Been working on a '92 s10 blazer, 4.3 tbi with what has turned into a persistent high idle and bad(even for a 4.3) gas mileage. was getting 16-17 average, down to 9 now
The high idle used to be random, but is now a normal thing. IAC is working, no vacuum leaks
gas mileage has been slowly dropping over the past 6 months or so. Plugs, wires, cap, rotor, icm, distributor and coil all new. icm went bad, got a faulty replacement, fried the coil and pickup coil in the distributor.
New o2 sensor and coolant temp sensor. TPS and MAP test good, timing spot on 0. Truck always starts right up and runs smooth, has plenty of power
exhaust smells very rich, worse than usual
No cats, truck is completely stock other than that

Anybody got any suggestions on what to check out now?

Also about to tackle control arm bushings, balljoints, and rag joint. sick of the slop in the steering and tire wear. already replaced the idler arm and it's still horrible

 

Ignition spot on 0???

They are a little particular to set properly. It needs a cable disconnected to set properly to 0 and will read some 8deg advance when reconnecting the cable. Could be causing the issues, especially low mpg and rich smell.

 

Base timing is set dead on 0 with the tan wire above the passenger side carpet disconnected. Distributor is installed correctly, unlike previously where it was installed so the #1 wire was on the left side of the cap.
I picked up a TBI gasket set and fuel filter, I noticed a hissing from the TBI and fuel smell under the hood when shut off and it's wet with fuel above the IAC passage. This will be my first time pulling apart a TBI unit, I've done carbs before, cant't be too hard.
Maybe I'll get lucky and this will fix the high idle and rich issues

 

Get a gasket set for the TBI which includes all the o-rings.

You will need wrenches up to about 1" for the external stuff and TORX keys, bits or screwdrivers for disassembly of the internals and a thread locker like LOCTITE for re-assembly.

I have some pics in my build thread.

https://blazerforum.com/forum/builds...t-92047/page3/

 

I had a leak in my '92 inside the intake plenum from a leaky hose going to the fuel injection spider. Before I knew what it was, it gave O2 sensor errors and I replaced the sensor. I believe the error originated with an over rich exhaust (perhaps). When I finally replaced it I had raw fuel draining into the intakes through the holes for the injectors.

I've seen a video in which the hoses inside the intake plenum that go to the spider only leaked when under pressure. You might look for this too. It would also explain you poor mileage.

 

The TBI is quite different to the spider injection which came onto the Blazers only in 95'.

 

I should have read the post more closely. TBI was no on my "radar" as my '92 had the CPI "Vortec" labeled engine. An easy google search revealed that TBI and CPI motors were offered simultaneously for a couple years.

Could there be some sort of flooding going on? I replaced my O2 sensor in the lead up to learning that it was fuel delivery that was over rich by dumping fuel in to the motor directly.

Keep us posted.

 

BTW

A TBI is pretty much a carb with injectors instead of the venturis that "draw" fuel. In idle some hissing "could be" normal when air passes past the throttle plates (with the airfilter OFF). This should not be heard or just hardly be heard when the air filter assembly is mounted correctly.

What happens sometimes is that all the rubber and plastic parts around the TBI rot away. Especially the rubber parts have a tendency to rupture with age. Then it starts drawing air from all the wrong places. As some of these small plastic hoses are feeding vacuum information to the sensors it can upset your TBI.

As with carbs, before doing anything I would make sure that all these hoses and attachments are in good shape and correctly placed. When you kink the little plastic hoses they tend to get two very small holes left and right of the bend.

When running it with the air-filter OFF and shutting it down the flow of fuel should STOP immediately. If the injectors still drip - bad.
Also check the wiring on top of the injectors.

WARNING: FIRE HAZARD!

With the air filter off, you have a lot of air and fuel under pressure and finely distributed present. Do so only if you know your ways around these things.

 

It was hissing after shutdown for several minutes. I found it was leaking some gas from a couple of spots, but not the injectors. I finally got around to the throttle body rebuild last night, was simple and straight foward. The truck runs better overall now, no update on the fuel consumption yet, it's only been driven about 20 miles. Definitely doesn't smell as rich anymore, but the warm idle is still slightly high. cold idle is slightly lower than before, and smoother both warm and cold. So far the only thing I've found that brings the warm idle down to normal is pulling the PCV and plugging it with my finger.

Aside from this, I've managed to get everything else done except for the upper control arm bushings. Attempting to do those now, not having alot of luck

 

Glad you got that fixed.

Has it also stopped leaking fuel?