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92 S10 Blazer TBI Rich

  1. Chevrolet
    S10 Blazer
    4.3L TBI
    Runs rich, limited power, excessive fuel consumption

    Hello there. So I changed the head gaskets on my girlfriend's truck that was severely neglected by the previous owner (not my first time, just my first time on a v6). After getting it back together it was running very rich, very limited power, double fuel consumption and overheating. The overheating turned out to just be the thermostat had decided to stick shut while the manifold was off so it has no thermostat temporarily while I figure this problem out. The only DTC is 45.

    I changed plugs, wires, cap, and rotor while doing the gaskets. I checked for and fixed all vacuum leaks and made sure the new gaskets weren't leaking. I triple checked the timing (though I just learned tonight that it's electronically controlled so I'll disconnect the timing wire and check it yet again tomorrow). I followed the procedure in the Haynes manual for adjusting the valves during the gasket change. MAP sensor is working. Injectors don't appear to be leaking and have a good spray cone. The rear bolt on the driver side exhaust manifold did break off in the head during reinstall though, so it does have a small exhaust leak (the first thing on my to-do list once I figure this out). I wouldn't imagine this small of a leak would cause this big of an issue on this truck, or am I wrong?

    In my searches tonight I found that TSB 476516 might have something to do with it so Monday I'll see if I can manage to get my hands on the TSB somehow and see what it says.

    I've racked my brain and all I've come up with is the exhaust leak or the RTV on the intake manifold possibly have gotten screwed up on install. Any input at this point is more than welcomed and vastly appreciated. I'll admit I'm a little out of my element when it comes to distributor-driven ignitions and TBI.
  2. We all loved these TBI engines -
    be sure the ECT sensor is operating If I remember 92 (been awhile), there are 2 one for gauge one for ECM.
    The inj wires were prone to grounding and dumping as if WOT - check shake tug wires where they pass under air cleaner assy look for pinch mark.
    Correct Base Timing is set with connector open. then connected the ECM will control.
    4.3 have to mention EGR - might want to check engine vacuum - they would have issues with stuck open EGR causing low vac and would go rich.
    Along that line TPS - check voltage at idle.

    SWAG is ECT .

    FYI 45 is an obvious o2 sensor hi voltage meaning rich.

    What was subject of that TSB? the number does not look like a GM #, a 1992 sould have had the issue corrected by now. But I will give a look time permitting
  3. TSB is not applicable this engine, so a dead end.
    POsted for your curiosity
  4. These things can either come with TBI or these;

    What do you have? I see the price is only 114 bucks, dealers wanted 700 bucks for this piece of plastic. Ours with around 80K miles on it, those pieces of platic were all broken up, combination injector and fuel regulator. Unlike real FI, any upper intake manifold leaks, thing wouldn't run at all, same with fuel pump pressure, wouldn't start unless it was 55 psi. Haynes is worthless, need a shop manual. Recall by pulling that wire to eliminate the spark advance for timing, was located above the blower motor.

    Other problems were just using an O-ring for the valve seals, pouring in engine oil like crazy, Fel Pro came out with the umbella type like they used on a 41 Chevy.

    Other problems we had with this thing is this, was also way overpriced at the time.


    Ha, hard to forget this, used CRS bolts in aluminum, both heads broke off. Is stepper motor controlled. 4.3 is a sawed off V-8, still using 90 instead of 60 degrees. Fortunately problems with the AT were all electronic, told my kid he needed a new AT. Ha, going back 12 years with this thing, no tears where poured. At this time, EPA banned electroplating, practically every switch in this thing was bare copper, major corrosion.

    TBI was less painful, what do you have? Recall something about a Z or a W in the VIN.
  5. Second this in a big way

    Live data would be nice, but for a 92 you can get away with alot of things.
  6. I think I saw a picture here of a EGR valve. That is a common issue. They won't code a simple OBD1 code, but you can hear the vacuum hiss from a mile away. Just blasting the base of the EGR gives a definite result. It changes timing, stalls, etc.
  7. Have you checked fuel pressure? Valve that controls pressure return can get screwed up and cause high fuel pressure.
  8. I agree, the ECT circuit is most likely the problem. We need the OP to advise whether this EGR is electric or vacuum, and to confirm it is the simple "injector on top" type of TB.

