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92 s-10 4.3 oil pressure switch, ohms of injectors ?

Discussion in 'The Garage' started by R72K5, Jan 18, 2005.

  1. R72K5

    R72K5 Banned

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    ok got my brothers 92 here, the one that wont spray fuel TBI at cranking speeds, but will run great if you prime it manually with fuel down the TBI barrels,.


    how can i bypass the oil pressure switch by oil filter and connect circuit to see if its that switch thats not letting the ECM inject cranking speed fuel ?

    how can i have a module tested ? auto zone says that wont test it,

    all we have is o reillys and napa otherwise

    fuel pump and filter are brand new, relay works fine, runs great once it does start, after much hassle and cussing

    also what is acceptable range of ohms resistance of TBI injectors ? i have a digital multitester, this is how we test MPFI injectors, 8-12.5 ohms is acceptable on MFPI systems i know, what about TBI though ?

    also i hear that temp sensor can keep injectors form injecting on these too, how do i bypass and eliminate/test that sensor ?


    any ideas appareciated

    yes this is sup[posed to be in s-series board but i need to get this thing fixed asap so i can get it out of herem more members will see this thread in this board



    thanks
     
  2. R72K5

    R72K5 Banned

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    plugged in another ECM temp sensor, did no good,

    is no oil sensor down by filter on this engine, is oil sensor back top of block by distributor, just has three wires sender up at top , unplgged it, i put wires together there in different series,

    nothing, no fuel spray still

    i give

    thanks
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Oil pressure switch has nothing to do with startup IF the fuel pump relay is working, as I recall. It's a failsafe, if relay fails, approx. 5 psi oil pressure will activate the switch and force the pump to run. If the pump runs for 2 secs (give or take) when key is turned to run, the relay is working.

    Injector ohms are different based on lb/hr. TPI 350 injectors (22lb/hr) are supposedly "good" from 14-16 ohms, but more importantly, when dealing with 6 or 8 of them, like a compression test, you want them all to be near the same readings.

    One of the first tests from GM service manual for a no-start condition with EFI is checking to see that the ECM is getting a crank reference signal from the distributor, which can be checked with a scanner or winALDL. Injectors won't fire if they don't see the engine cranking.

    In a roundabout way, putting a test light on one of the injector leads (ones hot, ones ground through the ECM, so just like ohm test but on the connector) will tell you the same thing...if the light doesn't blink as it cranks, the ECM isn't telling the injectors to fire. Not as "precise" as seeing if the ECM is getting RPM reading as it cranks, but will eliminate anything in the fuel system if the light doesn't blink.
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    Its probably the module

    A friends 92 C1500 chevy truck with a 4.3 V6 had a similar no-start problem,it would not start sometimes unless you primed it by using starting fluid or gas--he had several shops and the dealership try to diagnose it,they replaced a few sensors,checked the fuel lines,pump,filters,etc--it usually acted up again a few days after the last visit to the shops,after seemingly being "cured"--but his son decided to change the ignition module in the distributor,and it hasnt done it again yet after 5 months,so I assume that was the culprit--

    I know at my friends shop he has replaced a lot of modules on 4.3's,that and the wires to the injectors getting smashed under the aircleaner are the most common problems with them--next to the fuel pump itself ...he keeps a few good used modules from junkers for test purposes on hand,to avoid buying new ones when it might not be the problem....its possible for the module to not fire the injectors,but still have spark at the plugs,and not do it all the time...:crazy:
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    At least this problem is consistent. I've had an intermittent crank/no start condition on mine a couple of times, but the list of possible causes is pretty darn big.

    Ignition module is at the top of my list as the culprit as well though. I'd STILL like to see what "indicator" the GM modules have to show that they have failed.
     
  6. R72K5

    R72K5 Banned

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    so bottom line on these damn 4.3L's ? ign module or what ?

    wires we have been through a billion times, even replaced parts of harness, to no avail, will be fine for a few days then poof no start problem again, IE no injection at cranking only

    wtf ?
    these phuckin POS TBI systems i swear!
    junk!
    why anmyone would want to convert to TBI is beyond me, the most unreliabe crap ive ever had to deal with ever!
    and basically impossible to diagnose problems within



    thanks
     
  7. diesel4me

    diesel4me 1 ton status Premium Member

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    I know the feeling!

    Yea--the more I read on here about EFI,and all the troubles,cost of sensors,diagnosis,etc--I'm glad I own old smog exempt and diesel trucks!--I also see many newer trucks in the shop more often than the older ones...I know the new ones ride better,etc--but I'll stick with my prehistoric carburetors,hand chokes,and live in the past--and if my HEI pisses me off--I still have several points style distributors and coils hanging around--nobody can shut my truck off with a remote kill switch like the newer computerized ones....newer aint always better....:crazy:
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    How you can question 12 year old components (heck the whole systems) reliability that probably have in excess of 100,000 miles on them is beyond me.

    There is nothing inherently wrong with TBI or any other injection system GM used, short of the optispark problems that we aren't dealing with.

    Whether the no-start was TBI or a carb, it would still be the same if it IS the module...no start. On top of that, I'd argue that the troubleshooting flow charts in the new (injection years) service manuals make diagnosis an absolute snap.

    Throw parts at it, or diagnose the problem. Same thing whether carb or injection, just more parts to throw money at with injection, and you can find multiple instances of people wasting money on parts that aren't the problem on any automotive board whether carb or injection. Doesn't mean the systems are junk, since 99% of the time, it's one piece, not multiple, and the problem is that people won't spend the time to figure out which PIECE is the problem.
     
  9. diesel4me

    diesel4me 1 ton status Premium Member

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    thats what I mean..

    I agree that EFI is the best when all is working right--but I'd rather spend my money on parts that will fix it,than on a computer diagnosis that costs 150 bucks just to "maybe" tell you which part is bad--if I was more familiar with EFI,I probably would not feel this way about it,I'm an old dinosour that prefers things "the way they were" and what I understand--

    I think computers belong in a house where its warm and constant temparature,not in an automobile--but times have moved foreward without me--I'm still stuck in the 80's and beyond as far as automotive tech--I only know what I've seen other mechanics deal with on the newer trucks,and I do not envy them,needing code scanners that cost thousands,just to diagnose something....

    I think "progress" is going too far,they say most cars have more computers and sensors than the first apollo space rockets that went to the moon!--Is all this tech really nessasary????.Simple is better--too bad the automakers didnt keep it that way....your not only a mechanic now,you have to be a computer expert too,to fix a car nowadays....I suppose its easy for those who grew up with theese systems,like I did with points and carbs,but old dogs sometimes cant learn new tricks....I like the old stuff better...:crazy:
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    How about changing that to "parts that MIGHT fix it"? There is no guarantee that changing one component without proper diagnosis is going to solve the problem.

    A $150 scanner (or $10 ALDL cable and laptop) can end up SAVING you money in the end, for sure.

    There is no argument if you have to replace everything electrical in a carbed setup, it will be much cheaper than an injected setup, the tradeoff is better overall power, economy, and driveability. Reliability REALLY isn't that big of an issue...if an $8 part lasts 10 years/100,000 miles +, is it not reliable??
     

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