FD vs Modded STI
 

It's a little after 11 pm last night, and I am on my way home. As I approach the next intersection, I see a black car cross, and go to my right. I wasn't close enough to the intersection to be sure what it was, but it looked like a performance car. Maybe an EVO. I make the turn, and catch up to him. It's an STI with a loud exhaust. Obviously modded. We blip the throttle at one another, and go to get on the freeway. Its a cool central Ca night. Temps in the upper 30's. When its cold like this, my car doesn't fully warm up (over 180) unless I sit at idle. So I'm going to race this guy with my engine temps just below 180. At this engine temp, the car runs pretty good until about 7k. Then it really hesitates. If the engine is over 190, it runs great all the way to 8k. The hesitation is caused by the ecu thinking the engine isn't warm enough for full boost over 7K. Not the best situation for me. Wait a minute .......... was I describing a race??? :D

Anyway, there is no one on the freeway. We line up in 2nd gear, and hit it from about 35 ish. I immediately start to pull a little. Shift to 3rd, and start to pull a little more. I get to 7k in 3rd, and I have almost a car length on him. Damn .... hesitation hits!!!! I shift to 4th, but he has gained a couple of feet on me when it hesitated. In 4th, its quickly over as I put about another car length on him. I short shift to 5th at about 120 (avoiding 7k), and take it up to 130. By then he has given up, and slowed way down. I wait for him. We take an off ramp, and pull over to chat.

He's very surprised at how fast my car is. He fully expected to beat me. His car has all the bolt ons, full exhaust, and a tuned PFC. He said that he has a friend with a single turbo FD in Nor Cal, and that his STI is faster. I asked him if he noticed that at one point he started to gain on me. He said yes, and was thinking that he might pull me in at that point. I told him about my hesitation because of the cold temps out. "Very unusual" was his response. His car really likes the cold air temps.

Anyway, it was a fun race, and he was a really nice guy. We exchanged info, and may go to hit a 1/4 mile track at some point.

My mods are in my sig, and I'm running 13 psi.

good kill Adam!

I'm thinking his friend with the single was not runing right at all and your certainly is. Maybe it was an ebay special? lol

nice kill

^^He said that he has a friend with a single turbo FD in Nor Cal, and that his STI is faster. Nice job. It doesnt matter how much power you car can make. It matters how well it is set-up to get there. G

Nice kill.... yeah I am kinda agreeing here... If he is beating his friends single turbo FD either his friend cannot drive AT ALL.... Or it so running very poorly.... anyways again nice going!

The sweet smell of victory

Good kill! :)

We had the same response! :P

I don't mean to sound rude and turn this into a tech thing, but the above statement seems like it might not be accurate to me.

I assure you, if your car is sitting just below thermostat open/close, it's warmed up. The internals of the car are going to be seeing well over 160c, regardless of what kind of ducting and cooling system you have. I'm very sure that here in Minnesota, I have seen much colder temps, and my cooling system is more extensivly ducted then yours may be, and after a few mins, (5 tops) you are warm, regardless of your ambient.

I just don't think your engine is running cold enough to force the map to be modified for such a noticable hesitation. It is possible that your m2 ECU is programed in such a way that for every degree below a set point, you are seeing changes. Normally the computer adds fuel though when there is a colder condition, and unless it was DUMPING tons of fuel, you wouldn't hesitate like that.

It's more likely it's an ECU issue, or your ignition is failing. When was the last time you changed your plugs, coils, wires? You should try testing those, it will likely clear it up. Especailly an issue so high in the power band, it's got to be ignition related.

Good luck, just trying to help!

Keep owning those STI's'! :chomper:

-Rt4w

i thought that turbo cars loved the cold air/temps and not hot air/temps.

The explanation in my original post clearly states that the ECU is sensing that the engine is not fully warm, and is therefore restricting power at high rpm. I have no hesitation issues when the engine is over 190 degrees.

hmmm
 

Adam, when you say your car is reading at 190, you are obviously not looking at the stock gauge or a PFC, because the first does not give you values, and you don't have a PFC + Commander.

So I'm guessing you have an external temp gauge plumbed into your coolant system somewhere. Where is it tapped it?

I'm guessing your sensor is tapped on the outside of thermostat, so it is reading less then the temperature of the "inner loop" of your coolant system. (It reads less because the thermostat will open and close, and it's on the outside with the colder coolant that went through the radiator.)

