car jumping forth and back in lower gear at lower revs ?

[spatz]

I know I spend too much time here, bear with me....
I noticed that my CanAm tends to start jumping forth and back in first and second gear at low revs.
Is that a result of the low weight and a spring/mass system or can that be fixed by changing the map of the engine ?

thanks for hints

[MarkWebb]

This is usually caused by the cam overlap at low revs. I believe you have an engine which was designed for a race car? It will have a cam with big overlap in order to produce more power. basically exhaust and inlet valve are open at the same time in order to get more fuel in and exhaust out at high revs. At low revs it does not flow properly so exhaust is sucked back into cylinders when they should be filling with fuel/air. This causes bad running "off cam"
My old small block chevy has a big cam overlap to produce @ 550hp at the wheels (apparently) and is extremely difficult to drive below 3000 rpm I even get it at 65mph sometimes which is why I don't really want higher gears on my car

[spatz]

thanks also talked to the factory and they say it could probably be fixed with the map, could be too lean.
What I noticed is that the engine is running quite lean at low revs, around lambda 1,22.
I can turn on the closed loop then it should go to lambda 1 more rich and see if that
is fixing the issue. According to my engine supplier the engine is stock so standard LS7 cam
but thanks for the hint.

Edited by spatz on Tuesday 7th September 14:28

[MarkWebb]

I run closed loop all the time it makes sense to do so then lambda can be corrected to target whatever the conditions. Richer mix burns easier so may help.

[Gulf LS3]

Hi Spatz

are you running the map you sent me?

it definately needs some work if so, the closed loop is set to target .9 lambda on your map so plenty rich enough.

the spark table also wants a few tweaks, if you are running a standard LS7 cam it should be really smooth. Chucking more fuel in is not the solution. Can you not live map the problem areas with a friend on the road?

[k wright]

This is called "porposing" and is a sign that your mixture is too lean at low revs.

[spatz]

thanks I will play with the fuel when the wheather allows, the lambda reading is 1,22 at low revs which is probably too low.

[budala]

I have the same problem between 2000 and 2300 rpm and my engineer
is trying to improve the mapping to avoid this problem as much as
possible.
But he explained me that with my competition cam and big
injectors it's not easy to eradicate completely...

[Gulf LS3]

spatz said:

thanks I will play with the fuel when the wheather allows, the lambda reading is 1,22 at low revs which is probably too low.

the spark on your map is all wrong, dont just change the fuel levels you need to balance that with the spark tables

[spatz]

Hi Kyle,

my engine was mapped by very capable race engineers on a professional dyno, why do you thing the sparks are wrong ?
My map is actually the LS7 map you can download from DTA website, as the french have tuned it in with my LS7/DTAS80PRO combo and send the map to DTA.

[pilbeam_mp62]

spatz said:

Hi Kyle,

my engine was mapped by very capable race engineers on a professional dyno, why do you thing the sparks are wrong ?
My map is actually the LS7 map you can download from DTA website, as the french have tuned it in with my LS7/DTAS80PRO combo and send the map to DTA.

Spatz - you told us last October that it was bouncing around like a kangaroo :-

spatz said:

so if your clutch feels heavy this zylinder i was installing from MPL might work as advertised as my clutch is not heavier than on a porker still it comes very early - probably because new and as intended by the factory
i have some problems below 2000rpm the whole car starts bouncing back and forth have you noticed that too ? i had plenty of oil learks (probably mainly because of my high pressure) so glad to hear that you do not have this problem

Have you done anything to the map since then ?

Regards

[spatz]

no enjoyed the driving a lot and the little bouncing will be corrected soon.

[spatz]

Kelvin, out of interest why did you sell your car so quickly ? This was probably the fastest after completing the built sale I have seen.

[pilbeam_mp62]

spatz said:

Kelvin, out of interest why did you sell your car so quickly ? This was probably the fastest after completing the built sale I have seen.

