We recently had this Ranger come in with a freshly rebuilt engine installed by customer and it would idle fine all day long but as soon as you raised the RPM above 1200 it would fall flat and die and then it would take about 20 secs of cranking before it would start again. We found that it had no compression just after it died but compression would soon return. We checked the oil pressure and found it had 60 lbs cold at idle but would hit 120 lbs as soon as it was revved up pumping the lifters up and killing compression. We installed a new oil pump and pressure was 60 idle and 75 revved up and we thought all was well. Now it has returned 1500 miles later and customer says it dies at stops. After checking all the usual suspects (including checking for plugged exhaust) and not finding a cause I noted that I can simply rev the engine to about 2500 rpm and watch the vacuum drop to about 14" and if I snap the throttle shut it will either die or run really rough for about 10 seconds and then smooth out. I tested compression on #1 after shutting the engine off normally and it's always 175 lbs. but if I run it fast , snap the throttle shut and let it die then really quickly check comp I get 125 lbs.

I asked the customer if he changed oil since we put the pump in and he said yes, he had run break-in oil for 1000 miles then switched to 10-40. I can't find a spec in alldata but I believe it should be 5-30. Am I barking up the right tree? Again?

Steven Andrews
Owner/Technician
Cascade Park Automotive
Vancouver, Washington, USA