Soo, let's start with the basics. 1991 S10 Blazer V6 4.3 L TBI. I just purchased this little guy for $800 bucks and am having some trouble getting it to pass emissions.

At idle I get 440 ppm in Hydrocarbons but at 2500 rpm it drops to 90 ppm. I have changed plugs and wires, pcv, MAP sensor, fuel and filter, and run a fancy injector cleaner. Can't remember BGI or some deal with a half tank of gas.

Ok here is what I am thinking. I have that digital readout, which I think is rad by the way. I was getting some funky readings on the gauge. It seems that it takes a long time to heat up and by my estimation I never get a readout over 170. I changed Thermostat and the sending unit but my problem is still there.

Through my research I noticed that the gauge uses a separate sensor? But it's only linked to the gauge so it would not effect my fuel to air mixture, correct?

How would I check the wiring harness at either of these sensors to make sure the electrical is good?

Any other suggestions for my running rich problem or temperature problem? Thanks

 

A new ERG valve might help your mixture and improve your chances at passing smog. Having any rough idle issues? That might be caused by a failed EGR thats backed up. Worth trying it for the cost and you can install it yourself.

 

You have 2 temp sensors. The one on the passenger side of the block is for the gauge. The one beside the top rad hose is for the computer to tell it if it needs to be in closed loop or not. Do you have the service light on? Even with it not being 0bd2 (96'+) you can still check codes with a paper clip

 

I don't have a check engine light. I replaced the ecu sensor by the top rad hose but my gauge still reads around 170 roughly on a good day. On sat I am going to change the gauge switch and connector to see if I can get an actual idea of what my temp really is. I will also try ERG valve. It does idle somewhat rough, steady RPM at around 800 or so but kind of lopes a bit. It's got 234k miles so I guess it is to be expected. I will keep you all posted. Thanks for the tips.

 

You need to remove the throttle body and clean out the tunnels,i bet if its never been done,its clogged. they are bad for it. the egr should be cleaned too. use some brake cleaner and a toothbrush.

 

So finally got this issue fixed. New Cat. My emissions are so good now. I'm so green. Thanks for everyone's help

 

May I ask how you determined that the CAT was bad? Mine seems to be running just fine, and always ran at 190 or so. Now temp guage only goes up little past 100 that's it