TBI 454 lacks power

[Dr_Snooz]

I'm noticing a really bad misfire in the mornings on first start. It cleans up after the truck has idled a bit, but if I don't wait, it feels like someone is hitting the truck frame with a hammer. The misfire is random and erratic, not like a specific cylinder misfiring.

Performance is getting bad enough that I worry about making it up the one hill here. The idle is noticeably rough too now. Before, it alternated between rough and surging. Now it's really rough all the time. Sometimes, performance improves if I turn off and restart the truck. Gawd I hate this truck.

Any ideas?

[Irish_Alley]

just thinking of something else but what happens when you unplug the cts?

[Dr_Snooz]

I'll have to find out. Stay tuned.

[Dr_Snooz]

Okay, I swapped out the MAP sensor with an old one I didn't know I had. That seems to have resolved all of my lesser symptoms. The idle is smoother. The hesitation from stops is gone. Misfire is greatly improved. No more surging. The bogging out at mid throttle is all gone. Unfortunately, my main symptom, POWER, remains. My performance now seems more consistent with a low compression engine. Especially one with a vacuum signal that goes to crap at higher RPMs.

I'm pretty sure a valve job is in my future and I'm pretty sure it's because of weak valve springs. That is, after all, what the vacuum gauge is telling me. The machine shop insists that they test springs before re-installing, so I'd like to confirm this diagnosis before negotiating for a warranty valve job. Does anyone know a way to test spring pressure WITHOUT removing the heads and disassembling them? Moroso sells this rascal right here for that purpose.



http://www.jegs.com/i/Moroso/710/62390/10002/-1

It would give me a nice solid number to confirm or negate the diagnosis. Unfortunately, $90 is well outside the budget right now. Anyone have any other ideas for me or should I just save up?

[chase.grantham.7]

You can remove the valve springs on one cylinder at a time by getting the piston to almost TDC on the compression stroke. Then feed some rope through the spark plug hole and turn the engine to squish the rope a bit, it will hold your valves up without fear of them falling into the cylinder. Mark the rocker arm nuts and count how many turns/threads it takes to get them off.  You can get a tool that's pretty much a lever with a cutout for the valve stem to compress the springs and remove the keepers. I'm sure the shop would test them for free or much cheaper than buying that tool.  It would be pretty time consuming to do every cylinder this way but I think if you did a couple of cylinders (one at a time) it would let you eliminate the valve springs.

[Dr_Snooz]

Another update on my Gypsy Curse Truck. It keeps running worse, misfiring, hesitating, idling rough, etc. In desperation, I unplugged the ECT sensor and the truck started running better for a day, then started getting worse each day. I replaced the ECT and again, the truck ran better for a day, then progressively got worse until it was the same as before. FINALLY, the stupid thing gave a feeble pop and died near my mailbox. No spark. I tested all the ignition components again for the 50th time and they all checked out fine. I pulled the distributor and started tearing it down when I realized that the reluctor assembly was completely caked with rust. I replaced the distributor with a Richporter unit from O'Reilly and the truck ran again! It even ran well, though still with no power. 

But the Gypsy Curse still holds, so each day it runs a little worse. Good grief.

I did a leakdown test the other day and found ~70% leakage on all cylinders, past the rings. So this engine is a total loss. I knew the valves were screwy and was hoping I could massage them without pulling the engine, but with bad rings, there's no point. I'll get a different truck.

What a Charlie Foxtrot this has been.

[Dr_Snooz]

I went to the machine shop yesterday and talked with the owner. He has agreed to warranty the engine for me and do another rebuild. I still have to pull the engine and all, but at least it's not a total loss. The problem right now is that I'm driving the truck daily for work. I'm saving up for another truck right now, so this all will have to wait until there's yet another truck in the yard. LOL

I'm planning to swap the rebuilt engine into my '86 (AKA Chester), along with some other stuff that I'll detail in another thread.

All in all, this is a positive development.

[Dr_Snooz]

If you were chasing a weak spark condition and it persisted even after replacing the coil, the distributor and the ICM, what would you do next?

[Dr_Snooz]

Oh, and an update. Now it's running pig rich with a steady misfire that makes the truck hop at stop lights, but also a lot of random misfiring. It gets dreadful mileage and Civics are passing me on hills now. I'm shopping for another truck, ~2000, ~150k miles, 4x4, ext cab, long bed and they don't exist. No lie. There's nothing. I believe I have a weak spark condition and have a test to confirm that, but it doesn't seem weak enough to make it run this bad. Moreover, the entire ignition system is new, so now what?

[Dr_Snooz]

Solved the problem. I bought a new-to-me '09 Silverado.

The '90 is at another shop for a last Hail Mary effort before it gets parted out. The shop has spent $500 of my money and found bad plug wires. Correction: they have found BAAAAAAAD plug wires. They are literally burned up. When they went to pull the boots, the wires tore apart leaving the metal connectors on the plugs. They tell me the boots had holes burned in them. I told them that those wires were only 3 weeks old and good NAPA wires, not some Chinese junk from eBay. Now we're all scratching our heads. The entire ignition system is new from stem to stern. New coil, new distributor, new ICM, new cap, new rotor, new wires, new plugs. But the wires were still completely toasted.

I'm done with this truck. Every dollar I spend on it makes it run worse. I've spent a fortune on it and I'm not one iota closer to fixing the problem. I want no part of this truck anymore. I don't want the TBI. I don't want the long block. I don't want a single piece of trim or a solitary screw to remain in my possession. I don't even want a picture to remind of this misery. It's all gonna go, along with the Gypsy curse that is on it.

Good riddance.

[fitz]

Are you going to junk it?

[Dr_Snooz]

I think I finally figured it out. It was the cat. It's completely plugged. The shop tested it and told me it was bad. I Sawzalled it out and I have a 454 again! What a nightmare this has been. The restriction heated up the exhaust manifolds and cooked the wires, leading to the misfire. It didn't cause the truck to overheat though, I guess because I have a big radiator in it. ?

Normally for a power loss complaint, the cat is among the first things you'd test, and I did very early in this process. I tested it according to the GM manual and it tested fine. Shows what the GM manual is worth. I keep being disappointed by their manuals. Now that cat wasn't a year old when I dropped the new engine in, yet somehow it was cooked at that point. I'm not exactly sure how that happened but I do remember that the exhaust pipe was spitting lots of water for a few days immediately after the swap. The engine was out for almost a month but the truck was in my brother-in-law's metal shed the entire time, so I have no idea how the exhaust system filled with water. Maybe my nephews were screwing around? I'm not even sure if the water would mess up the cat, but I didn't have the problem before the rebuild so I don't know. To make the problem still more difficult was that the old distributor had some rust in it. That would corrode up the electrodes on the distributor cap periodically, making accurate diagnosis more difficult by pointing me in the wrong direction.

I'm still ironing out some final bugs, but I think I'm past the worst part. This is a low-mileage 1990 1-ton with a fresh rebuild, new tires, nice interior, good condition overall. It's set up to carry my camper with overload springs, battery isolator, etc. The paint is rubbish, but that's theft-proofing as far as I'm concerned. I'll keep it around because I really do need it.

Thanks everyone for your help on this.