Start up timing questions
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Start up timing questions
Ok more on the continuing fight to get my Blazer running right.
I read the article that RBob linked to (just what I needed!
) and I think I am on the right track with the fueling and IAC at idle, but I am now running into another problem that I think is spark related.
When I start it up in C/L the IAC counts start up around 75 and rapidly decay to 40, not where I have them set in the IAC vs. Temp table, but fairly close. The problem is that I have a really rough idle with what sounds like a miss in the exhaust (although at 750 RPMs, right where I set them) for 40 – 45 seconds (timed), then the idle smoothes out but the idle climbs to 1050rpms while the IAC counts remain stable.
As I was carefully listening to the exhaust note, I thought that it almost sounds like the timing is severely retarded at startup and advances to where it should be when the idle smoothes out and the RPMs climb. I have already set the IAC min air and TPS correctly. If anybody can point me in the right direction as to what I need to look at now, I will be extremely grateful!
I swear, if I keep on trying to figure out how to tune this thing, I will have to buy stock in BC!
I read the article that RBob linked to (just what I needed!
) and I think I am on the right track with the fueling and IAC at idle, but I am now running into another problem that I think is spark related. When I start it up in C/L the IAC counts start up around 75 and rapidly decay to 40, not where I have them set in the IAC vs. Temp table, but fairly close. The problem is that I have a really rough idle with what sounds like a miss in the exhaust (although at 750 RPMs, right where I set them) for 40 – 45 seconds (timed), then the idle smoothes out but the idle climbs to 1050rpms while the IAC counts remain stable.
As I was carefully listening to the exhaust note, I thought that it almost sounds like the timing is severely retarded at startup and advances to where it should be when the idle smoothes out and the RPMs climb. I have already set the IAC min air and TPS correctly. If anybody can point me in the right direction as to what I need to look at now, I will be extremely grateful!
I swear, if I keep on trying to figure out how to tune this thing, I will have to buy stock in BC!
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
At startup there are a couple of items in affect. There is timing and fuel added that is decayed out. The speed of decay is based on the coolant temperature.
The commanded AFR is lower from the startup fuel, it is also adjusted according to the coolant temperature. This can make the commanded AFR higher or lower.
The spark advance is higher from the startup SA which is further modified by the SA vs. coolant/vacuum compensation table.
The engine won't go into closed loop fuel mode until a certain time has expired from startup. The O2 sensor also needs to be active. The time it takes to go closed loop is typcially less with a warm engine.
My wild guess would be either too much timing or too much fuel. Checking when it goes closed loop and what the INT/BLM does will help figuring it out.
RBob.
The commanded AFR is lower from the startup fuel, it is also adjusted according to the coolant temperature. This can make the commanded AFR higher or lower.
The spark advance is higher from the startup SA which is further modified by the SA vs. coolant/vacuum compensation table.
The engine won't go into closed loop fuel mode until a certain time has expired from startup. The O2 sensor also needs to be active. The time it takes to go closed loop is typcially less with a warm engine.
My wild guess would be either too much timing or too much fuel. Checking when it goes closed loop and what the INT/BLM does will help figuring it out.
RBob.
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