2008 GMC Envoy

Hi, you could check your engine mounts.

does ur car has a computer system with it.?
if so u can try to retrive

After the MIL is turned off or the battery was disconnected for some time, all monitors are set to incomplete. However with several short trips with engine getting at least to hot enough for thermostat to open, (I believe 8 is the magic number of trips) most monitors are set, you may be able to pass the test with only one incomplete only.

If the engine is misfiring you would have a blinking check engine light and a fault code stored for the cylinder that is misfir9ing is that the case? If it was me I would replace the spark plug wires, they are cheap and most likely the problem.

Here is the OBD2 emission system drive cycle test procedure.
Engine coolant temp must be below 70c (158f) before starting the engine for either the first or second trip
The fuel level should be less than 1/2 full
First trip:
Start engine, idle for at least 1.5 minutes
Drive 3 minutes, hold b/f schdl: 1.5-2.0 msec, selector lever "3rd" eng rpm 1,800-2,000 A/C switch:ON Hold the recommended b/f schdl range. Allow road speed to vary as necessary.
Drive at 55-65 mph for 1.5 min b/f schdl 2.0-3.2 msec, selector lever "5th" Engine rpm 2,200-3,000
IGN "off" for at least 10 seconds (not more than 5 min)
Dive at 50-60 mph for 3 minutes Selector lever "4th" keep engine speed above 3,000 rpm Allow speed to vary if necessary. Do not decelerate for more than 3 consecutive seconds. A/C switch ON.
Drive at a steady state cruise of 53-58mhp b/f schdl more than 1.8 msec selector lever "5th" eng rpm 2,400-2,600
Downshift to "4th" and decel more than 5 seconds without breaking, then idle for 1 minute.
Drive two minutes b/f schdl less than 2.0 msec Accelerate to 41 mph, decelerate to 34 mph, accelerate to 41mph. Do not completely release the accelerator. A/C switch off.
Idle 1 minute in park or neutral
Drive two minutes Steady state cruise at 31-44 mph. Selector lever "4th" A/C switch OFF. Hold the accelerator pedal as steady as possible. Allow speed to change if necessary.
End of first trip. Turn the key off the begin the second trip.
Second trip:
Start engine, idle for at least 1.5 minutes
Drive 3 minutes, hold b/f schdl: 1.5-2.0 msec, selector lever "3rd" eng rpm 1,800-2,000 A/C switch:ON Hold the recommended b/f schdl range. Allow road speed to vary as necessary.
Drive at 55-65 mph for 1.5 min b/f schdl 2.0-3.2 msec, selector lever "5th" Engine rpm 2,200-3,000
IGN "off" add four gallons of fuel
Dive at 50-60 mph for 3 minutes Selector lever "4th" keep engine speed above 3,000 rpm Allow speed to vary if necessary. Do not decelerate for more than 3 consecutive seconds. A/C switch ON.
Drive at a steady state cruise of 53-58mhp b/f schdl more than 1.8 msec selector lever "5th" eng rpm 2,400-2,600
Downshift to "4th" and decel more than 5 seconds without breaking, then idle for 1 minute.
Drive two minutes b/f schdl less than 2.0 msec Accelerate to 41 mph, decelerate to 34 mph, accelerate to 41mph. Do not completely release the accelerator. A/C switch off.
Idle 1 minute in park or neutral
Drive two minutes Steady state cruise at 31-44 mph. Selector lever "4th" A/C switch OFF. Hold the accelerator pedal as steady as possible. Allow speed to change if necessary. I especially like the part where they want you to add four gallons of fuel. Not three gallons, not five gallons, four gallons. Gotta love those Nissan engineers. ...and of course they state that if the trace is not followed exactly (i.e. you botch the acceleration/deceleration) you have to start all over again from scratch

You did pull the little tab first, hidden in the seat right? If you're not sure, reach your hand in the seat seam and feel for a nylon pull tab and pull it to move the bottom half towards the front seat.

A complete check-up of the car which should include but not be limited to:

1. Change the oil (when was the last time you changed it?) Change the oil filter & the air filter (again, when were they changed last?)
2. Check the coolant and brake fluid
3. Check the brake pads - inspect all lights including turning signals (for safetys sake)
4. Check the air pressure in the tires (including your spare tire) Check your car's alignment, this can cause uneven wear on your tires and it will believe it or not contribute to making the trip more exhausting.

Make sure you get a good rest the night/day before you depart. - if you begin to doze off dont hesitate to stop at a rest stop. Dont fight against your body, if you are tired, stop and take a 30 minute power nap, wash your face and drink a cup of coffee before you get back on the road.
Make sure you have a bottle of water in the car and plenty of good music to listen to. - Speed wise I suggest you dont travel at more than 10mph over the speed limit, traveling a little over (up to 10 mph) is tolerated by police, but I strongly sugest going 5 mph over the limit, set the cruise control and enjoy the trip without worrying about potential fines. If you do the math, the difference in time traveled is not so great:
speed limit = 70 mph (just as an example) 1300 miles @ 70 mph = 18 hours 36 minutes 1300 miles @ 75 mph = 17 hours and 20 minutes 1300 miles @ 80 mph = 16 hours 15 minutes the difference between traveling 75 or 80 is only 1 hours and 5 minutes. Not worth risking a fine for

The following conditions must occur to complete a Trip and test all OBD II monitors and components including the Catalyst Efficiency Monitor:
-- The misfire, comprehensive component, and adaptive fuel monitors are checked continuously from engine warm-up and can complete any time.
-- The exhaust gas recirculation (EGR) monitor test requires a series of idles and accelerations.
-- The heated oxygen sensor (HO2S) monitor requires a steady speed drive for approximately 1 minute at 30 to 40 mph.
-- The catalyst efficiency monitor requires a steady speed drive for 1 minute and 20 seconds beyond the HO2S monitor test at 40 to 65 mph.
If you cut engine off before test are completed then you must wait for a 6 hour cool down before monitors will run again.

30-40 psi of oil pressure is fine for many vehicles including your GMC. I am assuming that the truck has more than 100,000 miles on it and still has the original engine in it. By rule of thumb you only need 10 psi per 1000 rpms in a typical street driven engine to give adequate oil pressure to keep the bearings from oil starvation. The oil pressure is typically higher when initial start up occurs because it is more viscous due to the temperature of the oil as the engines oil warms up the visconsity thins out and the oil flows more smoothly. The drop in oil pressure is a normal occurance. Above 45 is more than required for a daily driven street engine. I believe that the specs on that engine only list 30- 45 psi.

you jave a biggie here.
here is some info
CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) monitors the difference between engine speed and transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +60 RPM .

When the PCM detects excessive TCC slip when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC

• No TP sensor DTCs P0122 or P0123.
• No VSS assembly DTCs P0502 or P0503.
• No TCC solenoid valve DTC P0740.
• No 1-2 SS valve DTC P0753.
• No 2-3 SS valve DTC P0758.
• No 3-2 SS valve assembly DTC P0785.
• No TCC PWM solenoid valve DTC P1860.
• The engine is not in fuel cutoff.
• The engine torque is 40-400 lb ft .
• The TP angle is 12-50% .
• The vehicle speed is 56-112 km/h (35-70 mph ).
• The speed ratio is 0.64-0.95 (the speed ratio is the engine speed divided by the transmission output speed).
• The engine speed is 1500-3500 RPM .
• The gear range is D4.
• The commanded gear is not 1st gear
• The TFT is between 20-130°C (68-266°F) .
• The shift solenoid performance diagnostic counters are zero.