No fuel map past 10psi on ST165?

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No fuel map past 10psi on ST165?

Postby CodingParadox » Mon Oct 11, 2004 5:37 am

So, I read something in another post by someone saying the stock ST165 ECU has no fuel maps past 10psi? Is this true?

Might this explain why I can't get my MBC to go higher than 10psi?

Also, if so, this is an even better reason to wait until I get an ST185 harness before upgrading to my MR2 engine, because I plan to start running heavier boost soon, but I guess I can't off the stock ECU.

What do the fuel maps go to on an JDM SW20 ECU? At least to 15?
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Re: No fuel map past 10psi on ST165?

Postby illGT4 » Mon Oct 11, 2004 6:07 am

CodingParadox wrote:So, I read something in another post by someone saying the stock ST165 ECU has no fuel maps past 10psi? Is this true?

Might this explain why I can't get my MBC to go higher than 10psi?

Also, if so, this is an even better reason to wait until I get an ST185 harness before upgrading to my MR2 engine, because I plan to start running heavier boost soon, but I guess I can't off the stock ECU.

What do the fuel maps go to on an JDM SW20 ECU? At least to 15?


Your MBC will go higher. Nothing to do with the ECU or fuel maps. But going higher can be dangerous to your engine.

I do believe that the stock 165 ECU has maps to 10psi. The 185 has maps to 12 psi. I'm not sure about the later gen mr2. Might be 17psi like the RC/GrpA/CS 185.
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Postby Zomb » Tue Oct 12, 2004 8:53 am

I am certain all ST165 maps are to 12.5psi, ST185 pre-facelifts are the same at 12.5psi, RCs are 16/17psi, not sure about Facelift ST185s, ST205s are 17/19psi
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Postby ChrisD » Tue Oct 12, 2004 2:16 pm

I don't really buy the whole "fuel maps until x psi" arguement anymore... It is true that the gt4's have fuel cut at certain boost levels, however the fuel *maps* themselves are calculated on a certain amount of airflow, not boost. Whether or not they end at 12 psi or not doesn't really matter, since it will resort to a worst case scenario mode after you exceed that map. IE the maximum amount of load that it is mapped for. One would have to measure the injector duty cycle to see if it changed values for given amounts of boost to find out what load point is the last one used.

The real importance is being able to monitor your engine properly if there is an issue with insufficient fuel or detonation.

What you need to know is what the "load" values here actually are (1990 jdm st185 shown):

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Postby ChrisD » Tue Oct 12, 2004 2:19 pm

Also, I know I didnt answer your question...

Your MBC problem is of itself. It could be a problem with the MBC, it could be a problem with the stock intake or cat being too restrictive. It could be an engine problem or it could be that the ECU is pulling timing so aggressively that you can't build boost.

Start with the easy things. I'd take a look at the MBC first...is there a breather hole drilled in it?
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Postby MrWOT » Tue Oct 12, 2004 2:52 pm

Yeah, you guys are forgetting the true limiting factor on the 165 and 185. The VAM. The air door on the VAM is fully open at about 10-11psi and all the system has to rely on fueling after that is the O2 sensor and air charge temp sensor. This is iffy at best since the injectors are set to full rich after it maxes out, the increased duty cycle stresses the injectors significantly. An alternate method would be to install larger injectors on your car, then fit a spring with a higher return rate to offset the larger injectors. By doing this you can make the computer think it's not receiving as much air, and it will shorten the pulse, maintaining correct A/F ratio even with the larger injectors.

Oh, and of note is that while this will work, it will add increased resistance to flow and turbulance, so it's not all that great of a mod in itself, but if you feel the need to run higher without a standalone, it's a good way to do it cheap.
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Postby ChrisD » Tue Oct 12, 2004 3:10 pm

Are you certain the AFM is fully open at 10-11 psi? Do you have any data to prove this? From what I've seen, this is not the case. I remember one person that had readings and found that the AFM was only just over half open.

There is no temp sensor to measure the charged air. The only temp sensor is inside the AFM, pre turbo.

The ECU uses the AFM temp sensor to alter the timing maps by deducting the amount of advance allowed.

The ECU does not use the o2 sensor for maps at WOT, ever.

I agree there is a point where the ECU stops altering the fuel/timing maps, however I dont think it is 10-11psi. Instead, I say it has nothing to do with boost level and only airflow measured by the AFM.
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Postby MrWOT » Tue Oct 12, 2004 4:42 pm

I didn't say it used the 02 sensor to map at WOT, only that once the door is fully open that's the only device it has left to give fueling feedback. And you are correct, the 02 sensor is discarded whenever in open loop (wot). I was referring to part throttle closed loop, where most driving is done.

And as for the door being fully open at 10-11 psi, mine is fully open at 11psi @ 5500 rpm with a stock supra ct-26 fitted :( I suppose this could be due to a worn spring since my car does run rather rich, but I can't be sure. Hence why I am shopping for an alternative in the form of a MAF conversion (I drive at different altitudes often and prefer to keep the longterm flexability of MAF over speed density).
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Postby CodingParadox » Tue Oct 12, 2004 6:18 pm

Nah, I was guessing it was my MBC. I didn't quite build it correctly, it seems. I don't have a second slot in the end with the ball for it to have to slide up and out of. It's just against the hole, so if it moves at all it lets boost by. Time to go find a new fitting, methinks.

That's some interesting stuff about the AFM And ECU though. Good to keep in mind. I wasn't planning on running past 10psi for now, just because I'm on the stock intercooler and stuff for now, which really can't take anything past 10, but I'd like to be able to run 10, which my MBC isn't always so happy about allowing.

I also need to figure out why the hell my adjustable fuel cut mod is having the reverse effect, and showing a _higher_ boost level than actual boost on the tps. Gr.
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