Running pig rich during open loop (cold)

[MikesFixedRoof]

So I've almost given up on trying to figure out the cause of this issue. While driving on a cold engine (below operating temp) I have to be very smooth with the throttle, otherwise my wideband shoots down to the rich end of the gauge (9, maybe 10:1) for a couple of seconds, the engine occasionally stumbles, and then the afr comes back up. Car starts and idles fine. Afr's at operating temp are perfect. Definitely seems to disappear once the car reaches a certain temp. I have no codes, I've tested all my sensors according to the tsrm, and I cannot find anything wrong. I know our cars are notorious for running rich, but this just won't stop bugging me. Car is a '90 turbo 5 speed with a 3" turbo back & apexi intake.

 

[QWIKSTRIKE]

You need to know how an engine operates with an ECU. When an engine is cold, and the weather is very cold the ECU has a cold start that sends extra fuel to help prevent leaning out. You need to let it warm up a bit to offset this. Here in NY an engine will get more fuel since it is extremely cold. The only thing that you can do is let the car reach operating temperature before stepping into the gas tank. If you understand how cars function you would just let it warm up. What mods do you have along with the wide band? Is this a stock ECU or a standalone? If it is a standalone this can be corrected a little, However; in cold weather the cold correction should add fuel to keep leaning to a minimum.

 

[jetjock]

While some of that is correct, general speaking, the entire point of EFI is to make the engine driveable under all conditions and since this one normally enters closed loop very quickly, far before reaching operating temp, he clearly has a problem...

 

[QWIKSTRIKE]

While some of that is correct, general speaking, the entire point of EFI is to make the engine driveable under all conditions and since this one normally enters closed loop very quickly, far before reaching operating temp, he clearly has a problem...

I understand your point JJ, but when you say that the ECU goes into closed loop pretty fast at what temperature will that happen. For instance with my standalone I noticed that my air temps are negative 5-6 degrees on start up in the am. I am able to tune the fuel curve to what AFR that I feel necessary with a cold air correction curve which I tweaked a bit when it got extremely cold. So I was thinking that a stock car running in open loop may render more fuel under such conditions when it is 1st started, and clear up as the engine warmed up as he mentioned. I also was thinking JJ that before the car went into closed loop that the extreme cold weather here in NY with -6-10 cold start temps, and negative 5-6 engine air temps that the cold air correction would be adding a lot more extra fuel to the base correction fuel to compensate for the cold air. I also noticed that in this extreme cold that the engine takes a bit longer to warm up when it is 1st started here in NY.

I was thinking that if the cold air correction, and the engine temp cold correction was to the left of the normal fuel curve when 1st started that a more than normal rich condition would happen until warm engine temp correction exceeded a point were closed loop takes over. Even after going into closed loop would the fuel curve being to the left for extreme cold air modification cause temporary rich conditions until the engine temp were closer to normal. I.E. If he romps on the throttle when these extreme cold conditions exist would not the ecu cause a rich condition until a warmer operating temperature is reached with -5 air temps when 1st started. He does mention that it only happens when its cold after starting, and it does not happen when driving normal, and that it only happens after aggressive throttle until the engine is warm then it goes away. The question would be what temp does the car go into closed loop temperature wise, and does this happen before or after this point. If there is no check engine light or fault codes I would think that the extreme cold conditions at cold starts the culprit. I also know that load, engine speed, throttle position, cold air, and coolant temps are monitored under EFI control. I probably am not as versed as you are in this so I concede the expertise of this to you.

 

[MikesFixedRoof]

You need to know how an engine operates with an ECU. When an engine is cold, and the weather is very cold the ECU has a cold start that sends extra fuel to help prevent leaning out. You need to let it warm up a bit to offset this. Here in NY an engine will get more fuel since it is extremely cold. The only thing that you can do is let the car reach operating temperature before stepping into the gas tank. If you understand how cars function you would just let it warm up. What mods do you have along with the wide band? Is this a stock ECU or a standalone? If it is a standalone this can be corrected a little, However; in cold weather the cold correction should add fuel to keep leaning to a minimum.

I know how an engine with an ECU operates. I know that on cold starts the computer reads signals from various sensors (except the O2) to calculate how much fuel is needed, fires a cold start injector, and continues to run in a richened state until the computer sees that it's no longer needed. In the 6 years I've had the car, it didn't always do this. There's a difference between adding extra fuel when cold and adding so much fuel temporarily that that it causes the car to sputter.
Typically I let the car sit idling in the morning for a minute or two before gently driving off. Beating on a car when cold is one of the dumbest things anyone can do, and I never do it. Going from a closed throttle situation back to partial throttle can cause it. A typical scenario that makes the car sputter is leaving a stop sign in first. If I try to grab second too quickly, it will sputter for a second or two. Other than the modifications I listed the car is stock. It had a hallman mbc in it but it's been removed from the vacuum circuit.

