pcmhacking.net

Hello all,
I think I am starting to get my head around tuning the idle on my VN 5L. The only problem I have is when I start the engine from cold the A/F seems a little lean but once it warms up to operating temperature it runs a little on the rich side. The engine itself runs fairly smooth taking into account it has a 284 crane in it. I grabbed the VE and spark table from a 284 crane and standard injectors tune I found on this site and started from there. At first start I had to increase quite a few of the values in the VE table as the wideband creeped up to 17-18 on the wideband. It is nowhere near as bad now but a few things just dont add up to me. The MAT sensor readings are higher than the coolant temp readings when I first start the engine?
Is this normal or should I replace the MAT sensor?
I am only new to this tuning and would greatly appreciate if someone could have a look at my cold start log and see if I am on the right track?
Thanks, Jon

there are temp offset tables that effect things like if its lean on warmup etc.

also is the manifold stock and the MAT in the same place ? i did a 286 cam tune on a motor that had a dual plane manifold and 4 barrel throttle body and the MAT would read 90 degrees inlet temps on hot days, due to having the old carby style air filter and not the air box out in the front of the bay ... so those sorts of changes can come into account.

but if its stock inlet manifold and its reading that high then i would be inclined to think something else is wrong (wiring or sensor)

Its a stock manifold with a pod filter setup where the airbox used to be. The MAT sensor is in the original spot.
So the weird MAT sensor reading are not really affecting the A/F ratio from cold to operating temp?
What offset tables should I look for and Im guessing make small changes and retest once engine is cold again?
Thanks Holden202T

well its hard to know how much difference the pod would make, but if its getting heat fromt through the radiator straight into it then it probably will be getting hotter air than from the airbox.

do you still have the stock air box ?

Sorry i should have explained it a little more. The log file I uploaded is from this morning when it was about 26deg outside and the bonnet open. All I did was start the engine and then let it idle until it got to operating temp then switched it off. It was the first time I started the engine today. The MAT temperature was higher than the coolant temp before I had even started the engine.
Jon

in that situation i would have expected the MAT to be similar to ambient air then increase as the motor heated up.

Yeah, one of the basic tests I do before tuning is normally to key on without starting the engine when its cold and check that coolant and air temp read the same. They normally are within a degree of each other.

Just checked the log again. Before the engine was started the coolant was 26.8 and MAT was 27.5 so I guess they are both ok. Just seemed strange to me that at the 30 sec point in the log the coolant is at 27.5 and MAT at 40.3
Also what tables do I have to adjust to get the warm up A/F ratio closer to target?
Example: at the 30 sec point in the log Target AFR is 13.4 but wideband is showing 15.8
Once the engine is at operating temp the target AFR and wideband are really close.
Just not sure what table to adjust to get the cold starts closer to target AFR
Thanks, Jon

I hope this does not sound like a silly question but what controls or changes the fuel amount when the target is not 14.7? I know at 14.7 the engine can go into closed loop and then ecu uses the o2 sensor to keep the engine at 14.7.
This seems to be the only time I see the target AFR and the wideband the same when its at 14.7?
Sorry if this sounds like a stupid question.
Jon

click somewhere in the parameter tree and hit ctrl+f and pick find.. a table.. with this phrase in the title... and search for A/F

Thats all the Air/Fuel ratio tables.

"Map A: A/F Ratio - Cold Engine A/F Ratio vs Coolant Temp and MAP" for cold and
"Map A: A/F Ratio - 20-100kPa Air Fuel ratio vs RPM and MAP" for warm.

There are also a couple of "inital run" A/F Ratio tables, one with time and one with AFRs. I have not had to touch these, the defaults have been fine for my engine, perhaps someone else can explain how these tables are used.