I could not find this exact problem through searching so I thought I'd start a new thread...sorry if it's redundant.
My new wife's 2000 Blazer (4.3 ltr 4WD) recently started blowing white smoke out of the exhaust. When I came to the rescue, no smoke was coming from it so I checked the coolant (1 qt. low) and told her to drive it as it was running normal. Two days later she pulled into the driveway and it was running rough. I immediately opened the hood and the engine wiring harness was smoldering so I cut the engine off and pulled the battery terminal. Disgusted at the fried wiring I waited until the next day to investigate the damage. I checked all the wiring and none was burnt through, just the insulation burnt off and the wiring discolored. I cleaned and coated each wire with liquid tape (about 60-80). Then I noticed what caused the problem. The A.I.R. hose on the pass. side had burnt a hole through the rubber elbow and spewed hot exhaust directly on the engine wiring harness causing the short. Dealer wanted 162 for hose so I bought an old ford waterpump bypass hose , installed and cranked the engine. Started right up but idled at 2100 and rose to 2500 rpm within a few minutes. Checked wiring again and though maybe Ecm was fried. Replaced ECM, reprogrammed the passlock and it started again, still ideling the same with gas vapors thick from the tailpipe. After 3 days of checking for any possible clue it used 1/2 tank of gas in about 1 hr of "ideling". Bought an OBDII scanner and it threw a 0300 code. Yeah, I know something is misfiring cause of the excess fuel but don't know where to start. I'm an Old School (points and plugs) Mechanic but now am forced to learn and understand this "new to me" technology. I'm thinking the TPS but want to learn more about it before I try the "buy me-try me" approach. I have learned alot from this forum already and have a better grasp of the system but not enough to decipher this problem. I appreciate any advise. I'm Old, Broken and it's freezing outside.

 

...Ok...since I'm getting no replies I have to keep trying...it's 25 here...snow and I'm sick...but I need a vehicle. Can the wiring harness be installed with the engine and trans in place? Or is there that one impossible bolt to get out? Once I get that in I'll move on to other problems....

 

...Hey dude...bring that '64 out of hiding....

 

Thanks man....should have thought of that a long time ago.....

 

Gas smells like Turpentine from 10 ft. Battery dead as a doornail. Oil level hasn't changed in 10 years. Antifreeze checks to -25 degrees. Charge the Battery, pull the choke, pat gas pedal eleventeen times....rrrr....rrr....rrrr....Vroom!!!! Mouse family leaves seat due to smoke...five minutes later cold light goes out...idling like a Sewing machine. Throw bale of hay on flatbed, put "farm use" tags on her and Betsy is once again on the road....2000 Blazer now resides in her place to keep grass level to a minimum...All's well in the Va. Mountains and even the heater is blowing HOT air....and no check engine light/ ECM....life is again...GREAT!!!

 

The side you replaced hose on: Replace the check valve on the exhaust manifold on that side (hose goes to it, two 10mm (I think) nuts hold it on the manifold) or plan on a repeat performance.

 

Thanks Ron Jon...I removed it...cleaned it and it is working fine...only opens at start. Nice to see I'm not the only one experiencing this problem although a Chevy TSB reconized it also. Did your wiring burn also?

 

Not mine, friend of my brother. Check engine light and truck ran like garbage. Spliced the wires (he had some literally melted together), replaced the check valve, and replaced the AIR assembly. His pump was melted and fused. GM had a replacement assembly with a different intake hose, water ingestion is a common reason for pump failure. The check valve opens more often than start. When the AIR pump is running the air will pass through it between exhaust pulses and it's "supposed" to keep exhaust pulses out of the AIR system. You saw the ugliness when that goes bad. I don't know all the times the pump runs, but when mine went bad the data capture was pretty consistent around 28MPH and 15% throttle, so I know it runs periodically at light throttle.

 

Ron Jon, Glad to know that I'm not the only one although I'm sorry it happened to your friend. I know what he had to go through. From what I have learned researching and from the Stealership I believe that the A.I.R. system only allows air to enter the exhaust manifold at startup or extreme cold conditions to dilute the exhaust gases which are in a rich mode (choke) mostly only at startup. The valves work similar to a thermostat and SHOULD close upon engine reaching operating temperature. GM knew of this design flaw and issued a TSB which replaced the A.I.R. pump Intake hose to be rerouted. The water ingestion reaked havoc on both the pump and the Valves...leading to pump lockup and Valves corroding into neither open or closed position but rather one that would not fully close upon reaching Closing design Temperature. This allowed hot exhaust gases to reach the rubber hoses and ultimately cause a burn through. Not so bad on the D.S. but causing dirty bad no-no's on the passenger side due to the close proximity to the main ECM/Engine wiring harness. The replacement intake tube is an obsolete part from the Chevy parts counter as I tried to purchase one.
The wiring harness is $1722 from the Dealer and a minimum $800 to install not counting reprogramming the ECM ($300), which they claim will more than likely need to be done. ($2,822)
I believe I will just remove the air pump and make blockoff plates where the valves fasten...end of problem....except for the wiring. I believe my wiring got too hot leading to increased resistance causing incorrect readings from the sensors to the ECM. Hopefull my new (used) wiring harness will cure my problem. Thanks for your input...It's 14 degrees out so let's go see how brittle the plastic connectors are on the old wiring harness. One way or another it's coming off today....Allen

 

Do you have to worry about emission inspections in your area as doing this will certainly trigger an SES lite. Jerry