Chim Driveline Shunt
Discussion
I have test driven (at a dealer) 2 Chims today (my first ever Chim drive), a 4 litre and a 4.5 litre. Both cars were low mileage (30k ish) and with FSH and 1999 model years. In both cases when pottering along in 30 and 40 limits in 4th or 5th gear the car would 'shunt' slightly and feel like it was almost misfiring, it just wouldn't run as smoothly as I had expected. Both engines were up to temperature.
I was told that this is normal and can be even worse with a 5 litre.
Is it normal and can anything be done about it?
Thanks for any help you can give.
I was told that this is normal and can be even worse with a 5 litre.
Is it normal and can anything be done about it?
Thanks for any help you can give.
It is very common, and my 450 suffered from this too. It just wasn't happy with the engine running around 1500rpm (which is what was needed for 30 in fourth).
However, I fitted the TVR Power ECU chip (a drop-in replacement for the factory original, at about £75) and it made a huge difference. The engine is now very happy to chug gently at 1500 rpm without shunting, and it also revs right through the range much more freely. I've not measured power output, but it certainly feels stronger and more enthusiastic to rev
I put it in to cure the same problem you are complaining about, and it did exactly that, but it seems to have other benefits too...
Hugh
However, I fitted the TVR Power ECU chip (a drop-in replacement for the factory original, at about £75) and it made a huge difference. The engine is now very happy to chug gently at 1500 rpm without shunting, and it also revs right through the range much more freely. I've not measured power output, but it certainly feels stronger and more enthusiastic to rev
I put it in to cure the same problem you are complaining about, and it did exactly that, but it seems to have other benefits too...
Hugh
I used to have this quite badly, put an Emerald ECU on and not had it at all since! 
Someone told me that it was down to how accurate the fueling was at low speed sites but i'm not exactly sure how far out it needs to be before you start getting shunting. I'm sure someone smart will be along soon!
Someone told me that it was down to how accurate the fueling was at low speed sites but i'm not exactly sure how far out it needs to be before you start getting shunting. I'm sure someone smart will be along soon!
and come up with some very useful info.My 96 chim 400 used to be really bad for this, full TVR service history naturally.
I have had the Tornado Chip, Magnecor leads and RPI spark amplifier fitted and the fuel pressure checked (40 psi) and it is very much better, but still noticeable. I have advanced the ignition and this also seems to help (the RV8 timing marks were out).
Some peeps change the engine temperature sensor (£10) and it seems to work, others find a lobe off a cam, or a "dribbling injector", others do something similar to the above and others drive round it.
I wonder could it be that if something causes the ECU to "not compute" the result is this malady?
I concur that hopefully someone who knows what they are talking about will know the answer.
I have had the Tornado Chip, Magnecor leads and RPI spark amplifier fitted and the fuel pressure checked (40 psi) and it is very much better, but still noticeable. I have advanced the ignition and this also seems to help (the RV8 timing marks were out).
Some peeps change the engine temperature sensor (£10) and it seems to work, others find a lobe off a cam, or a "dribbling injector", others do something similar to the above and others drive round it.
I wonder could it be that if something causes the ECU to "not compute" the result is this malady?
I concur that hopefully someone who knows what they are talking about will know the answer.
A quick summary of what I found. At 1500 rpm, the airflow readings are very low on the TVR engine (compared to a stock RV8). The ECU limits the fueling because the airflow reading is so low, and the engine runs lean, making it snatch. I think the low air flow is due to the cam choice, being better designed for higher RPM. Its all very marginal, and I think anything that will improve the burn or put in a bit more fuel may help. Ive tried altering (raising) the airflow meters output by about 150mv on one car, and this reduces the snatching considerably. Ive not found any other local "guinea pig" cars to try this mod on so far unfortunatly.
Mark
Mark
blitzracing said:
A quick summary of what I found. At 1500 rpm, the airflow readings are very low on the TVR engine (compared to a stock RV8). The ECU limits the fueling because the airflow reading is so low, and the engine runs lean, making it snatch. I think the low air flow is due to the cam choice, being better designed for higher RPM. Its all very marginal, and I think anything that will improve the burn or put in a bit more fuel may help.
