Big block 4x4 just aint right - Great Lakes 4x4. The largest offroad forum in the Midwest

Go Back   Great Lakes 4x4. The largest offroad forum in the Midwest > 4x4 Talk > Chevy Tech
GL4x4 Live! GL4x4 Casino

greatlakes4x4.com is the premier Great Lakes 4x4 Forum on the internet. Registered Users do not see the above ads.
Search
Reply
 
Thread Tools Search this Thread
Old January 17th, 2007, 09:22 PM   #1
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Unhappy Big block 4x4 just aint right

riddle me this.....2000 GMC K2500 Crew w/7.4L Every time the truck is started...hot or cold....NO ASS for 25 to 30 seconds.Runs weak, coughs thru intake, codes PO171 and PO174(lean rt+lft). Then all of a sudden runs awesome for ever unless i shut it off. new pump installed last Sun. New O2's installed, new plugs-wires-rotor, new fuel filter, new air filter. local "expert" says bad maf and/or temp switch but im really tired of throwing $$$$$ into a problem that three reputable mechs cant seem to diag. Even Mr Goodratchet himself baffled Any similiar probs or more ideas would be great
Gr8wht2000GMC is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old January 17th, 2007, 09:58 PM   #2
Yetti
Buy a Fiat! Save the UAW!
 
Yetti's Avatar
 
Join Date: 11-05-05
Location: 20 minutes south of Hell...
Posts: 14,388
iTrader: (10)
Mentioned: 2 Post(s)
Default

The best Idea I have involves beer and a old buddy of mine who is a Chevy expert. I too can only guess on this system. one of the things that comes to mind is your ECM maybe having issues with the open loop function. its got 3 minutes to get the engine warm and after that it goes to closed loop to meet emissions. I am wondering if you have a bad injector or TBI Gasket is sucking air on one side real bad making a lean condition until the computor makes it to closed loop. its just odd. I did have one years ago that had a cracked intake and was sucking air under the tbi through the crack that went from one side to the other..
__________________
Yetti
Yetti is offline   Reply With Quote
Old January 17th, 2007, 10:06 PM   #3
mrbotie
recovery man
 
Join Date: 12-13-06
Location: chesterfield mi
Posts: 65
iTrader: (0)
Mentioned: 0 Post(s)
Default

im not saying i know the problem with ur truck but the same engine and truck combo same problem but it was not every time maybe every other it had to do with the computer its just an idea
mrbotie is offline   Reply With Quote
Old January 17th, 2007, 10:09 PM   #4
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Default

im leaning to the pcm myself... maybe ought to just drink beer and think some more.
Gr8wht2000GMC is offline   Reply With Quote
Old January 17th, 2007, 11:54 PM   #5
KILLER"B"468
Yankabilly
 
KILLER"B"468's Avatar
 
Join Date: 11-06-05
Location: Hendersonville Tn.
Posts: 7,945
iTrader: (19)
Mentioned: 1 Post(s)
Default

They had intake gasket leaks. Have you tried snugging up the intake bolts.
KILLER"B"468 is offline   Reply With Quote
Old January 18th, 2007, 11:09 AM   #6
nmeinc
Parts Galore Spokesmodel
 
nmeinc's Avatar
 
Join Date: 04-04-06
Location: Detriolet
Posts: 564
iTrader: (6)
Mentioned: 0 Post(s)
Default

did you reset to computer after you replaced stuff? sometimes it will hold onto a setting even if the part has been replaced.
nmeinc is offline   Reply With Quote
Old January 18th, 2007, 01:32 PM   #7
Bones
skillicous
 
Bones's Avatar
 
Join Date: 11-06-05
Location: Dearborn Heights, MI
Posts: 11,569
iTrader: (37)
Mentioned: 3 Post(s)
Send a message via AIM to Bones
Default

actually the temp senser might be a really good guess

Anyone with a scanner/reader should be able to read PID data. Monitor the intake air temp, coolant temp and any other temp sensors maybe oil) to see if any of them are unusual for the first few minutes of start-up.
__________________
Inviscid Motorsports

Special Thanks and Recommendations to;
Motorcity Machines
Ironman Offroad
Branik Motorsports
Maxxis Tires

Raceline Wheels
PAC Racing Springs
Joint Clutch and Gear
Bones is offline   Reply With Quote
Old January 18th, 2007, 01:39 PM   #8
Mud'N'Truck
I'll Finsh One, One Day
 
Mud'N'Truck's Avatar
 
Join Date: 11-30-06
Location: Interlochen, Michigan
Posts: 2,361
iTrader: (15)
Mentioned: 1 Post(s)
Default

After you install new sensors or thing of that nature the computer has to go though a few drive cycles. You can't just jump in and feel a differnce. So after replacing things drive it for a while (not just to the corner and back). If the problem is still there move on to your next idea. I also think you need to have it plugged in and see what the scanner says.
Mud'N'Truck is offline   Reply With Quote
Old January 18th, 2007, 05:33 PM   #9
Yetti
Buy a Fiat! Save the UAW!
 