I knew that I was never really going to be interested in driving it on the roads - I bought the kit as a project to keep me occupied at the weekends - I considered whether it would be suitable for competitive events (hillclimb and sprint) and decided that it might be suitable for sprints, but not hillclimbs, and in any case, I would only have wanted to take it to events on a trailer, which is what I have always done with my competition cars.

So that would have meant buying a new trailer, and then I would need somewhere to store it, and so I decided that I would draw a line under what was a very enjoyable experience (the building.... and a little bit of driving, to iron out any small problems)

I suppose that I could have waited till next year to sell it, but I guess the value would have dropped a bit by then, so I decided to act quickly and advertise it while the weather was still good. It sold for a price that I was happy with and I hope the new owner will be pleased with the car.

I have gone to the other end of the spectrum now and I have just bought a 1968 MGC-GT which is in good condition and just needs a little bit of tinkering - which is what I enjoy doing.

I hope you manage to get your mapping sorted out.
Best Regards

Kelvin

[Gulf LS3]

spatz said:

Hi Kyle,

my engine was mapped by very capable race engineers on a professional dyno, why do you thing the sparks are wrong ?
My map is actually the LS7 map you can download from DTA website, as the french have tuned it in with my LS7/DTAS80PRO combo and send the map to DTA.

I used your map as a base for mine.... well tried, Alan at DTA just supplied the map as a reference he is not aware if its good or bad!! Tim Adams who has mapped loads of engines said it was a strange map and mega rich at the top end.

the only way to see whats causing the problems is to put the engine on a dyno or live map

my views

setting closed loop target at .9 lambda makes no sense to me it should be at lambda 1 or slightly leaner ie around 1.05 as the bottom end is under no load when in closed loop so it does not need a lot of fuel

your spark tables looked weird and we changed them a lot but one example was that it was not running enough spark at the bottom end ie below 2000rpm so i think that will be causing some of your issues

[Gulf LS3]

race engineers always map rich, its in there nature ;-) It should be as smooth as silk, my ls3's will idle perfectly at 1500rpm in 6th gear and a 7 should be the same.

If you were closer i would like to help you with it.

[V8Dom]

pilbeam_mp62 said:

spatz said:

Kelvin, out of interest why did you sell your car so quickly ? This was probably the fastest after completing the built sale I have seen.

I knew that I was never really going to be interested in driving it on the roads - I bought the kit as a project to keep me occupied at the weekends - I considered whether it would be suitable for competitive events (hillclimb and sprint) and decided that it might be suitable for sprints, but not hillclimbs, and in any case, I would only have wanted to take it to events on a trailer, which is what I have always done with my competition cars.

So that would have meant buying a new trailer, and then I would need somewhere to store it, and so I decided that I would draw a line under what was a very enjoyable experience (the building.... and a little bit of driving, to iron out any small problems)

I suppose that I could have waited till next year to sell it, but I guess the value would have dropped a bit by then, so I decided to act quickly and advertise it while the weather was still good. It sold for a price that I was happy with and I hope the new owner will be pleased with the car.

I have gone to the other end of the spectrum now and I have just bought a 1968 MGC-GT which is in good condition and just needs a little bit of tinkering - which is what I enjoy doing.

I hope you manage to get your mapping sorted out.
Best Regards

Kelvin

kelvin do you still race?

Dom

[spatz]

thanks kyle,

i did drive with the computer on the passenger seat and a little more fuel at idle made my world happy, smooth as silk now....will do more mapping in the car.
Actually solutionf told me that the original GM ECU is running the engine even richer towards the end.
Having the lambda sensors installed was a very good idea because you can see your changes right away. btw my lambda target in the map is 1 not 0,9 but the first map I sent you did have no lambda settings at all. The one I send you yesterday has. They advanced the engine quite a lot they told me that.

[pilbeam_mp62]

V8Dom said:

kelvin do you still race?
Dom

Not since I sold my single-seater about 3 years ago, so that I could build the Ultima - I only ever did Speed events - not any wheel-to-wheel stuff - I still go to a few events to see my old mates though.

Regards