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TBI Blues.....

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by ford_assassin, Mar 22, 2004.

  1. ford_assassin

    ford_assassin 1/2 ton status

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    Hey guys, not a K5 question, but still a Chevy.

    This one has me stumped.

    Here it goes. My wife's '91 Caprice Classic is having issues. The car has a 5.0 (305), 700R-4, 3.42 posi rear, and the normal 2bbl TBI setup you'd find on some Camaros, and all '87-'95 trucks. The original motor, trans, and rear end all have just under 300,000 miles on them. Until now you'd have never known or guessed it had that many miles on it because it still runs great. Up until this problem, I have only changed the water pump, Alt, knock sensor, fan clutch and fuel pump.

    It all started in November of '03. My wife came to me and says that the car likes to fall on its face ramdomly when taking off from a light. I check for codes first and nothing is stored. So I change the fuel filter, run a few bottles of "fuel injector cleaner" through it and nothing changes and it still does it on occasion just like before.

    So, some time passes and nothing really gets worse and to be honest I didn't have the money to mess with it anyway. Then last week she wakes me up one morning and says it won't start. She also tells me its been giving her "check engine" lights on her way home for the last few days and forgot to mention it to me (women!). Again, I check for codes with my scanner and to my suprise....nothing is stored. That in itself is odd to me why she would she a light, but the ECM didn't store it.

    Anyway, I crank the motor for a good 30 seconds and it finally starts and idles very smooth once running. I rev the motor alittle while still in PARK and the motor stumbles, everytime I rev.

    Doesn't matter if I do it slow or fast, it stumbles just off idle. I took it for a drive and had it die on me when leaving a stop(s) if I gave it more than the tinyest amount of peddle to get moving. I was able to get to 65 mph, once it got to speed it drove fine.

    I get it home and do a complete tune up. I changed the cap, rotor, wires, plugs, change the oil, air filter, another fuel filter, and thermostat. No change.

    Then I changed the ignition coil (external), MAP sensor, tested the ignition module, checked the timing, and checked the fuel pressure after the fuel fiter (near the pump) and at the TB, both inline, both read 12 psi. The book says it needs to be between 9 and 13 psi. That means its its not the pump or the fuel pressure regulator, right?

    Still no codes either.

    At this point I am totally stumped. If any of you have any ideas, please tell me. If you need more info that I didn't mention, just let me know.

    Thanks guys.
     
  2. k20

    k20 3/4 ton status

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    Got a scanner? See what the temp sensor is reading. Ive had 2 go bad, and both times they did really weird things
    one time it made it go completely lean pain to start, finally no start, other stuck cold and kept floodin it out. If have a scanner is the O2 sensor putting anything out ?
     
  3. Hossbaby50

    Hossbaby50 3/4 ton status

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    Check the reading from the TPS (should be .540 volts or so). Might check into pulling and cleaning the IAC motor, check the O2 sensor. Like mentioned above check for the temp sender.

    Check for vacuum leaks too, you never know.

    Harley
     
  4. ford_assassin

    ford_assassin 1/2 ton status

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    I already checked for vacuum leaks, none found.

    I'd consider the temp sensor an issue, but the sensor isn't even used during the starting process. So it would have nothing to with the 30 second starting problem. It would also trip a code after 5 mins of run time if the ECM didn't get a voltage reading.

    The car has the same problem of hard/long starting and stumbling hot or cold, open and closed loop operation.
     
  5. k20

    k20 3/4 ton status

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    actually the temo sensor does have something to do w/ start. My first one that went bad got stuck on 210deg. It wouldnt give the engine any gas because it should lean it out when it gets that warm, and vice versa. It doesnt quit sending voltage, it just sends the wrong voltage.
     
  6. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    actually the temo sensor does have something to do w/ start. My first one that went bad got stuck on 210deg. It wouldnt give the engine any gas because it should lean it out when it gets that warm, and vice versa. It doesnt quit sending voltage, it just sends the wrong voltage.

    [/ QUOTE ]

    No disrespect intended, but I disagree.

    It would be different if the car was already in closed loop operation, which it isn't when still cold, otherwise you would be correct. But the computer doesn't even look at the coolent temp sensor (the one on the water neck) until the motor is already running. However, just to be sure I checked it and its working normally.


    Also, if the ECM thought the car was running hot it would fatten the mix before running lean would only increase the heat. Just like if the O2 sensor dies, the ECM defaults to "rich" because lean could cause the motor to run hot and/or burn a valve/piston.


    Regardless, I am really thankfull for the replies. Honestly I am really tired of dicking with it so its going to the dealer on Thursday. I'll let them scratch their heads over it and if they can't find it, I don't owe a cent.
     
  7. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    [ QUOTE ]
    actually the temo sensor does have something to do w/ start. My first one that went bad got stuck on 210deg. It wouldnt give the engine any gas because it should lean it out when it gets that warm, and vice versa. It doesnt quit sending voltage, it just sends the wrong voltage.

