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GM 290HP Performance Parts engine problem

Discussion in 'The Garage' started by RedBrute, Apr 15, 2005.

  1. RedBrute

    RedBrute 1/2 ton status

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    Installed a new GM crate engine in my sons "79 K10 this week. Got the engine running, did the breakin proceedure and took it for a ride. Engine is an absolute DOG!!!! The first indication of trouble was the engine needs a ton of initial advance to stay running as well as a the idle speed screw turned in almost till the spring bottoms out. If I try to set the timing to stock spec 8 deg before it barely stays running. Putting it in drive kills it. I verified TDC at the piston, valves closed, rotor pointing at #1 on cap etc. The dist is a remanned unit from napa and worked fine on the old engine, tried the original carb on it then swapped a Jegs Hotrodded Qjet on it with no improvement. It drives OK other than the rediculously high idle it needs to stay running in drive, but when you punch it, it doesn't accelerate, just continues on and slowly starts to load up. The original carb does the same. The manifold vac at "idle", 1500 rpm or so, is 22 and the ported vac is 15. The vac can on the dist does advance when I pull a vacuum with my MightyVac, the advance weights are free. I'm at a loss as to what the problem is. I plan on pulling the timing cover tomorrow to verify the cam is installed correctly. Does anybody out there know for sure if a SBC can even run if the cam is off a tooth either way? I'd like to have this fixed by sunday so he can drive back to school in Conn.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Are you sure there isn't a vacuum leak somewhere else?

    Only staying running with a high idle and bad performance off the line, among other things, is exactly the problems I had when there was a vacuum leak.

    Your vacuum numbers seem pretty high, but the only reason you can get those readings is because the idle is cranked up so high.
     
  3. Fierospeeder

    Fierospeeder Banned

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    double check all your spark plug wires. You might have put them in the wrong order.
     
  4. mojo-jojo

    mojo-jojo 1/2 ton status

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    The ported vac line should have no signal at idle, I guessing it's because the idle is set so high. Sounds to me like a major vacuum leak. Is the EGR valve hooked up correctly? I bought a used 350 years ago that had a bad block off plate on the EGR and it had the same symptoms.
     
  5. RedBrute

    RedBrute 1/2 ton status

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    I'm dead positive there isn't a leak from the top side of the engine, It has an edelbrock performer intake I got off ebay. Ive sprayed the intake down with carb cleaner twice very thoroughly, especially at carb base and manifold/head joint at a low idle and didnt find a leak. It has an EGR on it, but if I manually actuate the EGR, it drastically affects the idle both at a lower speed as well as higher and I have the EGR vac line disconnected and plugged for now. Plug wires are correct, it hits on all 8. Also with both carbs set at "bench settings" the idle is low and I would think that a vacuum leak would result in a high idle initially and cause me to back the idle speed screw out to lower the idle. Also I forgot to mention. With all the timing I've got cranked into this, the timing mark shows up under the water pump inlet! say about 11:00 as you face the balancer. Even with this much the engine doesn't ping at all! seems like I should at least be able toget some kind of spark knock out of it. I'm baffled.
     
  6. 79Stomper

    79Stomper 1/2 ton status Premium Member GMOTM Winner

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    I ran into the same problem when I put my GM Crate motor in. I set the initial timing to factory specs and had the same symptoms. Idled fine but when you started to get on it it would stall out. Thought it was my carb so tuned it but wasn't t. Ended up being my timing. I had to modify the vacuum advance in the distibutor to get timing set right. I believe I was offset by something like 37* BTDC (if I recall correctly). Took me a week to get it running right but just takes patience.
     
  7. fatbob

    fatbob 1/2 ton status

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    This is just a thought buttttttt on my old engine the timing indicator was towards the drivers side. When I put another newer engine in, the timing indicator was at 12 o'clock. Well I put all my old acessories & brackets on and couldnt get it timed right. The harmonic balancer had the mark setup for the 12 o'clock indicator, and my old style timing gear cover had the indicator off to the side. My solution was to pull the valve cover and get it on TDC. Look to make sure the mark on the balancer was straight up. Then make a NEW mark on the balancer where the indicator lines up with TDC. It may not be the best way but it was good enough to get me running.
    This may or may not be your problem, but it is worth checking out. :dunno:
    Good luck
    Bob
     
  8. Fierospeeder

    Fierospeeder Banned

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    i dont really mean if they all fire, which is a good thing thou. But did you put them to the corresponding cylinders?

    Or check the crate motor manual and see if they didn't change the firing order. It is possible to have a different engine design.
     
  9. RedBrute

    RedBrute 1/2 ton status

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    I have the same situation on this engine, the timing tab supplied mounts on the drivers side of the cover but the original timing tab is at 12:00 position and the mark on the harmonic balancer is also at 12:00 so I am timing it accordingly. So far nobody has stated that a chevy small block cannot run with the crank/cam timing off a tooth so today I'm pulling the timing cover and verify the timing marks on crank cam are correct.
     
  10. muscle

    muscle 1/2 ton status

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    this is my guess also
     
  11. 1977k5

    1977k5 3/4 ton status Vendor

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    Make sure you didn't hook the EGR up to a source with constant vacuum (it is supposed to have a valve in the vacuum line so it doesn't work all the time). Having the EGR on at full will make an engine run really bad.
     
  12. RedBrute

    RedBrute 1/2 ton status

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    Finally got this sorted out and running great now. I pulled the timing cover and the cam timing is correct. I went back to the distributor and found I has it off a tooth. :o I timed it and installed the original Qjet and it goes like a sumbitch now. There is definately a problem with the Jegs Qjet, it just falls flat and blows black smoke when the pedal is floored, the original carb works fine. Amazing what a full nights sleep and a clear head can do. I do think that the dist needs more total advance, I get about 11 degrees mechanical, maybe 6 on vacuum advance. Add in the initial 8 degrees and all I have is 25=26 total. I think the engine would be happier closer to 30 degrees total.Also Dorian was dead on about my vacuum. Once the timing was set and the carb adjusted properly I didn't have such a big vacuum signal on ported vacuum. I'm happy, son is happy, :D thanks to all who took interest and helped out on this one
     
  13. RedBrute

    RedBrute 1/2 ton status

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    James if you can remember did you have to modify your distibutor to get the 37 deg? If so how? I think the first thing I'll try is an aftermarket recurve kit and maybe an adjustable vacuum advance if that doesn't do it. Thanks for your advise, It got me going in the right direction.
     
  14. 1977k5

    1977k5 3/4 ton status Vendor

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    Remember that at WOT the vacuum advance does nothing, so you are seeing a max of 19 degrees at WOT.
     

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