Advice on new chip please.
Discussion
Just got car back from Peninsula after about ten weeks...new MC2 cam, pre cats removed and main box s/s sleeves through on a 5ltr '97 chimaera. Whilst it sounds absolutely fantastic, its very lumpy at a constant rev. On acceleration, fine. But on tickover (1000rpm) or driving through town in say 2nd at 1500 - 2000 rpm, feels like it's missfiring or shunting back and forth. Even on de-acceleration in higher gears it feels odd like its missing or something. Easier to stall at low revs also.
Does it need a new chip to cope with new cam? I chose the MC2 as I was told it was close to the normal cam and so would be ok with present set up.
Any help very welcome.
Thanks,
Steve.
Does it need a new chip to cope with new cam? I chose the MC2 as I was told it was close to the normal cam and so would be ok with present set up.
Any help very welcome.
Thanks,
Steve.
steve1c said:hi steve.thought i might be able to shed a little light on your problem.firstly i want to say that im no expert,but have just gone down a similar route as yourself,but with a few important differences.firstly the mc2 is a predecessor to the h404 that ive just had fitted,and although its not exactly the same,its quite similar.being a high lift cam its normal characteristics are to be lumpier at idle.it is also quite normal for it to be more difficult to drive at the revs you mention and wasnt designed to do drive smoothly at such low revs.this cam is more about increasing power and torque particularly in the mid range spread,so a little sacrifice has to be made somwhere and this comes at the bottom end.this is much easier to drive around town than an outright race cam for example,which has all its power at the hight of the rev range.you also havent mentioned any other mods you had in conjuction with the mc2.ive just had my inlet manifold fully ported,45mm trumpets,different tune resistor,increased fuel pressure,removal of vacuum advance and timing re-set,all in conjuction with my h404,and this makes a big difference both to driveability and also total performance throughout the range.with all these mods i still havent had a chip re-map and the car behaves superbly,much beter than you give me the impression yours does.i certainly wont be paying the £700 id need to budget for the first ma re-chip yet,until maybe ive modded further!in short it looks like youve fitted the wrong cam for your liking,imo its not that close to the original and you should have been warned about the driveability characteristics when you enquired about the change.the odd thing about a cam change is that when you have one,all the mods ive had done come labour free,so you only pay for the performance parts on top of your cam change.this makes it really good value to get a lot more out of your cam choice.you could get a re-chip,but i think youd be wasting the potential of your cam choice until youve made further mods on the induction side.however a re-map now will im sure give better behaviour.a simple increase in fuel pressure along with timing adjustment may also give a much cheaper,but less effective fix.if you want real expert advice,talk to the chaps at v8 developments(mc2 is their cam)im really happy with the above mods theyve just done to mine,and at £1065+vat i feel its one hell of a bargain.
Just got car back from Peninsula after about ten weeks...new MC2 cam, pre cats removed and main box s/s sleeves through on a 5ltr '97 chimaera. Whilst it sounds absolutely fantastic, its very lumpy at a constant rev. On acceleration, fine. But on tickover (1000rpm) or driving through town in say 2nd at 1500 - 2000 rpm, feels like it's missfiring or shunting back and forth. Even on de-acceleration in higher gears it feels odd like its missing or something. Easier to stall at low revs also.
Does it need a new chip to cope with new cam? I chose the MC2 as I was told it was close to the normal cam and so would be ok with present set up.
Any help very welcome.
Thanks,
Steve.
Mongoose, thanks for the info and detailed reply. Yes I could have been missinformed, we'll have to see. Spoke to V8 developments and they wondered if the fuel pressure regulator was high enough or perhaps timing was a bit out. The only other mods I've done is having pre cats out along with non reversal cones fitted. Accelerated like the clappers but on any kind of steady speed like tickover, steady 20mph in 2nd/3rd it shunts or misses. Taking off from the lights also requires 2000rpm or likelyhood of a stall is high.
high steve,fuel pressure sounds like the most likely culprit assuming your ignition is all in good working order.if they havent upped the pressure then it should make a nice difference id have thought.the chaps at v8d will set it up superbly for you and i wouldnt think itll cost too much to do this either.let us know how you get on.
