Interesting Spark Plug story

BobHyatt · May 24, 2008

A couple of weeks ago I posted about a spark plug where the center electrode broke and disappeared into #8 cylinder. We looked, could not find it, and eventually decided to remove the head for safety. No sign. Head back on. A couple of days later we heard that "burble" in the idle. I started pulling coil wires loose and when I got to #6, the burble disappeared. We pulled the plug, center electrode broken off but held in by the side electrode. But not firing very well. Looked inside cylinder thru plug hole, nothing loose in there (we were pretty sure since we had just removed the head. Replaced the plug. A day later, same problem, same plug hole. Now we are concerned. We don't see anything so we try a different plug this time (we had Bosch platinums in, replaced this one with a Motorcraft.) 5 minutes of idling and we heard the "burble" again. Went right to #6 and pulled the coil wire, motor slows down but burble is still there. Continue trying coil wires and find #4 is missing. Pull the plug and the same story, center electrode broken off and shaking inside the plug, held in by the side electrode. Replaced all plugs with Motorcraft this time around, drove for 2 days, took it to the strip, drove it some more. So far, nothing.

Anybody had issues like this with Bosch??? Never seen anything like it previously. The plug tips are not close enough to the piston to be an issue for indexing according to my depth-gauge measurements (and the plug is shrouded anyway and it would take a ton of force to first crush the shroud before the plug could contact anything...)

Friend's comment was "Germans couldn't get it right in world war I, failed again in world war II, and still can't get it right today with spark plugs."

rabidscoobie · May 24, 2008

I hat Bosch.few months back when i still had the GT I put new Bosch Plats in it.then I dunno maybe 5months later,the last week I had it,it started running really rough then it would not even stay running at idle,took out all plugs and the centers where all in bad shape,put some new ones in and all was good,I will never use Bosch again,got maybe 5k-6k out of them.

Mustang5L5 · May 24, 2008

Bosch plugs and Mustangs have never gone together

COramprat · May 25, 2008

Must have gotten a bad lot. I can't say one way or the other for them since I don't think i have ever used them.

rabidscoobie · May 25, 2008

I think its a ford issue,I dont think the bosch work well with fords,my dads ranger the plugs went in less than 10k miles also...same prob as my gt.

BobHyatt · May 25, 2008

There is more to this than meets the eye, as we just lost the center electrode on plug for cylinder #5. So far, #4, #5, #6 and #8 have had this problem. The #5 problem we just had was using a motorcraft plug.

Anybody have any ideas about what could cause this? This is a stock 4.6 motor except my sun has a trickflow plenum (been on for almost a year with no problems) and when we replaced a couple of bent valves a month or so back, he wanted to plug off the EGR while we had the exhaust manifolds out, to eliminate the crud that gets recycled thru the intake again. Motor has stock heads, cams, block, etc otherwise.Turning the motor over several times produces cylinder pressures roughly centered on 180-185 with a +/- 5psi range, so within specs. We put it back together with standard 4.6 head gaskets. Can't imagine what would cause this kind of problem, I've been working on cars most of my life (drag racing, etc) and thought I had seen everything by now. Apparently not...

BobHyatt · May 25, 2008

After looking, this case is just a bit different (the motorcraft plug mentioned above). The ceramic tip material broke off up in the plug, and can slip up and down the center electrode, but the center electrode is still attached as it should be, and the gap is still correct. Doesn't fire very well because that ceramic material slips down and touches the side electrode preventing the fuel-air mixture from contacting the spark...

strange stuff...

Can't imagine what could go on inside the combustion chamber to make it shock the ceramic material enough to make it fracture...

COramprat · May 25, 2008

Weird. Something bouncing around in there but what the hell it is...I dunno. Is it misfiring at all?

Timing may be off but it would be a hell of a lot to be jamming up the plugs.

BurningRubber · May 25, 2008

Mustang5L5 said:
Bosch plugs and Mustangs have never gone together

Agreed, same with Jeeps...

steve_stang2003 · May 25, 2008

BurningRubber said:
Agreed, same with Jeeps...

I won't put Bosch electrical parts in any car.
I went through 3 O2 sensors for my GM 350 before I finally gave up and purchased the OEM.
Car would hunt on idle in closed loop like it had a vacuum leak.

My personal feeling is that Bosch has gone downhill in recent years.

As for plugs, I use Motorcraft copper version of the stock plugs in my 2003 GT.
I forget the number but the reason I don't use the platinum plugs is because their is always the chance that the platinum tip can come loose.
Copper is a better conductor anyway and with the known head/plug problems on the 4.6l motors (blowout), the shorter life of the copper plugs forces me to change them haha!

rabidscoobie · May 26, 2008

BobHyatt said:
After looking, this case is just a bit different (the motorcraft plug mentioned above). The ceramic tip material broke off up in the plug, and can slip up and down the center electrode, but the center electrode is still attached as it should be, and the gap is still correct. Doesn't fire very well because that ceramic material slips down and touches the side electrode preventing the fuel-air mixture from contacting the spark...

strange stuff...

