I've owned this truck for two years, and lately it's been throwing 171 and 174 codes, and occasionally a misfire code. Looks like previous owner deleted the egr. I pulled the heads and both were cracked. Machine shop moved the valves, etc to new heads and put new valve stems in. I replaced the heads, using oem head and intake gaskets. Put new motorcraft spark plugs and wires, and motorcraft pcv valve in. New sealed power rocker arms and push rods. Got her back together and runs very rough. Hooked up my scanner and found long term fuel trims very high. At idle, bank 1 is around 15 and bank 2 is around 20. At around 2000 rpms, bank 1 is around 8 and bank 2 is slightly above 20. This was in the garage holding rpms steady at various rpms for a period of time. While driving, bank 1 fluctuated between 5 and 11, mostly hanging around 8 or 9, while bank 2 was between 18 and 25, with some spikes down around 10. Did a lot of sputtering while driving. When idling, it will run fairly good with occasional misfires. I've double and triple checked the wires and vacuum lines and everything seems to be connected properly. Spark plug wires are connected according to the label on the coil -- right side 1,2,3 and left side 4,6,5. Didn't run like this before I tore her down.

What would cause bank 2 to be consistently 10% higher than bank 1, and both to be that much higher than normal? Increase in rpms results in a corresponding decrease in fuel trim in both banks, but they are still too high. Thanks in advance your your help.

I have attached a graph showing short and long term fuel trims for both banks, compared to rpm. Are there any obvious things to look at based on this?

Attached Images

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Thinking about it I think it could be either bad intake gaskets, cracked intake manifold, or the replacement heads are not aligning properly with the intake.

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1999 Ranger 4.0 and extreme Snap-on tool fetish

Jswifto,

That's what I've been fearing. I read some suggest tightening the heads and intake manifold down in sequence and others said it wasn't necessary. I didn't, tightened heads then manifold. Used oem lower gasket, so it shouldn't be the gasket. Trying to rule all other possibilities out before tearing it back down. If anyone has any ideas to check before I do that, I'd appreciate hearing them.

You could smoke test it

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1999 Ranger 4.0 and extreme Snap-on tool fetish