I'm battling misfires now also, but here is my advice based on 30+ years experience.

Does the truck run rough? Idle or under cruise?

Run a scanner on the 02's, if they are cycling normally it is not fuel/air ratio, at least not consistently. If you look at recorded scans on the 02 sensors on a Disco you can see the computer do some strange things as part of normal operation. For example, the computer will occasionally send the mixture full rich or full lean just to make sure the 02's respond like they are supposed to. Watch them under WOT - should go full rich (1.0V).

You can disconnect both 02's - the program will default to using MAF and MAP sensors.

You can disconnect the MAF and the 02's - the program will default to speed/density programming which is based on MAP sensor and rpm. Gets most of the adjustments out of the way so you can see if the rough running is programming or actual mechanical problems, but it won't help solve the codes.

Leakdown test will tell you about ring seal or valve seals. I personally don't think the computer has the programming to discern leaking valves or piston rings.

You mentioned a Crower cam, not sure how aggressive it is but that could be causing problems if it is quite aggressive. More overlap reduces the vacuum at idle, has been known to cause misfires. You might want to consider swapping in a stock cam to see if it makes a difference.

 

I'm really not sure what to check on the flywheel. But tell me quick because I had it in my hands 36 hours ago and memory fades! I would rather set the truck on fire and roll it to the street for the fire department to take care of than remove he engine... Right now anyway.

 

Extinct:

Does the truck run rough? Idle or under cruise?

It is not as smooth as I'd like but it doesn't feel like it has a misfire. It revs fine. I haven't driven it because of the flashing SES after a minute or two. But for the flashing SES I am sure I could have driven it all over today. When I have had a single serious misfire in the past, it idled very rough and was super slow to bring up RPMs.

Run a scanner on the 02's, if they are cycling normally it is not fuel/air ratio, at least not consistently. If you look at recorded scans on the 02 sensors on a Disco you can see the computer do some strange things as part of normal operation. For example, the computer will occasionally send the mixture full rich or full lean just to make sure the 02's respond like they are supposed to. Watch them under WOT - should go full rich (1.0V).

All O2 sensors show changing voltages but I haven't gone WOT because I am technically in break in. No codes or pending codes for O2 related items so far.

You can disconnect both 02's - the program will default to using MAF and MAP sensors.

I'll try that.

You can disconnect the MAF and the 02's - the program will default to speed/density programming which is based on MAP sensor and rpm. Gets most of the adjustments out of the way so you can see if the rough running is programming or actual mechanical problems, but it won't help solve the codes.

I will definitely do that.

Leakdown test will tell you about ring seal or valve seals. I personally don't think the computer has the programming to discern leaking valves or piston rings.

I watched a video on that today. I am starting to think it is the valves. As detailed elsewhere I stupidly turned the crank to make sure nothing was hitting after I replaced my blown piston. I was just tired and forgot that the timing chain wasn't on yet. I stopped when I hit resistance but I may have bent a valve. When I put it all together this time, I put the chain in hen rotated it sixteen times. I felt a tiny bit on resistance at the same spot on every fourth rotation. I bet I have a bent valve. I have other heads "in stock" to chose from, including those on my good working 4.0. But I want to be sure the Rings are good because if I pull the heads that would be the time to replace them. The Rings are new.

I don't know what sets of valves are down at the same time but I'd sure like to know if 4 and 6 in particular are in sync (exhaust to intake)

You mentioned a Crower cam, not sure how aggressive it is but that could be causing problems if it is quite aggressive. More overlap reduces the vacuum at idle, has been known to cause misfires. You might want to consider swapping in a stock cam to see if it makes a difference.

The 229 is a mild cam. I still have the original cam but it has 130 thousand miles on it so that would be my last resort.

 

I'm back.

I have been work busy and haven't made much progress, but tonight I got my compression tester out and, recalling that I had misfires on 2 4 and 7, tested all of the cylinders. Max psi on all of the cylinders, dry and cold, was in the 150 range. Cold and wet was in the mid to upper 180s. That puts them all very high at operating Temps.

So that's good. Real good. But it is also real bad because I was expecting lower figures from a valve problem. Or even a ring problem.

