1999 envoy running problems

Hi all, looking for some help I just recently bought a 1999 gmc envoy which I like alot besides all the problems I've been having with it which ive fixed most of theres just one that i cant seem to figure out, at around 2,000~3,000 rpm it runs like crap surges back and forth at first I thought it could be the tranny going out but I do not believe that is it, it just seems like its missing out for some reason but only between those RPM's for some reason. I've changed the plugs wires caps and rotors i have a new fuel filter to put on it but havn't got that far yet as to putting it on. Any advice? thanks guys in advance
 

kylemc1990

Newbie
Thread Starter
I've had the Envoy for about 2 months now so I have no idea on the filter. Yes after 3k it smoothes out and runs like a dream thats what has me stumped. it has a tick over 164k
Thanks kyle
 

BRomanJr

Active Member
kylemc1990 said:
Hi all, looking for some help I just recently bought a 1999 gmc envoy which I like alot besides all the problems I've been having with it which ive fixed most of theres just one that i cant seem to figure out, at around 2,000~3,000 rpm it runs like crap surges back and forth at first I thought it could be the tranny going out but I do not believe that is it, it just seems like its missing out for some reason but only between those RPM's for some reason. I've changed the plugs wires caps and rotors i have a new fuel filter to put on it but havn't got that far yet as to putting it on. Any advice? thanks guys in advance


I don't know your skill level or tool inventory, but this is what I would do.
After checking for pending or current PCM Trouble codes,

I would start by checking fuel pressure.
Then check Fuel Trims.
Then check O2 readings and trends.

The results of those tests are likely to narrow it down.

Let us know what your results are.
 

kylemc1990

Newbie
Thread Starter
Ok i finally got time to work on it now that's its got worse, I know its not the fuel pressure and not the coil. I don't know how do any of the other stuff listed above. now it misses out on initial start up then smoothes out fine then when you give it gas it runs like crap again. What should I look for now?
 

BRomanJr

Active Member
kylemc1990 said:
Ok i finally got time to work on it now that's its got worse, I know its not the fuel pressure and not the coil. I don't know how do any of the other stuff listed above. now it misses out on initial start up then smoothes out fine then when you give it gas it runs like crap again. What should I look for now?

What is the fuel pressure? key on - engine off PSI ?
What is the pressure after 10 minutes?
 

kylemc1990

Newbie
Thread Starter
key on is 62. idle is 58 or 56 and holds steady there. I let it run for about 20 mins and it didn't come off of 58. I got a chance to take it buy autozone today and they checked the light and had two codes P0300 and p0440 both have a common cause of a vacuum leak is that a probable cause and if so where should i start looking?
 

kylemc1990

Newbie
Thread Starter
So the plot thickens a little bit,
1. pulled the throttle body off and cleaned it nothing new except a pound of carbon build up now on the garage floor ( I exaggerate a little)
2. where the pcv valve connects to the manifold found the elbow was cracked and broke I may of caused that when i pulled it off not sure but its fixed now.
3. runs like crap especially when cold but kind of all the time but worse when cold. So unplugged the egr valve seems to run a little better but will find out for sure in the morning when its cold again.
4. now it randomly has a high idle. turn the motor off then back on and its fine. then a little bit later it'll do it again.
5. Sometimes at higher rpms all the interior lights will flicker.
6. and the icing on the cake the transmission wont shift till about 3500 and sometimes around 2000 rpm it seems like it goes into neutral or the third gear is messing up. unless its going into limp mode if it has one?

Ok so I have no idea where to begin besides seeing if the egr valve is having problems then go from there. Do I just have one problem or a hole slew of problems?
Thanks in advance guys.
 

Mooseman

Master Blaster
Moderator
Lets look at the codes you got:

P0300: Random misfire. First do a compression test. Could be a leaking head gasket or (like what happened to me), a cracked head. After that, I would check/replace distributor cap and rotor, plug wires and plugs. Clear the codes and drive it. If that doesn't fix it, replace the ignition coil. Check, replace the oxygen sensor.

P0440: Evaporator system. Things to try:
Remove and reinstall the gas cap, clear the code, and drive for a day and see if the code comes back. Replace gas cap if it comes back.
Inspect the EVAP system for cuts/holes in tubes/hoses
Inspect for damaged or disconnected hoses around the Evap purge solenoid
Check and/or replace the sensor on the gas tank (I've had that happen to me)
Check and/or replace the purge valve
 

kylemc1990

Newbie
Thread Starter
Mooseman said:
Lets look at the codes you got:

P0300: Random misfire. First do a compression test. Could be a leaking head gasket or (like what happened to me), a cracked head. After that, I would check/replace distributor cap and rotor, plug wires and plugs. Clear the codes and drive it. If that doesn't fix it, replace the ignition coil. Check, replace the oxygen sensor.

P0440: Evaporator system. Things to try:
Remove and reinstall the gas cap, clear the code, and drive for a day and see if the code comes back. Replace gas cap if it comes back.
Inspect the EVAP system for cuts/holes in tubes/hoses
Inspect for damaged or disconnected hoses around the Evap purge solenoid
Check and/or replace the sensor on the gas tank (I've had that happen to me)
Check and/or replace the purge valve

I've replaced cap rotor wires and plugs already, I've replaced the coil no luck with that, haven't done anything with o2 sensor never really thought of that.

I've went through all the evap lines I can follow and all seem fine, now the evap purge solenoid would that be the solenoid kinda located above the spare tire with a 3/4 rubber hose going from it to the charcoal can? if so should the be vacuum there also? Because there isn't any coming out of the charcoal can at all.
Thanks again, Kyle
 

Mooseman

Master Blaster
Moderator
At this point, I would replace the pressure sensor on the gas tank. It's right on top in the fuel sender module. I've had one fail on my like that but it didn't affect driveability at all, just annoying with the CEL.

For the misfire, I would do a compression check before doing anything else just to eliminate anything mechanically wrong with the engine. If that checks out, then replace the O2 sensor as that is what would tell the PCM of a misfire.
 

dingle

Registered Member
This could be completely un related but my mom has an 05 impala and her car was running like absolute crap. Rpm's jumping like crazy. Misfiring. Hard to start when cold. It threw a cel and said it was the mass air flow sensor. I changed it and didn't change the symptoms. So she took it a mechanic and he couldn't find anything wrong with his snap on scanner but it was running like crap. Then it finally threw another cel and it was the maf sensor again. He changed it and its ran fine ever since. Something to look at.
 

Forum Statistics

Threads
21,616
Messages
614,953
Members
15,724
Latest member
Sam_Augusta_Ga

Members Online

Top Bottom