So my beloved old truck is being EVIL. It is running lean and has a lean backfire in the collectors at 1200-2000rpm. It has NO power over 3000 rpm and will hardly rev that high. Its only showing the "system lean code." Spark plugs indicate its running lean Fuel pressure is OK (over 30lbs even when driving down the road) at the fuel rail, all sensors have been replaced (some twice) I put a new intake gasket set on the truck and even swapped around a reman computer and still have the same problems. What gives? Anyone have any ideas?

 

The truck has GT40 heads with upgraded springs, a 351HO cam from melling and 1.7 Procomp rockers and pacesetter headers. It ran great and pulled great for 20k miles then started this mess. There was some valve train noise intermittently. And I havent read good things about the Procomp rockers. Could they have eaten the camshaft? Exhaust valves not opening enough to fully clear the chamber creating the lean condition?

 

Yeah you're gonna have to pull the valve covers and see if the rockers are lose, if they are it's most likely one or more cam lobes is wiped.. which sucks but it seems to be more common these days with potentially cheap offshore cams and the complete lack of the necessary additives in current engine oils for flat tappet cams.

 

Thats where I am at now. I guess I am looking at putting the Crane 444232 in there and find a set old used Crane Cobra 1.7s RRs and just to be safe put new springs on the heads. I guess I'll order that stuff and go to work. Its too bad. At least I got a good 20k miles out of the set up. Would the Crane cam start with a better core than the Melling 351HO copy?

 

There's no guarantee with any of them these days, if you're using common motor oil the only way to be sure is to swap to a roller cam but that's 3 times the money. Have a look for zink additives you can add to your engine oil with every change or buy an oil specifically designed for flat tappet cams.. Performance Oils and Additives: Got Zinc?: Engine Builder

http://zddplus.com/

 

I was using motorcraft 15w40, so no I wasnt. I really don't want to switch to a roller setup. I just did in my Fairmont Futura street strip car to the tune of $1000 because its 393 wasnt built on a roller block (which are VERY hard to come by). And then you have the quality of link-bar roller lifters issue when it comes to a street engine. I have read bad things about the Morrells (i think they supply the Howards and a few others) in street applications. Thus I dropped 700 for a set of Crane pieces and another 180 for the Crane cam.