Idles great, runs like poop

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Butt Ugly Chuck

Fish Biologist
Joined
Jan 31, 2007
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42
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1,941
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In a TACO down by the river!!
I'm going through the Emmisions manual and working out the smog kinks. My rig WAS running pretty good, even though I've discovered a few items that need attention (BVSV, EGR Vac Modulator, VSV 2, and maybe more as I've still got a ways to go through the manual). Got a hose kit and temp sending unit from CCOT and installed it while I'm working on everything. I had a heck of a time burping the thing and it would run hot, dang close to the red. Couldn't get the front end high enough with my wimpy ramps and bottle jack so I took it to a friend's house where I could park it on an incline. Got lots of air out of the system (thanks ellington12 for advice on that one!). It still ran hot on the way home. It never ran hot before changing hoses/sending unit. Then just before I made it home it started running bad . Idles like a champ, but craps out when I try to accelerate. Didn't used to do that either. I was worried I might have done some damage to the head with the heat so I compresion tested. Numbers still look great.

I let it sit overnight hoping the 2F fairy would make my problem magically go away. Started up first crank in the morning, but right away ran terrible at anything over idle. Had to feather the choke till it warmed enough to run OK at low idle. Took it out on the highway and it'll run OK at highway speed, but lower RPM's (under 2k) are especially bad. And it still runs hot.

I changed the fuel filter but that didn't help.
Fuel cut off solonoid checks out OK.
Vac lines recently replaced and routing double and triple checked.

It ran great before. The problem came on very suddenly. What did I mess up or miss that would make it go bad so fast:confused:.

Thanks
 
The CCOT temp sensor has been known to read the temperature as hotter than it actually is. The easiest fix is an OEM temp sensor. Do a search on CCOT temp sensor and you can read about it more. The idle thing - can't help you with that though.
 
Thanks for the heads up on the temp sensor Gulfshores.

Would a warped or otherwise damaged manifold give me the poor running symptoms I described at the start of this thread? Maybe I got it too hot? Will a rig run like that with intake leak and lean running condition?
 
vacuum?

Did you put a vacuum gauge on your engine yet? It will tell you if your issue is vacuum related, ie. if you have an intake leak of some other major leak. You can get one for $30 bucks at any auto parts store and it takes 20 seconds to hook up. Better yet, install a nice autometer vac/boost gauge... permanently.:beer:

You should also ground your IFC solenoid to the carb. Even if the solenoid appears to be working, the computer is notorious for acting up without the external ground. ou can't hurt anything by doing this and you can consider it preventive maintenance if you like.


good luck.
 
If you had a manifold vacuum leak below the throttle plate, it would idle poorly, but run fine above idle; exactly the opposite. It sounds like a problem with the accelerator pump or the main jets or nozzles being clogged.
 
Just starting to decipher the function of all those vacuum lines myself.

Check again the routing of the hoses to the Vacuum Advance Diaphragm on the Distributor.

If the two lines are swapped, you wont get an off-idle advance in the timing and this will cause your truck to run poorly when you accelerate.

My $.02

Matt
 

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