TOPIC: 2002 Chevy trailblazer 4.2

This vehicle was averaging around 15mpg before the groove mod, afterwards the customer has seen up to 20mpg hwy, but averages around 17mpgs. He is going to replace his intake manifold gasket soon, and check for other vaccum leaks. We have checked the condition of the 02 sensors and the post cat sensor is dead confirmed on my touque pro app. He will change that out too. No smell from exhaust anymore though and he was very pleased with that benefit, also says that he feels that the power increase has taken atleast a second off the 0-60mph time. There is no pcv valve for this 4.2 vortec engine, so why have it on other engines?! There is a vaccum port in the high pressure zone where groove is placed that needed to be filled with jb-quick shown in pictures. It is for the evap hose that requires vaccum, so we re-routed the hose near tthrottle body but did not recieve enough vaccum and got a CEL for it. Planning to re-route even closer to throttle body, or use a port readily available in intake manifold where a rubber cap already is. We will just remove that rubber piece and tap into there. Will post on that when i can. Shedule at work is crazy right now getting up at 5am, home at 6pm but will get it done. Wish i were Gadgetmanning full-time! Yes the temp was taken on the exhaust manifold at the hottest spot i could find. We let the engine warm up to operating temp both before and after the mod. I will also temp thermostat housing on vehicles to come.

those temperature readings - were they taken on the exhaust manifold, pre and post groove? almost 60 degrees is a big deal!

Moving forward for anyone reading this, I think a possible better location to test would be at the thermostat housing. In fact, documenting BOTH would be the ideal, to show just how much of the fuel is getting burned in the engine rather than in the tailpipe; theoretically, the water jacket should stay the same temp or even increase slightly, and the exhaust should do exactly what is shown here.

Michael, I need two things from you. First, write a description of what the post is about. "Posting pictures" and "More to come" tells us nothing about the post and is not searchable by Google. Also, please insert the pics into the post. I've been trying to, but it won't let me.

And that's impressive! 50 degree drop in engine temp is very respectable, but I believe you would've found them even MORE impressive if you had tested the actual manifold itself!

Ron

Greg, as the actual coolant temp is managed by the thermostat, I wouldn't expect to see any drop in the temperature of the cooling jacket.

right, the 'stat actuates around a specific temperature, but that doesn't mean the coolant flowing past it won't be warmer for a time (until the stuff in the rad cycles in to replace what the t-stat lets out...)
In fact, the owner's manual for my car clearly states that during normal operation, the temp gauge will fluctuate in a specific range (between 1/4 and 1/2) , and I've learned that at just above cold (when the EGR gets tested, 55-60 degrees C- the "clicka clicka clicka" ) it starts listening to the o2 sensor and just below normal (1/4 indicator, like a fuel gauge) it goes into closed loop, with the fan not coming on until just past halfway (the 2nd one kicks in at 3/4 to the top - a hot day in stop&go traffic).

This trailblazer got instant "steam clean" exhaust after placing the groove, and a power increase, but we have been noticing fluctuating mileage numbers with this 4.2L GM.
Have wondered where the vaccum leaks are, because this vehicle wasn't responding like the others that showed big gains.
Thankfully Ron sent out an email on 12/29/18 addressing these engines, and where a BIG leak can be found on all of them. Pictures attached.

All it took was a vaccum cap, and in 10 minutes of driving at 55mph we gained 5 MPG'S!!! You can see how the graph dramatically changes from around 15 to over 20mpg. Gained way more power too. Can't wait to update the latest highway mileage.

Here are some pictures of the engine, and where the hose is located.

"Almost completely hidden UNDER the intake manifold, leading from near center of the manifold, and turning directly toward the block"

In the future, ill attach a fitting to this hose (that's disconnected now) and extend it to a T connection at the crankcase breather tube.

Thankyou Ron!

After the groove, we noticed that on cold starts, the idle goes up to 1800rpm, then down to 1k. Then back up again. Sometimes it only happens once, other times it does this 3 times before idling smoothly under 1k. This only lasts about 20 seconds or so before it smooths out.
Also, when changing from park to drive, the rpms will go up for a few seconds without touching the pedal. Its an electronic throttle body. This is the first TB i grooved that has made an engine respond this way. What do you guys think is problem?