My 2003 S-10 4WD 2 Door Automatic Blazer is skipping for the first 10 to 15 miles, then runs great. CEL blinks and stops when the skipping stops. At this point the CEL stays on but doesn't blink.. The skipping and blinking CEL will stay off all day regardless of how long the car sits or how many times it starts and runs. Once I get home around 5:00 PM and it sits all night, it starts all over again. Instantly skipping upon start up the next morning with blinking CEL. So, in short, the car runs great once it's hot. Stone cold, it skips and CEL blinks.
Car has new wires, plugs, fuel injection spider, (for lack of a better term) O2 sensors and stuff I can't think of right now.
To me, it feels electrical, versus fuel, because once hot, it runs great. Reaching out to you folks for some feedback.
Thanks

 

Did this start after any of those parts were replaced?

Do you have any codes?

Do you have a scanner with live data capability?


George

 

It was happening before those parts were changed. Nothing seemed to make a difference. The person I have do the work on all my vehicles (professional mechanic and family business for over 60 years) is beside himself. After the last "fix" I figured I'd reach out to you folks.
No, I do not have any codes, as I don't have a scanner. Doesn't seem to matter what the scanner says anyhow, as he's fixed everything that comes up on it, and it lasts about two days, and starts all over again. Again, once it's hot, it runs great. The other day I was talking to a friend about it while we were standing next to the idling car. You could hear the skip right through the tail pipe. I had driven about 10 miles. As we were standing there, it suddenly stopped skipping and was good for the rest of the day. Sat over night, and went right back to skipping in the morning.
Thank you for replying by the way! Haven't had much luck on another chevy forum site. Lots of hits, but zero replies.

 

This can be caused by a few different problems so some detective work is required to avoid the parts cannon.

Some possibilities:

Intake air leaks
Compression issues
Sensors
Ignition
Fuel delivery

A good scanner with live data capability is your friend in a case like this because it can narrow down the possibilities. Some things to look at first:

Are the misfires random or just one/few consistent cylinders?
Does the problem go away at the same time that the fuel system transitions to closed loop?
What do the fuel trims look like? Do they start changing when the problem clears up?
Do the relevant sensors have readings that make sense for ECT, TPS, IAT, MAP, MAF?

Have you:

Done a compression test?
Checked for vacuum or air intake leaks?
Checked the condition of the spark plugs?
Done a fuel pressure test?


There is more but as you can see the possibilities are many and some elimination is required otherwise you can wind up with a rebuilt engine one random part at a time. Proper diagnosis can result in one targeted parts change or repair.

Also, a better shop can use a scope to look at fuel injector function as well as ignition waveforms which is another set of diagnostic data to help find the problem.


George

 

One more thing I forgot to ask:

How many miles on the vehicle?. Has the infamous lower intake manifold gasket been replaced?


George

 

181,000 miles. To my knowledge, that gasket has not been replaced.
Just seems odd to me that the longer it runs, the better it runs. Took it for a ride this weekend, over a hundred miles round trip. As usual, the skipping stopped after about 10 miles, and the CEL actually went out before I got home. Dash looked kinda funny with no CEL on. Thought maybe the damn bulb finally blew, but she lit right up the next morning!
Seems like if there's something wrong to make the CEL come on it should stay on due to that problem. Not go out on its own and stay out for hours.

 

Many things change as the engine warms up as things expand, electronics heats up, PCM switches control scheme:

Air leaks can seal
Ignition coils or ICM's can start/stop working right
System switches to O2 sensor control of fuel delivery instead of MAP/MAP./ECT/Fuel tables
Fuel pump changes
Sensors change
Compression issues change
Out of bounds fuel trims can drift back in spec
........

That's why we need the data that I have outlined to determine the cause.

The CEL light goes out because the issue has resolved itself for the correct number of cycles. Again, in live data or with freeze frame data you will most likely see the problem. If not then its on to the other items I have listed. Here is an example of a good diagnostic repair guy using his scanner and a testing technique to find/confirm the problem. This may or may not be your problem. Don't be discouraged because he has a $3K scanner, you can do the same thing for less than $30 and get as much scanner capability that you would ever use for under $150.:



I can give you a prioritized list of parts to throw at the problem but that's not the best approach to this.

George

 

Op,
Make a list, what exactly was done to it?

 

UPDATE
The skipping is gone, the car runs great, and she passed emissions!!
The problem ended up being the Fuel Injection Sub Harness. Once replaced, all is well.
Thanks again to all.

 

Glad you got it fixed. How did you determine the cause?

George