Mechanic question. new motor will not run smooth

vstechSeptember 18, 2005

it backfires uphills and when it warms up the motor cannot take even partial throttle.

I had the long block professionally rebuilt down to the cam berrings.

I had the heads built as well.

I installed the heads, and set the timing etc.

I am thinking it is in the rocker arm settings, but I would like someone to leave agreement to that before I delve much deeper.

I also get a trouble code on the dash, I have not checked what it is, but it could be from the extra fuel unburned...

this is an 1989 Chevy Astro v6 4.3 L motor.

looking forward to using this thread.

John

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jemdandy

There's lots of possibilities for your problem. Ones that comes to mind are:

1. Valve timing

2. Timing mark on vibration damper isn't a match for the timing indicator on valve cover. [Remove spark plug no.1. Move piston to top-dead-center. With the piston at the very top of compression stroke, the timing mark on the vibration damper should align with its indicator. It may be a couple of degrees off depending on how accurately you were able to find top dead center.]

3. If you have a distributor, make sure that it was inserted with the rotor pointing in the correct direction. Check this while you have no. 1 piston at the top of its compression stroke. The rotor should point to the no.1 electrode in the distributor cap. Most distributors are driven by a helical gear and its easy to be off by one tooth. If you have the type of distributor with a flat blade on the lower end of its shaft and the distributor comes out leaving the gear in the engine, check the position anyway. If the rotor is not aligned, consult the repair manual about repositioning the drive gear.

4. Make sure the electrical and vacuum conections to the MAP sensor are in place.

5. If you have an exhaust gas recirculator valve, check it out for proper operation.

6. Valve lash. I'm not familar with your engine, but I do know that some Chevy V6 engines have valve lash adjusters even though the engine may be equipped with hydraulic lifters. The adjustment procedure is designed to place the adjustment midway between the beginning points of "too tight" and "too loose". Procedures vary, but the end goal is as described in the forgoing statment. The procedure that I have used is a little messy because I do it the valve cover off and the engine running at idle. Precautions must be made to catch the oil splatter and be very careful that nothing gets caught in the drive belts and accessories, and keep your hands out of moving parts. Back off the adjuster until it begins to make a tapping sound, then tighten the stop nut the required number of turns to center the hydraulic valve lash adjuster. Adjust all adjusters, shut off engine and temporarily install the valve cover (don't fully tighten just in case you wish to return to this bank). Remove the cover on the other bank and adjust. Replace valve covers and tighten both covers to the specified torque.

7. I assume that the spark plug leads are on the correct plugs.

8. Does this engine have multipoint fuel injection, throttle body injector, or a carburetor? If it has a carburetor, insure that this is set set up properly. The float level can be off if the fuel fitting adaptor on the carburetor bowl was removed and reinstalled. The fuel line can be removed without disturbing this adapter, but if this adaper did get moved, it changes the float level setting.

9. And anything else you can think of.

    Bookmark   September 19, 2005 at 1:35AM
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vstech

yup that is where I was.
I hate the #1 possibility. I did not install the timing chain, it was installed by my assistant. and I did not check it... this van reallly has a lot of stuff and no room. jeez!@ I realy do not want to pull it all apart.
it is throttle body.
I made small adjustments to the valve lash and it did improve the operation of the motor, so I will mostlikely need to set them with the motor running... not fun in a van...

Gosh I hope this resolves itself today...
John

    Bookmark   September 19, 2005 at 8:31AM
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