    [/ QUOTE ]

    No disrespect intended, but I disagree.

    It would be different if the car was already in closed loop operation, which it isn't when still cold, otherwise you would be correct. But the computer doesn't even look at the coolent temp sensor (the one on the water neck) until the motor is already running. However, just to be sure I checked it and its working normally.


    Also, if the ECM thought the car was running hot it would fatten the mix before running lean would only increase the heat. Just like if the O2 sensor dies, the ECM defaults to "rich" because lean could cause the motor to run hot and/or burn a valve/piston.


    Regardless, I am really thankfull for the replies. Honestly I am really tired of dicking with it so its going to the dealer on Thursday. I'll let them scratch their heads over it and if they can't find it, I don't owe a cent.

    [/ QUOTE ]

    No disrespect but your assumption is wrong. The ECM DOES use a temp sensor reading during cranking. /forums/images/graemlins/yikes.gif TBI doesn't have a choke, so it has to inject extra fuel during cold starts and the extra amount is determined by ENGINE TEMPERATURE. /forums/images/graemlins/thumb.gif You car should have two temp senders, one for the gauge (or idiot light) and one for the ECM. /forums/images/graemlins/cool.gif
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Money spent on parts that didn't fix the problem could have bought you a manual for the car. /forums/images/graemlins/whistling.gif

    The long starting could be the fuel pump relay (although 30 seconds of cranking is a LONG time to crank before the oil pressure switch kicks in) and as suggested already, I'd look at TPS for the throttle issue.

    Of course, a manual would show you exactly what steps to take, how, and what kind of values to look for.
     
  9. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    Money spent on parts that didn't fix the problem could have bought you a manual for the car. /forums/images/graemlins/whistling.gif

    The long starting could be the fuel pump relay (although 30 seconds of cranking is a LONG time to crank before the oil pressure switch kicks in) and as suggested already, I'd look at TPS for the throttle issue.

    Of course, a manual would show you exactly what steps to take, how, and what kind of values to look for.

    [/ QUOTE ]

    This why I don't like posting stuff on this board. Too many assholes with nothing better to do than run their mouths.

    I have about 3 'manuals' smart guy, none helped. Oh, guess what? I dropped the car off today and even the dealer can't find the problem with all their fancy 'manuals' and tools I don't have. So I guess I didn't do such a bad job after all huh? /forums/images/graemlins/ignore.gif

    Do yourself a favor and go live in the woods and stop bothering everyone. /forums/images/graemlins/waytogo.gif
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    You know why I don't like posting on this board? Because idiots like you won't ask for help first, instead spend hundreds of dollars in parts, THEN come on here and bitch about how you can't figure it out and expect someone else to. When someone does offer help, they get called names because you don't like what you hear.

    If you were half as smart as you think you are, you'd have figured this out yourself, instead of coming on here acting like a crybaby when someone points out your faults.

    If you think a "dealer" is smarter than you are, I pity you.

    You know, before, I didn't like the way people like MJ (just as an example, not the only one I'm sure) post info, but now I see why they do. If you add anything more than data, people fly off the handle the first time they don't like what they hear. Just because you don't like how it was worded, doesn't mean there isn't good info.

    So on that note, screw you. I think you are the only one on the board at this point I won't be responding to. I don't typically hold grudges, but a personal attack because you are incompetent, and insecure with your own self, will certainly make me remember you. Good luck with your atitude.
     
  11. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    So on that note, screw you. I think you are the only one on the board at this point I won't be responding to. I don't typically hold grudges, but a personal attack because you are incompetent, and insecure with your own self, will certainly make me remember you. Good luck with your atitude.

    [/ QUOTE ]

    Ohh, don't do that. Your hurting my feelings. /forums/images/graemlins/rotfl.gif

    Free advise, don't let your mouth overload your ass and you have alot better time making friends.

    Tell your wife and my kids I said Hi. /forums/images/graemlins/waytogo.gif
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Don't worry, I've got better things to do than waste my time attempting to help those that won't accept it.
     
  13. ford_assassin

    ford_assassin 1/2 ton status

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    It just keeps getting better and better.

    Dealer #2:
    Bob Williams Chevrolet called about a hour after I dropped off the car (around 9 am). They told me its the fuel pump, I was pretty quick to comment that I checked the pressure at idle and under load while driving and it always maintained pressure at 12 psi.

    They insisted that was the problem and said if it wasn't, they would just pull it back out and not charge me.

    4:30pm rolls around and I am just signing off of work. My cell phone rings, guess what? "Mr. Bright, we changed the fuel pump, but its still doing the same thing. We have three other techs helping your guy troubleshoot the problem right now."

    At this point I am laughing to myself over the whole thing.

    He tells me that they aren't going to charge me any extra if they find the real problem with the car. He also adds that will be keeping the car another day.