    I gotta ask... what is compression now that the heads have been R & R?

    With OBD1, checking the ECT circuit with a voltmeter back at the PCM connector is probably the most practical way.
  9. Parts lookup shows an Air Charge Temp Sensor (ACTS) that checks intake air temperature, like the ECT checks coolant temperature.
    If that ACTS is failed open, or not connected, the ECU will command the Injectors to go Full Rich.
  10. Thank you everyone for the replies.

    It has the two injectors above the TB and the EGR is vacuum.

    Both my vacuum pump and multimeter are in a different town at the moment but I had already planned on going to get them tomorrow just so I can have actual data to work with. As soon as I have them I'll post those results. As for the compression check, that will have to wait a little bit longer. Can't rent a gauge in this town and I'd go broke trying to drive this thing to get one. But I can say for sure that it no longer burns water or oil.

    I can almost guarantee low vac isn't an issue thanks to the on board whistler (the climate control panel has been broken for years and lets you hear the vacuum as you're driving lol). Not to mention that before the repair no vac hoses were collapsing and afterwards the main vac coming from the intake started collapsing (fixed immediately). So, if vac does have something to do with it, it would be high if anything.

    To the tune of fuel pressure, I haven't checked that since I changed the pump back in April. After I have lunch I'm gonna tear into it again today and I'm going to try pinching the return line while it's running to see if anything changes, as well as checking the injector wires again as suggested.

    And as far as an ACTS, it doesn't have one.

    Days like this make me miss my old workhorse 4.0 Cologne. And I completely agree, Haynes manuals are a joke. Mostly the only reason I use them is for torque specs. But when we get a new vehicle at tax time (maybe an old Tempo/Topaz [I like the old 2.3 when it's paired to a 5 speed, so sue me] or an old Explorer with AdvanceTrac) I'll be getting an actual shop manual for it as suggested.
  11. Oh, I'm pretty sure it does have an ACTS, also called a MAT sensor or IAT sensor, but it is much less influential than the ECT.
  12. Any chance you could tell me where the Air Temp sensor would be on this engine? I've looked for one previously, going through and visually checking all the possible sensors I could think of, but I never could find anything that checks the air coming through the intake, for flow or temp.
  13. I do not think there is a AIT/ACTS - very basic ECT, TPS, MAP. If anywhere incorporated into air cleaner assy.

    Check ECT - one at thermostat other would be between #1 and #3 plug in cyl head.

    $.02 If undrivable as you say - injectors likely going WOT....

    Quick thought do they spray KOEO?
    If no then ck TPS.
  14. Redid the ignition timing with the wire off and after restart it advances it just past the timing plate.

    As Kev said, there's definitely no sort of intake sensor.

    When I head back outside I'll double check if the injectors are firing KOEO, but I'm pretty sure they aren't. Also, I don't think they are going WOT. Hitting the throttle under the hood and watching the injectors, you can see them spray more as RPM increases.

    Once I get my multimeter tomorrow I'll start actually checking these sensors for operation. And I may be wrong, but I don't recall any sensor in the head between 1 & 3 but I'll also check for that one once outside.

    And now that I know for sure that the ignition timing is right (I was wondering if the dist was possibly one tooth off, but now I'm positive that it isn't), I'm in the middle of making sure the rocker arm nuts are adjusted properly.

    Also, it's not completely undriveable. It just has severely limited power, runs very rough, and uses more than double the fuel that it should.

