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tbi 350 dies when warm?

Discussion in 'The Garage' started by mikayak390, Mar 10, 2005.

  1. mikayak390

    mikayak390 Registered Member

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    Hi

    I have to look help with a friends repair tonight. Its cold and the truck is stuck outside so I am looking to minimize my troubleshooting time.

    Im told the truck starts easily when cool. Runs about 5-10 minutes then dies. tries to re-start, nothing but cranking motor. Wait two hours and it starts fine for 5 minutes or so. Spark is constant, but there is No fuel spraying once the engine is warm. Once cold the fuel system is fine.
    no check engine warnings until motor is already dead. With a cheap code tool he thinks he gets an oxygen sensor failure.

    I know that an O2 sensor will make it run badly, but Should still run correct? I do like the idea of an easy fix however :)

    My thoughts so far are: disconnect the o2 sensor, possibly swap map sensor from my truck, use a real code scanner, and hope to figure it quickly. Preferably before the parts stores close or we freeze.

    Temperature sensor and thermostat should not stop fuel flow correct? Btw he said coolant temperature on dash guage seems to be working normally. Engine is not overheating.


    Any other suggestions?
     
  2. miniwally

    miniwally 1/2 ton status Premium Member

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    Fuel pump getting weak and causing a vapor lock.


    Happens to mine sometimes if it gets real hot.
     
  3. diesel4me

    diesel4me 1 ton status Premium Member

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    mite bee

    It could be a bad ignition module,its a common symptom of a bad one to fail only when hot or cold--it controls the firing of the injectors as well as the spark,and often only one or the other fail,not both--meaning you can still have good spark,but no fuel,and vice versa--the module usually wont show up a code when this happens either--but do some testing before buying parts,they arent exacly cheap,and are non returnable if its not the problem--I have seen the modules fail this way quite often,but that does not mean its the problem on your truck--it pays to have it diagnosed properly..:crazy:
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Thermostat can affect fueling, but not to the degree you would see the engine actually die.

    The temp sender for the ECM CAN hurt fueling, but it's essentially the same design as the gauge sender (although not shared)...it is somewhat unlikely, but not impossible, that it's malfunctioning and goes from reading accurately at a low engine temp, to telling the ECM the engine is 300*+, which can mess with fuel, spark, and idle depending on the calibration in the PROM.

    In any case, *typically* failure of the temp sender for the ECM is exhibited by hard starts when cold or when the engine is hot. If you've got access to a scanner/winALDL, you can verify operation of the temp sender for the ECM. You asked about the temp sender/thermostat, theres my input on it.

    Many potential issues, service manual is a big help in troubleshooting these matters in a logical, cost effective manner. Watching to see if the ECM is getting a distributor reference pulse (telling the ECM "the engine is cranking, fire the injectors") is another advantage of a scanner/winALDL.
     
  5. Thunder

    Thunder 3/4 ton status

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    I agree with diesel4me. Sounds like a dist module to me. Pretty common for them to work fine when cold and fail when they get hot and resistance builds up. I would pull it and have it tested.
    Many auto parts stores will test them for free.( napa, AZ, Kragen, ect) They should plug it into their tester and put a heat gun on it to do the test properly.
     
  6. Fierospeeder

    Fierospeeder Banned

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    CTS and O sensor will not cause an engine to die.
     
  7. miniwally

    miniwally 1/2 ton status Premium Member

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    After re-reading your post I would start the truck and let it run until it dies. At that point I would verify spark at the coil. If spark is good then check for fuel, no fuel pull the feed line from the back of the throttle body and see if you get fuel. If you do get fuel then check fuel pressure some how, If that is good then you need to look at all of the above stuff.

    If you do not have fuel, the pump could be bad and not able to push fuel.

    One other thing you could do is to grab a bottle and fill it with fuel and when the truck dies try starting it by putting fuel down the throttle body, if it runs well that way you probably have a bad fuel pump.

    Thats how I see it
     
  8. Fierospeeder

    Fierospeeder Banned

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    very true with the advice on both topics.

    some people rather change parts then to diagnose. :laugh:
     
  9. mikayak390

    mikayak390 Registered Member

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    Its definatly a fuel cut off once the engine is warm. Spark is good all the time. I can actually see the fuel spray stop from the injectors. At that point a can of starting fluid will keep the engine running regardless of engine temp. a few good squirts will get it started after stalling as well. It seems like a sensor is telling the pump or injectors to shut down.

    I guess it could be a pump issue. but I hate to deal with pulling that out when it pumps normally when cold. I may try checking line pressure at both temps.

    Thanks.
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    testing...

    Yes,even my friend who runs his own garage and has most of the scan tools usually gets impatient and just takes a guess and throws in a module--it does save time troubleshooting--but more than once the problem returned,and then he had to diagnose it correctly--as an instance,a truck came in with similar symptoms as described ,except it would not start cold after sitting overnight--he checked fuel pump pressure,it was normal--so he threw a module in it,it started right up--problem solved,right??--NOPE!--next morning he had an angry customer that was late for work--again!(and he was warnred he might get fired if he was late again!:blush: )--so he had to pay the tow to bring the truck back--after trying to scan codes and diagnose it with his computer,he learned he lacked the software for the year the truck was,so his scan tool didnt read properly--he had to borrow another one from another mechanic--he had to let the truck sit overnight before it wouldnt start again--then he put the scan tool on it,and it said"Crank Sensor"--he replaced the crank sensor,put the original module back in,and kept the "new" one as a spare-it has started every day since-- he often puts in the module in the next vehicle that has similar symptoms--sometimes you get luck--sometimes you dont...I'd rather spend TIME finding the real problem ,than money--:frown1:
     

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