GreenV8S said:no,not running open circuit peter,i didnt change anything-honest!the guys at v8d did it all and it was part of the final set up.i dont know the reasons behind it all,i just like the end result
Just out of curiosity Mongoose, why did you change the tune resister and remove the vac advance? Are you running open circuit (without lambda feedback) now?
david beer said:
Hi mongoose
i understood there were only two "states" recognised by the ECU, closed or not. Do you know what value "R" is in there ?
sorry david,i dont know the value,its definately a non cat one(green wire instead of white apparently)so itll be the same as the one youve tried i imagine.-edited to say,ive just found out that it should be 470 ohms apparently.
>> Edited by mongoose on Monday 7th March 19:19
GreenV8S said:hang on a minute
Just out of curiosity Mongoose, why did you change the tune resister and remove the vac advance? Are you running open circuit (without lambda feedback) now?
,perhaps i am running open now?
now ive had a think about it,i undersand why you think so peter.ill be talking to shaun later on today about some info on new omex system about to be released,so ill ask him then. david beer said:
I Run my standard 500 without vac advance, as i have said on many occasions !V8, i hear tell everyone to disconect the vac advance.I have also tried the non cat tune resistor, felt very smooth but just lost a bit on performance. Now over to someone who knows what they are on about.
What difference does disconecting the vac advance have on the engine?
mongoose said:found out im running a little of both closed and open circuit!closed with the labda control at idle and low revs,then open from there on to increase fueling.the lambda sensors dont work briliantly with the std fuel injection system(banked)and are better taken out of the equasion in this way when tuning for performance apparently.the vac advance is disconnected to prevent pinking low down as it gives too much advance in this area.
Just out of curiosity Mongoose, why did you change the tune resister and remove the vac advance? Are you running open circuit (without lambda feedback) now?
hang on a minute
Cured my jerky low rev drive around town. ie 30-40 mph on a very small throttle. Too much advacnce for the engine load, same speed up hill was nice and smooth. Downside being less mpg, so say, never noticed any difference myself and most certainly could not go back to being connected. Before anyone asks, yes my timing was correct. Everytime i collect from service i pop it off.
mongoose said:found out im running a little of both closed and open circuit!closed with the labda control at idle and low revs,then open from there on to increase fueling.the lambda sensors dont work briliantly with the std fuel injection system(banked)and are better taken out of the equasion in this way when tuning for performance apparently.the vac advance is disconnected to prevent pinking low down as it gives too much advance in this area.
Just out of curiosity Mongoose, why did you change the tune resister and remove the vac advance? Are you running open circuit (without lambda feedback) now?
hang on a minute
david beer said:
For me it cured the jerky shunting i was getting at low revs very light throttle, ie speed constant,fourth gear 30-40 mph in town. Means i can poodle around in fifth at 30 mph, if i want. Reason being there was too much advance for the load.
Right, first chance I get its whisk the vac tube off and go around town. Not a mech/tech person so dont understant what the vac does exactly or how it does it, but I'll give it a go. ( Said the actress to the Bishop...)
mongoose said:
found out im running a little of both closed and open circuit!closed with the labda control at idle and low revs,then open from there on to increase fueling.the lambda sensors dont work briliantly with the std fuel injection system(banked)and are better taken out of the equasion in this way when tuning for performance apparently.the vac advance is disconnected to prevent pinking low down as it gives too much advance in this area.
The standard ECU switches from closed lambda-based operation to open mode at around 3500rpm IIRC.
However the lamda sensors should still be connected and the cat-based ECU resistor should be used. I've run mine without (for mapping reasons) and it promptly failed the MOT by a LARGE margin. Reconnected and it passed by a LARGE margin.
The vac advance only affects fuel economy apparently and can often cause more problems than it solves.
Ian A.
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