2003 Oldsmobile Silhouette Spark Plug Cross Threaded

Service Engline Light came on, and van began to run rough so I brought van into nearby mechanic to diagnose the problem.

He said one spark plug was cross threaded and not seated correctly. – this was causing the problem.

I had similar problems 20 months ago and was told that a fuel injector was malfunctioning, so the fuel injectors were replaced (all of them) along with the spark plugs.

Now, I’m told that due to the cross threaded spark plug, that I need to have the head milled so that it can be repaired.

The cost would be $250 for parts and milling, $850 for labor about $1100 total.

Is there a less expensive fix for this problem?

Is this the responsibility of the first mechanic?

If the plug is really cross-threaded then it’s likely caused by Mechanic No. 1.
Considering No. 1 replaced all of the injectors, this makes his abilities look even more suspect because injectors do not fail en masse.

Now to Mechanic No. 1. The spark plug hole can be repaired with the cylinder head in place on the engine. A thread insert, Heli-Coil, etc. can be used and it should not run more than a 100 bucks, give or take, to fix this.

Responsibility is really hard to prove but it seems you have a stripped spark plug socket threads. There are options cheaper, they can retap and put an adapter socket in if you find the right mechanic.

We both jumped on the same parade at the same time, not meaning to dish your answer.

No problem and to correct my typo in the second paragraph I meant Mech. No. 2 instead of 1.

Oops… I remembered the events wrong.

After the first mechanic had trouble diagnosing the problem, I took the van to the dealership. The mechanic at the dealership wanted to replace all of the injectors for $2600 saying that since one was faulty they all might be.
(This could be why GM is going bankrupt.)

This sounded strange to me, so I took the diagnosis report to Mechanic #1 – he replaced the single faulty injector and spark plugs for $1200 (most of it was labor)
The van worked fine until now.

Mechanic #2 said that he could not easily get to the damaged cylinder head since it is in the back and that he could not get the heli-coil in to repair it, so it would have to be completely removed.

Do you have a misfire code on the cylinder that has the crossthreaded plug?

Simply because a plug is cross threaded does not cause a miss (the plug seals on the crossed threads).

It sounds like the mechanic is unsure of the cause of the misfire and hopes to discover the reason while removing the head or he already knows the reason and can easily fix it but wants to make a little more money so he tells you the head must come off. Just what I suspect.

I can’t say as I’m too enamored of the dealer’s recommendation about replacing all of the injectors or the mechanic who hit you for 1200 bucks for a set of plugs and one injector.

With some ingenuity there is usually a way to get into those tight spots, be it an angle head drill or whatever.

I also agree with oldschool that a cross-threaded plug will not cause a misfire.
The exception might be if the installer cracked the porcelain insulator while ramming it in there.

This also illustrates why a spark plug socket and extension should never be used to start a spark plug into the hole anyway. Use a short length of stiff vacuum hose wedged onto the end of the spark plug to get it going first.

With some of these sideways V6 engines, getting to the plugs on the firewall side is next to impossible. More than a few models must have the engine lifted up off its mounts to gain access. It’s easy to see how this could happen…In the hands of a SKILLED mechanic, a simple thread chaser might be able to restore the damaged threads to usable condition for a fraction of the money you have been quoted…You put in platinum plugs and you never mess with them again…

Yes, the code was for that plug. He showed me the numbers of missfires for each cylinder… most were 0 or less than 50, the plug in question over 100,000.

He gave me the plug… it looks as if it was not screwed in all the way… there is a clear line of wear about 1/2 way on the threads. A new plug was put in, (just as far as the original) and car runs fine for now.

All plugs were replaced 20 months ago, but problem continued so I took vehicle to dealership. Dealership narrowed down problem to faulty fuel injector and wrote: “recommend injector service other injectors will follow and needs fuel evel sensor replacemetn”

When I took it back to Mechanic #1… Only faulty fuel injector was replaced and car worked fine until now.

Your latest post regarding the plug only going partway in and having a “visible line of wear halfway up the threads” makes me question if the plug were really cross-threaded in the first place. Your car has aluminum heads, and if it were cross-threaded then removed, installing another plug would be out of the question. There would be no more threads left!

That being said, I am thinking a more plausible explanation is that the plug was not tightened in the first place by the mechanic who replaced them 20 months ago. You said it ran fine until recently, then started misfiring. The plug was removed then would not go back in all the way because it was “cross-threaded.” If the plug were left loose and never managed to work its way completely out, which is entirely possible, it would leave a nice cavity in the combustion chamber for carbon to build up, eventually preventing the plug from firing, which would cause you to take it to a mechanic, who would find a plug not fully installed and would not fully install. This could fool someone into thinking it was cross-threaded, but I think it is carbon buildup. Have the mechanic try running a grease-covered tap (to prevent carbon and metal shavings from getting into the engine) the same pitch as the spark plug into the head. I think it will clean up and you will be on your way.