Mark
What may contribute is the finding of my engine builder who had to actually weld material back into my 4.3 (non-BV) heads' ports to avoid fuel stand-off at low air velocities, or something along those lines...Mark
Chequred Demon said:
Looking back on some old bills for my Chimp, the cleaning of the Stepper Motor and Plenum was also completed to fix this kind of problem.
How do you do it?
If you do a search for "clean stepper motor" you will find most of the answers, also the bible has a handy section on it. The stepper is very easy and the plenum is not much harder. Have you got a copy of the bible?How do you do it?
http://www.tvrcc-south-wales.co.uk/stepper.asp
Hope this helps.
Chequred Demon said:
Looking back on some old bills for my Chimp, the cleaning of the Stepper Motor and Plenum was also completed to fix this kind of problem.
How do you do it?
I would not spend too long on this one, the stepper motor is not the reason for it running lean at 1500 rpm. Its more stuff like high idle, or stalling at junctions. Fuel standoff could account for the apparent lean "hole" in the fueling, as its fine above and below this RPM. Its due to resonance or shockwaves in the inlet tract bouncing the airflow back, but Ive personally never come across it at such low RPM. The TVR power chip is an interesting one, as the standard TVR chip is already modified over the Range Rover map. I guess that they could have increased the fueling a bit in relation to the air at this specific rev range. I tried a stock Range Rover chip,TVR and Adams 4.2, and a JE engineering chip and they all displayed the same fault, even though the overall fueling maps where different. I would be REALLY interested at looking at one of these chips, if anyone feels willing! It would be an interesting thought that TVR had not already optimised the fueling on the stock motors....How do you do it?
Mark
Being a bit if a newbie; how exactly did TVR improve the performance over and above the basic RV8 engine, when they were new?
Some people say it was just hype and that very little was done to them and the power figures quoted by TVR are very optimistic??
Other people say heads,cams, chips etc? Did TVR Power supply tuned engines to TVR?
Certainly putting in the Tornado chip has made a world of difference. If TVR changed the ECU chip, why not do it right in the first place?
Some people say it was just hype and that very little was done to them and the power figures quoted by TVR are very optimistic??
Other people say heads,cams, chips etc? Did TVR Power supply tuned engines to TVR?
Certainly putting in the Tornado chip has made a world of difference. If TVR changed the ECU chip, why not do it right in the first place?
The basic Range Rover fuel map has some serious restrictions when put into a TVR. The worse bit is it runs lean at above 4500 rpm, in some attempt to limit the fuel consumption, and also has a pretty low rev limiter built into it. TVR had the mixture richened above this, that gives about another 12 bhp on a stock 3.9. The standard fuel map also does not provide any more fuel above 5500 rpm, but I think there is some way to scale to fuel map up to a higher RPM by off setting it in some way. The Rev limiter point is also raised. TVR power said the 3.9 map they had done was pretty spot on,(this work is sub contracted as they dont have the required hardware to program the ECU) but on the larger engines the scaling values could be improved to improve the "drivability". Mark Adams (as in Tornado chips) has made his trade by tweeking everything very accurately, and removing some of the poorer Range Rover mapping faults like overfueling on idle that are also in the TVR chip, and raising the tickover a bit. If you look at his ebay shop,(Tornado systems) he does explain the various tweeks, but you do pay top dollar for it. Its worth bearing in mind the the ECU will clamp the mixture below about 3500 rpm or 2/3 throttle, so power improvements will only occur above these points. Looking at how the maps work, I think it should be possible to tweek the fuel specifically at points where Lambda control cannot keep it rich enough, but with the limited number of chips I tried, the fault persisted. As with most things there are multiple software revisions of fuel maps out there, so it would be almost impossible to get it spot on first time (Just like microsoft Windows !!).
Mark
Mark
My 4.0hc did it . But my late 5.0 did not , smooth as like . One thing i did notice even on the 500 they both ran better on Esso super certainly less shunty in 4.0Hc . Interesting in a recent mag this gave much better performance times than any other of the 97 ,98 ,99 rated fuels .
Edited by Rum Runner on Saturday 16th February 07:55
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