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injector low slope


scotty
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I am trying to sort my low slope and I am running in open loop, and when i start the car and

let it idle it is sitting exactly where I am commanding it but once I drive it when I pull up it

idles richer. I can then turn the car off and let it idle and its back where I want it. Any ideas?

Thanks Scotty

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Hi Scotty. Open loop fuel needs very good injector data as there is no compensation done by the PCM. To get a bit more information what injectors are you using and what do you have for them? 

It is not until you get into the larger sized injectors that you will be idling on the low slope at all (Factory injectors do not). 

With my car idling and the air conditioner running but not in gear my car has an AirCharge of 0.000377lb. The fuel mass required for an stoich value of 1.0 on 98 is:

      0.000377/14.62 = 0.0000257 (2.575136612021858e-5)

Which is just below the breakpoint for ID1000 injectors (4.0 bar rail pressure).

A quick way that some tuners use to dial in the injectors like ID1000s is to start the car in Open Loop, look at the commanded lambda vs actual lambda and then scale both both slopes until they get commanded lambda matching actual lambda.

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27 minutes ago, Darryl@pcmtec said:

A quick way that some tuners use to dial in the injectors like ID1000s is to start the car in Open Loop, look at the commanded lambda vs actual lambda and then scale both both slopes until they get commanded lambda matching actual lambda.

 

I've done this and it works quite well. I set the entire base map to 0.82 lambda and went from there. With no trans trunc you can stall it up in the driveway to check it. 

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Sorry Daryl should of mentioned I am using xspurt 1000's (actually ordered bosch and these should up lol).

I have been using the id 1000 as reference data. I just found an offset multiplier I missed in changing right at 4bar

fuel pressure where I am running, so I have changed that and now it is start up idling at the same rich point as when

I pull up so I am just changing my low slope at the moment to idle where I what it.

Thanks scotty

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A walbro 520 as the primary pump and an adjustable fuel pressure reg. I used the injector dynamics spread sheet to obtain the scalers for my pressure, they were a little off, but I found the right setting but it seems to run smoother when it is slightly richer. Not sure if it's a spark issue or the cams (stage 1 crow) throwing it off. It's a boss 260 if that helps.

Thanks for the help

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  • 3 weeks later...
On 3/10/2019 at 10:24 AM, Puffwagon said:

 

I've done this and it works quite well. I set the entire base map to 0.82 lambda and went from there. With no trans trunc you can stall it up in the driveway to check it. 

When doing it this way do you set the low and hi slops the same.

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7 minutes ago, Carl said:

When doing it this way do you set the low and hi slops the same.

No. You set the entire base map to 0.82 lambda, then with the car in open loop you adjust the slopes until it idles at 0.82 lambda and stalls up or holds medium rpm at 0.82 lambda. Then you fix your base map and test it out. The slopes may need further adjusting but it won't be much.

Edited by Puffwagon
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With it in open loop it's still tries to track 1 lambda at idle is this normal. If I stall it up to say to  3000 rpm would it be on the hi slope or still on the low slope. 

Edited by Carl
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It won't keep stoich in open loop unless the fuel maps ask for it and the slopes are correct.

To answer your question, it should be on the high slope near idle or not long after, depending on injector size.

The low slope only accounts for injector non linear output at low pulse widths. Having it too high is a common cause of cold start issues. 

The break point dictates when the slopes swap from low to high, and this is tuned subject to some variables. 

There is some good info on the injector dynamics website.

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