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PeteMck

Rover 4.6 V lumpy idle then revs by itself

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Good pic :)

The 3.9 has a cap just like that, so suspect it has the same bypass screw.

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Yer that's the screw I've been playing with. Presumably opening up that too much would have the same effect tho? OK so the hunt for a vacuum leak begins. What kind of pressure should I be expecting? 

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Most I have tuned end up in the region of 40-45 kpa at idle.

Best test is if you can get the idle down to ~650rpm.

 

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If this is a fresh install that's never run then you need to double triple check the basics - and perhaps post up a photo or three of the installation in case anyone spots a mistake.

There's a big difference between "it ran right yesterday and now it doesn't", "it ran right on GEMS and now doesn't on MS", and "This collection of parts has never run together"

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What Fridge said^

But I'd add that you're looking at the manifold vacuum the wrong way: if it's running rough, you're not going to be producing as much power as you should, which means the idle will drop. To maintain idle speed, you open the bypass or throttle stop screw. There's no air leak here, just poor tuning; this applies to timing and air/fuel ratio. As the tune improves, you'll find you have to close the bypass or stop to get the idle back down with a corresponding drop in manifold pressure. There's even a section in the manual about tuning idle for best vacuum iirc. 

Key here is understanding how and why to adjust timing and fueling. The manuals are your friends there: no amount of mechanical tinkering or dumping on a "working" map from somebody else's setup is going to shortcut that beyond getting it running to start with as you've already done. With a DIY install, there's always going to be something different from the other guy and the tuning needs to take that into account. 

Have you looked at how to adjust the tables real-time? 

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I'm gonna say it : plug leads are probably wrong as well.

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OK. So I have no manuals. Where can I find them? 

I initially thought plug leads so have triple checked those. After hours of googling I am starting to wonder if my edis ABCD wires are round the right way so need to check them. Will post a load of pictures when I next get over to the vehicle which should be Wednesday. 

I know there is no easy shortcut, I just don't want to spend hours and hours tinkering with a map to find its a mechanical issue and visa versa. 

I really appreciate all your help as I'd be screwed without it 😁

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OK. So I've rechecked the plug leads and they are correct and the edis ABCD wires are all round the right way. I did have the bypass screw wound out 5 1/2 turns. No idea if that's a lot or not...

 

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Right, bit of an update. Resealed plenum, etc,  only one I haven't done is valley gasket. Can get MAP down to around 43-46kpa rpm float from 790-860. Ive got fuel map around 58-60 and it sits there and hunts a tad, hence the rpm all over the place. Then if I stick the fuel values up to 65-67 the rpm will change between 960 and 990 and the map stays at 39 kpa. If I drop my fuel values bellow 56 then it stalls. To put fuel values into perspective required fuel set to 20. Any suggestions? Could it still be a vacuum leak? 

Edited by PeteMck

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Doesn't sound like terrible hunting, if it's running smoothly I'd say that's a level of variation you might see with a fuel/ignition map that needs a bit of tweaking around idle - I'm sure Nige and/or Bowie wrote some good stuff about tuning on here somewhere.

The short version for the fuel map around idle is you want a little bit of slope; as the RPM drops or vac increases (load) you can dip slightly lean, which causes the engine to idle a little faster and come back to the right spot. Too much slope and it'll hunt around in little circles on the map, not enough and it'll wander around naturally in a very similar way. There's a few other factors to tweak as well (did I say it's like juggling?) but that's one part.

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Yer I was reading something about that earlier. What I'm concerned / confused about is why my ve table values seem so high? Anything bellow 57 and it starts hunting like crazy. Could this be due to a poor spark map? Did get a timing light on it and it seems pretty close. Maybe only 1 or 2 degrees off where it's set. Was around 8 degrees advance instead of 10. Assuming this means I need a trim value of 2. 

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What is your required fuel setting?

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1 hour ago, Bowie69 said:

What is your required fuel setting?

20

 

bit more reading later and starting to wonder if ive got my spark settings right. does that look right?

image.thumb.png.fc12c7b026e21e2871010fdafae21216.png

Edited by PeteMck

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OK, spark settings look OK to me.

Have you verified TDC?

you mentioned earlier that fuel pressure was dropping, I'm beginning to suspect fuel pump/reg issue.

I am assuming you have fixed the spark table :)

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yer i checked tdc.

fuel pump is straight out of a p38, took it out the tank and checked to make sure it wasnt blocked or anything, plastic tank so no rust issues. did wonder about the regulator on the end of the rail. is there any way of checking them? now that ive managed to get a more stable idle and stopped the wild hunting the fuel pressure has remained more constant. the engine will rev though, so surely its getting enough fuel to hold a steady idle?  

when you say fixed the spark table...?

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If you hold the revs at, say 2000, what's the fuel pressure?

What injectors are you using?

Fixed your spark map, I mean repaired, you mention it being corrupted?

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Don't no has can't see the rail (where I have the gauge) and rev it. Will try and find out. Injectors are standard gems. Oh right Yer well I found a spark map that looked like it made sense so used that as a starting point. Same for ve table. 

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11 hours ago, Bowie69 said:

you mentioned earlier that fuel pressure was dropping, I'm beginning to suspect fuel pump/reg issue.

That's what I was thinking in my earlier post. I've seen setups which drop fuel pressure as manifold vacuum increases, which means large injectors can be run without having ridiculously short opening times with light load, but it makes no sense for fuel pressure to drop as demand is increased as Pete suggested in an earlier post. This really ought to be looked at. It's either pump, a blockage or the regulator at fault if that is the case... 

Could you post the spark table you're running, Pete? There's a lot of absolute garbage out there so it's worth checking you're starting with something sane. 

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Hmm so then if I need 60 in my ve table to get a half decent idle with req fuel at 20 does this suggest fuel issue? 

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You probably need to think about the fueling a different way: the only way to get it right for your setup is tune it yourself. With a spark table, a well set up not-too-aggressive map for a standard rover V8 will work for just about any standard rover V8. What defines it (head design, compression, head flow) doesn't change much unless something quite radical has been done to an engine. 

The fueling is quite different: There are a few injector, pump and regulator options to choose from. Displacement, manifolds, exhaust, air filter, valve size and a multitude of other factors (even the spark table) affect the fuel requirements. A map for one setup will be less that optimal for another - possibly completely off - and it might only be one of those things that's slightly different.

Gef it running using whatever means you have to. If that means changing the req fuel, so be it. If you find down the line that you're having to put silly vales in the table, go back and change the req fuel and scale the map. The actual values are not crucial so long as they give the correct AFR. 

What I'd suggest you do before going any further is verify that you've got stable fuel pressure. If its wavering about all over the place, you've got zero chance of getting a solid fuel map regardless of what you do with the req fuel, and even less chance that someone else's map will even get you in the ballpark to build on. 

 

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Right. Well I've got just over 1 bar of fuel pressure / 18psi. Standard 4.6 gems. Anyone know what the pressure should be??

I get what your saying re each map / engine being different but surely if I end up with req fuel 70 or something stupid something somewhere is wrong?

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