I think I know whats going on...AIT is giving me grief

kawizx12r · Post by **kawizx12r** » Sun Nov 27, 2005 9:57 pm

My MS&S that I have run for about 6 months now has always had one major problem...Inconsistencies in tuning...I can set up my VE table to run perfect and then it all of a sudden I get a change that seems to come from nowhere..to rich, to lean...it varies..granted this change happens even with o2 corrections off. I believe I have narrowed this down to the Air intake temperature.. I have a turbocharged vehicle and my air temps can range from 80 degrees F at a light cruise to as much as 190 degrees F under 10psi of boost going up a hill. Does anyone know how much AIT changes the amount of fuel and is there anyway to limit its input. Theoretically with o2 correction off, the results should be very consistant. Nothing else is going to change that much.. engine temp, TPS, RPM, and MAP are all going to be within 5%...

Maybe I need to drag out the digital storage scope and mock up an MS to a function generator and some inductors for injectors and do some calculations and see if I get consistant results.

keithmac · Post by **keithmac** » Mon Nov 28, 2005 3:38 pm

Mabe worth swapping the IAT sensor? the reading is part of the fuel equation, you don`t really want to limit the IAT correction on boost as it directly relates to air density. What about heatsoak, could that be a problem?

The later extra codes have coolant temp iat correction to combat heatsoak, may be worth a look?

mops · Post by **mops** » Tue Mar 07, 2006 12:26 pm

i have similar heatsoak problem...

cold start and run is near perfect... good fuel economy and power, but if i stop for 2 minutes, it's really difficut to start... engine bucks and sputters, but as ve table takes over durning starting the engine dies quickly.

ambbient is ~20*C and normally iat reads about 22-24 while driving, but for a short stop it will creep up to 45*C or over.

djandruczyk · Post by **djandruczyk** » Tue Mar 07, 2006 12:39 pm

mops wrote:i have similar heatsoak problem...

cold start and run is near perfect... good fuel economy and power, but if i stop for 2 minutes, it's really difficut to start... engine bucks and sputters, but as ve table takes over durning starting the engine dies quickly.

ambbient is ~20*C and normally iat reads about 22-24 while driving, but for a short stop it will creep up to 45*C or over.

I think a code mod to clamp the IAT compensation during startup should be in order. It seems like the IAT readings seem to have WAY too strong an effect when the temp starts rising. Can you get a datalog of pulsewidths during a cold start and warm start, including both cranking and running for a short whilethereafter. If IAT is biasing things too much the datalog will show it with very low pulsewidths. this way we can come up with some ideas on how to remedy it.

mops · Post by **mops** » Tue Mar 07, 2006 1:00 pm

definitely. i did datalog last night, and i can see exacly that. at over 40*C IAT, air density is about 93-94% and my gammae is ~93% making car extreamly hard to start, and even if it does, it cant idle by itself, cos it's getting something like over 17 afr at idle, so I have to keep reeving it for about a minute, until AIT gets back to ~30... then it might possibly idle by itself...

i think of two very easy code modifications....
1. iat enleanment should be disabled durning afterstart enrichment (nore that iat enrichment should stay on).

2. iat correcting should be scaled by a single factor (i.e 0.5) - thats pretty crude, but i think it would be really easy to implement.

it's really hard for me to get a working set of values for my car. intake runners are long and very hot once warmed up and i can imagine they heat up air durning slow speed/idling. i so far tried two different temp sensor d(one ford, one from honda) mounted in two differnet locations and they both experience rather significant heat soaking, making my car run really badly after warm start.

note that semi warm start (i.e. long drive. 1-1.5 hours stopover, clt 60, iat 30) starts first click. aswell on cold starts first clock, but on warm it's a major drama....

djandruczyk · Post by **djandruczyk** » Tue Mar 07, 2006 2:14 pm

mops wrote:definitely. i did datalog last night, and i can see exacly that. at over 40*C IAT, air density is about 93-94% and my gammae is ~93% making car extreamly hard to start, and even if it does, it cant idle by itself, cos it's getting something like over 17 afr at idle, so I have to keep reeving it for about a minute, until AIT gets back to ~30... then it might possibly idle by itself...

i think of two very easy code modifications....
1. iat enleanment should be disabled durning afterstart enrichment (nore that iat enrichment should stay on).

