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HELP suburban running rough is it the timing chain???UPDATE

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by LucasinAlaska, Feb 21, 2003.

  1. LucasinAlaska

    LucasinAlaska Registered Member

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    Hi all this is my first post and I need some help with my suburban.

    I purchased my 1989 Suburban 2500 4X4 last fall with a bad engine; the suburban had been sitting for about a year. I had a 350 long block rebuild put in and it ran rough. I installed new 3in exhaust and an oxygen sensor and left out the catalytic converter, it so needed new exhaust. I also drained the fuel tank and changed the fuel filter. I could not find the problem so I took it to my local mechanic. We put in a different TBI and it improved things but it still runs rough.

    Symptoms, When initially starting the suburban takes about 5 sec to turn over and then starts. At low idle the engine goes from normal rpms and then drops rpms then they come back up. Sometimes it will die because the rpms get too low. Accelerating the engine hesitates until the rpms come up (I dont have a tach). Upon stopping the engine runs great but after a bit of time the engine does start running rough again. It seems more like the engine is running a little rich and power is low.

    What I do know.

    My mechanic hooked it up to the computer and said NO codes came up. He also unplugged several sensors to make sure the computer worked by making sure the Check engine light came on. The first TBI the spray pattern from the injectors was not real fine, but with the new TBI the spray pattern looks real fine. The pressure from the fuel pump is 14lbs but my mechanic was wandering if it might not be going bad.

    One question my mechanic had was where are the timing marks supposed to be on this engine. Apparently when using the timing marks that are on the engine/rebuild the engine will not run (I have not looked into this yet).

    I am running out of ideas here I have looked over a lot of the past posts and cannot find anything to help me. I want my Suburban to run decient and idle well.

    Thanks you very much

    Lucas
     
  2. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    A couple more things to add. When driving down the road at 45mph the engine seems to run fine. The general trend is lower rpms rougher running faster rpms better running.

    When idleing sometimes you have to really rev the engine to clear it and get it running smooth again.

    Thanks again
     
  3. JimmyJuneau

    JimmyJuneau 1/2 ton status

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    Re: HELP with suburban. running rough and can\'t figure it out.

    What part of AK are you in?
     
  4. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    Sitka
     
  5. YtseJam

    YtseJam 1/2 ton status

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    Re: HELP with suburban. running rough and can\'t figure it out.

    Make sure the EGR isn't opening at idle. Sometimes the EGR solenoid goes bad and lets vacuum apply @ idle. Pull the vacuum hose off of the EGR valve and see if that helps. Put your finger over the vacuum hose and make sure there is no vacuum present with the engine idling. Also timing should be set to 0°s BTDC with the black and white wire connector on the drivers side by the bulkhead connector disconnected. If everything looks ok, have your mechanic scan it with a scan tool, not just a code reader. See what the IAC position is at idle. I'd say anything over 38 counts start checking for vacuum leaks. See what Map voltage is. Although it may be a little high if the engine is runnig like [censored]. See what the TPS is set at. Should be about 550 MV @ idle. See what coolant temp reads. Don't bother looking @ 02 voltage until it has gone into closed loop.
     
  6. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    YtseJam
    Thanks for the help but so far nothing. I checked the EGR and it is fine. I then went down to my mechanic and he said he has done everything that you suggested and still a no go. We both agree it is running rich. Monday we're going to switch out computers and see if that helps.

    I did find a pigtail on the wireing harness it is oval shaped and the wires are black and dark green. I think it is soposed to go onto a temp sensor on the air cleaner but I have no such sensor.

    Thanks

    Lucas
     
  7. the professor

    the professor 1/2 ton status

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    Re: HELP with suburban. running rough and can\'t figure it out.

    You said something about timing..
    --
    There are severl different procedures for timing..
    --
    Computer Carbs...unplug the connector with 3 wires comming from the dist..and check the timing.
    --
    TBI's are different...usualy you jumper the last two pins on ALDC under the dash..and check it there..(same way you check for codes)
    --
    The data plate in the engine compartment may list the procedure..you may need a manual
    --
    --
    With no codes, I doubt if it running rich..it would set a code..

    One possiblility for rich running without a code:

    The diverter valve might be stuck or leaking, letting upstream air in when warm...causing the engine to run rich...

    The diverter valve, routes AIR pump air upstream into the exhaust manifolds during open-loop (cold engine)..to warm the O2 sensor and heat the cats...

    When warm, the diverter directs air to the aircleaner..doing nothing.

    When you get upstream air in closed-loop (warm engine), it causes the O2 to read a lean mixture and the computer richens up to correct...

    It will not always set a code

    You could also have a bad O2 sensor

    Also check for a plugging fuel filter...replace it its cheap..

    Your tech must not be familiar with computer cars..

    The EGR idea was good...It may be working, but be leaking from carbon build-up..Pull it and pour water or light oil in one side and see if it comes out the other..it should be gas tight..

    It might not be computer related at all

    You could even have a bad ign wire or bridged plug (pull and inspect)

    A scope would be the easy way to find that, more dfficult without

    These are just a few suggestions, with out more data, it is difficult to diagnose...

    /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     
  8. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    professor,

    When I took it in to my mechanic he initially said the plugs looked like the engine was running rich.

    To discribe my exhaust it goes to the headers to a Y pipe, a straight pipe to the muffler then out the tail pipe. I just replaced the Y pipe and the rest on back. I also put in a new oxygen sensor.

    The housing for my air filter only has the hole for heat via the heat riser. There are no other holes or sensors in the air filter housing.

    I had also just replaced the fuel filter,cap and rotor.

    I checked the EGR valve and I found no vacuum at idle.