Yetti's Avatar
 
Join Date: 11-05-05
Location: 20 minutes south of Hell...
Posts: 14,388
iTrader: (10)
Mentioned: 2 Post(s)
Default

I need more info. I went to pick some brains at the dealer I worked at and everyone was baffled. it seems something is missing in our info stream. It might help to know everything that has been done to and with this truck and if its been in a wreck or anything like that.
__________________
Yetti
Yetti is offline   Reply With Quote
Old January 19th, 2007, 03:54 PM   #10
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Default

thanks for all the ideas...well Yetti, never wrecked. Icant even remember exactly when it began. the local "expert" I refered to owns a respected mech shop. i took it over to him yesterday and he scanned with a snap-on diagnostic tool. everything looks cool....except MAF readings a little off. EVERYBODY seems baffled its really like the thing wont run in open loop. its a dd and ocasional offroad. it has tru dual ex. all the new parts listed +fuel pressure reg. NEW intake gaskets and computer reset after work requiring it to be. going to get temp switch now.....add more l8r
Gr8wht2000GMC is offline   Reply With Quote
Old January 19th, 2007, 04:07 PM   #11
ScOoTeR
hoo dat. wat.
 
ScOoTeR's Avatar
 
Join Date: 11-09-05
Location: Howell
Posts: 21,607
iTrader: (36)
Mentioned: 11 Post(s)
Default

You have a massive airleak or fuel restriction somewhere. You're running wayyyyyyy lean in open loop - coughing and popping are a good sign of that, also the lean codes are from the ECU having to compensate for the lean condition.
__________________
@clarkstoncracker
ScOoTeR is offline   Reply With Quote
Old January 19th, 2007, 04:19 PM   #12
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Default

fuel pressure is constant at 62psi, static test and running thru rpm range. fuel volume is really good as well. what i cant understand is how it cleans up so suddenly and runs like a awesome beast until i start it the next time. what about a stuck EGR????? could it be dumping in exhaust gas during those fisrt 23-30 sec?
Gr8wht2000GMC is offline   Reply With Quote
Old January 19th, 2007, 05:19 PM   #13
Haggar
Covered in mud...
 
Haggar's Avatar
 
Join Date: 11-06-05
Location: Oxford, MI
Posts: 17,795
iTrader: (58)
Mentioned: 4 Post(s)
Default

Quote:
Originally Posted by Gr8wht2000GMC View Post
what i cant understand is how it cleans up so suddenly and runs like a awesome beast until i start it the next time.
Quote:
Originally Posted by ScOoTeR View Post
You have a massive airleak or fuel restriction somewhere. You're running wayyyyyyy lean in open loop - coughing and popping are a good sign of that, also the lean codes are from the ECU having to compensate for the lean condition.
Quote:
Originally Posted by Yetti View Post
I too can only guess on this system. one of the things that comes to mind is your ECM maybe having issues with the open loop function. I am wondering if you have a bad injector or TBI Gasket is sucking air on one side real bad making a lean condition until the computor makes it to closed loop...
I'd try hunting this down.

Open loop is generally during start up, and heavy throttle up around 70% and higher.

So, at stat up/idle, it'll run like ass.

In closed loop, it'll compensate for it pretty well.

In wide open throttle, you might be running lean and not knowing it. In fact, you might be happy getting more power and/or better mileage. Factory calibrations are generally based on SAFE operating conditions. There's almost always power/mileage to get had by leaning a motor out, at the risk of detonation, etc.
Haggar is offline   Reply With Quote
Old January 19th, 2007, 05:43 PM   #14
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Default

aside from near death experiences while initially entering traffic.................I am pleased with the 12 to 13.5 mpg Ive been getting. Actually starts and idles smooth as glass. if i had to describe exact symptoms id say...its like the feul lines are all fulled up and as i apply throttle, i consume the fuel and have to wait for the pump to "catch up"..but all fuel tests are cool. I would agree with massive unmeasured air causing lean...but can pcm really correct that much? and ...in order to compensate shouldnt i see poor economy...HA thats funny using the word economy in a post about a 454...anyway if all i wanted was economy id buy a toyota. just really frustrated not like the good ol days of carbs

