99 k1500 engine miss while stopped in drive

SierraDually · November 18, 2017

Have a 99 k1500 with a 350. It's a Tahoe. Recently acquired it and trying to figure out. It idles fine in park but when in drive and stopped like at a red light or stop sign you can hear it miss like its about to stall but catches itself and that all happens in like .75 seconds and happens at a steady interval of maybe 3 seconds apart.

The previous owner is less than reliable for info but did tell me he had a CEL with a code for cylinder 6 misfire. (P0306 if I recall correctly, but don't quote me on that). He said he had it fixed but that's all he knew. It was a while back.

Anyone have this exact problem before? Sounds like an ignition problem to me like maybe plug,wire,coil or something? There's no codes for it. If there was a code pinpointing cylinder That's missing I could switch with another word, plug etc and eliminate causes by seeing if it switched to another cylinder. But I have no codes or check engine light. Any suggestions?

Also, on another note I have a 97 and a 99. Both same exact truck. The 97 I've had for years. It shifts smoothly. I can hardly notice it shift. But the 99 truck I just acquired recently. the 1-2 shift in particular I noticed a few times it sounds like it shifts a little harsher. Not slipping just like not as smooth as my 97. Maybe the shifts happen at slightly different times too but I'm not sure if that. But I am sure it doesn't shift smooth like the 97. do you think it's because this one is a different truck with a different history that it just acts different or should these two transmissions be identical in operation?

We're talking about a 99 and 97 Tahoe 4x4 350/4l60e the 97 has 450,000kms and the 99 has 222,000. I have a chance to sell the 99 and I'm just trying to decide if it can be cheaply brought to where I need it to be and give me another 100,000 or if I should get out now before something breaks.

Thank you all!

green 788 · November 18, 2017

It's always a gamble, guessing how long a truck will live. If you know it's got a problem, it's best to solve the problem before selling it, or at least declare to the potential buyer what the issue is.

Hard shifting occurs when the transmission goes into default or "limp" mode because it isn't getting all of the info it needs from the sensors (road speed, RPM's)... there should be a speed sensor on the transmission (or transfer case if it's a 4x4 I believe, that's where the speed sensor is on my 96 K3500 anyway...) Then there is another sensor on the transmission as well, driver side IIRC which may need to be checked.

You should have a check engine light on I would think. If not, does it come on when you do key on/engine off?

It's not necessarily bad for the transmission to shift hard. With the truck in drive and the engine trying to stall, you probably have a transmission error code... P0700 is what my truck set when I had the head gasket issue (and my truck was idling rough in drive, and not so well in park either). So the transmission decides the engine's signals aren't trustworthy and it defaults to those hard shifts. Sorting out the engine issue will probably fix the transmission after several miles of driving and re-learning...

If you have a cylinder that is not firing, you can figure out which one it is by letting the engine warm up to normal operating temperature, then take a squirt bottle with some water in it and squirt each exhaust outlet at the cylinder head/exhaust manifold junction. If you find one that doesn't steam the water off immediately, that cylinder is not hot, and not firing.

A V8 running on 7 cylinders sounds pretty good going down the highway. If you suspect a particular cylinder of not firing, pull that plug wire loose with some insulated pliers while the engine is idling and see if you hear a difference. If you hear no difference, you've found the dead cylinder. See if you're getting spark by slaving in an extra spark plug to that wire, and holding it to ground with the insulated pliers while the truck is running. If you are getting spark with the test spark plug, remove the plug from the engine and see if it'll spark with truck running (put the test plug back into the head to seal that port while you do this, of course). If there is spark on the plug, then that cylinder is getting fire. If it's staying cold (as per the spray bottle test) then it's not getting fuel. That would indicate a bad injector on the injection spider (probably)... or less likely a bad valve train component. If you have a bad valve or lifter, you'll probably be hearing a pecking noise during idle.

Dan

SierraDually · November 19, 2017

It's not so much a hard shift as a shift that takes too long to happen. It hangs in 1st an extra second. And then Goes into 2nd but doesn't really bang or anything. Just a lot more noticeable than it should be.

It only idles rough or feels like a miss when it's in gear at a dead stop with my foot on the brake. There are two codes. P0141 for an o2 sensor and p0306 cycl 6 misfire. Fuel system status in live data on the scanner is "cl-fault" which means I believe that it's basing its fuel trims on only one o2 sensor. But if o2 sensor was the cause wouldn't the rough idle also be at park not just while in gear as I described? It idles much better in park. Almost good but not perfect. Drives down the road fine.

I can hear the fuel pump starting to whine but I've had fuel pumps go and this is not that. It may be getting weaker but it's still up to task.

Logan Lanfear · November 19, 2017

I would start with some basic tests. Are you getting a consistent spark on cylinder 6? Test it in park and in drive. Sometimes the miss fire can mess with the trans shifting.

SierraDually · November 23, 2017

I sold that damn truck. No more POS 99 Tahoe. I still have my 97 Yukon and 88 Sierra.

I can't tell you exactly what was causing that rough idle and now we will never know. It's totally crazy how that 99 Tahoe with 230k was in way worse shape mechanically than my 97 Yukon with 450k. Maintenance and how you use your truck really does determine the lifespan. Once they have been way too neglected, like the Tahoe this post was about, they are never the same.

Luckily for me, I got that Tahoe for a song. Made a dollar and moved on. RIP Tahoe. Thanks for the input everyone.