I have a 93' 4.3l W vin# with 190,000 still getting good gas milage 23 avg, but I have a rattling noise that sounds like a spark knock but it only happens when the motor is warm, and Iam taking off from a dead stop. I tow a boat with it and it only seams to act up on take off with or without towing. No rattle at normal speeds. Anybody know what this could be? besides gas related?

 

Oil pressure does what when this is happening? something may be gummed up or the oil pickup tube faulty? Just taking a stab at this one.

 

Oil pressure is holding about 40 psi Although Im not saying that this is correct. digital dash, and some of the tach lights are out but all of the oil pressure seam to be there.

 

Possibly the PCV valve. It should be located in the driver's side valve cover. I know on the SCFI (96+) motors, it was possible for the PCV vacuum hose to rest against the cruise/throttle cables and create what sounds like gears grinding against each other during acceleration and cruising.

It is also possible that it is detonation. Have you tried a different gas station? It is possible that you have gotten some bad gas and it is causing the issue. You may want to try a can of IsoHeat in the next tank just for kicks. It'll disolve any water that may have ended up in your tank and it's cheap enough at less than $2 for the bottle.

On the oil pressure suggestion, the dash gauges aren't always that reliable, but if it does climb from zero to 20+psi when started, you shouldn't have a problem there, but it may not respond correctly to dropping pressure. You may want to verify the pressure with a mechanical gauge just to make sure that you do not have an oil delivery problem. If the oil level were low, you could be starving the top end of the motor, causing the lifters to collapse slightly, slackening up the rockers, making a tapping noise. But a low oil level would affect it more than just low speed acceleration. Does the oil pressure hold at 40psi while idling as well? Does it increase as the RPMs rise? What type of oil filter do you have on it?

 

I have tried several differant gas stations with the same results. I will try the PCV valve and the isoheat next and see if this helps. As far as the oil pressure it does drop a little when at idle and increases when accelerating. The level of the oil is correct also. Thanks for the ideas.