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Learning to tune

M

Mitch R

New member
I figured I'd start a new thread since this is for a different vehicle. I got my dhp tuner and have been playing around with it and I decided to start learning to tune on my 98 GTP since my other car which is getting the turbo is still waiting on some parts. My GTP has a canned tune as well as a cai, slp catback, ubend delete, 1.8 (iirc) rockers and a smaller puller (believe it's a 3.4). Everything was installed by the previous owner.

So I first took some scans and not surprisingly my ltfts were between -8 to -16, also seeing kr once I start making boost. I've come across many guides on correcting this and am going to try to follow those over the next few weeks, however my first big question is do I try to retune the canned tune in the car or do I start from a stock bin and modify from there?
 


it's really up to you if you keep it or switch back to stock. if you keep it, it would be easy to do a maf adjustment to bring in your fuel trims and cut timing. going back to stock will change how the car drives, and you would probably get bored with it. but that can also be fixed by changing the transmission shift settings. a 3.4" pulley sounds like it is too small for those mods, but you can just take out some timing advance to fix the kr.
 
SgtMarshal said:
it's really up to you if you keep it or switch back to stock. if you keep it, it would be easy to do a maf adjustment to bring in your fuel trims and cut timing. going back to stock will change how the car drives, and you would probably get bored with it. but that can also be fixed by changing the transmission shift settings. a 3.4" pulley sounds like it is too small for those mods, but you can just take out some timing advance to fix the kr.
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I wondered about the pulley size myself as I've been reading and learning more about these motors. I took a tape measure to it and it is definitely a 3.3 - 3.5. I'll probably change the timing to pull the KR, as I don't think the prior owner gave me the stock pulley when he sold it.

Explicit_Spade said:
Depends on who made the canned tune. See if the PCM has any kind of marking on it.

How much KR are you seeing?
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I just checked the PCM, no marking other than 1998 GTP, -B152 and the prior owner's last name. I saw 7.3 at 144 kpa, 51% throttle and 2930 rpms, but its worth noting that this was on 87 octane as my wife filled it up last, so that certainly didn't help. I didn't go harder into the throttle knowing that, especially after it spiked like that. This car has kinda become the family sedan, its the most comfortable for long trips and it easily fits our two carseats. Is it even possible to tune these cars to run 87 without blowing them up? I would like to try to get a little more mileage out of it, while still retaining some of that get up and go, but perhaps I'm asking too much of it.
 


You'd never get away with 87 octane and a smaller pulley that's for sure.

At the very minimum run 89 octane to try and save your bacon but even that really isn't enough. Always run 91+ or switch to a rather large 4.0 pulley to limit boost to a low number.

Fuel grade will not change mpg either, stoich is stoich for regular unleaded gas. In MN it ranges anywhere from 0-10% ethanol content but that is the only difference. The computer will still try to achive the same commanded air fuel ratio for the regular fuel no matter the grade. Mainly your foot/driving habits/vehicle condition controls all mpg and if any sensors are acting funky.

It's possible to raise timing a few degrees in the area's the engine run at during freeway cruise speeds but don't expect world changing results. Maybe ~1 better mileage.
 
If you're running way too rich, a good tune could give you quite a big difference in mpg.

I don't see it being implausible to get +5 mpg just from a tune... +10 maybe kinda stretching it.
 
If getting 4 or even 5 mpg from a tune was really just that simple, don't you think more people would be doing it??


Driving style/habits play the biggest roll in mpg if the engine is totally up to snuff. I played around with timing many times when I owned my grand prix, made MAF adjustments, made corrections for mods done and even with all that and a steady foot on the freeway getting 30-31 mpg was about all it could do.
 


I will admit there's a limit, but if before the tune gas mileage isn't what it should be with these cars, it can help a lot.
 
before the switch to the 10% ethanol blend, I would drive from Evanston, Wy to West Jordan, Ut and average about 35, but that was because the elevation dropped from 7000 feet to about 4600 feet, after the switch, I got about 31-32. Ethanol might burn cleaner, but it doesn't have as much energy. Ethanol also works well to prevent detonation, so if you run ethanol free gasoline you might get a little better gas mileage, but you might also have a bit more KR at full throttle. I've messed with timing advance on the highway as well, and nothing seems to make much difference. I run about 35* of timing advance on the highway and get about 28 mpg. There is an exception to every rule, but if everyone was getting 5 miles per gallon better gas mileage from a tune, than everyone would be doing it.
 
Well even if I can get 1-2 mpg more out of it, I'll be happy, as people have stated everything has its limits and this car has seen a lot of miles. Have you found that pulley size makes any difference in regards to mpg when not making boost?
 
Would everyone be willing to spend $250-$400 on DHP or HPT just to tune their cars for a 5% increase in gas mileage?

Not everyone can get the same effect, but is it really that hard to believe that one could get an increase in MPG by adjusting for a LTFT that reads excessively rich? You would think that by leaning it out, you would actually be putting less fuel into the engine?

It may not be 5 mpg for every person that does it, but it can be substantial for some who aren't exactly running "up to snuff" and need a tune in order for it to be perfect.
 
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Mitch R said:
Well even if I can get 1-2 mpg more out of it, I'll be happy, as people have stated everything has its limits and this car has seen a lot of miles. Have you found that pulley size makes any difference in regards to mpg when not making boost?
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You could run a 2.8 or a 4.0 pulley out of boost and it wouldn't change because the BBV vents all boost pressure under normal throttle conditions.
 


Mitch R said:
Well even if I can get 1-2 mpg more out of it, I'll be happy, as people have stated everything has its limits and this car has seen a lot of miles. Have you found that pulley size makes any difference in regards to mpg when not making boost?
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I don't think pulley size affects miles per gallon at all. you really can have the best of both worlds with a pulley size drop.
 
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