Lean Start issue

turbosl2 · Post by **turbosl2** » Sat Apr 15, 2006 10:02 am

Car specs are as follows. 4cyl MPI MS2 2.33 code, MT 2.25, 1000cc injectors, 3bar map, Custom cams.

My car idles around 12.5-13.8 and seems to run well at idle and when i rev it up (when is warm too). My starting PW at 0F is 8.5ms and at 0F its 1.3ms. My idle PW is around 1.2-1.3ms. When i turn the car off, after its warmed up, and the CTS is at 195 degrees, i try to restart it, my cranking pw seems to be around 1.4-1.5 but after it starts it will run extremly lean, such as 22:1 or higher on my LM1 but if i rev it up or let it sit for a minute it will come back to normal and all is good. Seems to only do this when i turn the car off and restart it after its warmed up.

any ideas?

Thanks guys

Jim · Post by **Jim** » Sat Apr 15, 2006 12:04 pm

You say Hot Idle PW is 1.2 to 1.3 and Hot Cranking PW is 1.4 to 1.5 .

This sounds OK .

Then you say right after a hot start the AFR is almost full scale lean ,
but what is the PW reading ?
Your engine probably won't run at an actual 22 to 1 .

It sounds like you are expecting your WB to operate instantly , it will
have to have some warm-up time , maybe 30 seconds or more , before
it starts working .

I don't know what kind of WB 02 you are using .
I use an Innovate LC-1 , it has a setting in the software that allows you
to set the output voltage during warm-up and fault conditions .
I set mine so that it puts out 2.5 volts during warm-up .

If you have your MS setup to use O2 correction at idle speeds ,
and your WB is setup to go to one extreme or the other when warming up ,
weird things can happen .

...................Jim

turbosl2 · Post by **turbosl2** » Sat Apr 15, 2006 9:41 pm

my wideband is a LM-1, it has a external power source so i warm it up before the car even starts. There is def a problem because the car BARELY runs, and it is in the 20s for the AFR. It sputters like its getting no gas and if i touch the gas hard it backfires through the intake. Its weird it only does it sometiems and right after startup even if the car is warmed up and my CTS reads 195 and the pulse width reads normal at around 1.3, judgeing how the car runs it feels like its so much less.

Jim · Post by **Jim** » Sat Apr 15, 2006 10:37 pm

Does your PW stay where it should while the AFR goes way lean ?

Have you tried watching the AE Meter during this time ?

Some times you can get away with almost no AE under normal circumstances ,
but what could be happening is the engine is right on the edge of a backfire when
you crack the throttle because of not enough AE ,
and circumstances right after a start are such that the
engine does backfire ,
causing everything to go wacky for a short period of time .
This same senario can be caused by too much AE .
All of this can be agrivated by a choppy cam .
Does your car have a choppy idle normally ?
What idle rpm do you have set ?
Manual or Auto trans ?
If Auto does it do this in gear or in park/neutral ?

Another thing that could be happening is a heat soak on your fuel injector rail .
The engine normally gets its hottest about 5 minutes after hot shut-down .
By the way , do you have a return line back to the tank from your regulator ?
Some of the newer cars are eliminating the return line ,
this can cause "vapor lock" in your fuel rail after a heat soak .

...................Jim

newtyres1 · Post by **newtyres1** » Sun Apr 16, 2006 12:30 am

It sounds like a heatsoak problem of your MAT sensor, if the MAT sensor warms up with the engine stopped the engine will run lean on the restart until the incoming air cools it down to ambient temp again. Keep an eye on the MAT in Megatune to see if this is the case.

rs2000 · Post by **rs2000** » Sun Apr 16, 2006 8:48 am

I agree with newtyres1, i had the same issue to a lesser degree when i had the air temp sensor in the aluminium inlet manifold. The simple solution is to mount it in the intake hose, or just near the intake in the engine bay..

turbosl2 · Post by **turbosl2** » Mon Apr 17, 2006 7:52 am

Jim wrote:Does your PW stay where it should while the AFR goes way lean ?

Have you tried watching the AE Meter during this time ?

Some times you can get away with almost no AE under normal circumstances ,
but what could be happening is the engine is right on the edge of a backfire when
you crack the throttle because of not enough AE ,
and circumstances right after a start are such that the
engine does backfire ,
causing everything to go wacky for a short period of time .
This same senario can be caused by too much AE .
All of this can be agrivated by a choppy cam .
Does your car have a choppy idle normally ?
What idle rpm do you have set ?
Manual or Auto trans ?
If Auto does it do this in gear or in park/neutral ?

Another thing that could be happening is a heat soak on your fuel injector rail .
The engine normally gets its hottest about 5 minutes after hot shut-down .
By the way , do you have a return line back to the tank from your regulator ?
Some of the newer cars are eliminating the return line ,
this can cause "vapor lock" in your fuel rail after a heat soak .

...................Jim

The PW stays the same and really does not change at all, even after it clears up i see no change in PW at all. THe car is a Manual. It idles around 850rpms and normaly has a choppy idle because of the agressive cams. The car is a 95 and does have a return line back to the fuel tank. I never thought about the heat soak on the injector rail, would it really make it that bad. I am not 100% sure but i think it does the same thing sometimes when cold and i first start it, it seems intermitant. I know for sure when its warm because i thought i had the cranking PW perfect after 180F when its warmed up and i turned it off and it started perfect. Restarted it about 10 times and most of them it was super lean like it would BARELY run, so i rev it and it dies, but i keep trying and get the rpm up to around 3k and let off, and its back to normal. This whole time i am almost sure the PW is where it is when it runs normal. I never really watch the AE, i think mine is set at 40% and 300 cycles. Would the AE matter if when i watch the MS and it never goes red in the afterstart box?
Thanks

turbosl2 · Post by **turbosl2** » Mon Apr 17, 2006 7:53 am

newtyres1 wrote:It sounds like a heatsoak problem of your MAT sensor, if the MAT sensor warms up with the engine stopped the engine will run lean on the restart until the incoming air cools it down to ambient temp again. Keep an eye on the MAT in Megatune to see if this is the case.

My MAT is mounted in the incoming pipe just before the TB. I will check it out, i think it should be in my datalog i posted. THanks

turbosl2 · Post by **turbosl2** » Mon Apr 17, 2006 8:07 am

2 Datalogs while i was tuning AFR. Can be downloaded here.

http://serv01.siteground118.com/~albany ... Start1.xls

http://serv01.siteground118.com/~albany ... Start2.xls

Jim · Post by **Jim** » Mon Apr 17, 2006 9:56 am

Looks like you are running a Narrow Band 02 Sensor ,
so you can only guess that it is going lean .

You need to be more specific , when you say
"I'm tuning my AFR" , it sounds like you know what your AFR is .
You should say that you are adjusting your VE table .
You can only guess AFR with a Narrow Band 02 .

It could just as easily have the same symptoms from running to rich .

Your a brave man , trying to do this without a Wide Band 02 !!!

You are already running fairly rich to start with ,
because your choppy cam requires a richer mixture because of
exhaust gas dilution of the intake charge .
So you could easily be flooding your engine , especially because of opening
the throttle to try to save it from stalling ,
this should give a big AE shot and make things worse .

Have you watched your tail pipe ? or had someone else watch it ?
Any black smoke ?

I can't make a graph out of an xls file , but from looking at the numbers
it also looks like you are not running much Spark Advance .
A choppy cam allows you to dial in a good deal more advance at low speeds ,
this will make the engine much more responsive .
Also with a choppy cam you would be better off running your idle speed at
around 1000 to 1200 rpm , this can "fix" alot of things .

...................Jim