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Need Help Solving a TBI Engine Problem - SOLVED

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Gandolf, Sep 24, 2002.

  1. Gandolf

    Gandolf 1/2 ton status

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    My '89 TBI engine has been running great. It passed smog a month ago with great numbers. The engine has 164K miles on it and only burns 1 quart of oil every 3000 miles. It had been 30K miles since the last tune-up, so I decided it was time to do one. Yesterday, I put in new Bosch platinum plugs, plus a new cap and rotor. With the plugs out I did a compression test and all cylinders were 145 to 155. I didn't replace the wires, but during the cap swap, I decided I would do that soon. I also tightened up the bolts that hold the TBI unit to the manifold, and snugged up the torx screws in the TBI. Most of them were fine and I was careful to not overtighten anything. When I was done with everything, the truck started right up, and when I drove it, I could immediately feel the results of the fresh tune-up. I drove about 2 miles to a freeway on-ramp and then floored it. It accelerated about 3 seconds, stumbled once, with a backfire thru the TBI, and then accelerated like normal, thru all the gears, up to 75 mph, where I backed off due to traffic. It was running strong but I was wondering why it stumbled. I stopped for gas and then drove home. It ran like normal.

    When cold, the engine will usually start with just a tap of the key, but this morning it fired once and then required cranking for about 15 seconds before it began to start. When it was starting it ran rough, like it was flooded, running on a few cylinders in the beginning, and then adding more as the engine cleared. When it was running on all 8, I started driving and everything seemed normal. I drove about 15 freeway miles at 65 mph with no problems. I then exited one freeway to get on another, and when I accelerated, it started to stumbling again, backfiring thru the TBI. It cleared and I continued on, but after a mile or so, it stumbled again and it was clearly getting worse. I decided to take the next exit to get to a gas station so I could check things out. As I got to the end of the exit and made a turn, it was barely running and I had no choice but to pull to the side of the road. As I came to a stop, it was even sounding kinda like it was dieseling . The engine temp when I exited the freeway was a normal 190F. Now, stopped on the side of the road, I made multiple attempts to re-start it but it would just stumble and backfire thru the TBI. It would kinda start on a few cylinders, but it would never clear the other cylinders enough to run on it's own. Eventually it wouldn't fire on any cylinders.

    I checked for crossed wires but they were all correct. When a stranger stopped (in a Blaser S-10), I had him crank it while I looked into the TBI. I saw good injector spray patterns and ruled out a clogged fuel filter or fuel line (I may check that again). I then checked for disconnected vacuum lines, plugs on sensors, anything and everything I could find, but everything looked normal. I double checked everything I could have bumped while doing the tune-up. I could find nothing wrong, so at this point I had it towed home.

    Tonight I bought new plug wires and swapped them in, but they made no difference and it still doesn't start. The starter spins it good but it doesn't even fire. My next move is to replace the coil since it's the original. If a new coil doesn't fix it, I'll check for codes and see if anything is there (even though the check light never came on). If that doesn't accomplish anything, I guess I'll be looking for a bad ignition module, EGR, or maybe a plugged cat converter. What could cause the catalytic converter to suddenly plug or go bad?

    I'm running out of ideas and may be missing something. Have any of you had this happen, or do you know what is causing this problem? I could use some fresh ideas. Thanks in advance.

    BTW. I called my friend Rene (tRusty) during this adventure and he helped me think it thru. He also provided the firing order so I could check for crossed plug wires. Thanks Bro, you da man!
    Rod, (Savage1) also called to offer help. Thanks amigo! /forums/images/icons/cool.gif

    This problem is gonna teach me a lot. Here's what I have learned so far:
    1. Get a fuel pressure guage.
    2. Put my repair manuals in the Blazer, permanantly!
    3. Carry more tools and spare parts.
    4. Add towing to my insurance. (the tow cost me $125 today)
    5. Cell phones are great! Today would have been a total nightmare without a cell phone.
     
