'02 Trailblazer 4.2 liter I-6

[Z06VetteLover]

I have a 2002 Trailblazer 4.2 liter I-6 vehicle with a 4L60E trans., & a 3.73:1 axle ratio w/posi. I am wondering if an HPTuner could add more power & torque as it is a 10:1 CR engine & book says to use 87 octane which tells me that I believe this motor is severely detuned & could probably really benefit from a 93 octane tune. Also the trans. seems to hang in the lower gears quite awhile before upshifting unless I let off the gas which is not depressed very far to start with. Any ideas on some gains & to what approximate values would be very much appreciated. Thanks!

[justin99]

i just received my software today and just started tuning my 04 envoy 4.2 so i'll let you know. So far all i have done was remove torque management and it seems better. Can anyone tell me what rpm to set the PE at on the 4.2?

[redhotjamedjimi]

Yes. Especially with non stockish parts. intake etc. hard to make a econmy built into a hp built.

[justin99]

also if anyone that has tuned the 4.2L would chime in that would be great. My main focus is to continue running 87 octane and get the best mpg possible. Just not sure on what to change on the high and low octane tables yet. I have downloaded some tunes and they are both totally different. Dont want to use one that requires 93 octane but since i am unsure of how to read the charts yet i didnt want to touch any of them. Any help would be great.

[Z06VetteLover]

Justin99, You mentiioned that you are looking for max fuel economy, & that is yet another problem that I have with my Trailblazer. It is advertised at 15 & 21 & I am lucky to get 16 or so highway. That is why I am thinking that going to 93 octane fuel as I did in an older '97 Z28 & tuned for it I gained power & about 3.5 mpg, plus programming the T/Blazer to upshift faster & lockup to come in sooner to keep the rpms down would definitely raise power on 93 octane, mpg's., & not staying in the lower gears so long just revving with very light throttle. On my inst. mpg display it goes up instantly when it finally upshifts. I don't have the HPTuner yet to play with it yet, but am just trying to put some 2 + 2's together with this thing. Hope this will help you some!!!

[justin99]

I have changed the shift points and firmed them up as well as removing the TM. Plus changed the PE delay to 1000 rpms and I took a 90 mile trip pulling 2500lbs and i averaged 15.6. I normally would do around 14.6 to 15 so it has mpg has gone up alittle but the power is quicker and the shifts are much better. Im going to stay with 87 octane and normally without pulling a load i can get 21 to 22 on the hwy. I also have a drop in k&n and airraid throttle body spacer which did help. Im waiting for some good tuners to chime in on what other parameters to change for some better mpg though.

[justin99]

I am also curious about the low and high octane tables. I have been reading that people copy the high into the low. Does this mean that you have to run premium gas? What is the purpose of this?

[Mep_q8]

U will get some great results... at least 10whp over stock, faster shifts, firmer shifts, and a smoother ride....

I did some tests with my friends LT with 3.42s.. he has the onboard timer, we cut at least 3 secs from a 0-170kph run, so it deffinately does the job.. my friends trailblazers can take on yukons, muranos, V6 dodge chargers.. not bad for an I6 with only intake and tuning!

[redhotjamedjimi]

the whole high octane into low is good to a point. u have to remember low octane is used alot of before pe when your at stoich afr. so premium fuel would help alot and get the extra hp but you should get 30 mins of logging when u do it for knock issues. i dont think a trailblazer has the hard internals it needs for that matter. and if it does advance it and forget all the stock numbers.

[justin99]

U will get some great results... at least 10whp over stock, faster shifts, firmer shifts, and a smoother ride....

I did some tests with my friends LT with 3.42s.. he has the onboard timer, we cut at least 3 secs from a 0-170kph run, so it deffinately does the job.. my friends trailblazers can take on yukons, muranos, V6 dodge chargers.. not bad for an I6 with only intake and tuning!

are you referring to the high and low octane tables.

[Russ K]

I am also curious about the low and high octane tables. I have been reading that people copy the high into the low. Does this mean that you have to run premium gas? What is the purpose of this?

This is from the help files:

If the VCM detects knock it will instantaneously reduce timing (Knock Retard) but will also modify the Knock Learn factor to affect the proportion the VCM uses to interpolate between the High Octane and Low Octane Main Spark tables. If no knock is detected over a reasonable period then the Knock Learn factor will slowly return to the High Octane table.

No, you don't need premium gas if your spark tables are set up right. I always copy the high octane spark table to the low. The purpose of the low octane table is so if the engine was overheated & pinging, and the driver just kept on driving. So it will save the engine from serious abuse.

Russ Kemp