Fixed! #8 Cylinder Dead - TBI

[rebelgregory]

Not sure if this should be in the injection section or not, but I need help and I know all the smart guys hang out in the garage.

My #8 cylinder is dead. I installed new headers and spark plugs, fired it up, and it idled a little rough with some sporadic popping. I have true duals so it was easy to narrow down the problem to the right side. Pulled out the temp gun and all cylinders were warming up to about 170deg, but #8 was about 80deg. I pulled #8 plug and it still looked new and smelled like gas. Swapped it with another cylinder and tried again - #8 was still dead, so not the plug. Checked the wires and distributor and found no signs of trouble.

Truck ran fine before. My next step is a compression check, but I doubt that it's an issue. Truck has a crate motor with about 30K miles on it and has been babied maintenance-wise. Also, it ran fine before and this is a sudden issue unlike a gradual loss of compression.

Could a leaky injector be causing this? Something else? What am I missing?

 

[tRustyK5]

You swapped the plug, did you try and swap the #8 plug wire? It's obviously not getting spark to that hole...

 

[Keitha]

2 main tests to do:
verify spark. If spark then do a compression test.

 

[rebelgregory]

I didn't swap wires. I did pull the wire off the distributor and got about a 3/4" spark (It has an MSD 6A box). I even sprayed a little water all over the plug wires to make it arc if if it was shorted, but nothing.

I'll add 'swap wires' to the to-do list b/c you never know. Good call.

It's too late to go play with it now since it's late, the truck is loud, and I don't want to piss off the neighbors. Here's what I'm going to try tomorrow:

1. Swap plug wires - see if the miss changes cylinders
2. Check injector spray pattern
3. Compression test - please don't let this be the problem
4. ????

I should add, that when I put on new headers, I also swapped to a heated O2 sensor and the thing went closed loop almost immediately. To be honest, I'm not sure it was ever in closed loop with the old one. The exhaust out of the left side sounds perfect. A small part of me thinks that possibly could lead to an injector-related problem since this is the only other thing that could cause a step-change in injector performance. Why it would cause only #8 to be dead, I have no idea.

Of course, this is assuming it's not something more obvious like a wire or compression.

 

[paratrooper307]

I didn't swap wires. I did pull the wire off the distributor and got about a 3/4" spark (It has an MSD 6A box). I even sprayed a little water all over the plug wires to make it arc if if it was shorted, but nothing.

I'll add 'swap wires' to the to-do list b/c you never know. Good call.

It's too late to go play with it now since it's late, the truck is loud, and I don't want to piss off the neighbors. Here's what I'm going to try tomorrow:

1. Swap plug wires - see if the miss changes cylinders
2. Check injector spray pattern
3. Compression test - please don't let this be the problem
4. ????

I should add, that when I put on new headers, I also swapped to a heated O2 sensor and the thing went closed loop almost immediately. To be honest, I'm not sure it was ever in closed loop with the old one. The exhaust out of the left side sounds perfect. A small part of me thinks that possibly could lead to an injector-related problem since this is the only other thing that could cause a step-change in injector performance. Why it would cause only #8 to be dead, I have no idea.

Of course, this is assuming it's not something more obvious like a wire or compression.

1. Your most likely problem. You could have a bad wire with an internal break or a bad boot. Moving and disconnecting wires can often cause trouble. That would support that the findings that there was unburned fuel and lack of combustion (low cylinder temp.)

2. Check the pattern, but unlikely. Since fuel on a TBI is injected at a central point, more than one cylinder would be affected. Plus you said #8 was getting gas.

3. A possibility, but you still would have combustion, just no power. Given your temperature measurements and the smell of fuel, combustion isn't taking place.

 

[diesel4me]

First,you did make sure the #8 wire didn't get crossed up with any of the others on the dizzy cap?..make sure the firing order is correct..

If the new spark plugs were platinums,especially Bosch platinums,I'd put an old "known good" plug in #8 and see if there is any improvement...

I've seen many chevy's exhibit a dead cylinder after changing the spark plugs to platinums,and the Bosch ones seem to do it most...I cant say why a brand new plug wont fire,or only in one cylinder ,but I've seen this enough times at my friends shop to know it happens..he wont use anything but AC "non platinum" plugs in his customers vehicles now after experiencing this more than once..

 

[rebelgregory]

I used Delco plugs. I've had the same bad experience with platinums. Gonna put the kid down and go tinker in a bit. I'm suspecting...and hoping for ...a bad wire, which will be easy enough to diagnose. Picked up a set on the way home in case that's the problem. Thanks for the sanity check, fellas. I'll let you know.

 

[rebelgregory]

It was the #8 wire. Replaced the set. All is well. Thanks for taming my paranoia.

 

[tRustyK5]

It's the simple crap that trips us up...happens to me all the time. Glad it was just a wire.