    And one last thing, not sure if it helps or not, but after shutting it off, some smoke drifts up through the air bypass and the butterflies if you open them.
  15. No, I can't tell you where the Air Temp (IAT/MAT) sensor is located, but keep looking for it. Rockauto lists it as an SMP #AX32. It is such an integral part of the fueling calculations for any EFI that I find it very hard to believe there isn't one. I know GM was using them in '86, for sure.
  16. If ROCK's picture and another I found are accurate, this sensor pokes into a grommet somewhere, like a PCV valve pokes into a valve cover grommet. I remember changing one that screwed into a branch of a Ford V6 intake manifold, but this AX32 looks different. Does your V6 have a Space Age Plastic Composite thingamajig with a sensor sticking out of it?
  17. Nope. The air cleaner assembly looks like one you would find on a carbureted engine. When you open the hood, you might actually think it has a carburetor until you either take off the wing nut or notice some of the other components that you'd only find for fuel injection.

    As intimate as I am with the top half of this engine, I am 100% certain that it never came with any sensor to measure the flow or temperature of incoming air. I'm familiar with the IAT sensors shown in those pictures, and they just push into the intake tube. One of those would never work on this tube as it's just thin, flimsy plastic and not "rubberized", so it would never seal. Plus, there are no pigtails disconnected anywhere.

    And there is definitely no temp sensor in either head. The only temp sensor I can find is at the front of the intake manifold next to the thermostat.
  18. Sensor at thermostat 2 wire? this is ECM use, Its a 5v reference and other is ground... testing is ohm reading of sensor terminals.
    - There is a 'memory' of a ECT sensor issue* BUT this is a 92 and would be addressed by now.
    Dave mentioned fuel pressure - I am thinking why would it run OK before head R&R but go to shit now, same EGR, fuel pump, MAP, TPS, my thinking kind of leaves wiring, sensor inputs GIGO.

    * something about plastic type vs improved type ? hoping this helps someone remember OR as often I am confused.
  19. Did you rebuild heads while off?
  20. Hello again everyone. I've been very busy over the past couple days and didn't even get to go get my multimeter and vacuum pump as planned, but I was able to pick up a new multimeter and a compression gauge today. Tomorrow afternoon I will definitely be doing some checking on sensors and testing compression on all cylinders after we pick up our daughter from Head Start.

    No, I didn't have the heads rebuilt. This truck was destined for the scrap pile long before I ever touched it, and will be going there come Tax time. I hate to see vehicles get scrapped, but this one just flat out isn't worth fixing everything that's wrong with it. New front diff, door panels & hinges, rear hatch hinges and latch mechanism, etc etc. The list goes on. The parts alone, new or used, would cost more than the truck would ever be worth. I'm just trying to make it last 6 more months, and if I hadn't changed the gaskets it might not have. The pistons were starting to burn through from the antifreeze in the combustion chamber, but they should be perfectly fine for a while longer as long as it's not burning anymore antifreeze.

    On a side note, I accidentally caused a vacuum leak readjusting the rocker arms. One of the bolt holes in the intake manifold (used for the MAP/Purge solenoid mount only) stripped out, so now it's running so bad that it actually dies when idling occasionally. I'll be taking care of that tomorrow with some Ultra Black that I picked up as well. If anyone has any recommendations on where to buy an affordable, but not crappy, Tap set, I'd appreciate it. I should have bought one long ago.

    Thank you again everyone, and I will be getting back to you tomorrow afternoon/night with some hard data.
  21. look at a "heli coil" repair kit for the manifold. NAPA part.
    Maybe 1 size up self tapping bolt. - not critical fit more of a clamp am I right.

    don't rush into a full tap set purchase either you will over pay or get 'screwed'.
  22. Yeah, it just holds a bracket on that never has any sort of stress.

    But I have a much more critical issue and somewhat found the source of all the issues. I'm in the middle of testing compression, finished the 1-3-5 bank. 1 & 3 are good at 152 psi. But I have absolutely no compression whatsoever on 5. Yay....
  23. Can't come up with a phrase for how sick that makes me. Let me try these silly things...:(:giveup::eek:
  24. You sure you set valves right on #5?
  25. Lol Thanks JD.

