Re: rough running at high engine speeds

Posted by HH56 On 2017/10/22 11:49:40

Another hard to find and weird problem with high speed operation was if for some reason the oil pressure increased over the normal maximum, then at sustained higher speeds any weak valve springs would let lifters pump up to the point those valves did not close tightly. When the oil pressure was back in proper range the lifters reverted back to their normal bleed down and all was well again.

Can't really see that happening but since you have looked at all the usual and do have hydraulic lifters, it might be worth looking at weird. Verifying with a known good gauge if the oil pressure is stable and staying in the same range as when the engine is OK would be easy enough to do. The pressure regulator valve could have started sticking or acting up.