Hi everyone,

I have a 2002 Ford Taurus wagon with 24V DOHC 6 cylinder engine. This weekend I changed the spark plugs and wires, I believe they were original and with 117000 miles on the car it was long time to change them. I had been experiencing lack of acceleration on the highway and the car has just generally been sluggish over the last 20k miles .. I was hoping a tune up would help.

Anyway, I've changed plugs on other cars before so the change proceeded without much issue. It took me some time to figure out the air intake plenum which I had to unbolt and swing out of the way to reach the rear plugs, but I did manage without issue to finish.

I started up the car and it's running like crap. The idle jumps from high to low and the engine seems to be misfiring or backfiring, I can clearly hear pops under the hood. I checked for lose hoses and found everything I had disconnected to make sure it was reconnected... it all looks good. One thing I did "cheat" on temporarily was I did not replace the EGR valve gasket when I removed it during the plug change. I didn't have a new gasket so I intend to get one this week and put it on. I didn't think this would cause a problem (especially not the symptoms I am having). Advice welcome if I'm wrong here.

At this point I am thinking it is simply the plugs, and perhaps they are gapped wrong. I purchased Bosch 4005 plugs. Under the hood it says to gap plugs between 0.052 and 0.056, so I did this with a plug gapping tool, the kind that looks like a small disc, which I've used many times before on other cars. The Bosch plugs came out of the box set to what appeared to be around 0.035, so naturally I widened each one. The strange thing is the plugs that came out of the car were gapped at a whopping 0.080, and I am thinking this is just from wear (that the electrode has worn down from overuse). What is confusing me is the new plugs and setting the gap - on the Advanced Auto website it mentions the Bosch 4005 is set to 0.054 out of the box, which would have been fine without touching it -- except my gauge didn't measure that at all, like I said it was more like 0.035. So I'm wondering if these little discs are just crap and maybe I should get some feeler gauges. I'm wondering what I should do next -- because I feel there is misfiring and no vacuum leaks I am thinking I will buy new plugs. I was going to try Bosch 4305 instead, they say on the box they are pre-gapped and cannot be re-gapped.

Anybody else have any problem like this from a routine plug change? Any other suggestions?

Thank you.

 

I have seen bad plugs right out of the box, but then again you may have boogered up the center electrode by using the disc feeler gauge as it is a fine wire electrode. I use the the Bosch 4005's in my Son's 2000 DOHC with no issues. I always use a standard ground electrode bender to make adjustments on platinum and iridium fine wire plugs. You should never gap by forcing anything between the ground and center electrodes.

You might also have a vacuum leak on the upper intake is one of the O-rings dropped out and got pinched.

 

Thanks for those tips. My friend told me he had seen bad plugs on occasion as well. I've learned my lesson with the fine wire plugs and won't do that gapping again. Today I replaced the plugs again with preset 0.054 AutoLite plugs, standard type. When I took the Bosch plugs out they were already blackened. I replaced them and reconnected everything, but still no dice! I am experiencing the same problem. I was unable to get a pair of EGR gaskets (the shop only had one) so I am still using old EGR gaskets... and need to replace them. But could that really be the source of such erratic idle and apparent misfiring? I'm stumped. I tried running the old plug wires to the front cylinders (4-5-6) since I didn't want to go through pulling the plenum just now, to see if there was a 50% chance of bad wires, but this made no difference. I triple checked wire routing, all wires are connected firmly and in correct order to the coil. I also read on the Internet that the big vacuum line falling off under the plenum is a big 'gotcha' but I saw this line and double checked it. It's not loose and did not fall off. Triple checked all other vacuum lines and no sign of problem. I glanced at the O-rings when I had the air plenum off again and they appear to be still seated properly, and not loose, so I don't believe I've pinched one. Everything looks good. The car's computer is not registering any codes that would help, either. Such trouble from a 'simple' plug replacement. Ugh. I am not sure what to do next, other than those EGR gaskets.

 

Plug wires? Didn't catch that in the first post. If you have plug wires, then you have the 3.0 OHV Vulcan engine, not the 3.0 DOHC Duratec engine. Different animals as the Duratec engine has COPs instead of a coil pack and plug wires as the Vulcan does. Are you double sure that the coil wires are in their correct connection on the coil pack?

