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| Stupid Leanburn https://www.slantsix.org/forum/viewtopic.php?t=17283 |
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| Author: | Jeb [ Thu Apr 27, 2006 6:36 pm ] |
| Post subject: | Stupid Leanburn |
What are the symptoms of a failing lean burn computer? My 87 Fifth Avenue has became balky lately and seems to have a perpetual bog in the midrange. Press the gas too far accelerating and it stumbles and bogs. Back off of it and it runs normal again. If I floor it though it smooths out very nicely. I have changed the oxygen sensor and the carb was rebuilt two years ago. Car has over 200,000 miles on it so is it about for the comp to go south on me? This car has a Holley 6280 carb  .
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| Author: | SlantSixDan [ Thu Apr 27, 2006 6:51 pm ] |
| Post subject: | |
Weird driveability faults are the hallmark of the Lean Burn system when it's out of order, but first try this: If you disconnect the EGR valve and plug the hose, do the symptoms change? |
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| Author: | Jeb [ Thu Apr 27, 2006 7:00 pm ] |
| Post subject: | |
I''ll try that and let you know. DO you think it could a malfunction in the EGR system? If the car runs good without it and doesn't ping I will leave it plugged. |
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| Author: | Reed [ Thu Apr 27, 2006 10:10 pm ] |
| Post subject: | |
Sounds like the vacuum advance might not be working. Check the vacum pod on the computer and see if it still will hold a vacuum. |
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| Author: | Jeb [ Tue May 02, 2006 6:43 pm ] |
| Post subject: | |
Okay Dan, I capped off the EGR valve line and the car still runs like crap. This morning it backfired through the carb a few times and idled a little rough. My catalytic convertors have also started to stink badly also. The carb was rebuilt last year and the it ran perfect for a quite a while but this problem showed up suddenly. The Vacuum pod is still good because it runs really bad without it hooked up. |
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| Author: | SlantSixDan [ Tue May 02, 2006 9:30 pm ] |
| Post subject: | |
Woe is you...time for some systematic diagnosis of a notoriously difficult-to-diagnose system. You might get lucky and find it's something simple like a bad O2 sensor (what happens if you unplug the O2 sensor?). Could be carburetor trouble again. Could be the lean burn computer. Could be a problem in the vacuum hose system (shudder) |
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| Author: | Super6 [ Wed May 03, 2006 6:48 am ] |
| Post subject: | |
How is the timing at idle...solid or wandering? Same question for mid-range throttle (within reason, ~2000-2500 rpm). -S/6 |
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| Author: | Jeb [ Wed May 03, 2006 8:25 am ] |
| Post subject: | |
The O2 sensor is new. I have checked all of the vacuum hoses and they all are fine and go to there respective places. I haven't checked the timing at idle but I think it is pretty stable because this car idles smooth as glass, sometimes. Every once in a while it shows its a#*. |
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| Author: | Reed [ Wed May 03, 2006 8:39 am ] |
| Post subject: | |
Quote: Sounds like the vacuum advance might not be working. Check the vacum pod on the computer and see if it still will hold a vacuum.
Do this. My 86 van behaved similarly before I swapped to HEI. I later discovered that the vacuum pod on the computer no longer held a vacuum. Snce this is one of the main sensors for timing advance it could very well be causng your problems (as well as a vacuum leak).
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| Author: | 440_Magnum [ Wed May 03, 2006 9:35 am ] |
| Post subject: | |
Quote: Okay Dan, I capped off the EGR valve line and the car still runs like crap. This morning it backfired through the carb a few times and idled a little rough. My catalytic convertors have also started to stink badly also.
It could certainly be any number of parts associated with the Lean Burn system, but frankly it sounds more like a carburetor that's gone wacky. The electronics themselves are darn near bulletproof. Wiring and vacuum hoses cause most lean burn problems, but the next most common thing is the carb.
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