Hi all, Ive got a 2000 F150 4.2 with about 128xxx miles. Everything stock but custom exhaust and Airraid intake. I do al normal maintainence myself and most other repairs but I had a P0171 so i took it to the shop and they replaced a shot vacuum line. SES was off for about 30 miles, took it back, they said exhaust leak may cause the lean code because of fresh air being drawn in. What worries me worst is the fact that on a 200 mile round trip, my antifreeze level in the tank has dropped 1/2 inch and now has developed a misfire at around 1400 rpm. Headgasket???? Im takin it back monday to do a test for exaust fumes in the radiator. Any suggestions?

 

First thing to suspect is lower intake manifold gasket.
Very early (Jan '98 and prior) 4.2 had higher than normal failure.
Fix implemented in Jan '08 by Ford, but the problem can - and does - still occur.
My 2000 model had a LIM gasket fail at 158,000 miles.

Pull all the spark plugs and inspect. I could see a build-up of crud on one spark plug due to LIM leaking.

A compression / leak down test should show you where the problem is.

Here are 2 threads from back then....
https://www.ford-trucks.com/forums/3...hydrolock.html

https://www.ford-trucks.com/forums/3...he-gasket.html

Best of luck!
Let us know how it turns out.

Thanks.

 

well they pressure tested it and it didnt leak down so its not the head gasket... He knew it was running rough so he put a new coil on but to no avail it still misses. He said the next step is to try the egr system. He cleared the codes and it ran fine on the way home? They found no external antifreeze leaks so that worries me about the LIM gasket. He said drive it till the miss gets worse so that they can pin point it better.

 

I fit continues to lose antifreeze, it is going somewhere.

Either external leak, or internal leak. If you are concerned about internal DO A USED OIL ANALYSIS. for sure way to determine if you have antifreeze in the oil.

If you think it external, stop by the auto parts palce and grab a bottle of UV dye for detecting coolant leaks. A "black light" should show and leak that might be occurring while driving and therefore getting blown around/away, makign it hard to pinpoint.

Regarding the lean codes:
still suspect (another?) vacuum leak.
Possible clogged EGR port9(s).

yo can use the "search" button up top and look for "egr ports" or similar terms in this forum and you should find some good info.

Keep us posted!

Thanks.