OK my problem seems very similar to alexdabest’s, but I have good, steady vacuum and no codes. I had my block done by a reputable machine shop, bored .060 over, polished crank, new pistons, sized/balanced rods. Replaced everything on engine except rockers and pushrods. Put EQ heads on it w/ comp cam 20-608-9 (RV cam). 119/206 @ .050 112 deg lsa and .480 gross valve lift.replaced all other internal parts, does have a throttle body spacer, I did the plenum mod before engine swap. I bought a mt2500 scanner and did the fuel sync. Engine starts and runs fine, but drivability problems in real life. For one in idles quite low after warmed up, 600rpm max. When coming to a stop the idle drops down sometimes stalls out. Other times the IAC will kick it up back slightly and keep it going. Second major issue is the truck shakes real bad when it shifts into 4th when the tranny previously had no issue. As you go faster (higher RPM) it shakes less. Starting to think it’s the low-RPM load making it shake. In general moderate throttle seems even but same power as the worn out engine it had. At WOT it seems to accelerate with decent power. BTW 5.9L. With no codes or bad readings I’m running out of ideas. I put a lot of money into this to make it reliable and problem-free and so far I have the opposite. Any advice would be appreciated, I have the snap on scanner so I’m sure I can check a lot of values but don’t know what values I should have. Previously the truck ran fine, engine just had worn out rings and smoked some.

 

What plugs are you using? Usually shaking when in OD is an ignition issue.

 

Auto lite AR3923

 

Change those to some standard copper plugs, and recheck your firing order. I suspect you have a couple wires mixed up.

 

I double checked the wires b4 fuel sink but definitely won’t hurt to do it again since it’s tight back there. So should I go with the auto lite 5224 or are the champion RC12LC4 better? The gap se .040?

 

Not a fan of Champions personally, I think I went with the autolites last time around... (been a while.)

I went thru the plug wires on my 96 with the 5.9 three times, and still managed to get it wrong. Seems to run ok, if down on power, until it hit O/D, then it felt like the truck was going to shake itself apart.

 

What timing set did you put in ? There are some that have confusing markings.

 

Well I don’t know why my last post didn’t load but… I took my smartwatch+ to test voltage at the wires and found two w/ breaks in insulation so hoped that was it but no. Rechecked firing order again. The voltage at the wires read 39k+ Except cylinder #3 at 23k so I’ll have to look further into that. I bought the copper plugs but haven’t swapped them yet. Gonna test that one wire first. Trying not to add more variables.

since I have a snap on mt2500 scan tool I’m wondering how that may help me diagnose? I’ve only used it for fuel sync so far and the truck is yet to pull a code.

 

Look at what the sensors are telling the PCM, do their readings seem reasonable? Look at misfire counters as well. That should tell you something.

 

I’ve made some progress but still have some work to do. I tested the resistance on the #3 wire and it was similar to a new wire, 9500kohm but when I lifted to take another kv reading I felt some voltage in my hand. I put another new wire on and the voltage jumped to 29k min and jumping into the mid-35k range. All the rest are pretty steady around 39k tho. Test driving it though the truck breathed a new life. Much more responsive across the board and most the shaking is gone except when the converter locks up and it’s running at 1500rpm, still not horrible. The only thing that hasn’t improved is the idle. It still likes to stall 50% of the time when coming to a stop. I can put it in gear at home and it will idle all day at 600rpm but in real life situations it drops when stoping and often cuts out. I figure this can still be a ignition voltage thing. I would expect the IAC to compensate but not happening. I know it physically works because it has pumped up the idle before I did the sync. I’m wondering if the spark plug may not be grounding well, I painted the heads but didn’t exactly shoot paint in the plug hole. I don’t want to just throw parts at this since everything is new like performance ignition stiuff I don’t need. I still have the copper plugs… my next plan is to ditch the throttle body spacer to remove the variable and venture more with the scanner. I’ve never used more than a cod3 reader so it will be a learning process.