Misfire on Cylinders #3 and #5

[Frances G]

I have a 1999 Chevy Tahoe. I had the engine block replaced  about 2 weeks ago . My son was driving and all of a sudden the Tahoe started shaking very badly. He said It felt as if the engine was about to fall out. Took it to a mechanic and he said that cylinders # 3 and # 5 were misfiring. He said he wasn't sure if something else could be the problem as well. What do you think?

[Jsdirt]

I have more questions than answers for you at this point ...

 

Was it a short block, reusing the original heads off the old engine, or was it a long block with new heads from the manufacturer? Were all the injectors swapped over to the new engine, or were they all replaced with new?

 

On a new engine, especially an LS, the first thing I suspect with a violent double-dead miss is valve train components - valves, camshaft, rockers, lifters. I would say this is guaranteed if the engine is a '07 or newer with AFM, still running the AFM lifters with them tuned out of the ECM.

 

Compression & leak down tests would be mandatory, following fuel delivery (to those cylinders) & ignition checks. Even better would be a relative compression waveform for us to look at ... but if you had that sort of thing, you'd have already fixed the engine. 

[Doug_Scott]

Without knowing what "replaced engine block" means, it is difficult to give any answers as Jsdirt says.  With 3 and 5 cylinders being side by each, I would do a quick compression check with all plugs removed.  If you have a way to put compressed air into the cylinder, turn engine until one of those cylinders is on compression stroke, then with all plugs in, except 3 and 5 cylinders, put compressed into the cylinder that is on  ompression stroke.  Don't put in full compressed air charge, you want to see if you are getting air out of the other cylinder.  This will check for headgasket blowout between 3 and 5.

[Frances G]

It is a short block with new heads.

 

Took 99' Chevy Tahoe to place that put in the engine block. They initially were saying nothing was wrong with the engine. We left Tahoe for them to fix. They have done their own compression test and yes misfire on Cylinders #3 and #5 and said the engine is bad. That it would cost more to fix cylinders #3 and #5 than to replace the whole engine again. Is that true? Also, is there any way Auto Zone is liable for us having to replace the bad engine since it only lasted 2 weeks before this problem happened? I would hate to have to be out of another $1,068 to put yet another engine into the Tahoe.

[riverbanks]

So,long block,block and heads,short block,no new heads,that aside,the word "misfire" is more engine control problem,i.e.,computer,dead cylinder is mechanical,so no compression in 3 and 5?,more info the better

[Doug_Scott]

Your question is not very clear.  Please try reading your reply before posting.  You will find that you will end up editting the post once or twice to make it more readable before you post it. 

 

A short block is essentially engine from the camshaft down, minus sheetmetal and covers.  A long block is a short block with cylinder heads, lifters, push rods and rockers, and a drop in engine is everything from top of air filter to drain plug in oil pan, plus forward to engine fan mount. An engine block is just an engine block, no other parts. 

 

When you buy a short block from from an auto parts store they will have a warranty on just the short block, not the labour to replace it.  Problem with doing an engine this way is that short of a main/rod bearing fail, or a skirt breaking off a piston, just about every other failure is not caused by short block.

 

You need to get the shop to tell you how cyl 3 and 5 are bad.  Do both cylinders have 0 psi compression?  If that is the case, why are both cylinders at 0 psi?  There are really only 2 ways can have 0 psi.  Either the pistons both have holes in them, or head has a valve issue. Now, there can be many reasons WHY those 2 things can happen. 

 

I watched an episode of gas monkey garage(couldn't find remote, too lazy to get up) last night that actually may fit your scenario.  They had an engine rebuilt, then installed it and got it running.  They knew enough to run the engine at speeds over 2000 rpm for 10 minutes or so in order to break in the camshaft.  If you don't do that you run the risk of wiping the lobe off the camshaft.  No lobe, no compression. If you can, take the rocker cover off and have someone crank engine over and watch the rockers for cylinder 3 and 5 and also watch cylinder 7.  Watch for a rocker not moving the same as the others. If you see that, the engine was not broken in correctly, and that missing lobe is now floating in the oil as fine metal dust that is likely pressed into the rod and main bearings, requirering replacement. 

 

Let us know the answers you find. 

[Frances G]

Received a 2nd opinion .  The result was the same as the first opinion with misfire in cylinders #3 and #5 .  Either have blown head gaskets or cracked heads, but the engine is no good. We'll return engine to AutoZone for refund.  Will proceed with an auto mechanic shop that will give 3 year warranty on engine and labor.  Thank you for all of the answers to my questions.

[Jsdirt]

The auto parts store strikes once again ... 

 

Never had so many problems with junk new parts when I was younger - it was a rarity to have a defective new part, regardless of what it is. These days, it's becoming par for the course. It's become so bad that I refuse to shop at Advance, Auto Zone or O'Reilley's. I stick with NAPA, or a quality brand from the internet. I can say that NAPA has been above average for decent parts all through this cheapout era.

 

Sorry to hear you've become yet another victim of this. Since I work in this industry, it happens to me alot these days ...

[riverbanks]

Same here,but it's the people here,there is one great parts pro at my a.a.,I get a nod of his head on the choice of his,done,and with Napa,one great pro there,she's been there since there was 13 stars on our flag,ha,those make my day do alot easier

[riverbanks]

One other thing, Eddie lampert ran Auto zone for a stint,look what he's done to sears

[Doug_Scott]

15 hours ago, riverbanks said:

One other thing, Eddie lampert ran Auto zone for a stint,look what he's done to sears

 

Sears?  The company that closed in Canada a while ago leaving me with Kenmore everything, and no where to get parts that were always correct because they would give you a parts manual if you asked when you purchased the appliance. Sears USA will not ship to Canada.