This is my first post, but I have been lurking for a while going through old posts. I have finally decided that I need to ask for help. The background: I recently bought a 99 blazer LS 4dr 4WD, 4.3l. I did all of the normal tune-up procedures (plugs – ac delco platinums, wires, cap and rotor – ac delco and a new fuel and air filter). It still wasn’t running quite right and I thought that maybe it was the tranny so I took it to the AAMCO down the street for a diagnostic…came back with a clean bill but they said it needed a new crankshaft sensor. Had them install it, but a few days later it would not start. I finally traced the problem back to the pigtail from the crankshaft sensor (it needed a new one as the old one had bad wire). Running car again, but still a miss at freeway speeds. Bought an autotap diagnosis setup to help out. My short term fuel trim from O2 bank 1 sensor 3 was reading 99.2%, figured that was not good as it was way out of parameter from the others (and I still cannot find anything anywhere other that that is a max value for that field) so I replaced the O2 sensor. In doing so, I noticed that the catalytic convertor was rattling a bit and 2 of the 3 flange bolts were rusted out and missing, so I decided to go ahead and replace the cat and muffler before the third gave up and left me with a hanging muffler. Sometime in the past couple of weeks I started developing a shifting issue. When I take off from a light if I accelerate very slowly to get to speed it seems to shift OK, if I accelerate even moderately quickly it wants to rev up and then surge when it shifts to 2nd and it does about the same thing going into 3rd. Funny enough once in 3rd if you shove the throttle past half way it really picks up and goes, but until that point it is kinda doggy. Tonight I found a vacuum hose that goes from something under the battery and back to a three-hose plug at the rear of the Tranny. The hose had gotten onto the exhaust manifold and was melted, cracking and had a good size chunk out of it (not sure how long it has been like this). I replaced the hose and took it for a drive, but I still had the same shifting issue although it did seem slightly better. No codes have been thrown since correcting the Crankshaft sensor and wiring problem and it seems to shift and operate normal while in Open Loop but starts acting up shortly after going to Closed loop. Sorry for the long post, but any ideas what could be causing the shifting issue?

 

i have the same shifting problem just bought the truck tring to find a cure for problem you getting any luck
but i ghave a engine code 1870 which alot of people with the code has 1-2 shift problem

 

99pdx,
welcome to the site.

that house you cound provide vacuum to the front axle, locks in the front axle whne your in 4x4 mode. the three hose connector it connects to goes to teh t-case on the drivers side next to the front driveshaft. one of those hoses runs up into the engine compartment and isa breather tube, that hose shoula slo tie into the hose on the back of the t-case, the thrid hose goes to the back of the engine and attaches to the vauucm system. Verify your vacuum lines are hooked up and working problerly. Vacuum is suppied off the back of the intake manifold next to the dietributor, goes to the t-case, goes to the vacuum ball, goes to your hvac controls in the cab of the truck.

On to other possible problems.
Pull your upper intake maniolf off and look at the spider assemble. If you see clean areas under or around the hoses, you have a leak and that fuel is cleaning the carbon deposit on the intake manifold. Plus that fule is getting sucked into your exhaust stroke and pushed into your exhaust system, bank 1 code. Has your CEL flashed? If so your Catalytic converter may be going bad. When the cat fails it plugs up the exhaust system, signs of a plugging cat is you can acclerate slowely and everything is fine, Stomnp on it and everything goes OK, however moderate throttle seems to be the worst. Next stage when teh cat is completely toast you wont be able to get over 65, then 55, then 40mph, going up hills will be painful, and your engine will fight you the whole way.

The problem is the engine cant breath, its like running a marathon while breathing trhough a straw. At first you start out with a great big honking straw, but near the end your using a coffee straw.

Pull the 02 sensor and swap sides, see if the code moves with the sensor.
pull the 02 sensor ans see if that imrpoves your moerate throttle performance. If so you have a failing cat.

Welcome to the site.

 

Thank you. I think I may have uncovered the problem. It seems that my Blazer has a California emissions (I live in Oregon) exhaust. When I had the Cat and muffler replaced, they only replaced one of the two convertors. It is sitting at the shop now waiting for the parts. I was thinking that as Oregon does not require both convertors, is there any performance downside to just welding in a straight pipe in lieu of a new second convertor?