Can't imagine what could go on inside the combustion chamber to make it shock the ceramic material enough to make it fracture...

Just a thought,does the part# on the plug match what it is suppose to be?The reason I ask is that when i took the bosch out of my 01 i then got Motorcraft and for some reason all 8 plugs where wrong but the part#'s on the box was right.The auto parts said that they were getting a few like this from the manufacturer...

BobHyatt · May 26, 2008

1. Plugs look right to the eye. They certainly do not protrude thru the head enough to come anywhere close to the piston top...

2. As far as cam timing, I don't see how it could affect anything. All that does is change where the valves open with respect to the piston and TDC. Nothing comes close to the plugs no matter what the timing.

3. As for something "bouncing around"... we can't find anything, we removed the driver's side head after two plugs went south. Absolutely nothing in the cylinder bore, trapped up on top of the valves in the intake/exhaust runners, nor in the exhaust manifold or intake manifold passages. And remember that this has happened on 4 different cylinders, one on the passenger side bank, four on the driver's side bank.

The motorcraft plug shows _no_ signs of any impact of any kind. Side electrode is perfectly normal, side electrode to center electrode gap is still right around .054, only the ceramic covering of the center electrode has snapped.

We are torquing the plugs to 15 foot pounds as per the latest ford tech note I have seen. I wonder if it is possible to "stretch" the plug and when it gets hot it stretches more since the head expands more than the steel plug, so that it is breaking the ceramic insulator. The plug system is very poorly designed. If you look carefully the plug seats on the spark plug opening at the top of the threads, but only the bottom 4 threads actually thread into the opening. Meaning that there is a stretching force from the bottom four threads applied across the center of the plug to where it actually contacts the head to seat.

In any case, we are studying the issue, but nothing stands out...

Notchbck93 · May 27, 2008

http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php

Have you removed your EGR?

EGR lowers combustion chamber temps which retards detonation---which is not always audible while driving the car.

A lot of aftermarket tuners brag peak numbers but their tunes are on the edge of detonation to make their given claims.

BobHyatt · May 27, 2008

Notchbck93 said:
http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php

Have you removed your EGR?

EGR lowers combustion chamber temps which retards detonation---which is not always audible while driving the car.

A lot of aftermarket tuners brag peak numbers but their tunes are on the edge of detonation to make their given claims.

Actually I had mentioned that previously. While replacing 4 bent valves due to a missed shift at the strip, my son wanted to cap the EGR and eliminate the pipe and the crud in runs back thru the intake, which he did. So there is no egr and at the moment we regurlarly get a CEL for "insufficient EGR flow" which really means _no_ EGR flow.

I had thought about possibly increased combustion chamber temps, and perhaps that is where the problem lies. However I know of others that have disabled the EGR via a tune and have not heard of this being a problem... We do need to add a tuner to our list of things

Will Smith · May 29, 2008

BobHyatt said:
Actually I had mentioned that previously. While replacing 4 bent valves due to a missed shift at the strip, my son wanted to cap the EGR and eliminate the pipe and the crud in runs back thru the intake, which he did. So there is no egr and at the moment we regurlarly get a CEL for "insufficient EGR flow" which really means _no_ EGR flow.

I had thought about possibly increased combustion chamber temps, and perhaps that is where the problem lies. However I know of others that have disabled the EGR via a tune and have not heard of this being a problem... We do need to add a tuner to our list of things

the insuficiant flow code you are getting regularly is a problem with the DPFE sensor.... its very common in the fords to fail... it doesn't mean the egr valve is bad nor the solenoid..

BobHyatt · May 30, 2008

Will Smith said:
the insuficiant flow code you are getting regularly is a problem with the DPFE sensor.... its very common in the fords to fail... it doesn't mean the egr valve is bad nor the solenoid..

No, the insufficient flow code is caused by insufficient flow. As in no flow. The computer can open the valve and notice there is no effect on engine performance and conclude something is wrong. In this case, the EGR pipe is missing and the manifold openings are plugged. So the MIL is actually correct...

we reset it regularly, and will one day get a tuner so we can turn it off.

nyuk98gt · May 30, 2008

BobHyatt:

There might have been a bad "lot" of ceramic material used to make the insulator. Some ceramic likes to be warmed up at a slow rate (like xxx degrees/hour), some ceramic tolerates quicker heating. I suspect that the material is off-spec. If you have the patience, you can try to call Bosch and speak to one of their tech types who will probably ask you to send the plugs in for examination. I would pull the other Bosch plugs and put in something else so you don't have ceramic bits loose in the cylinders. Even if they are small, they are pretty hard and might mar the valve seat(s) or something else.

My 2 cents.

Chris

Interesting Spark Plug story

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