I've not heard of there being a problem switching grade of gas when almost on empty so I can't really comment on that. The other thing to check if it is getting worse would be to look for a vacuum leak. If you have a cracked vacuum hose or something along those lines it will pull more air into the intake causing a lean condition.

 

Nope ... the less 87 there is in the tank, the less the 93 will be diluted with it. You can change octanes at will ... doesn't hurt a thing.

Puting 93 in on a half tank of 87 will give you about 90 (89 is mid-grade).

 

Bah, then the internet lied to me =(

About the spark plugs/wires. Whats the benefits of changing them to better ones? I have not changed mine (owned since August of 05) and I don't know when it was done before that. Shop never told me they did it so I don't know if they looked at em and decided they are okay or just didn't do anything with them. And I read this giant post (from HankL of course, who else rights more in a post than I do for a term paper?) about all different kinds of plugs. Basically from that thread it came down to Champion and Autolite. I heard champions were good, and were stock on trucks from 93-98 but over the years they starting becoming of less quality. And I have no idea about the wires, all I know is that there are the 8 plugs with 8 wires coming out of each but I do not know where they go to. Thanks for the help.

 

Unplugging the battery for a few hours fixed the problem for about 5 miles, indicating that the ECM is learning a faulty fuel curve based on sensor readings. It isn't as bad as before, but it's still there. The question is: why?

Could the IAT and CTS be affecting this somehow? The only other variable in this is that the weather got drastically cooler the day after I changed the sensor. It's also remotely possible that I got some bad gas, but not likely.

Could the cat be plugged and gasses are backing up in the Y-pipe, causing faulty rich readings at the sensor?

What about pulling 1-2 degrees of timing out at the distributor?

I'm going to try some higher octane at the next fill-up, but that seems like a band-aid approach. A big low-compression V8 like this should not need premium fuel. I'm 90% sure it's not the plenum--there's been no oil consumption in the last ~3500 miles and the intake is dry. I'd like to try everything else before I tear into the engine (again).

Thanks for the suggestions and keep the thoughts coming!

PS: As a side-note to the octane thing--your local gas station only stocks 2 kinds of fuel: regular and premium. The mid-grade(s) are mixed at the pump using a measured combination of the two.

 

Matt with your knocking, after the truck being off over night and then you go to use it in the morning, does it knock then before the engine has time to warm up? I found mine does not making the noise until its probably around 160* judging by how far the little gauge.

 

bud, I had the same problem, I was on the verge of selling my truck i was so pissed, but i changed my plugs, wired, new 02 and it's perfect. I used to have a hard time starting on rainy and cold days. Not ne more.

 

On our trucks you can't adjust the timing from the distributor. The only way would be to slot the crank postition sensor and retard the timing that way. Dodge did this among other things to get rid of the ping by retarding the timing on the computer when they implemented the death flash.

 

Hi Matt, I have a 98-360-2wd-quad cab. I have to run high octane or the motor sounds like a bag of ballpen hammers flying around. Keep that coil wire away from your fuel injectors any leakage could take out one of your injectors and what happen to me it also fried my computer in a way that it would lean out the fuel delivery.
When I had my problem the dealer had the truck for two weeks, only to find out the computer was lying and giving all false codes. Replaced computer and put a set of 8mm wires and relocate the coil wire off the valve pan cover, my troubles were over. But at one point I was like you ready to drive it off a wharf. Hope I was of some help.

Cheers KayakMan