Ken,

 I'm working on a '99 Chevy 1500 4wd. 5.3 liter V8. Engine has a "miss." Someone did a tuneup recently and I found that the wrong plugs were installed.

My scanner shows a multiple cylinder misfire and a #7 cyl misfire. I installed the correct plugs. Cleared the code. Misfire on #7 cyl still shows up.

I've changed around plug wires..still #7 cyl misfire shows up.

Replaced the coil pack and even moved around the individual coil packs from cylinder to cylinder. Still misfires on #7 cyl.

Has spark at the the end of each plug wire. But noticed that once the revs are brought up it seems that the spark fades away.

What am I overlooking here. This truck is driving me nuts. 

    Sounds as though you may have a plugged injector.  Very common on Chevy trucks from 1997-2002.  GM has extended the warranty on them (in California at least ) to 200,000 miles. Contact your dealer. You may have to sign for a diag charge, but if it IS the injector, it is covered.

                                                 Reid    '72 T-top

May I also ask a question??

My 99 Tahoe 1500 every 5K miles or so trips the engine light. It starts with a severe miss (??? engine sounds like a big hammer)  when towing the boat, or just driving up a long, steady hill for several minutes. The dealer can't find the trouble, it is soooo intermittent.....it goes away by itself and the light clears a few days later

Plugged injector?? Ignition? I change the gas filter every 30 K.

Thanks

Sarge, touch the injector on 7 with listening device (screwdriver etc) and listen for the injector click to know it's working mechanically and electrically.  Then you can add some propane or carb cleaner (fuel) and see if it smooths out.  My guess is the wrong plugs caused a carbon build up that is affecting the injectors.   A good cleaner may do the job.  And the build up in the cylinder can affect this as well, so a good carbon cleaner is in order.  Techtron, GM Top Engine Cleaner, and Justice Brothers are all good.

Blu72, Check and see what code sets when it does this.  You don't have to have the light on when it does it.  But if you drive too long without the light, the code will clear.  AutoZone, Murrys, etc, will check the code for free.  Don't have them clear it, just record it.  Let me know.

Bruce, I did a bit more checking.  I seemed to remember something else about your truck.  Sure enough.

This is often a result of carbon build up in the cylinder head and on top of the piston.  Under a constant pull, the engine runs a bit warmer and components start to expand.  The larger components are closer to each other.  The carbon no longer fits where it is deposited, and causes the piston and head, through the carbon, to collide.  Thus the severe knocking noise.  When you back out of the throttle, the engine combustion chamber cools and the noise stops.

The cure is a good carbon cleaner through the engine.  Probably the best for this one is GM Top Engine Cleaner.  The others metioned would also work.  Keep in mind, some aftermarket carbon cleaners don't clean carbon.  Get the good stuff.

The OBDII system (computer system) saw a problem and turned on the light.  If the sees two drive cycles without the problem reoccouring, it then turns out the light.  That's why the light goes out after a couple of days.  Keep in mind a drive cycle is not just a trip, but a specfic combination of driving conditions.

I would have thought the GM dealer would have caught this.  They should read their bulletins.  But it's tough to catch everything, so I forgive them.  I had a lapse myself.  

Excellent my friend Ken.....this make perfect sense....YES, the hammering goes away when you let off the gas, then a few moments later it ceases to make the noises. Yes. I understand the drive cycles......I explained this problem in detail to the dealer till I was blue in the face...surprised they did not pick this up. These modern CPU cars must drive you guys nuts. THANKS...I will get the good stuff, and if it happens again, I will get the code for you somehow before the light goes out.

You are INCREDIBLE!!!! You da man!!!!

Ken, you have a personal message. Thanks man!

Reid, thank you for your input also.

I think you guy's hit it on the head.

I removed the fuel rail containing injectors 1,3,5,7. And found that "Bubba" replaced injector #7. It was different from the others. Tomorrow the new injector from the dealer will be in. And I also noticed...the fuel rails and the inlets on the injectors were loaded with this brownish clumpy crud. I cleaned all the junk out and replaced all the o- rings, and even did the opposite side 2,4,6,8.

So tomorrow night I will let you know how it runs.

Thanks again for your help!

Sarge

              Blu72- Tell your Chevy dealer there is a service bulletin on  the knocking. Does it sound like a diesel on cold start? Wakes up the neighbors in the morning? Ken is right about the carbon build up and us ing GM Top Engine Cleaner. Also, for a while when I was a service advsor at a Chevy dealer when this problem first started appearing on a regular basis, GM was replacing engines. They came back about a year later (2002) with a bulletin stating that this problem had no detrimental effect on the performance or longevity of the engine. Part of the knock is from the short shirt piston used in the 5.3 and 5.7 engines of this era. After that, I would explain this to the customer and hand them a copy of the bulletin along with the phone number for GM customer relations.

  Also, another thought is intermittant valve stick which I have seen in engines of this era with higher mileage. It usually occurs under heavy load such as steep grades or towing as you mentioned.  And change that fuel filter every 15,000 miles.  I used to sell a LOT of fuel pumps in these trucks at $900.00 a pop when the filters went that long without  being changed.

                                      So there you have it

                                              Reid  '72 T-top (red)

Wow...thanks Reid. No, it is not sounding like a diesel. But it does make some slap noise at start up...goes away in a few seconds. Mentioned this to the dealer and got the answer you posted. The truck has 94K on it now, and changed the fuel filter as required by the owners manual...I am a rule follower. But, if a pump is $900...oh my god...I'll junk the damn thing first.

So, you guys have the part # for the cleaner?.... and I'll change the filter more often. I notice that the FLAPS or Dead Zone almost always has an empy hanger in the spot for my filter..... must use these a lot LOL

Thanks   

The problem is all fixed. Cleaned out the fuel rails and injector inlets real good. Replaced #7 injector and all the o-rings. This truck runs like a scalded cat.

Thank you Ken and Reid for your help.

Sarge

Moderator, you can can close this thread down. My business is done here. Thank you.