New 6.2l owner questions

[callmebob]

Hi guys!

I just picked up my first diesel rig, a 1993 Chevy G30 Air Force Hi-Cube with 74,000 miles. I ordered a factory service manual, but while I wait for it to arrive I have a few questions about the 6.2l and 4l80E.

1. I was told by the P.O. that I should keep it off overdrive unless I'm on the freeway to prevent transmission damage. That seems like baloney. Can I keep it in OD (except on hills?)

2. When Im at a stop, the engine vibrates quite a bit. It doesn't feel like a rough idle, but the van sure rattles a bunch. The vibration goes away at first when I shift into neutral, but slowly returns to almost the same level over the course of a minute. Shifting back into drive brings the vibes back down, but only for another minute. Could this be the dreaded balancer?

3. I got 10.1 MPG on my first fill up after driving in LA traffic for a few days (with OD off until I get to a constant speed) My van has the aerodynamics of a house, but is this right?

I'll post up pictures of my rig soon! Thanks guys!

[Robyn]

Hi

The OD thing is very subjective.

Pulling a heavy load and such does place more stress on the OD but normally the tranny will shift into third gear when your into the throttle very much.

The weak link (If there really is one) would be the converter lockup clutch and again very much throttle and it will drop out anyway.

Keeping the tranny fluid cool is the biggest issue, and not worrying about what gear to run it in.

My technique is to avoid letting the tranny "hunt" (up down up down up down) constantly when its working hard.

Get it in a gear that it can pull the load and let it run there.

The bad vibes ??????

Does the vibration get worse with speed???

Couple things come to mind.

The dampener up front and the torque converter

A bad dampener can destroy the engine (Crank shaft)

If the rig has had a tranny replaced the converter may have been rebuilt and not reassembled (Welded) correctly, allowing the entire unit to wobble.

Also possible is a bad injector/s

Pull the serp belt off and run the thing for a few moments and see if the vibes change, and look at the balancer for wobble.

If this reveals no results then remove the flex plate cover and start the engine
(OBSERVE ALL SAFETY PROTOCOLS WHILE DOING THIS. PARK BRAKE, GOOD BLOCKING. KEEP LOOSE CLOTHING AWAY FROM ROTATING PARTS)

With engine running, observe the flex plate and see if it is running true.

If not then remove the 6 bolts that hold the converter to the plate, then slip the converter back away from the flex plate and restart the engine and observe the plate again plus WHAT ARE THE VIBES LIKE.

This should give you someplace to start anyway.

I have seen rebuilt converters that the snout was welded on crooked shake a rig so bad that the mirrors looked like they would fall off.


Now I mentioned the SERP belt..

Does this rig have a serp drive or v belts ???

The old v belt drives would make lots of vibes if the belts were not super tight.

[callmebob]

Thanks for the info Robyn!

The vibes go away the instant I hit the gas. She's smooth for all driving purposes.

I do have the v-belts. I get squealing for the first 30 seconds when the belts are cold. Turning the power steering makes the slippage worse. The PO removed the vacuum pump pulley and belt on a trip. He assured me that pump is AC related only.

I believe I have a front seal leak. Ill replace the dampener, pulley thing, and seal all at once. The rubber could be 23 years old.

I don't plan to tow much, even though I could. The rig has enough space for two motorcycles, compact appliances, and seating and sleeping for 4. :D

Any answer to my terrible gas mileage?

[Robyn]

Really hard to say on the mileage issue.

Military equipment generally has low rear end ratios which does not help, plus a high cube van is like hauling a barn down the road as far as drag goes

The injectors may be getting to the point of needing replacement as well.

Does it smoke a lot on cold start (Blue/white) ????

Any white or bluish white smoke at idle ?????

Bad injectors can contribute a lot to fuel economy as can other things.

If it starts up clean and crisp and no smoke then likely the issue is elsewhere.

Mil vehicles especially used 4.56 gears in many and these are certainly not stellar for mileage.

The other thought that comes to mind is that the timing could be a tad retarded.