The Project Pad

Though I would post my Vems tuning experiences here, and possibly get some tips from any community member or help some other vems newb with my limited knowledge at this point.

So I've had Vems since November now and done about 3 different fuel tunes for my S4. First tune was on stock everthing using the target lambdas that came with the ecu. I was running only 15 psi at first to get my bearings with the Vemstune software. I quickly realized that the stock injectors were no fun and got deka 60's with an 044 pump(with a modded stock basket). That was when I retuned the car again with the 60lbers. This time I noticed some pinging or at least I think it was pinging at 15psi at around 5k. I checked and found I was running .85 at 15psi and 5k rpm. I then changed the targets for that boost level to .80 just to be safe.
I attribute this to some oil burning I am getting. Oil getting in the combustion chamber will lower the octane of the mixture and can cause pinging and det. I burn about a quart in 3k miles. Im hoping it is just vlave stem seals and I plan on doing a cyl head refresh soon.

-Will

(Just got the head back from the machine shop this is what was done:
-Valve stem seals
-Ex. Vlave guides
-Checked for straightness and cracks
-Supertech +.5mm inconnel ex. valves
Plus my machinist threw in a free exhaust side port job which I was hyped about. The head went back on and after some cam sensor issues the s4 is back on the road again and it actually makes 5 extra pounds of boost and spools noticably faster even with a leaky 710n dv.

So now I hope Iam not burning as much oil anymore so I changed the lambda targets to .82 at 200kpa(15psi). My max boost now is 25psi after some wg spring adjustments. It still flutters alot but its only a stock spring so I may need to upgrade. I did some tuning of the high boost cells to get it around .79 at 272 kpa. The cars pulls hard now it does feel faster than MTM 1+ by a significant amount. The most noticeable advantage over MTM is how hard it pulls in 5th gear from 60mph.

I have been also chasing a hot start issue. After getting the car up to temp then letting it sit for about 45 min to an hour it cranks really long. I noticed that opening the throttle blade while cranking helps it start. So I assumed it was a rich starting condition. After a bunch of different prime pulse adjustments and cranking VE changes I have made no progress. I also noticed that the car will start perfectly after the first failed start attempt. So about 2 hours ago I changed the fp priming pulse to about 4 sec and it seems as though that fixed it after an hour of sitting hot. I will test it again 2morrow to verify. Any other suggestions are welcome.

-Will

I've been looking into setting up this WOT shift cut on my s4. What does this feature exactly do?

You might want to get into touch with Marc Swanson about some of your questions. He pretty much knows VEMS like the back of his hand.

I think WOT shift cut is kind of overrated, but it can be effective if you really want/feel you need it. It just cuts fuel or spark (your choice) when you push the clutch in so that the RPMs drop while you still retain boost.

You mentioned that you thought it was rich on hot starts... When you tried adjusting cranking VE and prime pulse, did you go both leaner and richer than you started with? It could easily be too lean if it always starts after the first failed start.

Yes Chris I went leaner and richer and no real change. I think I have fixed it by primming the Fuel pump an extra 2 seconds. Im going to verify that 2nite. It doesnt make sense to me why that would fix it but it has so far has. I am running an 044 with no check valve however so that might explain it partially.

Got it! Hot fuel vaporizes in the lines and the pump cant compress all that vapor to start to move fuel fast enough to start the engine on the first key cycle. Giving the pump more primep fixes it, also just putting in a check valve would do it but this is easier.

Screw the check valve, I WANT 700 HORSEPOWERS

Yeah I have to increase the prime length on dad's car too for the same reason (sort of, happened all the time). We were just cycling the key a few times every time.

Yea dont feel like going back in the gas tank. I'm just wondering if it will return in the hot weather?

Has anyone on here tried relocating the the IAT sensor to remedy the heat soak it encounters? I was thinking of relocating it to the pipe right before the throttle body. What say you?

DuBistS4 wrote:Has anyone on here tried relocating the the IAT sensor to remedy the heat soak it encounters? I was thinking of relocating it to the pipe right before the throttle body. What say you?

Easier to just swap to a 1.8t sensor and keep that stock location...

I have a 1.8t sensor already but the sensor type isn't the issue, its the location.

Moving it out of the IM would be ideal.

I have my sensor on the output side of the intercooler

How did you do this, by installing a 1/2 inch bung on your intercooler? I am trying to find a way of attaching the sensor to my intercooler pipe some how.

AngryTaco wrote:I have my sensor on the output side of the intercooler

Was this modd worth it?

DuBistS4 wrote:How did you do this, by installing a 1/2 inch bung on your intercooler? I am trying to find a way of attaching the sensor to my intercooler pipe some how.

Weld a small piece of flat aluminum stock into the pipe, drill center hole for sensor and tap for the screws

Aha! Thanks Ed

Something like this

Yes! How did u get the curvature?

I believe that piece was CNC'd - look at 42draft designs website, they have some MAP sensor flanges that may work. Or you could make your own using a drum sander/etc. Doesn't need to be curved though, just weld the gaps.

Whats the most stable latest firmware for vems now adays. I've been using 1.1.95 is their a better working later frimware out?

Hey whats the best lambda targets for a good gas mileage cruis? I am set right now to 1.05 wondering what the limit is as far as leaning it out more.

You can go as lean as you want under no load... you'll know when it gets too lean as it will start to break up/miss. 1.10-1.15 is a good range for most cars.

I did my senior paper on this topic. My findings are that 1.00 Lambda will result in the best fuel economy. 30-40 hours of dyno time revealed that to get X amount of power required to keep a steady 75mph cruise, you need XXX amount of BTU's expended. It doesn't matter how lean you make it, you will need X amount of gasoline matched with y amount of fuel. If run at 1.0 lambda, you will have the most efficient burn, and result in the lowest TPS reading as you burning the least amount of air mixed with that constant of fuel required. If you pump it up to 1.10Lambda, you may need 10% more TPS to sustain that same speed, so the there will be 10%(theoretic) more air, mixed with an A/F ratio will result in the same amount of fuel used at 1.0 lambda. Test my findings on your own and you will find the same thing. Before I did this, I found myself thinking I aws getting better economy because I would tip toe around at cruise trying to get good economy. If I did the same thing with 1 lambda values, I would see the same thing plus the added efficiency of being at 1.0 Lambda.

The big gains in fuel efficiency gained with good gas like e85 ( or good knock control), is the light to moderate load(that 30-70 TPS). Turbines don't like being run at 1.0Lambda at WOT, nor do a lot of other components such as valves, pistons, rings, ect. Running that lean will make a ton of heat. If you are able to cool the EGTs, you could theoretically run 1.0Lambda everywhere to be the most fuel efficient. This is what the new 1.8T motor does, as the exhaust manifold is in the head. The manifold is basically watercooled to allow the lambda values to hover around 1 all the time, resulting in a very fuel efficient engine at the cost of spool. Boats do this as well on turbo applications of sustained WOT