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VP SS surging/hunting idle after rebuild new 260 Cam

dans28

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Hi All

I have a VP SS which has been recently rebuilt using a spare VS Stato V8 which was rebuilt with Flattop pistons we added a 4001 Crow Cam which is advertised as [email protected] or real [email protected] LCA 112

This has been a bit of a project and not many parts were in working condition so I would say all the common things have been replaced with new or checked.

New: TPS, IAC, Fuel pump, Map Sensor, Bosh fuel pressure regulator, ignition module, coil dizzy etc etc.

We even brought a direct replacement for the metal bosh injectors when using these injectors the problem is substantially worse.

So at the moment the car is using the old factory injectors and using a tuned copy of someone’s 5.0 conversion dyno with a stock or near stock engine, if we try to use a stock memcal in the same ECU it’s also substantially worse...

Now with the slightly tuned chip and the old factory injectors it idles the best of all options however the hunting/surging idle is less obvious but still there.... and every now and then it has what I call rough spot(rough idle) where it kicks... then comes good then returns to a slight surging/hunting

No codes on this setup

When driving with the old injectors the mid range to high range power feels like it’s lacking a little compared to the other injectors which feel very responsive and feels fantastic above idle (plenty of go) and sounds smooth etc, but as I said using the new injectors increases the surging/hunting at idle and has also caused the engine light to come on occasionally and indicates the car is running to rich.... the engine light does go out after a while and other times it doesn’t even come on..

Having said that the old injectors still give good power the new ones just seem to give a more responsive feel...

Hopefully the information isn’t to confusing too what’s happening however I just wanted to make sure it’s right before paying for a day on the Dyno only to discover there’s an issue

I would’ve thought with the small cam and minimal engine/head work the car should’ve ran perfectly well on a stock memcal....

Cheers in advance.
 
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immortality

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Did you check/set the base timing correctly to 10°BTDC?

You will need to use what ever injectors the tune was done with, using anything else will change the fuelling and effect how it runs.
 

dans28

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Did you check/set the base timing correctly to 10°BTDC?

You will need to use what ever injectors the tune was done with, using anything else will change the fuelling and effect how it runs.
Thanks for the quick reply yes the base timing was done as specified in diagnostic mode by my young workshop mechanic....

So you mentioned I have to use the same injectors to suit the tune however it still has slight issues with those too, I would’ve expected the factory ones to work perfectly...

if I had to replace a set of injectors for the average bloke who just wants to buy a replacement set, remove the old install the new ones... and away you go... without dyno are you saying it can’t be any other type other than the factory ones... or something that has the same flow rate as the metal bodied ones? Would I be better off buying a refurbed set of the metal body injectors?

Cheers
 

EYY

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That cam will be fine with stock injectors and I'd be surprised if you'd have any issues with the stock tune especially given the conservative stock timing, even with flat tops.

I've got the crane 268 (which is the same grind as yours) in mine, and it ran almost flawlessly with a standard tune and injectors etc. Only time the idle was unsteady was when sitting in park or neutral for long periods of time. It's pretty much the smallest cam available second to the standard replacement cam, so I'd be hesitant to say the cam's causing any of these problems.

Did you buy cheap dizzy, ignition module, injectors and sensors? If so, there's a good chance you'll be having issues with those too. Also check the vacuum lines that connect in the middle of the manifold behind the throttle body.
 

immortality

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Well you need to know what injectors were used in the tune you have. Stock injectors should work with the stock tune however you have increased the CR ratio a fair bit with the flat top pistons which will effect things.

Have you checked the fuel pressure?

It sounds like you have the H268 cam which is a very small cam and should run ok'ish on the stock tune bar the fact you have increased the CR.

Sounds like something in the combo is off or as above one of the replacement items isn't working right. Try retarding the timing to 6° or 8° BTDC base timing and see if it effects the idle stumble
 
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