workshop manual.

On the 3.9 there is a concealed screw on the inlet to the plenum, which controls how open the butterfly is at idle. You will need a tachometer and a warm engine, but with a bit of fiddling you might be able to get it to run for long enough,

Cheers Charlie

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OK. So managed to get it up to temp and had a fiddle with the idle screw and once up to temp it will at least stay running but is idling around 1200/1400 rpm. It will rev but it's slow to react and gives off a few pops while doing so. Also pops while cold and trying to get the temp up. Any suggestions on how to get the idle down? Also not getting anything from the lambda sensor. I've got white grey and black wires on mine and have swapped the white and grey round but as far as I can tell its made sod all difference. Also is it wide or narrowband? (from nice) Could this be why it's now running badly when up to temp? Thanks again for any help.

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The lambda will be narrow band. Pretty much totally useless while getting it running; semi useful for tuning cruise and idle sections of the map when you're up and running. 

Does the fuel pressure regulator have a vacuum connection to the plenum or manifold? Pressure dropping when revving doesn't seem right at all, so there could be a problem there which is going to make things very hard to tune around. Some regulators are designed to change pressure depending on load, but the other way round usually! I'm not familiar with the RV8 setup, so maybe someone else could chime in here? 

All else being equal, popping is usually caused by a lean condition, not rich. Misfiring can be caused by running rich, but unless the ignition system is particularly poor, this usually only occurs when really rich (9:1), at which point you'll see black smoke out of the exhaust and it'll just sound a bit rough. Sounds like you're fighting a mis-fueling issue with the idle and getting "lean surge" to me, particularly if as the revs pick up it briefly moves into an area of the map which gives a not more fuel. Lean can give a smell of fuel if its misfiring and heading out of the exhaust unburned, so don't always trust your nose...

If I could offer one piece of advice it would be to get a wideband with digital readout. You can get by without, but it's a bit like reading tea leaves and chicken entrails unless you've got some solid prior knowledge of what lean/rich, under/over advanced sound, feel and smell like as you're tuning. Which you'll gain doing what you're doing, but might as well give yourself an easy time of it in the meantime :i-m_so_happy: You'll also end up with a much better final tune, so a good investment all round if the budget stretches.

HTH! 

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Hmm 🤔

The fuel regulator goes to the plenum, which the ECU is Teed into. 

As for running lean I've got a gauge on the fuel rail which reads 2 bar and the engine splutters away, then it will rev up to 1400ish and the pressure will drop to 1.5 bar and the engine drops back down to spluttering and the fuel pressure goes back up to 2 bar. Doesn't stay at 1400rpm, it's just as though someone has blipped the throttle. 

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You need to get the basics right, block-off the PWM IAC pipes and see if you can get it idling steady with no IAC control, just the base fuel + ignition map - only then should you be worrying about the idle valve.

The surging/stalling could easily be a simple setting in the PWM control but there is no point f***ing about if the engine won't idle on its own.

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Will blank that off and try it. Does anyone have a base map for a 4.6 that they know works? 

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OK. So blanked of pwm. Have got a an idle that floats around 950 - 1000rpm MAP around 52. Fuel pressure 1.5 bar once coolant temp at 180F it's pretty stable. Big delay if you try and rev it at all though. Any ideas on how to get idle speed down? 

Edited by PeteMck

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From memory idle speed should be about 750rpm, so it is not far off the mark.

Have you checked the ignition advance with a timing light? Too much advance will increase rpm,

Cheers Charlie

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nope. havnt done that yet as only just been able to get it to idle :D  guess thats the next thing to check. Anything i need to know when doing it? Anything i have to change in MS? do i have to disable spark table and use a fixed advance? TIA 

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Again, start from basics;

A Rover V8 will start & run from a wildly "wrong" map - as long as some sparks and some fuel happen in roughly the right order it *will* fire. Your engine starts & runs so that's step 1 sorted.

A bit of hunting on idle can be caused by the fuel & ignition maps when it's in the idle zone - so unless anything is obviously broken you just need to play with those until you get a nice steady idle.

Hesitation on acceleration (once your map is reasonable) will be down to accel enrichment (what would be a throttle pump on a carb) but there is NO POINT worrying about that until you have the basic map somewhere sensible-ish, otherwise you're "fixing" the wrong thing in the wrong order, and when you DO get the fuel map right the accel enrichment will then be way out of whack.

I thought Nige wrote a big thread about basic setup & tuning, might be worth a look if you haven't read it.

When all your settings are out of whack there's no point running around fiddling with fuel pressure and stuff - cover the basics 1st before going off on one and potentially creating 5 new problems!

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Could the maps be causing the high idle then? Will have to have another read of that to remind myself. Have read so many different things recently it's all becoming a blur. Lol. 

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😣 any suggestions on what mechanical issues could be causing it? This is starting to hurt my head 😂

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Throttle butterfly adjustment, vacuum leaks in all sorts of places (Brake cleaner is good for finding them), not blocked off the ISV port properly, worn out throttle butterfly mechanism/bushes and knackered seals, leaking brake servo diaphragm, just about any air hose on the engine, not to mention inlet manifold not seating properly, misalignment issues due to having heads shaved too much, excessive blowby ramming air into the crank case, not using the proper restrictor on the engine breather to plenum.

This is is all very basic stuff, you need to realise an engine in poor health will still not run right just because you MS it.

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Reconditioned engine gone into it so hopefully should be in reasonable health. Will double check all the pipework again. Have next to no experience with v8s which makes life harder. Should have stuck to diesel. Lol have been fiddling with the butterfly valve to try and get a stable idle so may have opened that up to much. 

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If my idle pressure is at 52/53kpa is it possible to tell if it's got a vacuum leak or not? Or do they vary to much? 

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Erm, you don't adjust the butterfly to set the idle, setting idle is done by the idle bypass hex screw, next to the butterfly.

And yes a MAP of 50+ will indicate a vacuum leak, either that or a very racey cam.

 

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18 minutes ago, Bowie69 said:

Erm, you don't adjust the butterfly to set the idle, setting idle is done by the idle bypass hex screw, next to the butterfly.

Depends, if it's a 4.6 it might not have an idle screw?

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I thought they all did, but then I more often play with the shorter stroke motors... is it the later banana plenum that doesn't then?

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Just checked my photos, the early plenum does have the covered hole but can't remember if there's an idle screw in there (circled):

RV8_46_idle_screw.png

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