93Bandit

Hey guys.

I was heading home from work thursday evening and a few blocks away from my house I was driving about 15 mph coming out of a turn and had to go WOT to get out of someones way. I was WOT for maybe 3 seconds total. Once I let off the throttle I immediately noticed something was different. The truck started kind of shuddering when I would give it light throttle like a miss, and seemed to idle rough. At that point I was already home and in the drive way, and I had lots of work to do that evening so I just parked it and forgot about it. I wasn't too worried because in the past I've had a few instances where it would run kind of rough for a little bit then be fine after a little driving.

Friday I carpooled to work, and when I got home I went out and started the truck. It started a little rougher than usual, and once it came down from high idle I ran down the street to the store. I immediately noticed that the miss it developed when I last drove it was still present and quite noticeable. I got it to operating temp and it no change. It drives along ok but I can definitely feel a lack of power and it still shudders under acceleration. It seems to smooth out at higher RPMs, but I could be wrong about that.

Listening to the exhaust you can hear the "Thwap thwap thwap" noise associated with a miss and the motor rocks a lot.

I haven't done any diagnosis yet, but I hope to either this evening or tomorrow. I'll start by doing a fuel pressure test, test for spark, vacuum test, dead cylinder test, compression test. I also have a new ignition coil I never got around to putting on so I'll do that too.

Truck had a tune up about 3k miles ago. Plugs, wires, cap and rotor. I also recently replaced the timing chain and gears, water pump, radiator and hoses.

Any suggestions of what I should look for? I'm worried that something went totally wrong since it happened right after a WOT incident. Also, the engine light has not come on but I doubt I've driven it enough for that to be set.

Thanks

Ol' Navy

My 4.9 developed the same issue. Come to find out a spark plug was loose and backed out of the engine just a tad. Tightened it back up and all is well now.

cts2433

First thing that comes to my mind is that a piece of carbon has lodged between against the spark plug electrode during the WOT run. I would try and cancel out the cylinders by pulling each wire of the cap one at a time until you narrow it down to the particular cylinder.

93Bandit

I went ahead and replaced the coil since I had a new one laying around and checked fuel pressure. Pressure was good. The old coil had visible damage to the nipple the distributor wire connects too. Then I started it and it's running much better. Miss is completely gone. Must have been coincidence that it started acting up after WOT. I'll keep an eye on it though.

Chris_1

iTrader: (1)

Put something like this together with a weak coil and you'd get a miss for sure.

93Bandit

When I replaced the coil, I also unplugged the battery because I didn't want any bad learned memory in it. After I unplugged the battery and changed the coil, I now has a kind of weird hot idle thing it does. When its up to op temp and you park it and put it in P or N, the rpms drop enough that the battery charge gauge needle dips a good amount, then it catches itself and then dips again, it'll do that a few times before it settles down at a constant rpm. But that hot idle rpm seems lower than it used to be. Then if you put it back into drive or reverse the rpms go up instead of down while in gear. Does that sound like normal operation as it is relearning? This is all after about 30 min of city driving.

cts2433

Yes, disconnecting your battery cleared the keep alive memory (KAM) in the PCM This has reset the base idle strategy. The reason for the low idle is sludge deposits around the throttle flap. You can drive the truck until the PCM adapts to the build up or go ahead and clean the throttle body with mass air flow cleaner or carb spray and a tooth brush.

93Bandit

So this morning I started my truck (32 degrees Fahrenheit) and it started ok and once it came down from high idle I dropped it into reverse to back out the drive. When reverse engaged, the rpms went up a little which I thought was odd, and once I was in the street and changed to drive the truck sputtered and died. I was able to start it again but it was running like total crap, and I had to used approximately 75% throttle to limp it back into the drive.

What's going on? Throttle body dirty? I wouldn't think that would cause my problem to all of a sudden arise? TPS? Crank position sensor?

In case it may be related, over a month ago I had a crank no start after driving the truck a few miles and letting it sit for an hour. It cranked for an extended time and did not start. I ended up cranking it 3 times before it finally started. Ran great once it finally fired. Haven't had it happen since. I did notice that while the no start crank was happening the check engine light remained on which I heard somewhere means the crank position sensor is working?

93Bandit

I'll definitely clean the throttle body. I've been meaning to do it for a while, I've just been putting it off.

Ol' Navy

Clogged catalytic converter?