92 S10 Blazer TBI Rich

Discussion in 'Domestics' started by Gunnsmith57, Aug 27, 2017.

  1. Gunnsmith57

    Gunnsmith57 Newbie

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    Chevrolet
    S10 Blazer
    1992
    198,000
    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. kev2

    kev2 wrench

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    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. kev2

    kev2 wrench

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    TSB is not applicable this engine, so a dead end.
    POsted for your curiosity
     

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  4. NickD

    NickD wrench

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    These things can either come with TBI or these;
    [​IMG]

    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.

    [​IMG]


    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. nickb2

    nickb2 Wrench. I help when I can

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    Second this in a big way

    Live data would be nice, but for a 92 you can get away with alot of things.
     
  6. nickb2

    nickb2 Wrench. I help when I can

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    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. dabunk

    dabunk wrench

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    Have you checked fuel pressure? Valve that controls pressure return can get screwed up and cause high fuel pressure.
     
  8. billr

    billr wrench Staff Member

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    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. jd

    jd Hero Member

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    Parts lookup shows an Air Charge Temp Sensor (ACTS) that checks intake air temperature, like the ECT checks coolant temperature.
    [​IMG]
    If that ACTS is failed open, or not connected, the ECU will command the Injectors to go Full Rich.
     
  10. Gunnsmith57

    Gunnsmith57 Newbie

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    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.
     
    Last edited: Aug 27, 2017
  11. billr

    billr wrench Staff Member

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    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. Gunnsmith57

    Gunnsmith57 Newbie

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    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. kev2

    kev2 wrench

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    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. Gunnsmith57

    Gunnsmith57 Newbie

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    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. billr

    billr wrench Staff Member

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    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.
     

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