My 454 Rebuild

[Spareparts]

No. Months ago i removed them and put the stock setup back on trying to eliminate what could be potential problem.
The truck should be considered stock as all electronics are stock. all engine mechanical parts are stock except the cam that was changed to a mild Comp Cams computer compatible "RV" cam about a month ago.
It's just perplexing as sometimes it feels like what i did almost fixed it and im on the right track to fixing it but the next day it's back to the way it was. A few days later it will run good again with only a very slight miss and LOTS more power. The next day back to cr*p running.
I have checked and rechecked all electrical connections. Slowly replacing all none GM sensors with genuine NOS ACDelco stuff. Nothing fixes it.
Im thinking about removing the exhaust manifold and spinning the engine over to see if i feel/hear a leak on #7 exhaust valve. It has good steady vacuum and with the upper intake off i can't see or feel any leak on a intake valve blowing back spinning it over.
Im really starting to think there is something going on with the valves I'm just not figuring out.

 

[Spareparts]

Here is a pic of where the crack is.

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[454cid]

Weird. Those valve covers are pretty thick. Was there a high spot on the head? I wouln't think a 1/4" bolt could be tightened enough to crack one.

 

[Spareparts]

Im pretty sure it was already cracked but when i first saw it the crack was maybe 1/4in long. It just grew with heat cycles possibly?

 

[L31MaxExpress]

If you checked the airflow with a handheld anemometer in front of the grill the multiple obstructions represented by the grill and everything else in front of the fan blade are all acting to artificially increase the indicated CFM via the velocity of the measured air column. The actual volume of air moved by the fan at a given speed and clutch engagement will be less. I did not put the fan in a wind tunnel - that's too much effort and expense just to satisfy my curiosity. I did a rough calc based on the OEM 9 blade fan in my possession and used typical thermal clutch values. Utilizing measured blade pitch, area, swept diameter, etc., it is mathematically impossible for the 9 blade fan to move anywhere close to 6,000 CFM at 650 engine RPM when fully engaged even after artificially biasing every assumption in the fan's favor.

The only reason I invested that much effort was because I've grown weary of losing my cool (pun intended) every time I come to a stop light. I paid a shop to work on my AC last year because it wasn't cold enough. Their work left it warmer than it was when I took it to them and now it apparently leaks, which it did not previously, so I think I will use this opportunity to make some improvements. It sounds like your investigation has produced good results optimizing the AC system. You found the same thing experimentally I found mathematically: the air moved by the cooling fan is not the handicap. Following your lead, I think I'll replace the condenser with a parallel flow and a different orifice tube than stock. Can you elaborate on the variable orifice as it would be implemented in this application? I can be the guinea pig if it has only been theorized and not actually attempted previously. I have never been impressed with the truck blower, either. The van blower does not look like it will conveniently interchange with the truck/Tahoe/Suburban version, but that is just another problem solving exercise. Have you been using 134a or a different refrigerant? What about the compressor? I miss the A6 with R12 that could turn the inside of your vehicle into a functioning meat locker. Whomever signed off on the 76 degree center vent temp as acceptable clearly did not need to operate the vehicle anywhere AC would be required.

Apologies to Spareparts for the threadjack.

I measured the CFM using airspeed with the grille removed. I wanted a number that was an accurate representation of what was flowing across the condenser, since its area is easily calculated.

9 bladed fan I referenced was not a GMT400 fan and unless you have had one in your hand you cannot begin to get an idea of how much more CFM it is capable of. When the clutch fully engages it actually causes the belt to slip on the water pump pulley as the rpm increases. Compared to the 11 bladed GMT400 fan. The blade chord/width is much greater as is the pitch. The duramax fan is on a roughtly 60° pitch, where the GMT400 fans are barely half the pitch. The duramax needs a ton of CFM at a low fan rpm and GM designed it for that. As GM increased the Duramax engines power output the fan grew in diameter.

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[Erik the Awful]

it feels like what i did almost fixed it and im on the right track to fixing it but the next day it's back to the way it was. A few days later it will run good again with only a very slight miss and LOTS more power. The next day back to cr*p running.

I have checked and rechecked all electrical connections. Slowly replacing all none GM sensors with genuine NOS ACDelco stuff. Nothing fixes it.

That does not sound like a mechanical problem, it sounds like a wiring problem. Being intermittent, it will be a major pain in the rump to find.

 

[1990Z71Swede]

That does not sound like a mechanical problem, it sounds like a wiring problem. Being intermittent, it will be a major pain in the rump to find.

Yepp, I think so too. Post #731 made me change my mind. Lean missfire maybe. If it where the O2's It would run Alright In open loop. If it where way retarded ignition I dont think It would missfire, but Exhaust manifolds would run hotter than normal.

 

[Spareparts]

I have been thinking electrical all along also for the most part.
The thing is the misfire never goes away. Sometimes feels almost gone other times worse. Always worse cold (contract) but less severe when hot (expand).
Here is what im thinking could be possible.
The #4 and #7 valves are not seating properly. Im wondering if the valves are slightly bent and with having exhaust rotators sometimes they are seating pretty good when hot and other times they are not as they turn, cold or hot. Possible?
Watching o2 volts B1 is pulling more fuel than B2.
B1 has #7 cylinder and it's the worst misfire. Up to -13%
B2 has #4 cylinder and has a misfire but not as bad. up to -11%
Front o2 sensors are constantly fluctuating and the rear o2 sensors generally are a steady 0.1v but will sometimes jump up to .06v for a second.

I have been using Torque Pro to monitor all this stuff but last weekend i acquired a Snapon Solus Pro scanner with 9.4 software so this weekend i will get some data that should be trustworthy.

 

[Spareparts]

Thinking of buying HP tuners cuz it more user friendly than the free stuff from what i read and i need user friendly.
HP tuners website is kinda confusing. Looks like the setup i need is $500. Can anyone tell me if this is the setup i need, MPV3 and 2 credits
Thanks.

 

[Spareparts]

Finally, got some good data!
Ignition voltage varies between 14v to 13.8.
Injector PW 4.3ms
I did a injector balance test and with the FP starting at 58 here is where they end up.
1, 38
2, 38
3, 38
4, 38
5, 36
6, 36
7, 36
8, 36
I read that ± 4 is good but i dunno. 2lbs difference seems like a lot of fuel to me.
It also looks like my o2 sensors are bad?. All 4 were replaced with Walker brand sensors about 6 months ago. Cross counts go from 0 to 260 over maybe two minutes.
Here are two pics showing o2 sensor data.
Is there any data i can get that you might wanna see?

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