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  1. Ruthven13

    Ruthven13 1/2 ton status

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    Well... I am sold. Just decided to buy a membership. With all the info i have pcked up here, i felt guilty /forums/images/graemlins/smile.gif... Ok, now with the question. We put a IROC TPI setup on my buddy's '86 shortbed. Problem is that after it warms up and the computer goes into closed loop mode, the power really cuts off. WHen it is cold it sounds really cool throught the glasspacks and hav a good set o' nuts. Then drops off when it starts to warm up. It is on it's 2nd O2 sensor, and that seems not to be it. He thinks it has the wrong injectors, and it is running lean. Does anybody have a clue?!
     
  2. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">What size motor did the TPI come off of? Does it have any engine codes?
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Is this a complete setup from the car, or are there things such as aftermarket wiring harness to deal with, etc?
     
  4. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    Are you running headers? If so you need to run a heated 3-wiring o2 sensor. I don't think it's the injectors b/c the only difference between closed loop and open loop operating is the o2 sensor input. What ever the o2 sensor is telling the computer is driving it into a lean condition. You can look at the o2 output by either a scan tool or a good ol' voltmeter.

    Mike
     
  5. Ruthven13

    Ruthven13 1/2 ton status

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    It has the original manifolds, and the entire unit and harness was taken out of the donor car. Nothing aftermarket. We ran the codes and they are pretty normal, but shous it a little lean... We have been trying to figure this out for quite some time now!!!
     
  6. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    I assueming orignal TPI maniflod and not the truck ones. The location of the o2 sensor is important if it's too far from the engine and not heat it will not work propertly. Check the out what the 02 sensor is reading. Assuming that the truck runs better when in open loop, check the voltages that the o2 sensor is outputing. How are you determening it's lean, from the Block Learn variable or something else like plugs.

    Mike
     
  7. BurbinOR

    BurbinOR 3/4 ton status

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    Though it is a good idea to put a 3 wire O2 sensor in, that is not your problem, unless it is going in and out of closed loop, indicating the sensor temp is dropping below 600*, usually because of header use in cold weather and sensor too far from the motor. I ran headers with the O2 down past the collector 4" in Oregon and never had it go out of closed loop. All a 3 wire will do is get it into closed loop sooner.

    Get a scanner that reads information, not just a code reader. Absolutely the first thing anyone with FI should get. Mine is from www.autoxray.com - cost about $150 and paid for itself the first month. You can see all kinds of operational data realtime as the truck runs, and can help troubleshoot drivability problems, which usually do not throw codes. You'll be able to tell from the scanner if the rig is running too lean (block learn upwards of 160), etc. Gotta do that first.........the next thing to buy is a fuel pressure gauge - www.tpis.com has them, I paid about $35 for one IIRC. You have to know that you're getting enough fuel pressure (TPI needs about 43.5 psi) and then you can adjust up from there with the other trick item to get - an adjustable fuel pressure regulator. Buy it from www.tpis.com or make your own by reading the how-to on www.thirdgen.org - THAT is the place to hang out and get TPI info. Dorian has incredible knowledge on FI, I have TPI knowledge, there are a few others on here that can help, so ask away.

    But buy that scanner............and get us more info. What size motor did his TPI come off of? 305? 350? It matters as to which size injectors he has - might well have 19 lbers, which is not enough for a 350 with some nuts. My 406 had 19 lb units /forums/images/graemlins/blush.gif for a while, and I always wondered why the damn thing seemed to not want to rev - duh!

    Buy a scanner......... /forums/images/graemlins/deal.gif
     
  8. Ruthven13

    Ruthven13 1/2 ton status

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    Right, 87GMCJimmy, BurbanOR... We are getting a high block learn code... He put the O2 snsor in the pipe right below the exhaust manifold. Being as though it runs like crap in closed loop, the o2 sensor makes sense... Will have to test it and the wiring going to it... I think the unit came off of a 305 as well. How can i tell which injectors we have? The TPI is all that is done to the motor, no other mods... Thanks Guys!! Anymore help would be much appreciated.... /forums/images/graemlins/laugh.gif
     
  9. 88streetblaze

    88streetblaze 1/2 ton status

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    305's as far as I know are all 19 lb injectors......

    Injectors Id
     
  10. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    I live in AZ, had headers and I would get a lean run condition with out it dropping out of closed loop. Closed loop operation is based on engine temp(I think over 160) and not the 02 sensor input. Once in closed loop and the 02 sensor is not hot enough it will give lower voltage readings which cause the lean run condition. When mine did this it never set a error code. If the 02 sensor is not in a stock cast metal exhaust manifold I would imaging its not hot enough all the time. A good test would be take it out and drive it hard for a while ensuring the 02 sensor is plenty hot. Does the lean condition go away, mine did but as I would sit at a stop light or easy cruising it would start running crappy again as the 02 sensor cooled off.

    Thridgen.org rocks for TPI info also try FBody.com

    If you put 19lb injectors on a 350 you need to bump up you fuel pressure some or do a custom prom or something. I still don't think this is the issue because you say it runs good with when in open loop.

    And the way I figured this all out was using a autoxray and looking at all the sensors inputs and seeing what didn't make sense. /forums/images/graemlins/thumb.gif

    Good luck and may the FI gods look upon you favoravbly. /forums/images/graemlins/cool.gif
    Mike
     
  11. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    Closed loop operation is based on engine temp(I think over 160) and not the 02 sensor input.

    [/ QUOTE ]
    My factory service manual says that this is incorrect. It says that TWO things are required for closed loop operation, engine temp of at least 160 degrees, and a valid signal from the O2 sensor. It even states that it is possible for the ECM to fall back to open loop operation during extended idle times, as the 02 sensor temp can drop below 600 degrees F, at which point it stops functioning.

    Newer vehicles burn much cleaner when cold and during long idling periods by using a heated O2 sensor. I've also heard that they go into closed loop with an engine temp of around 120 degrees.
     
  12. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    Yes that is correct. However there is not a temp sensor on the 02 sensor, all it is doing is reading the voltage. If the voltage is low enough long enough it will drop out of closed loop(or high enough also). This never happened on my system. The o2 sensor limits I assume are based on the o2 sensor being installed into a stock manifold that has a huge thermal mass versus a thin walled pipe. I wounder what is the valid range of o2 sensor readings?? Anyway, I can only speak to my setup but there was a definite range of closed loop operation where the 02 sensor was giving low voltage readings causing lean condition. Which in turn made the engine run crappy. I installed the heated O2 sensor and it was all better.

    Mike
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    The "band" of the older O2 sensors is VERY narrow, which is why the newer "wide band" O2 sensors are becoming much more common, both OEM and retrofit.
     

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