Ok guys,
I have trolled the forums long enough.

I have a 97 Ram 1500 with a 5.2 318 in it. I was driving down the road and she quit running like I had turned the key off. I had it towed home and started doing some research on this great forum. I replaced the o2 sensors fore and aft, new catalitic converter, plugs, wires, cap, rotor. At that point she managed to fire up and run but now I have a cyl 8 miss fire. I have checked spark and I have plenty, swapped plugs and wires and the miss is still there. Tested the injector and it tested fine. Used a noid light to test the harness and it checked out fine. Replaced the plenum gasket and it still misses on cyl 8. What could it be I am pulling my hair out. Is a compression check and leak down test next? I am at a loss as I have thrown alot of money at it lately which I do not mind because every thing I have replaced needed to be replaced. I am not happy to think about a cracked head but it seems to be the last hurah that I can think of. Did I overlook something or did I not dig deep enough? Help I am drowning

 

Your wires aren't crossfiring and are connected in the correct firing order, right?\
Our distys are a pain to get to...not allowing much seeing room back there.

Welcome to DF!

 

Compression test..... Yep.

 

I rerouted them as done in the service bulletin.

 

I went thru the same thing. Do your compression check and leak down test, if good then CPS $35.00 (culprit in my case) and reset your PCM.

 

CPS? Cam position sensor, crank position sensor or something else?

 

Cam Position Sensor. Crankshaft sensor is CKPS.

 

Compression test numbers
1) 180 psi
2) 190 psi
3) 190 psi
4) 190 psi
5) 187 psi
6) 190 psi
7) 185 psi
8) 190 psi

I was expecting lower numbers for a 148,000 mile motor but I will not complain. Now I am thinking a clogged injector or something. The injectors ohm'ed out to spec but a clogged injector will test good but perform bad I would think.

Would a leak down test help if my compression numbers are good? Any other suggestions that I may have overlooked would be appreciated.

I have been around wrenching a long time but this one stumps me. I still do not know why it just shut down the way it did. When I towed it home I had spark and fuel and it would not start up at all, got that fixed to where it would start, now this miss fire is taking a whole different round of diagnostics and brain sprain

 

Will a leak down test tell me anything different? Is it necessary with good compression numbers?

 

I'm wondering if maybe the CPS got damaged when the engine had the failure. Which is why it wouldn't start before you tuned it up, then functioned mostly after the tune up.
CPS's do some weird stuff to these trucks. I would start looking at that.