  2. wayne

    wayne 3/4 ton status

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    Re: Need Help Solving a TBI Engine Problem

    1. I doubt it is the EGR valve.
    2. Is it getting fire to the plugs?
    Not really sure what to tell you but if you are getting fuel then check to make sure the plugs are getting spark.
     
  3. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    Re: Need Help Solving a TBI Engine Problem

    Make sure they sold you the right plugs and that the gap was correct.. A napa dealer here sold me the wrong ones for mine.. I gapped them and put them in.. It did fire right up.. But it ran like crap.. Just shooting out ideas...Dan
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Re: Need Help Solving a TBI Engine Problem

    I am pretty certain that if you get those platinum plugs out of there and install something other than platinum your problem will be gone. Some vehicles just don't like the platinum plugs and yours is probably one of them. I personally have had very good luck with the NGK V-Power plugs.
     
  5. jjlaughner

    jjlaughner 3/4 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Tried platium plugs OK for about a year, tried truck plugs from champion and fouled out one right away, Went back to AC DELCO plugs (got a step hotter than the book said) and its all better now. Make sure your cap is back on right and all the wires got snapped back on tight. I've actually pulled a clip off the wire in the boot... you can't see it and the boot feels like it snapped on. I also done the Accell super coil and street wires after the new plugs and it made worlds of difference.
     
  6. Thunder

    Thunder 3/4 ton status

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    Re: Need Help Solving a TBI Engine Problem

    I with 4X4 high. I have had nothing but trouble with bosch platinium plugs. I tried then in 2 of my vehicles and was not impressed. But I dont think thats your problem.
    It sounds like it may be the dist module. Pull it out and hav it tested at a auto parts store.
    Before you start replacing parts. Check the codes.
    Also you should add a good Scanner to your must have list. It will save you a lot of money in the long run.
     
  7. milspecjimmy

    milspecjimmy 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    i had the same problem about a year ago, and it was this. i bought plugs from napa and put them in, the truck ran fine till i mashed the throttle, and it felt like a misfire. so i got out the ir temp gun and shot it at the headders. sure enough 6 and 8 were colder than the others. so i yanked the plugs, turns out that all the plugs were too long of a reach, and were directly in the hot part of the combustion chamber, and melted, they were still sparking at low speeds , and constant speeds but when you floor it the extra air and fuel blew out the spark.
    good luck
    ~~~jeff
     
  8. Skigirl

    Skigirl 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Hi Mark! I haven't the faintest idea what could be wrong, just wanted to say hi, and I'm glad you weren't in Barstow at the time. /forums/images/icons/wink.gif Wish I'd have been closer to help.

    Thanks for the list, I've added a fuel pressure gauge to mine.
     
  9. monte0172

    monte0172 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    The bosh platinum plugs suck especially in engines with alot of miles. Go buy you some good ac delco plugs and your problem should be solved!!! I have had the same probs more than once and will never buy them again. Now ac delco makes platinum plugs but they are pricey but worth it. Hope you get it going.
     
  10. Gandolf

    Gandolf 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Thanks everyone for the replies. I'm going to replace the plugs first and go from there. I'll post the results.
     
  11. 4x4Freak

    4x4Freak 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Did you gap the plugs? The Bosch platinums arent supposed to be gapped because the tip can break off. I've been running em in two of our trucks and have had pretty good luck so far. Our 49 Jeep truck with a Chevy 283 fouls plugs pretty easy and the Bosch are the only ones that will work halfway decent in it.
     
  12. Blue85

    Blue85 Troll Premium Member

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    Re: Need Help Solving a TBI Engine Problem

    Definately backtrack and try to put back each thing that you replaced. It ran fine, you changed some stuff and now it runs bad. Odds are good that it's something you did. Try putting the old plugs back in. Take a look at the new ones when you pull them out.
     