The sensor that get's the reading for the water temperature to your ECU, to adjust the values for the map, is actually inside the system. (There are actually two water temp sensors, one for your stock gauge, and one for the ECU, so you likely have three sensors total for that system).

So, unless are drawing your aftermarket water temp gauge data from the voltage of the internal sensor that is giving information to the ECU, those two values could be different. So when the sensor you see shows 190, that does not mean that the signal to the ECU, which would effect the fuel, would be seeing 190 either.

The only way to really test this, would be to wait until you either get a computer that allows you to view the actual sensors that are being used for your computer (PFC + Commander) to see if your theory still holds true. I'm guessing it won't.

Did you have the ECU mapped specifically for your car, or did you buy it used with the "close" mods to your own setup?

I still think that you have an ignition issues somewhere... I'll do some research to see what I can find though.

Just trying to help bro! :P

-R4tw

They do, you are correct. What he is saying is technically possible, though highly unlikely. You could program your PFC to do an insane 80% fuel add anytime the car is below a certain temperature, and you could set it at 179f in theory. (I think)

This is not very likely, but it could be his ecu has a bad value for when the car isn't up to opperating temp.

But that doesn't make much sense, because once your car is warm, it's not possible for it to get "unwarm" to the point of fuel dump and retard, regardless of how cold it is or crazy efficient ducting... Unless your thermostat was never opening or something, but if that happened, your car would be rich and in "warm up" mode all the time, not just from 7k and beyond. (Thanks for the insite GooRoo)

Btw, when you Dyno that 500r, make sure to get a dyno sheet that shows both the HP also graffed with your turbo pressure so we can see where your turbo spools up at. I'm really really curious to see at what RPM the 500r makes 10psi of boost and where it makes full boost. :)

-R4tw

Nice kill

I have also beat a highly modded sti, they are great off the line but easy to catch ;)

Rotary4tw,

My coolant sender is in the throttle body coolant line. It gets constant readings, whether t-stat is open or not. I know it is accurate because I checked it at several different temps compared with my old sender location. The old location was just after the t-stat.

The other night, my car never got up to 180. It was cold out, and the engine never did get to 180, and it never would have as long as I was traveling at over 40 mph.

My M2 ECU is my original ECU that was upgraded by the people at M2. It was not purchased used.

I assume that the ECU is causing the hesitation under 180, because the car runs strong all the way to 8k when the coolant temps are over 190. I don't know what else it could possibly be.

say... nice kill... did that STI owner happen to be a guy named Sean??

dont sniff the glue....check out my subaru!

His name was Phung. Nice guy.

nice kill man!

Hey Adam, Rotary4TW pointed me at this thread to see if I had anything to add/change from what he said... I think I agree with most everything he mentioned, however:

If your car does not get to 180 with the temp sender in that location, I would suspect a thermostat issue.

It should get to 180 regardless of outside temp, really regardless of basically everything else. When it's cold it will of course take slightly longer, but even here in Minnesota when it's 10 degrees out, within 5-10 minutes of highway driving I'm at exactly 180 on my (throttle body line) temp gauge and 82-83C on the PFC.

I had a thermostat issue in my S4, where it would work normally in the summer, but as soon as the temps got cooler, I'd never get fully warmed up. Gas mileage suffered because the ECU was always in warm-up mode. Took the thermostat out (massive pain in the S4) and tested it on my stove and sure enough, it started opening at 55-60C, when it was supposed to start opening at 78-82C.

Swapped it out and it was fixed.

There's generally 3 failure modes for the thermostat:

1) Stuck Open

Not a huge deal, but car doesn't regulate it's temperature anymore and never warms up (except under heavy load.) This leaves the low temp correction map still modifying the fuel values to add fuel, and leads to crappy gas milage and cat failure, since it has to burn all that extra gas.

2) Stuck Shut

Really really bad, since this overheats the motor.

3) Early Open

Causes the same problems as the 'Stuck Open' case, with a lower amplitude depending on what temp it decides to open at.

Thankfully it's really easy to get to on the FD, so you might want to try checking it.

I'm not 100% sure which corrections the stock/M2 modded ECU has, but if it's like the PFC there's two that might be causing your hesitation.

