Hello. So my girlfriend and I have a 92 S10 Blazer with the 4.3l TBI. She's had it for a few years now and it was sitting for almost a full year because of a bad fuel pump (she didn't know anyone who was willing to drop the tank and replace it). I changed the pump for her after we got together (a 2 day affair having to soak the front strap bolts with PB cuz they were so incredibly rusted).

Anyhow, I changed the oil the day after I got it running and it was very milky. Dun dun dun... We know what that likely means. She drove it to work for a while and I constantly monitored it for leaks (none other than a little oil from the rear main) and the oil/water levels. Of course, it was burning both and didn't take long for it to start needing both topped off almost daily.

So I told her the head gaskets were almost certainly blown and we decided to try and make this truck last a little longer and change them. I almost immediately regretted tearing into this poor, neglected engine. Everything was a fight to get off and even worse getting back on. Vacuum hoses deteriorated trying to disconnect them, spark plugs broke off, and even the coolant quick-connect on the intake manifold sheared off flush with the manifold when reinstalling.

I lost all long-term hope for this engine when I saw the tops of the pistons. Two of them were obviously beginning to burn through from the antifreeze entering the combustion chamber. Apparently it had been leaking for quite a while.

Anywho, long story short... After getting it back together it was overheating very quick and running incredibly rough. Double checked the timing and it was right, and also double checked my valve adjustments and they were good. Noticed the SES light on and checked the codes to find a code 45, then pulled a plug to discover it was covered in soot, then noticed the soot from the tailpipe on startup. I pulled the thermostat just so I could get it home and it never even got up to normal op temp.

Now there is a tiny exhaust leak from the flange on the passenger side (can't explain that one) and another, only slightly bigger one, at the manifold on the other side (rear bolt broke off in the head and didn't have the time or money to fix it, but plan to in the very near future).

My question is, are these very small exhaust leaks enough to cause a fuel rich problem so bad that it barely holds an idle, uses double the fuel, and has maybe half its normal power? Or should I keep looking for another cause like I suspect? I can't really imagine this small of an exhaust leak is enough to cause this big of a problem on a 92, but I'll admit to being wrong a few times in life. At the moment, with no advice, I'm leaning toward redoing the intake manifold gaskets (maybe the RTV somehow got screwed up during reinstall).

Just for info, it has new plugs, wires, cap & rotor, checked for leaks in vacuum lines, and checked to make sure the new head gaskets weren't leaking.

Sorry for the long post and thank you in advance for any help offered.

 

The 92 should be similar to the 94 I have.

Exhaust leaks before the lambda sensor could have an impact. It would suggest a lean condition when pulling in air adding oxygen to the sensors reading.

Another possibility is the water temperature sensor. The 94 has two of them. One for the gauge and one for the TBI. Measuring for correct resistance or voltage would show if it is one of these or just replace. The water temp sensor broken would suggest to the injection that the engine is still cold and needs more fuel.

Another sensible part is the vacuum lines to and from the TBI to MAP sensor. I found that the lines can be perfectly good but the rubber knees and sleeves can fail and crack.

 

I have to agree with 401. the engine coolant temp sensor will fail and tell the ecm that the engine is-40 degrees and the fuel will just poor in. try unplugging it and see if the rich condition stops. by the way, the temp SENDER for the gauge is in the head and the SENSOR for the ecm is in the intake near the thermostat. also if the map sensor fails it can cause a rich condition. try unplugging that and see what happens. to replace both is not that much of an expense- so might just change them and see. good luck!

 

Have you tried unplugging the battery over night to reset the ECU?

 

Disconnecting the battery could actually clear the fault as it would reset the short and long term fuel trim. Then it will re-start monitoring. DTC 45 is set when the voltage from the oxygen sensor (lambda sensor) is above a certain value for more than 3 1/2 minutes when operating in closed loop with the throttle closed or within just 10% of opening. Not sure if it clears the DTC45 thou. Just checked manual and it says - YES - it does clear a DTC when off power for 30 seconds or more. Best would be to disconnect the battery as proposed because there may be more than one fuse to pull depending on the vehicle.

Manual says: possible causes

- fuel pressure too high (is your fuel pump the correct one with the correct delivery capacity and pressure) The pressure regulator in the TBI will take care of that but if overloaded it may rise the pressure. Also check both fuel lines for kinks and bends or dents. A damaged return line could also cause a rise in pressure.

- A leaking injector. Should be visible when putting the car into ACC without starting. It will run the fuel pump shortly to rise pressure. Absolutely no dripping allowed when the engine is not turning from the two injectors in the TBI.

- Fuel contaminated engine oil. Pull the dipstick and have a good look. If a lot of fuel is present it becomes diluted and runs off, plus it may smell from gas. (This is normally not a problem of the TBI engines but more of the TPI)

- Oxygen sensor wiring. Go along the wiring of the oxygen sensor. No kinks or bends should be there and no contamination on the wires. It needs the one wire with the sleeve to be free as it is from there that it receives the atmospheric reference oxygen.

- Distributor ignition. Check the wiring, ignition wires and cap for arching, damage or other defects which could cause a spark to go haywire. It could lead to electronic noise which the PCM interprets as higher rpm and delivers more fuel.

- Fuel vapor canister. Is it full of fuel? Then the flooding in the canister will add fuel as it is pulled in by the TBI.

- MAP sensor. Can be disconnected to check if the "rich" condition disappears. If it does when disconnected replace the MAP. Also check all the tubing to all the sensors.

- TP (throttle position sensor) Could have an intermittent signal which could lead to a rich condition. Might be an indication to check if the rich condition comes on as soon as the throttle is opened but not when left in idle.

- ECT (engine coolant temperature sensor) The above mentioned which can cause underreading of the temperature and trigger the cold start increase in fueling.

 

Bought a blazer from a 19 yr old kid that wanted it louder so he cut the exhaust to **** I've got it back together but I've got exhaust leaks at the 3 spots he cut it at I'm getting ready to have a new exhaust system put on but I'm curious to know if I'm right about the compression being lost out the exhaust do to the extreme exhaust leak at 3 different areas n the Cadillac converter I've got the 4.3 vortec motor and it's wanting to run at 2500rpms which with the way the exhaust is is way louder than I feel comfortable with