2. iat correcting should be scaled by a single factor (i.e 0.5) - thats pretty crude, but i think it would be really easy to implement.

it's really hard for me to get a working set of values for my car. intake runners are long and very hot once warmed up and i can imagine they heat up air durning slow speed/idling. i so far tried two different temp sensor d(one ford, one from honda) mounted in two differnet locations and they both experience rather significant heat soaking, making my car run really badly after warm start.

note that semi warm start (i.e. long drive. 1-1.5 hours stopover, clt 60, iat 30) starts first click. aswell on cold starts first clock, but on warm it's a major drama....

I assume the sensor is mounted in the manifold ? Try using one that's in the airbox away from as many under-hood radiant heat sources. Air can hold only a fairly small amount of heat compared to a solid or liquid, by having the sensor mounted into a fairly good heat conductor (aluminum/iron) with a very high thermal mass (intake manifold) that heat will conduct into the sensor body and artificially raise it's temp skewing the readings, as the sensor will report it's body temp conducted by the manifold more so than the air temp itself. My car's OEM efi (99 cougar, duratec 2.5 V6) has the IAT mounted in the airbox which is as far as you can get from any under-hood heat sources, and the OBDII palm based scanner I use shows IAT readings very close to ambient, and they don't heat soak like what you seem to have in your setup..

I do agree though that IAT compensation should be disabled during cranking and ASE, (or at least switchable) so it can be tried...

mops · Post by **mops** » Tue Mar 07, 2006 2:29 pm

ok, well the first sensor i used (ford one) was mounted just beofre TB and it suffered severe heatsoak. upwards or 50*C. it was just under the bonnet where there's most heat and reading were seriouslt affected.

now i use an airbox mounted honda IAT, which suffers heatsoak as described in pervious posts in this thread. It's very stranve.. it's mounted just at airbox entry, lower in the engine bay, just behing headlamp, and i thought sthat location will be good. heatsoak there is reduced compared to my first sensor, but still exsists.... or it might be miscalibrated sensor possibly ?

jonfx4com · Post by **jonfx4com** » Tue Mar 07, 2006 2:41 pm

I think for a turbo application you need the air temp sensor in the boosted side of the engine to see the true charge temperature but you ideally need it to not see the temperature of the metal its screwed into. A bit of lateral thinking is needed here to insulate it from the manifold. Also look at the fast response (open element) sensors for turbo applications. In these the element is exposed so the reaction to charge air temp is very much faster. This is essential when the temp can change from 70 f to 190f in 2 or 3 seconds. A standard GM or similar solid sensor just cant do this. Put a meter on it and dump it it in boiling water, you will wait seconds not milliseconds for it to respond.
To track the charge temp you need to see at any instant and pretty much at the back of the inlet valve what the charge temperature is, certainly you need to be on the engine side of the intercooler. You cant fix this in software only at best botch it to make it work a little better.

Jon

mops · Post by **mops** » Tue Mar 07, 2006 2:46 pm

yes, I agree for turbo motor, iat shoulc be after intercooler, preferably just before or after throttle body.

i'm still N/A.... and having hard time...

I can tune and engine responds, but as the temp sensor soaks.....

best restults i have is when I disconnect temp sensor alltogether, then ms thinks it's 21*C and then air density correction is 100% and it all works great

but i'm sure that's not the right way...

jonfx4com · Post by **jonfx4com** » Tue Mar 07, 2006 2:53 pm

Open Element Temp sensors:
GM #25036979
Wells #Su107
GPSorensen #77919001
Niehoff Dr-136W