Did an engine swap and now I have a P0300 - Randmom/multiple misfire.
 

I just did a 350 Vortec engine swap into my 2000 Blazer. When I crank it up it idles VERY roughly and wants to die. If I don't give it gas it goes down to around 200rpms and then eventually evens off at around 600rpms, but still misses. If I give it gas up to 1,000 rpms for a few seconds and let off it comes down to 600rpms, but still misses. I've installed the distributor properly and the gears on it are in good shape so I don't think that's the problem, but it is a loud hiss sucking in air so it's a decent leak.

Here's a list of things I've checked:

Followed the how to install a Vortec Distributor located HERE. (4 times)
MAP sensor
IAC sensor
MAF sensor (although it's getting a reading of 0?)
TPS sensor
Fuel pressure:
-Reached 60psi after 4 on/off cycles.
-Dropped to 55psi instantly
-After 5 min it had dropped to 40psi
-At 10 min it was at 35psi
Injector pod wiring
Injectors for voltage
Crank sensor wiring and it's a new AC Delco 2wd crank sensor (engine is out of a 4wd, but I don't see how that would make a difference)
Intake manifold pressure test (I found I have a vacuum leak where he spider injector seals against the plenum, but I don't think it's bad enough to cause it to be un-driveable.
The gears on the distributor look fine
EGR is removed both physically and in the PCM
Pulled plenum off and checked each poppet to verify it has a nice even fuel flow, it does.
Plugs are suity and black
New oil turned black and smelled of gas, but I think this is from flooding.
Compression test:
-#1 138psi
-#3 132psi
-#5 132psi
-#7 120psi (was hard to get on because of the headers, but I'm pretty sure I got it tight)
-#2 132psi
-#4 144psi
-#5 Couldn't get the fitting in there because of the header.
-#8 Couldn't get the plug off because of the header.

NEW:
Plugs
Wires
Cap/rotor
Crank sensor
Spider injector rebuild kit (o-rings)

Everything worked fine before the swap btw and I have checked to make sure which sensors interchange between the two engines.

Reading from my iPhone.
http://i49.tinypic.com/33omweg.png

That's all the info I can think of right now.

On a MAF sensor engine, any vacuum leak is a bad one. Try running it with the MAF disconnected until you get the leak fixed.

Well I did that and it didn't change anything. I just found out that app reads 0 until the engine is revved up so I need to try that out. There's another app I have that should give a reading at idle though as it measures in grams not lbs.

Ok I fixed the vacuum leak and got it started. I removed and the replaced each plug wire one at a time. It didn't change anything with the way the engine acted except on #4, it ran rougher and when I reconnected it I heard a "clang" noise and the engine started running the way it was before. Someone on another forum seems to think its the check valve on my fuel pump.

fuel pressure regulator?

Nope, it isn't leaking

Replaced the dizzy. Nothing.
Replaced the spider injectors. Runs like a new vehicle! Still has a little of a rough idle and when you start it doesn't want to stay running for a the first few seconds. I had it running for a few minutes and no codes though. Could it just be the fact that I need a crank relearn and the timing needs to be adjusted in the PCM? Timing is jumping from 18 to 24 and the rpms are jumping from 684 to 727.

Here's a video of start up. I didn't give it any gas during this video.
http://i1176.photobucket.com/albums/..._0991_x264.jpg

Yea you need to get the crank relearn done and get the cam timing set to 0. Check that you're getting signal voltage to the maf and that you have a good ground. Redo the fuel pressure, check both KOEO and leak down check. You can't do a power balance test on modern vehicles like you can on older ones because the pcm will pick up the slack and make any negligible changes unnoticeable. The clank you heard could have been some detonation from the over rich condition. How are the 02's acting? Are they dithering correctly? under 100mv-above 900mv for a healthy sensor. GL:icon_toast:

Ok I'll check the MAF, while the engine is running correct?

Why do I need to do the fuel pressure test again?

I haven't tested the O2's. Just swapped them out for some that I know works.

You can do it with key on, one wire will be the ref. one will be the sensor output and the last is the ground. Can you check how many counts the iac is at with your app? You should recheck the fuel pressure to confirm the repair. I was asking about the 02 mostly to know if it's showing a richer or leaner condition not if they're performing correctly.