Hi
Well Im new here so bear with me, I have a 2000 Blazer Zr2 with 62,000 miles on it.. Just had the Transmission rebuilt for 2000.00 last month.. everying was working great up untill about a week ago when the Service engine soon light came on. Ive noticed during startup the engine lopes as if it has a huge cam in it.. and misses very badly.Once the blazer has run for a few minutes the loping is gone and it is running perfectly. I took the blazer in for a code reading and recived P0300"Random misfire detected" and pending code P0410 "Secondary air injection system malfunction".

To start with Ive installed new plugs and wires+ distributor cap n rotor. No diff whatsover.. Checked the EGR nothing blocking passages and seems to be functioning well I know the fuel filters new.. No vacume leaks and am clueless as to whats going on with this thing..Today I had my wife start it while I held a finger over the air inlet of the injector pump and felt no suction at all. So I guess Im wondering if the air injection pump is not operating.. Could that cause the 02 sensors to take readings that would cause the ECM to make improper fuel calabrations making it lope and miss when cold??? Id hate 2 go buy a new pump and have that not be it.. Im hoping sombody here will have had a simular problem and could shed some light on my conundrum. Anybody replace a air injection pump? If so what where your symptoms? In the meantime Im going 2 pull out the old pump and break it down to see if I can find anything amiss with it.. Thanks[X(]

 

Update,

Well I pulled the secondary air injection pump to find about a cup worth of water in it .. being in Alaska Im sure it was freezing the pump. I also opened the valve on the hoses and drained more water, cleaned the filter inside and dried it out, then tested the motor and it worked perfectly,"not hooked 2 vehicle". I also found a emmisions hose that was split in half and replaced it. For now the loping is gone along with the missfire.. I wont know for sure if the problem is fixed until I do a cold start. Btw.. Was wondering if anyone knows any tricks for reseting the PCM? Would help if I could erase the codes. I know on my old 98 Dakota with obd2 I could dissconect the battery then turn the key 2 start for 40 secs and the comp would reset does that work on Chevy PCMs?[sm=burnout.gif]

 

Hmmm,

Well did a cold start tonight and the same old problem reared its ugly head.. Thought I had figured it out.. I guess not.. Still doesnt sound as if that pump is turning on when the vehicle is started.. had read somewhere "but cant find it agian" that there is an inline fuse located in the fender area somewhere but have been unable 2 find it, was thinking that water could have shorted it out. Im really lost about now and any educated ideas would be greatly helpful.

 

I would suspect something in your choke, IAC, is not functioning properly. I believe the air pump only pushes air into the exhaust system and helps with the emissions. I also believe the air pump serves no purpose until the engine is warmed up, might explain why its not coming on. The engine must run rich (more gas then air mixture) while cold, and will lean out (add air, IAC job) as it warms up. Once warm the pump should be pushing air into the exhaust system again. That is how I understand the system to operate on cold starts.

 

Hi and thanks for the reply,

Well I pulled out the IAC and cleaned the plunger along with the housing for it inside the TB, checked its operations and seems 2 be working great..Idle returned to 600 rpm. After this was done though unfortanatly the same loping problem is present when cold and it seems the colder it gets the worse the problem. Replaced PCV valve and I also double checked vacume hoses under the hood agian as well as sensor connections 2 no avail. Such a wierd problem once the loping is gone it runs like a new engine... Im sure the air pump system is in order now.. but that leaves me with the P0300 Random Cylinder missfire detected problem.. Couldnt be the coil.. plugs wires, cap roter,... Unless the PCM is altering timing for some reason.. So that leaves fuel? I should mention the engine starts on the first crank so no leakage from a injector is going on.. @ WOT there is no hesitation and its running like new "when warm" threwout the RPM range. And with no codes other codes 2 work with .. Should the gas cap have a rubber seal on it? "wondering" Im just really stumped. Again any input would be helpful Ill be happy to attempt about anything with it at this point. Thanks [X(]

 

Hello,

I just joined the forum for the same reason. I am not sure if you are still battling the AIR pump or not. I do know that the fuse is located next to the fender by the battery. You will have to remove the battery to get to it. It is sealed with a plastic cap that needs to be removed to get the fuse out. I have read in other forums that the fuse does go out when the pump gets wet.

Like you, my pump works when connected to a 12V power source but not in the truck. I have checked the fuses and relays as well as the wiring, nothig seems out of whack and its driving me nuts.

Not sure about the loping you mentioned. I dont think the cap has a rubber seal. Even if it is not sealed properly, the engine will still run fine, it will just through up a SES light. This happened to mine.

Anything anyone else could offer would be appreciated!

Mike

 

Checked the distributor and inside parts for condensadion and/or wetness or signs of having been wet such as corrosion might indicate? The vent system on these caps is not as good as it ought to be and they sometimes hold onto wetness more than they should. Once corrosion sets in it takes just a little more humidity to have the same problem. Simply changing the cap and rotor may not solve the problem if it has affected things further down into it. Corrosion combined with high humidity can be a nightmare in any ignition system.