Dominique
09-20-2011, 20:46
I'm stumped please help!!
2000 GMC 1 ton Dually with a 6.5 126,000 miles.
First off after a cold start (60-70F) it runs a bit rough like it's not hitting on all 8, that usually quits after 10 seconds or so and then sounds normal. Next problem is if I head down the driveway and hit the road you can pin the pedal to the floor and maybe hit 30mph in a mile. Once it gets up to normal operating temp full speed operation comes back but there is still a strange stumble/miss/surge while at crusing speed 60 to 65mph.
No noticeable surge under full acceleration, but if I take off from a stop and hold it to the floor until I get up to speed around 60 and back off the throttle it will stumble a few times.
Now here it starts to get more confusing. If I set the cruise control at hwy speed (65) it stumbles when you go down a hill, or on level ground, not feeling it going uphill. It seems like it only happens when your coasting or just under light load to maintain speed, it kinda feels like I lifted the throttle for a second. The stumble can be once in a mile or 10 times, it's random. Now I have noticed that whenever it stumbles there is a noticeable drop in voltage on the gauge, not much but whenever I see the voltage twitch I feel a surge.
Suspecting alternator issues or some kind of electrical problem I disconnected the alt and tried running just off the batteries, and took it for a ride. WEIRD! It runs terrible, has little to no power and struggles all the way, can barely get it up to 55mph. Now I did this at night so I was running the lights aswell. Now I'm confused here because with the alt disconnected I did notice I have no tach so I'm thinking maybe there is no RPM signal going to the computer and that's why it barely moves. Hooked it back up and it's back to normal.
Today after taking it for a quick ride to get it up to temp and returning home to tinker in the driveway I noticed that in park if I slowly apply the throttle and rev it up to 2k it starts to miss, then slowly applying more it will get to just over 2500 and then suddenly jump to over 3000. Maybe this is normal but around 2000 it feels like it fighting against it's self to rev higher.
I tested LP and have 6PSI, good flow, and did not see any air comming out of the 10 ft line. Also replaced this last year because it was rusted out and leaking.
No SES light - I replaced the wastegate controller almost 2 years ago with the GM96 Manual controller and once in awhile I'll set a code for overboost :-) but have not done that lately.
I had the PMD stalling Issue almost 2 years ago and was able to get the dealer to warranty it under the "Special Policy" Thanks to Budroe for the post. I ended up with a whole new IP & PMD so there is maybe 6000 miles since then.
Replaced all glow plugs last winter.
The darm thing idles just fine, and if I only drove it around town under 40mph I would likely not even notice a problem if I make sure it's up to full operating temp before leaving the driveway.
Sorry for the super long post but want to make sure I give as much background as possible.
What else can I check? Maybe I have multiple issue going on but need to start narrowing it down to something becasue it's getting annoying and I'm afraid to go any real distance from home.
Thanks ahead for any input
2000 GMC 1 ton Dually with a 6.5 126,000 miles.
First off after a cold start (60-70F) it runs a bit rough like it's not hitting on all 8, that usually quits after 10 seconds or so and then sounds normal. Next problem is if I head down the driveway and hit the road you can pin the pedal to the floor and maybe hit 30mph in a mile. Once it gets up to normal operating temp full speed operation comes back but there is still a strange stumble/miss/surge while at crusing speed 60 to 65mph.
No noticeable surge under full acceleration, but if I take off from a stop and hold it to the floor until I get up to speed around 60 and back off the throttle it will stumble a few times.
Now here it starts to get more confusing. If I set the cruise control at hwy speed (65) it stumbles when you go down a hill, or on level ground, not feeling it going uphill. It seems like it only happens when your coasting or just under light load to maintain speed, it kinda feels like I lifted the throttle for a second. The stumble can be once in a mile or 10 times, it's random. Now I have noticed that whenever it stumbles there is a noticeable drop in voltage on the gauge, not much but whenever I see the voltage twitch I feel a surge.
Suspecting alternator issues or some kind of electrical problem I disconnected the alt and tried running just off the batteries, and took it for a ride. WEIRD! It runs terrible, has little to no power and struggles all the way, can barely get it up to 55mph. Now I did this at night so I was running the lights aswell. Now I'm confused here because with the alt disconnected I did notice I have no tach so I'm thinking maybe there is no RPM signal going to the computer and that's why it barely moves. Hooked it back up and it's back to normal.
Today after taking it for a quick ride to get it up to temp and returning home to tinker in the driveway I noticed that in park if I slowly apply the throttle and rev it up to 2k it starts to miss, then slowly applying more it will get to just over 2500 and then suddenly jump to over 3000. Maybe this is normal but around 2000 it feels like it fighting against it's self to rev higher.
I tested LP and have 6PSI, good flow, and did not see any air comming out of the 10 ft line. Also replaced this last year because it was rusted out and leaking.
No SES light - I replaced the wastegate controller almost 2 years ago with the GM96 Manual controller and once in awhile I'll set a code for overboost :-) but have not done that lately.
I had the PMD stalling Issue almost 2 years ago and was able to get the dealer to warranty it under the "Special Policy" Thanks to Budroe for the post. I ended up with a whole new IP & PMD so there is maybe 6000 miles since then.
Replaced all glow plugs last winter.
The darm thing idles just fine, and if I only drove it around town under 40mph I would likely not even notice a problem if I make sure it's up to full operating temp before leaving the driveway.
Sorry for the super long post but want to make sure I give as much background as possible.
What else can I check? Maybe I have multiple issue going on but need to start narrowing it down to something becasue it's getting annoying and I'm afraid to go any real distance from home.
Thanks ahead for any input