  13. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Re: Need Help Solving a TBI Engine Problem

    It could be lots-o-things but here are some items to check:

    Vacuum Leaks: Spray carb cleaner around the base of the TBI and along all vacuum hoses. If the rpm's change you may have a leak/bad gasket. You tightened up items that may have caused a old hardened gasket to crack and allow air in, and/or you may have moved/nicked/cut/etc a portion of vacuum line causing problems. Considering the mileage, it would probably be a good idea to replace all the vacuum lines and eliminate them as a source for your problem and you shouldn't have to worry about them for a long time to come (plus it's easy to do).

    Replace the platinum plugs with "regular" plugs. The platinums are great for the newer style motors, which run hotter/cleaner. The platinums don't perform well in older style lesser efficient motors (know from first hand experience).

    Check all electrical connections. Probably not a bad idea to clean them with "electrical contact cleaner" $4, pipettes (25 cents apiece at the local arts/crafts store), and then put dialectric grease in the connectors before reassembling $4 for a good size tube.

    Good luck and let us know how you make out.
     
  14. BoyNamedSue

    BoyNamedSue Registered Member

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    Re: Need Help Solving a TBI Engine Problem

    I agree with leadfoot.


    (thanks leadfoot for typing all that out /forums/images/icons/grin.gif )
     
  15. Gandolf

    Gandolf 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Update:

    I replaced the plugs with AC Delco's and it still won't start.
    I have replaced most or all of the vacuum lines within the last year.
    There are no fault codes. I only get code 12

    Here's a clue. I was getting spark yesterday, even after the rough running. I'm not getting any spark now, so I will probably put in a new coil next.

    /forums/images/icons/tongue.gif
     
  16. 90K5

    90K5 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Check the ignition module and the pick up coil too.
     
  17. rh88k5

    rh88k5 Registered Member

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    Re: Need Help Solving a TBI Engine Problem

    check your pick-up coil in the dist. It may test ok with an ohmmeter, but dont trust it, the insulation could be breaking down. It only costs ten bucks and its piece of mind knowing its good.
     
  18. Gandolf

    Gandolf 1/2 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Before I bought a coil, I decided to get out the books and do the proper test. I removed the coil and tested it the way the Haynes Repair Manual said to do it. It PASSED the Haynes test method. From the thread suggestions, I then decided to read up on the ignition module and pick-up coil tests. I read the Haynes information, and decided to cross check the information with the Chilton Repair Manual. While reading in the Chilton book, I saw their coil test proceedure and noticed it was slightly different from the Haynes test method. I got out the ohm meter and coil, and tested it the Chilton way. It FAILED the Chilton test method! I got the Haynes book back out and re-tested the coil. It PASSED! WTF? /forums/images/icons/tongue.gif

    I went ahead and got a new coil...an MSD Blaster (GM External HEI PN 8226). After installing the new coil, the Blazer fired up instantly. I took it for a test drive and it performed just fine. Problem solved. /forums/images/icons/smile.gif

    Now, I am a curious guy and would really like to know why the coil failed the way it did. I've NEVER had a coil go bad on me before. Did I do something to cause it to fail or was this just a coincidence? That coil failed, in a progressive way, in the first 25 miles after doing a tune-up. I find that really odd. Something must have triggered the failure. Does anyone have a theory as to what caused the coil to fail the way it did? BTW, I'm glad I got those platinum plugs out of there. Thanks to everyone for the input. /forums/images/icons/cool.gif


    Note to self:
    Replace the ignition module and pick-up coil ASAP.
    Carry a spare coil, ignition module, pick-up coil, cap and rotor.
     
  19. wayne

    wayne 3/4 ton status

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    Re: Need Help Solving a TBI Engine Problem

    Nothing you did probably caused it to go bad. It was probably going bad to begin with and just by luck it went when it did. /forums/images/icons/tongue.gif I did not think the plugs caused it because unless all 8 fouled at once it would probably start. Hell my 90 was running on 5 of the 8 when I got it. /forums/images/icons/crazy.gif
     

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