 

[3p141592654]

On a 40degF cold start the car will be in closed loop in under a minute. It will still be adding more fuel to the model, but it will be maintaining stoichiometric operation.

 

[QWIKSTRIKE]

On a 40degF cold start the car will be in closed loop in under a minute. It will still be adding more fuel to the model, but it will be maintaining stoichiometric operation.

Here in NY its has been in the 30's and lower over night. I find -5 to -6 degree air intake temps at cold start and it takes a longer time for engine to heat up. I am know expert so reread what JJ said!

 

[MikesFixedRoof]

On a 40degF cold start the car will be in closed loop in under a minute. It will still be adding more fuel to the model, but it will be maintaining stoichiometric operation.

Hmm. If that's true then the car does it in both open and closed loop until it reaches a certain temp. What about on a cold start below 40 degrees F?

 

[MikesFixedRoof]

While some of that is correct, general speaking, the entire point of EFI is to make the engine driveable under all conditions and since this one normally enters closed loop very quickly, far before reaching operating temp, he clearly has a problem...

I'm very interested to know what you're thinking a possible cause of this is JJ

 

[jetjock]

You said the afr is rich only upon cold tip-in which is opposite of what normally happens. What is it steady state cold operation? Before the engine warms up?

 

[MikesFixedRoof]

You said the afr is rich only upon cold tip-in which is opposite of what normally happens. What is it steady state cold operation? Before the engine warms up?

My apologies for the late response. Work has been killing me this past week. To answer your question, no it's actually rich all the time, until it reaches a certain temperature. I watched the wideband closely the other morning. Once the gauge goes through it's warm up cycle (15-20 seconds) it sits right at 10:1 (my analog gauge doesn't go beyond that) for maybe 2 to 3 minutes. If I feather the throttle, it will quickly jump up to 11:1 or so, and then return to 10. After idling for ~5 minutes (still cold on the factory gauge) it will lean out to between 12 and 13. Any throttle at that point will make the gauge go right back to 10 momentarily, and then it comes back up to 12-13. Within 10 minutes of cold idling it reads at least 14. I think I will try to take video of a cold start & drive one morning this week.

 

[QWIKSTRIKE]

My apologies for the late response. Work has been killing me this past week. To answer your question, no it's actually rich all the time, until it reaches a certain temperature. I watched the wideband closely the other morning. Once the gauge goes through it's warm up cycle (15-20 seconds) it sits right at 10:1 (my analog gauge doesn't go beyond that) for maybe 2 to 3 minutes. If I feather the throttle, it will quickly jump up to 11:1 or so, and then return to 10. After idling for ~5 minutes (still cold on the factory gauge) it will lean out to between 12 and 13. Any throttle at that point will make the gauge go right back to 10 momentarily, and then it comes back up to 12-13. Within 10 minutes of cold idling it reads at least 14. I think I will try to take video of a cold start & drive one morning this week.

Whats the weather temperature and air temperature. I am here in the Bronx, and I can tell you that -10-(-8) air temps with 5-9 degree temps may be something to consider. Make sure you have no vacuum leaks also, because with a vacuum leak I had issues that I could not solve until I inadvertently discovered a vacuum leak on the intake. The hose going to a barb fitting cracked on the under side at the end of the fitting. Because the crack was on the under side of the hose it took a while to find the leak.

I feel that if no issues are found the extreme cold negative air temps, and single digit cold air may contribute to this cold start anomaly. I am no expert so take what I say with a grain of salt.

 

[MikesFixedRoof]

Whats the weather temperature and air temperature. I am here in the Bronx, and I can tell you that -10-(-8) air temps with 5-9 degree temps may be something to consider. Make sure you have no vacuum leaks also, because with a vacuum leak I had issues that I could not solve until I inadvertently discovered a vacuum leak on the intake. The hose going to a barb fitting cracked on the under side at the end of the fitting. Because the crack was on the under side of the hose it took a while to find the leak.

I feel that if no issues are found the extreme cold negative air temps, and single digit cold air may contribute to this cold start anomaly. I am no expert so take what I say with a grain of salt.

So while checking a few things under the hood I discovered that little vacuum hose on the bottom of the stock intake accordion boot was off. Think that could be it?