Recalling that I wholesale swapped over coils, plugs, injectors and wires, I am at a loss again.

Definitely not a head gasket issue.

No vacuum or O2 codes.

What the heck?! As I understand it, a leak down test is to determine why compression is low. If mine is not low, then there is no point, right? That means that even though I am using the same plugs, wires, coils, and injectors that were happily making my 4.0 work four days ago, something has gone awry. The exhaust smells gassy.

So, basically, I'm back in my wheelhouse unless someone tells me different. Even though the parts are the same ones that oo2ered my other engine, I need to get plugs, wires, coils, and injectors checked, bought, or reconditioned.

Confused.

 

I've been thinking a lot about your cam - even a mild 229 cam could make the computer unhappy due to limits on the LTFT. I had a late 80's Silverado I put a mild cam in (fuel economy engine build) and I fought the programming on it a lot to get the A/F ratio right on - it was bumping up against the LTFT limits. Look at your 02 data and see what you see, I would not go by smell with respect to A/F ratio. If you had one you could put in a wideband in one back and see what the actual AF ratio is - would tell you how far off you are. When one 02 goes bad it does not really change the program - the ECU uses the other cylinders data to run the opposite bank.

130k on a cam really isn't much if it has had the oil changed regularly - I would give consideration to swapping that in if 02's look out of whack.

You could try the disconnection of the sensors if your 02's are spot on and see what happens.

2,4, and 7 are all on different coil banks, so I think you can rule out coils because if it was coils the paired cylinders would be giving issues also.

Leakdown probably won't tell you much given the compression - that's true.

Good luck, let me know how you make out.

 

Charlie, have you pulled the plugs and done a quick inspection of them?

And you are correct. If your compression numbers are good, leak-down test is pointless.

 

Thanks for that last. I am really weak on things I haven't done and have no one local to ask.

I pulled the plugs for the swap and the compression test. Here are two representative ones.




I just recently switched to Champions from Bosch +4s. These have maybe a month or two driving time. These are 322s. I checked the gap on all of them but I can't recall now what I I was looking for. . Maybe 40 but I just don't recall. I was careful to swap them from the 4.0 to the 4.6 same cylinders. I have done so much on this truck I would share that I have swapped them around with no change in misfires but I can't specifically recall. That will be my next step. I do specifically recall swapping wires around, and I have checked the wire placement three times. They are definitely going to the right cylinder.

Yesterday, I ordered a new HG kit, plenum gasket, and some ARP studs for a head swap but I'm wondering if I shouldn't just get new coils, wires, and plugs, and take my injectors to have them redone.

I cling to he thought that parts that worked on my 4.0 should also work on my 4.0. The only difference in these engines is slightly lower compression on the latter.

I am open to all suggestions. All!

 

I was mentioning flex plate because if it damaged at all it can skew the CPS readings, but you definitely need to rule out simple things first.

You can open up the inspection plate underneath and if you have a timing light point it on the plate and see if you see a bend or warble. Also any metal shavings or chips can mess up the readings as its magnetic.

 

I'm guessing your using the 4.0 ECU?
Maybe you are are getting miss fires because your to lean?
Are the O2's ever getting out of closed loop?
No vacuum leaks?

I assume you have checked fuel pressure?

 

I did check fuel pressure. It was good and the pump is about a year old. I'm not getting any vacuum leaks that I know of but I haven't smoke tested this intake. I am sure the plenum gasket is tight (and new) but I am always leery of that brake booster line fitting on the upper intake. So much so I even put duct tape over it for break in. But I had the same misfires with my other upper intake so I don't think that's he issue. I could have a vacuum leak elsewhere (but I have no other codes indicating it and I have smoke tested the whole system with the older engine in place, recently. The only leak I found was at the plenum gasket, which I replaced).

Thats an excellent point about the O2s. I haven't checked to see of they get out of open lop (one of us OS saying that wrong, but either way I know what you mean) because I've been so focused on the SES light and misfire codes. I will check that when I get the plugs back in.

I am using the 4.0, non SAI, ECU. The 4.6 heads were SAI but I plugged them.