Michael55123

iTrader: (3)

I'm going to try to explain setting up and tuning a dry shot of nitrous, on a 98 ECU that's running speed density (no maf). Normally you'd just trick the iat by adding a resister to a relay that runs off your WOT switch. This would in turn change your timing, and pe table. There's a iat vs. pe adder, and a iat vs timing table. But not in 98 ECU's. Those with 99's and 00's can always do a full write to a 01 or 02 os and solve this problem. Those with 98's aren't so luck. Luckily there's a simple solution, just use the ECT sensor instead of the iat. The ECT in 98's are a little different, it uses a 3 wires, not two. It's not really a big deal, you just want to worry about brown and yellow. This is where you're going to use your relay and resistor to trick your car into thinking it's REALLY cold. We used a 47k ohm resistor, and the car thought it was around -28 degrees F. This works great for our purposes, but won't work if your car will ever have a coolant temp around -28, but if that's the case, don't drive it???? Lets take a look at the ECT wiring diagram real quick:



Alright, simple enough. This isn't a definitive nitrous tuning guide, just showing you how to tune your nitrous on a 98 with SD, and no iat table in hptuners. You're going to wire the resistor up to run off your wot switch, with a 87a relay. I don't have a way to make a diagram, but if there's enough interest I'm sure I could come up with one. Moving on to the tuning.

You're going to change the Add Vs. ECT under Engine -> Fuel Control -> Power Enrich. You're going to go down to the negative numbers, -40, -22, etc... Change the ones at and around the value of your resistor to add fuel. For my friends 408 with a 150 shot, we needed to add about 45% of fuel on top of what PE already adds, so we simply set the value to .450. You're going to have to experiment to see what value you need to run the right AFR. We had a wide-band, and dialed it in just about perfectly.

We also wanted to take out some timing, so we goto Engine -> Spark Control -> ECT Base. We then want to change all the cells in the -40, -31, -22, -13, or whatever is around the value of the resistor you're using. We took out 6 degrees of timing for the 150 shot, I've head 2 degrees per 50hp, but whatever works for you, just watch for knock, and make sure your AFR's right. Hopefully this helps some poor 98 guy out who doesn't have a IAT. If you have any questions let me know, I'll be more than glad to help out.

Robert56

iTrader: (2)

Not new but the best write up I have seen for the SD guys. The problem with using a the IAT vs fuel adder table, is it will have a lag time and thus a healthy lean spike. it just dosen't work well for most. Maybe it could be set-up to come on before the n2o sprays through a delay. thanks for the write up, as I am adding it to my stash of notes.
Robert

383LQ4SS

iTrader: (33)

You guys that are using the IAT should use a resistor to change the ohm value instead of relying on actual temp drops. Simialir to what Michael is doing with the ECT. You can even wire in the swap between actual IAT value and the value of the resistor on a relay that runs off the main relay. That way it activates instantly as nitrous comes on. No lag.


Good write up Michael

383LQ4SS

iTrader: (33)

Robert...when you say there is lag time...are you saying it lags because the computer isnt adding fuel fast enough...or because the IAT isnt cooling fast enough?

If your relying on actuall cooling of the IAT...why not just do what Michal does above and use a resitor inline with the IAT circuit to immediatley boost the value upon nitrous activation?

GTA91

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subscribing

Robert56

iTrader: (2)

Well I never personaly had any lag time that i remember, but most guys that have done report a lag time. Yes the resistor could be used and was the prefered method in the begining. Not sure off hand if the lag is the iat, or the comp responding, but likely it's the iat cause the pcm responds in milla seconds to most all commands. I have found better ways to add fuel as discussed in the other threads for MAF style dry anyway.
Robert