Last edited by Gr8wht2000GMC; January 19th, 2007 at 05:48 PM.
Gr8wht2000GMC is offline   Reply With Quote
Old January 19th, 2007, 05:46 PM   #15
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Default

Quote:
Originally Posted by ScOoTeR View Post
You have a massive airleak or fuel restriction somewhere. You're running wayyyyyyy lean in open loop - coughing and popping are a good sign of that, also the lean codes are from the ECU having to compensate for the lean condition.
agree 100% but wouldnt a MASSIVE air leak be pretty obvious? gonna geta barley pop and think some more
Gr8wht2000GMC is offline   Reply With Quote
Old January 19th, 2007, 09:15 PM   #16
Haggar
Covered in mud...
 
Haggar's Avatar
 
Join Date: 11-06-05
Location: Oxford, MI
Posts: 17,795
iTrader: (58)
Mentioned: 4 Post(s)
Default

Quote:
Originally Posted by Gr8wht2000GMC View Post
agree 100% but wouldnt a MASSIVE air leak be pretty obvious? gonna geta barley pop and think some more
Get out some carb cleaner with a straw on it, and start spraying it around anywhere that might have a gasket leak.

I think its carb cleaner.... or maybe it was starting fluid. Or that might go boom..



No, I doubt you'd necessarily notice it. Its just like having a carb leak at the base, its not always obvious.
Haggar is offline   Reply With Quote
Old January 20th, 2007, 05:49 PM   #17
Yetti
Buy a Fiat! Save the UAW!
 
Yetti's Avatar
 
Join Date: 11-05-05
Location: 20 minutes south of Hell...
Posts: 14,388
iTrader: (10)
Mentioned: 2 Post(s)
Default

yea I still stumped. I have run every senario I know I can't come up with a reasonable explanation. If had to chose another route to explore I would look at the exhaust side of things. and yes to answer your questio the EGR could mess it up by being open when its not supposed to be. the other thing to consider would be a blockage at the catylitc converter that is opened by heat. it could be the opening to the monolite converter are collapsing and blocking the exhaust enough that it runs like shit cold. I would drop the exhaust pipe off to the end of the manifold bolts and test run it. if it runs right cold I would remove the curent converter and try again with a test pipe or replacement convertor.

ps, I had the worst TBI 454 ever. it was bone stock and got a 3.5 mpg
__________________
Yetti
Yetti is offline   Reply With Quote
Old January 20th, 2007, 06:09 PM   #18
Haggar
Covered in mud...
 
Haggar's Avatar
 
Join Date: 11-06-05
Location: Oxford, MI
Posts: 17,795
iTrader: (58)
Mentioned: 4 Post(s)
Default

Out of curiousity, have you tried unplugging the O2 sensor and starting it with it unplugged?

I'm curious, with no O2 it can't go into closed loop. If its an open loop/closed loop issue, then it'd continue to run crappy even after the 30 seconds.

Any results from checking for air leaks?
Haggar is offline   Reply With Quote
Old January 21st, 2007, 07:45 PM   #19
Gr8wht2000GMC
Senior Member
 
Gr8wht2000GMC's Avatar
 
Join Date: 12-25-06
Location: Bellevue Mi
Posts: 247
iTrader: (1)
Mentioned: 0 Post(s)
Default

i wil definately try removing exhaust as this has crossed my mind as well...i will also try the o2's unplugged even tho they are only a week old...no luck with spraying carb cleaner around intake....i tore the whole top plenum off today and replaced upper gaskets.. no evidence of any intake leaks top or bottom...replaced a suspect vac line from egr to purge canister . in fact if i remove the air filter and put my hand over the tube it tries to pull my fat ass in and the truck dies instantly so i cant see any excess unmeasured air contributing to this prob. the only other thing i havent explored yet is the fuel rail and injectors. but i dont know what to even suspect on an injector, much less 8 of the things.
Gr8wht2000GMC is offline   Reply With Quote
Reply
Great Lakes 4x4. The largest offroad forum in the Midwest > 4x4 Talk > Chevy Tech

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 08:15 AM.


Powered by: vBulletin, Copyright 2000 - 2012, Jelsoft Enterprises Ltd.
User Alert System provided by Advanced User Tagging (Lite) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd. Runs best on HiVelocity Hosting.
Page generated in 0.31229 seconds with 78 queries