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engine problems - need ideas

Discussion in 'The Garage' started by mouse, May 26, 2006.

  1. mouse

    mouse 1/2 ton status

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    The problem - engine cannot rev past 2500 rpms, and doesn't pull well when on the road.

    The engine - (1977 block/heads) 350 SBC, 882 heads, 8.8:1 compression, Comp cams XE 249H cam (.434 intake lift/.444 ex lift, 206/212 duration at .050 lift), 1989 TBI system using all stock components (most new). Cam was installed straight up.

    Diagnosis - After changing the cam and getting the heads reworked with bigger intake valves (1.84's), I encountered this problem. The engine ran well before it rounded a lobe on the old cam.

    Initially I worked with the static timing, and was able to get the engine past 3000 once I set the timing to 14* (it sounded weird, but would pull the rpm sitting in the garage). I have since swapped out the ESC controller and distributor, but no change. I received a new custom chip yesterday to deal with the engine differences, but again no change (set timing at 0*).

    Tried disconnecting the knock sensor, but that did not change anything.

    Fuel looks good in the TBI, good pattern and flow. All new wires, but dizzy cap was new in December.

    The trans is shifting high, so I will be looking for a vacuum leak on that line. I also have another coil to swap in, but I've never seen one cause this sort of problem.

    Winaldl showed a rich condition flag, but nothing else. I have a hard time decyphering the Winaldl info, so any ideas for this are welcome.

    What am I missing?
     
    Last edited: May 26, 2006
  2. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    That's a weird one. Double check all your leads are correct and that you're not timing it 180* out.
    Nothing else comes to mind as long as you're sure you got the cam timing right.
     
  3. mouse

    mouse 1/2 ton status

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    Dizzy definitely in correctly. Both #1 valves closed when pointing to #1 spark plug wire.

    BTW, it seems to break up a bit around 200 until it can't pull any more around 2500. Seems like it would be a timing or computer issue.
     
  4. resurrected_jimmy

    resurrected_jimmy 1/2 ton status

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    timing or spark breaking down under load come to mind first but when it comes to EFI you have a whole new set of things to check
     
  5. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    No codes?
     
  6. mouse

    mouse 1/2 ton status

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    Just the 45 for rich condition. I have not data logged since the new chip last night. I'll get some today.

    I'm going to do some basic things this morning - change dizzy cap, double check the trans modulator (it idles nicely, so I don't think I've got a vacuum leak), and probably swap the coil.
    And, I'll double check the firing order.

    I'll report back after all this.
     
    Last edited: May 26, 2006
  7. theperfectgarage

    theperfectgarage 1/2 ton status

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    Pull the air cleaner off and rev the throttle by hand .I bet you will see/feel air/fuel coming out of the carb inlet. Thats reversion. I'm guessing you lined up your timing gear dots wrong and your cam is out of phase. Is it a multiple position timing set?
     
  8. hack500

    hack500 1/2 ton status

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    are the plugs new? are they the right plugs?
    your throttle cable and/or linkage isn't binding up anywhere is it?

    from personal experience, if the engine gets a deluge of fuel it can act like it just hit a wall and won't rev(running so rich there's no combustion).
    other than that I dunno.
     
  9. diesel4me

    diesel4me 1 ton status Premium Member

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    might be....

    There could be a restriction in the exhaust..clogged catalitic converter,crushed pipes,muffler baffles,etc...that would limit the amount of air getting into the motor,as well as letting it out,and limit the rpm's...:crazy:
     
  10. mouse

    mouse 1/2 ton status

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    Yes, you are right, I see air coming out...I guess its back to pulling the front of the engine down.

    New plugs, wires, cap, rotor. Free flowing true dual exhaust, no cats.
     
  11. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    You could work out if your cam timing is correct by observing the valves on No.1 and at what point they open and close in relation to turning the crank. Just put a degree disc on the crank/balancer and slowly rotate the engine. Your new cam should've come with a spec sheet. It's easier than taking the front off to check.
    You will always get a small amount of air/fuel backing out of an inlet port. Some engines are more noticeable than others.
     
  12. mouse

    mouse 1/2 ton status

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    I've given the possibility of incorrectly installing the timing chain additional thought. Normally I would say that only an idiot could screw it up, but as I dwelt on the matter I remember last year when I installed this timing set that the "0" marks were very difficult to see. Specifically only the keyway mark was visible, and I had to take extra time to figure out where the tooth mark should be for the crank gear.

    When I installed the timing set this time I just installed it without any problems...How could that be? I didn't re-mark the gear.

    I will pull the front of the engine down to check, but I am relatively sure at this point that I aligned the crank key mark with the cam marking.

    I guess I am calling myself an idiot!
     
  13. theperfectgarage

    theperfectgarage 1/2 ton status

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    Hey D.W., I have been there and done that and I can assure you I am not a idiot. Therefore, by default you are not a idiot! :D If this does turn out to be what I thought I'm willing to bet it will never happen again to you.
    As I recall your cam is fairly mild lift so your prob. ok... but it is possible to kiss a valve. Do a leak down test to check for bent valves. best of luck, Cary.
     

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