It all started when I got my truck back from the transmission shop on Wednesday. I had them do a rebuild because for years it was feeling worn and muddy and I plan on keeping the truck for as long as I can. When I go to pick it up, they inform me it ran out of gas. Not sure how they burned through a half tank but okay. It ran rough on the way home especially at idle. I throw a fuel pressure gauge on there and my idle psi is 50. Pressure also dropped immediately to 0 when I turned the key off.

I had a buddy jump the fuel pump with that little connector under the hood and as soon as he pulled the electricity off, I clamped the rubber feed line and pressure held, then dropped immediately when I unclamped. They fried my fuel pump.

So I replaced the pump, filter, and strainer since it had a lifetime warranty. Now idle pressure is 54 psi and pressure holds when the key is turned off. Awesome.

I also noticed the FPR side of the intake was cleaner than the nut kit side. It wasn't leaking when I pressurized the system but it also had a lifetime warranty so I replaced it anyway.

At this point, I had a new distributor in my garage waiting to go in. I wanted to replace it because the truck would suddenly die in the hottest part of the summer from time to time. The distributor is one of the only components I've never replaced so I figured it probably needed it anyway. It's a Cardone from Summit with a lifetime warranty.

I drove it to work and back over the weekend and it did okay. Seemed to have a small miss or something. It feels way down on power because the new torque converter stall speed seems to be around 1200 instead of the stock 2000. I brought that up with the transmission shop and they blamed the engine performance.

At first I was ready to argue, but then today out of the blue it started missing real bad. I parked the truck for maybe a minute, then when I started it again, it was like one cylinder was totally down.

So I replaced plugs and wires with new NGK copper plugs and NAPA wires. I checked timing by unplugging the brown wire under the passenger side dash, clamping my timing light on cylinder 1, and idled the truck. The mark on the balancer was actually looking a little advanced so I turned the cap until it lined up with the 0 on the saw tooth thing. When I plugged the brown wire back in, the mark on the balancer was bouncing around between 8-12. Did I do this right?

It made no difference, still has a miss and truck still shakes. I connected a diagnostic light on each spark plug wire one at a time and each cylinder is firing. I feel like this leaves the CPI unit. Is there a way to test it? Did I miss anything with the ignition system?

 

You need three things for a cylinder to fire. Fuel, compression, and properly timed spark. You already checked spark. Check the compression before you blame fuel.

 

How could compression cause these symptoms so quickly though? If cylinder walls or rings were to wear down, shouldn't that take a while?

 

Some causes (like broken valve springs or sticky guides) can happen suddenly.

 

Good point.

I had another idea though, not sure why I didn't do this sooner. I used my IR thermometer to check the manifold primaries. All primaries are at about 400F except cylinders 3 and 5. Those are about 160F. Sounds like they're dead right?

I'm going to try my spark plug wire light on those again to make super sure they're getting spark, otherwise would this point to the CPI?

 

It definitely sounds like you have a problem with 3 and 5. Now that you know which cylinders are missing, it shouldn't be too hard to determine why.

 

Yep, they both held 84/90 psi on the leak down. New CPI on the way.

 

Cool. Let us know how it goes.

 

Fail. Still missing, cylinders 3 and 5 are atill cold. Theres no extra noise, no ticking or anything. Im stumped.

Edit: I should mention when I did the leak down, it was a few weeks ago before all this so I guess its possible a spring could've broken.

 

Pulled the valve cover and watched the valve train as someone cranked. Everything looked okay. Now I'm really stumped.