help, 99 f250 7.3l cylinder 3 and 4 dead
 

99 f250 7.3l with 200,000 miles. cyl 3 and 4 are dead and has alot of blue smoke.
I ran the injector buzz test and all buzzed and sounded good. I ran the cylinder contribution test and cylinder 3 failed. I replaced the cyl 3 injector, and test drove it. The truck still had a missfire. So i ran the buzz test again and code p1668 (IDM EF circuit failure) came up. A few minutes later i ran the buzz test again and the code would not come back. I ran the contribution test again, and cylinder 3 and 4 failed. I guess i am leaning twards the IDM but any known problems or advice would be great. Thanks in advance.

I believe the buzz test only tells you that there is power to the injector, not if the injector works. Have you installed the new CPS (gray one) yet? There are problems with it more likely with #8, but it could be the problem you have. Disconnect the batteries for a while to clear things and then hook them up and test it again. What are you testing it with?

Why are you leaning towards the IDM? Does not say faulty IDM.

<table border="1" cellpadding="3" cellspacing="0"><tbody><tr><td align="center" valign="top">P1668 </td> <td align="center" valign="top">— </td> <td align="center" valign="top">PCM/
IDM </td> <td align="left" valign="top">PCM/IDM diag. communication error </td> <td align="left" valign="top">Open/shorted EF or FDCS wire, open IDM grd.</td></tr></tbody></table>

look through the pinpoint test and you will see that it could be wiring, pcm, or IDM

And the crank position sensor is not going to give me 2 dead cylinders

no, but a chaffed under valve cover harness will.