1) Water Temp Correction

At progressively lower temps, the ECU will add progressively more gas. My knowledge is somewhat limited, but I believe this is because at low coolant temps you will have low air temps, and need additional fuel. I think it also will slow combustion and limit power, which is what you want at lower temperatures: a smooth consistent rise to operating temp.

2) IGN vs Water Temp Cool

At progressively lower temps, the ECU will retard the timing, so that the combustion pressures are lower. The reasoning is the same as before. Limit power and load on the motor while it warms up.

Both of these could cause the hesitation, but if you can feel it, I would suspect that it's probably the 1st. The 2nd would mainly just feel like less power, not a choppy hesitation. The interesting thing about that is that the fuel correction maps are applied in a linear fashion. If the stock/M2 maps are the same as the base PFC map (which admittedly it may not be) then at 50C you are at about 8% extra fuel, and by 80C you are at normal fuel. So if you were running at 65-70C, then you'd have about 4% extra fuel. This is probably enough at high rpm to cause a hesitation if the map there is already somewhat rich (as I expect the M2 ECU is) especially if you're not running some sort of ignition amp.

To my knowledge there's nothing in the ECU that restricts boost when the motor is cold. And even if there was, Mazda would definitely have not let any power/boost restriction feel like a hesitation for the driver.

So, to sum up, I think Ben might be correct, but with the additional information you provided that that the ignition issue is not the root cause. The root cause might be the thermostat. Could also be something else.... but if it was my car I'd start there.

Just trying to help, you probably already know some/all of this but I decided to be super expository for the other guys that may read the thread.

Yep. We're freezing our asses off here and my temps warm up to 180F and then park there no matter how hard I drive the car when it's really cold out. It takes me a few minutes longer to warmup of course but it will make it to 180F and hold.

As for running rich when cold my car certainly does. If I start the car in the driveway and let it warm up in the cold, cold winter time you can smell the raw fuel in the exhaust. Lots of soot in my tailpipe as well which is never present except when it's really cold out. The ECU seems to only do this at lower RPM because it doesn't pop any more than normal when driven hard but that's just a guess.

Stock ECU restricts boost until the water temp reaches 165F. As a rule I never run my car hard until I see at least 160F of water temp.

How does it restrict the boost? I'm assuming it just lets the wastegate see full pressure, if so it can't restrict it down more than 7psi correct? Because that is the wastegate spring pressure?

I don't see any setting like that in the PFC.

Correct. Stock ECU holds boost to 7psi until water temp is over 165F.

Hmmm, I wonder if the PFC does that as well. I don't see any setting for it.

Anyway, probably none of that would have to do with Adam C's problem, since he is only seeing the issue at high rpm only, and it's a studder, not a low power problem.

GooRoo & DamonB,

Thanks for your comments. I believe that my t-stat is operating properly. My regular drive to the office is about 2 1/2 miles on city streets. It normally takes 6-8 minutes. The coolant temps are generally almost to 180 when I arrive. That should rule out a problem with the t-stat being stuck open. In addition, I don't have any overheating issues, (note second comma for DamonB ;) ) so it isn't sticking closed either.

As far as boost limit vs extra fuel, I'm not sure. I have a feeling that it is not limiting boost. I'll check at my next opportunity. My guess is that the ecu is going to extra rich at 7K when is senses that the engine isn't fully warm.

DamonB, have you considered the possibility that your (and my) "exposed" throttle body coolant senders are influenced by outside air temps? Do you think they may be showing slightly cooler readings with the cold weather? I would be interested to hear your thoughts on this.

Adam

Yeah, 6-8 min won't warm the car up. However you said before that it would run under operating temp when on the highway. It should definitely progress to 80c and not go below there unless you shut the car off.

I have the same throttle body coolant sender location, and while it may be slightly affected by outside air temps, it is not enough that I've ever seen it on the gauge, even when the temp outside is 0 degrees and I'm cruising on a highway at 60-70mph.

After the car "should" be warmed up, I still get readings under just 180 while on the freeway on a cold night. My VDO gauge could be off a little. Even if it is off, the fact remains that I don't get full power at high rpms under those conditions. I'm convinced that the ECU is "protecting" the engine .............. from the driver ;).

Are we having an intelligent discussion (without arguing) in the kills section???? That never happened before :D.