Bad engine misfire?

Hey ya'll. Im a newbie on this forum. I have a bad engine miss on my 99 prerunner. Here's a little background....
99 PreRunner 2.7L
319,000 mi. ( 125k on engine)
AUTOMATIC
replaced radiator (20k ago)
CEL : coded p0420 for 10k miles or so.
New wireset, new denso plugs, new twin coil packs, new fuel filter

Recently started experiencing a bad miss. Pulled a p0301 misfire code. Changed the plugs, wires, fuel filter and "seafoamed" the intake via the brake booster vacuum.
No change.
Did compression test today. Numbers all over the plce. Not exactly sure if i did it right.... pulled efi fuse and relay then turned the engine over for 7 seconds. Then recorded my #'s one at a time after 6 seconds crank on each cylinder test.
#1 - 99
#2- 120
#3- 109
#4- 114

Used jumper cables to keep battery hot...
Do i need to crank it for a longer period if time for each cylinder? Or could it really be that bad?
I use

$25 BG44K BG 44K Fuel System Cleaner Power Enhancer 11oz.

BG44K fuel treatment monthly.
i am open to any and all help.
Thank you all!

 

Welcome to TW , did you pull all the plugs first ? & actually your numbers are within specs for the most part..

 

Thx Doug. Yes, i did remove all plugs at one time, then I began the compression test.
Could it be an issue that is symptomatic from the EGR code? I still havent corrected that yet. Forgot To mention I replaced the o2 sensors about 4,000 miles ago.
Any other suggestions?

 

P0420 means "Catalyst System Efficiency Below Threshold (Bank 1)"
Did you mis-type? P0402 relates to the EGR system.

 

Yes sir. My bad p0402.... mis type. I was trying to narrow down cleaning the egr..... the vacuum switch replaced.... or the temp sensor? Too many variables to decide... hate to just throw $ at it. Ive never seen the specs on the conpression test i did... do u happen to agree with Doug? I am clueless.clueless

 

Its is entirely possibly a typo..... ill have to check it again in the a.m. thanks for noticing Rick. Any other suggestions are greatly appreciated!

 

No one ever agrees with me..... I say your numbers are within specs for combustion, if you take your lowest (99) & if the highest (120) that makes a 20lb +/- difference which may be a tad wide but you'd still have enough to fire pretty normally, but I notice that the highest & lowest are next to one another cylinder wise, something could be suspect.. How's the CAT ? Any unusual odors coming from exhaust ? Bad CAT doesn't always throw a code I'm told..just throwing it out there

 

P0402 - "Exhaust Gas Recirculation Flow Excessive Detected"

This sounds like there is too much exhaust being recycled.
2 possible culprits come to mind:
- the main EGR valve stuck partially open (which should also cause a bad idle)
- bad EGR modulator

The valve can be removed and cleaned (via soaking in a solvent ?)
The modulator can be VERY EASILY swapped out with a known good one for a test. I'd go to a nearby pick-n-pull for the modulator.

 

Yes, I agree with him. The compression is a bit low on all cylinders, but pretty consistent (therefore has less power, more blowby, but shouldn't cause a mis-fire). However, I'm not a real expert in this area. Doug likely has more experience in rebuilding than I do (I've only done one).