 

Hmm, well the car is bagded 24V DOHC on the fenders, and it says Duratec right on it... but I didn't think this was coil on plug, each wire feeds to the central ignition coil mounted behind the Upper Intake Manifold. Below is a couple snapshots from my 2002 Ford Service Guide. #3 & #18 show the plug wires, the ends are quite long to reach into the valve covers and connect with the plug ends, but I didn't think there was a coil in there. Plug wire set is about $45 if that helps determine ... I'd think COP is more expensive? I've never seen COP so you can tell me if the diagram below is standard wire and coil or COP.

 

Well, the verdict is in ... I don't know what the hell is going on. Frustrating to say the least. On top of my new plugs and wires, I tried the WD-40 trick where you spray around intake and hoses to see if the idle surges from unmetered air sucking in the liquid. When I started around the UIM, I did notice an idle increase, so I whipped out the handy replacement gasket set I bought and went ahead and replaced all those gaskets. I replaced the EGR gaskets on top of that, and I also tried wiggling and pinching the hose&tube connection which goes toward the oil separator from the underside of the UIM (and possibly the other end connects to the PVC filter but I can't figure out if this car HAS a PVC filter). This hose assembly seemed a little loose so I thought it could be the culprit, but there was no effect in adjusting this during engine running. I am way past the point of diminishing returns and labor & effort involved here, and beyond my expertise for what I hoped would be routine maintenance... so reluctantly I am going to arrange to have it towed to my mechanic and hand off the problem to him, which he can hopefully fix in short order without a ton of money. Barring any other miracle suggestions or solutions, this is what I'm going to do at this point. Ugh.

 

You are correct in that your engine is a Duratec 24 valved engine. I forgot that Ford got cheap and went with a standard coil pack with goofy wires for the 2001-2003 model years before going back to the COP system. The COPs are a better design and are a more efficient ignition system.

Might just be coincidence, but check your fuel pressure regulator to see if the diaphram is leaking. This will cause the engine to run rich and the idle to jump around. Remove the vacuum line that connects to it and see if there is fuel in it. If there is, than the regulator diaphram is bad and the regulator needs replaced.

 

What was the fix for this problem?

I just replaced the plug wires on my Vulcan last weekend. I was surprised that the coil pack was numbered like 123465 or something odd like that. Did you need to pull the EGR to get to the plugs?

On mine, there were four of one heat range of plug and two of a different heat range. There were gaps all over the place. From seeing that, and things I have read, there is a lot of mis-information about the heat range and the gap. Also, the wire type of gauge is considered the best, but I ususally use the disc, like you do. The book strongly recommends against using feeler gauges because they are not accurate on a spark plug.

 

Thanks for replying -- I regret I didn't circle back and update this post with the results ... so, here goes:

Yes, I did resolve it -- or, I should say, my mechanic resolved it. Defeated, I had it towed by AAA to my mechanic. It stumped him for quite a while and he eventually did identify a loose vacuum line underneath the UIM that I had missed. To be honest, I still don't quite know which one it was, I was just happy to have it fixed. Fortunately my mechanic is awesome and fair and didn't charge much for the fix.

Unfortunately, I switched out from the platinum plugs to regular plugs at the end of troubleshooting and so that's what is in there now. In 30,000 miles therefore the plugs will have to be changed again... and this time I'll put platinum plugs back in.

Yes, I did remove the EGR. It helped me to tilt the plenum up and forward to get at the rear plugs, without removing the plenum entirely.

In the end, with regard to spark gap, I did not adjust the gap on the new plugs at all... I put them straight from the box into the engine. I believe they were gapped properly out of the box for my application, and that the disc adjuster I was using isn't really too accurate.

The difference in overall performance was quite startling after this was finally all fixed. The plugs were well overdue for replacement. Not much was left of the electrodes and the gaps were huge on the old plugs. It was definitely the source of bad acceleration and a little bit of stumbling which felt like a transmission issue but was just spark plugs. Particularly on the highway, acceleration was quick, smooth, and responsive. It felt like when I first test drove it at 27,285k in 2005. Boy, what I had been missing! My bad for going nearly 120k on one set of plugs! Ooops.

 

I have a 2004 ford freestar 4.2 changed wires and plugs still has minir misfire but not throwing any check engine light. I can tell you the brake problem. When changing the rear plugs you probably accidently disconnected the power assist. I did the same thing. Its a small hose running from the power assist to the back side of the engine.