Miss after heavy acceleration

[Bob Oney]

I have a '99 Yukon SLT with 123,000 miles, 5.7L, 4WD. A couple of years ago I had 2 injectors replaced to cure a miss that occurred after heavy acceleration, such as when merging onto an interstate from a ramp. The miss has returned, and I'm looking for a way to avoid the nearly $900 charge it took to fix it again. (The heads have to be removed). Is there a good injector cleaner I can put in the gas to clean the injectors, or is that a waste of money? I just put in some this morning (Greased Lightning brand, I think). It misses only after I have quit accelerating and resume with light throttle. I think the plugs and wires are OK. It otherwise runs fine -- starts quick, accelerates well, idles and runs smoothly. What causes the injectors to clog anyway?
Thanks,

[MIkeman28]

You sure its injectors? How can you tell theyre miss fireing without dio?

[Bob Oney]

Originally Posted by MIkeman28

You sure its injectors? How can you tell theyre miss fireing without dio?

All I know is that it is doing the same thing as when I had the injectors replaced two years ago. At that time, various local shops had put new plugs and wires in and run intake cleaner through it to no avail. I thought it was the transmission, like a torque converter failing, but their diagnostics reported the transmission was fine. BTW, the fuel injector cleaner did nothing. As long as I don't wind it out under heavy acceleration, there is no problem, but if I accelerate strongly going onto an on ramp, for example, then begin letting off the accelerator it will shudder for 10-20 seconds as I let off or give it lighter throttle. I just take it easy until it settles down then resume driving as usual. I don't know what else it could be, unless perhaps a fuel pump malfunction.

[2000CAYukon]

It would be nice to know what the fuel pressure is doing when this "shudder" happens. It could be a drop in fuel pressure when you let off the gas. The fuel pressure regulator works off engine vacuum so that could be related.

For problems like this, I have hooked up a fuel pressure gauge and taped it to the windshield so that I could monitor the pressure while the problem occurs.

Another option is to find a shop with a dyno. Then they can watch the fuel pressure when the problem occurs.

//2000CAYukon

[markdpro]

Originally Posted by Bob Oney

I have a '99 Yukon SLT with 123,000 miles, 5.7L, 4WD. A couple of years ago I had 2 injectors replaced to cure a miss that occurred after heavy acceleration, such as when merging onto an interstate from a ramp. The miss has returned, and I'm looking for a way to avoid the nearly $900 charge it took to fix it again. (The heads have to be removed). Is there a good injector cleaner I can put in the gas to clean the injectors, or is that a waste of money? I just put in some this morning (Greased Lightning brand, I think). It misses only after I have quit accelerating and resume with light throttle. I think the plugs and wires are OK. It otherwise runs fine -- starts quick, accelerates well, idles and runs smoothly. What causes the injectors to clog anyway?
Thanks,

I have experienced the same problem. The miss is after the high throtle setting not during. I had good success after using a spray cleaner in the induction system. I don't like better living through chemistry but this worked. I begin to think some airflow instability or seed of carbon in the intake was icing or just making the computer goofy for a few seconds.