    Yep, Krazy, same as all the other cylinders. I even did #5 again today to be sure. There was a 1 psi difference between 1 and 3, then pretty much no compression at all on 5, and I can hear the compression just hissing out of 3 and 5 when turning the engine by hand, so I'm betting that it's the gasket and not a valve. Maybe something got stuck between the head and block at the rear without me realizing it. (Thankfully the other bank is fine, 170 psi across)

    My next move is to take the head back off and see if it's the gasket or a valve (Pretty sure we all know it's the gasket after today). Since this gasket is new, what are the chances that I'd be able to reclean my mating surfaces and reuse it (even if I put an extra 5-10lbs of torque on the bolts)? I'm just wondering because I can't rent a pulley puller this time. I'm going to have to buy one, and it's going to cost an arm and a leg in this town. Or is it possible to remove the head without taking that entire Alt/Pump bracket off? Would it be possible to pop the alt off, take out the bracket bolts that go into the head, and squeeze it past? If I can get away without buying the puller I have no problem buying a new gasket for that side.

    Thank you everyone for your time, and I only wish it had been the TPS or a temp sensor.
  26. Thats a bummer bro, but as they stressed to us in college... "Haste makes Waste" if you try to shortcut you typically end up in a worse situation than you started in, as painful as it sounds its best to take your time. Depending on type of gasket you may b able to reuse but if a tinybit gets left on block or head must replace. I would check for warpage on cylinder head while u have it back off. Good luck and my condolances
  27. Before you remove head, you should loosen valve adjustment for cyl 5 so that rockers have a little slack and retest for compression. Also, do a "wet" test...where you squirt some oil into cylinder and see if that gets you some compression. Do you know what a "leakdown test" is?
  28. billr suggested compression ck early on, his first reply-

    there will be no living with him now.... :beer:;)
  29. No, I won't gloat, but I do have to ask if the compression there is really "near zero"? If so, I'm betting it is not a simple gasket issue. Something would have to be grossly bad for a gasketed joint to leak that bad.

    Resist the urge to tighten those head screws "a bit more". It isn't going to cure the root problem and may leave you with broken screws to dig out or stripped threads to repair. Don't make a bad situation worse...
  30. Bill is right again. When I put the spark plug for #5 back in last night, I loaded the threads with Ultra Black as a thought. Went to get a new gasket for that side just now, and it purred like a kitten the whole trip.

    I'm still going to do that gasket again tomorrow since there was a 20psi difference between the banks, and while it's off I'm going to fix the threads for the plug.

    Thank you everyone for the help!
  31. Well, I'm really confused now. The spark plug threads/gasket were leaking that bad? That seems impossible. Likewise, the compression gauge should have its own gasket or O-ring there, not dependent on the plug gasket at all. If the gauge worked in the other cylinders, it should have worked OK in #5.
  32. I'm wondering if a "foreign object" was preventing valve closure on cyl 5. Perhaps it finally broke up and valve is sealing again. I would not tear engine apart unless the cylinder "died again". Was the manifold bolt problem on the cyl 5 head?
  33. I was thinking the same thing Bill, but the gauge doesn't have any kind of seal at all. I even tried Teflon when I was testing it.

    Dan may be right about something keeping the exhaust valve from closing all the way, but it was driven a couple weeks like that before I ever did anything so I don't know. I figure if it was something, it would have came out before now.

    And the bolt on the manifold was on the other side, so it wouldn't have anything to do with that cylinder.

    I'm inclined to not touch it while it's running better, but at the same time, this weekend is a perfect time to do that gasket again if I had to. I'm thinking this afternoon I'll check compression again on that bank and see what the difference is from the other bank. If there's still a 20psi difference, or if I can still hear the compression hissing out, I'll go ahead and change it.
  34. My question about manifold bolt location was in regards to "The list of reasons why Gunn should pull that head off again".