    I was looking at the engine some more tonight and pulled the PCV valve tube out of the TBI and the rpms picked up and the engine ran real smooth without any hesitation. I cleaned the PCV valve and put everything back together and it started running rough again.

    Sitll ????????

    Monday I will work on the timing and put the new computer in.

    Many thanks

    Lucas



    professor just let me know what other data you need.
    Thanks
     
  9. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    An update on whats going on.

    We tried a diffrent computer and that didn't do it.

    My mechanic worked on my Suburban for quite a few hours yesterday and tried several diff things.
    Checked TDC on timing and that lined up.
    Tried a new MAP sensor.
    Checked EGR.
    Tried a new distributer<sp>
    Checked compresstion-all good
    Right now we have a diff. TBI still installed

    My mechanic so far has went thru everything on the engine and has come to one conclution. The timing chain was put on wrong from the place we got the rebuild from. Is this within resoning?? The rough running, poor idle, no power, low gas milage??? I don't even like to drive it because it runs so rough. Let me know because I don't want to have him rip everything down for nothing.

    Thanks

    Lucas
     
  10. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    A few more things.

    The fuel pump is putting out sufficient pressure. I'm also on my second fuel filter.

    There is a new O2 sensor.

    The exhaust smells like the engine is running rich.

    New plugs all around.
     
  11. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Re: HELP with suburban. running rough and can\'t figure it out.

    DO NOT BRIDGE THE A/B TERMINALS TO CHECK TIMING! This will fry your computer! You only do that without starting the engine to check for codes!

    Anyway, running rich is something in the computer and sensor area. If the timing chain was on wrong from the place of rebuild, the people who did it are COMPLETE morons. It sounds like he thinks the chain is off a tooth or so, which is possible. If you are not showing any codes, it could very well be the computer itself. It has to be either EGR or O2 sensor, but you say those things have been tried. I'd still push for those, just for the fact that those control the metering of fuel, specifically the O2 sensor. This is a tough one, but I have a similar deal after changing the engine. Mine will be cruising, and my engine light comes on and says codes for running rich and ESC. Shops don't know what it is... I'll pull for you, but I imagine, if it was really running rich, you'd have a rich code. Make extra sure ALL sensors are plugged in and working. The Temperature sensor to the computer when unplugged made my truck run rough and have a wavy idle.
     
  12. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    Here's one more thing I thought of tonight while fiddleing with the burb.

    When my mechanic checked TDC on the engine the tick mark lined right up with 0 degrees on the timing cover.

    Now the funny thing (I don't do the timing my mechanic does) according to my mechanic the engine barely runs when setting the timing where it should be. The engine runs better with the timing set somewhere else. I don't know how far off it's set and I forgot to ask.

    So with this info is it likely the chain is off a tooth or so on the timing??

    Thanks

    Lucas
     
  13. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    ttt
     
  14. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Re: HELP with suburban. running rough and can\'t figure it out.

    That sounds like a good possibility if it runs better with different timing. You've checked everything else, might as well dig in and check the chain...
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    Not likely the chain is off the tooth. I've seen GM's with the nylon gear worn, it's really frustrating...you set timing, it fires, runs, dies, and timing is all wrong again.

    You can check timing chain "slop" by popping the distributor cap off and turning the crank...the rotor should move with the crank, with very little "lag".

    I would imagine that a "loose" chain would give intermittent problems...while running at a constant speed, there would be no "slack" in the chain, but changing engine speed (such as decel then accel) you might notice some engine "problems" such as sputtering or lack of power, but it would clear up pretty quickly.

    Does your mechanic know how to set the timing? Injected setups need baseline timing set without ECM input, then you hook the ECM lead back up and let it do its thing as I recall. I'm sure that timing an injected GM of your vintage has been covered before, a search in a few places (google, here, etc) probably will turn up the correct procedure, and you can make sure your mechanic is doing it that way.

    Of course, if you find the procedure, you can do it yourself for free, and know its done right.
     
  16. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    Dorian,

    The engine rebuild I got had a new camshaft timing gears and chain so I really can't see it being slop.

    As far as my mechanic. He is the best there is and very few things stump him and this happens to be one. I'm sure he knows how to do the timing I've seen him work on other Chevy TBI trucks.

    The company that did the long block rebuild is a very reputable one even in these forums. I don't want to name them until I do find out the problem do to the fact it could look unfavorably of the company.

    Thanks

    Lucas
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    If the "setup" is new, then I see what you mean by being off a tooth. You've really got to be ignorant to miss the alignment on them when assembling, but in mass production, or in a hurry, I can see it happening.

    I'd still research how to time it myself if I were suspecting that as a cause. If you know it's being set correctly, yet is still incorrect, then you've at least eliminated one issue.

    I know the direction of distributor rotation, doesn't mean I haven't done it backwards before /forums/images/graemlins/smile.gif
     
  18. RustBuket

    RustBuket 1/2 ton status

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    Re: HELP with suburban. running rough and can\'t figure it out.

    I'd check the chain. But hey, what do I know about TBI? Not very much at all! :lol
     
  19. LucasinAlaska

    LucasinAlaska Registered Member

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    Re: HELP with suburban. running rough and can\'t figure it out.

    UPTATE

    Well here's the lowdown. My mechanic set the #1 pistion TDC and pulled the front of the motor apart. Low and behold the DS timing mark was pointing straight up BUT the camshaft mark was straight up too/forums/images/graemlins/shocked.gif. (Has anyone ever heard of this????) Well it was retimed with the marks facing each other and..... it would not run. So monday <tomorrow> the rebuild shop will get a call from us and figure out whats going on. I'll keep you all informed.

    BIG letdown. /forums/images/graemlins/frown.gif
    Thanks

    Lucas
     

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