    Six mechanics, two different shops, and still a sh!tty running Caprice.

    What a great day.
     
  14. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Strange... no one mentions worn timing chain or worn distributor.

    No codes... that worries me as well. Any chance you have another Chevy ECM handy in another vehicle that you can use for testing? I've seen similar behavior in cars with ECMs failing (not storing codes, running like HELL, etc).

    Finally, have you changed the oil lately? Any material in the oil? Even a slight silver tint could suggest failing bearings (esp. at 300k mi.! /forums/images/graemlins/yikes.gif). The knock sensor could be picking up knock, and severely retarding timing when under heavier load than when crusing (IIRC the ECM will retard timing 4* at a time until the knock goes away).

    Just a few off the wall suggestions. /forums/images/graemlins/dunno.gif Hope it helps.

    -Dan
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Now don't smart off to Dan, jackass. You already pissed off Dorian who is about the most helpful guy with EFI around. You're down to a handful of remaining members that really know this stuff and Dan is one, so before you shoot off at the mouth, think about what they have to say.

    That said, without any codes, I'm thinking you've got a mechanical problem as well. Start with a compression test and a leakdown test if possible.
     
  16. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    Now don't smart off to Dan, jackass. You already pissed off Dorian who is about the most helpful guy with EFI around. You're down to a handful of remaining members that really know this stuff and Dan is one, so before you shoot off at the mouth, think about what they have to say.

    That said, without any codes, I'm thinking you've got a mechanical problem as well. Start with a compression test and a leakdown test if possible.

    [/ QUOTE ]
    Did someone hear something? All heard was blah, blah, "I'm a dumbass!"

    Seriously Tim, when you will learn to shut up? I have zero interest in ANYTHING your moron 18 year you brain has to say after you last stunt, not to mention this one. I've asked you before, PLEASE DO NOT RESPOND TO ANY OF MY TOPICS.
     
  17. ford_assassin

    ford_assassin 1/2 ton status

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    [ QUOTE ]
    Strange... no one mentions worn timing chain or worn distributor.

    No codes... that worries me as well. Any chance you have another Chevy ECM handy in another vehicle that you can use for testing? I've seen similar behavior in cars with ECMs failing (not storing codes, running like HELL, etc).

    Finally, have you changed the oil lately? Any material in the oil? Even a slight silver tint could suggest failing bearings (esp. at 300k mi.! /forums/images/graemlins/yikes.gif). The knock sensor could be picking up knock, and severely retarding timing when under heavier load than when crusing (IIRC the ECM will retard timing 4* at a time until the knock goes away).

    Just a few off the wall suggestions. /forums/images/graemlins/dunno.gif Hope it helps.

    -Dan

    [/ QUOTE ]

    Thanks for the suggestions Dan, I too thought about the dist, but they said the "scope" didn't pickup anything.

    I change the oil (among other things) when I was first hunting for the problem. Nothing eventfull. I still have 30 psi when cruising, and about 10-15 psi @idle. I use 10w-30 in the winter and 15w-40 in the Summer.
     
  18. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    10-15psi at idle is getting down there IMO. At 300k, you could very likely be chasing this one around and around for some time.

    As a last ditch effort before getting rid of that car, I'd consider finding another Chevy 305/350 that you could use for swapping parts for testing. Most electronics can be tested out at Autozone for free. Compression, bearing clearances, and general wear and tear on the motor though require inspection. Again, IMO - you're probably better off just dropping in a newer engine or getting a new car for her. /forums/images/graemlins/thinking.gif

    -Dan
     
  19. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    Did someone hear something? All heard was blah, blah, "I'm a dumbass!"

    Seriously Tim, when you will learn to shut up? I have zero interest in ANYTHING your moron 18 year you brain has to say after you last stunt, not to mention this one. I've asked you before, PLEASE DO NOT RESPOND TO ANY OF MY TOPICS.

    [/ QUOTE ]

    My junk all runs and drives, I'm not the one whining that I don't know how to fix my own simple problems.

    Nor am I 18.

    And as for my intelligence, well, at least I can form a complete sentence.

    Normally I wouldn’t waste my time even replying to such nonsense, but for someone that can’t even form a complete sentence, much less wrench on a vehicle, to question my intelligence, is pretty damn pathetic if you ask me.

    That said, I won’t offer you any additional technical advice. I deal with jackasses with you all day long. I’m glad to sell them all the electrical parts that they desire for me to sell them. I simply inform them of the return policy, offer to help them solve the problem, and typically they’re stupid and just buy the parts, only to act surprised when I tell them that once installed, they own them, whether they like it or not.

    Maybe your local auto parts store will put parts out on, “Loan” to see if it fixes the problem if you ask nicely. /forums/images/graemlins/rolleyes.gif

    Or, you could get out a multimeter and learn to fix something the right way. Nah, who'd want to do something like that. /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/whistling.gif
     

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