Recently purchased 2004 3.7 V6 4x4 Manual Quad Cab from Oregon, Picked it up in Southern California and drove it back to Maine. Great performance, gas mileage, all that.. I am a clutch miser, so I don't rev my engine before it is in gear (and don't even give it gas to back out of a parking space). It began to stall out at those low RPMs and I thought I was losing my touch, and my check engine light began to light for a while when this happened. I then checked the spark plugs. The anode of the plug was quite rounded and slanted, and measured nearly a .070 gap. I thought to myself "no s*** Sherlock, there's your problem!" I put in (and I know I'm gonna get flack for this *cringe*) Bosch IR +4's. I did see an improvement in low RPM's, no CEL and no codes, and acceleration was great when I first put them in.. but now the thing is boggy as h*** and seems to be losing gas mileage and seem to have to push the accelerator more towards the floor to get where I want to go. Not stalling at all, but I'm just about ready to put those old plugs back in! I'm not all that up on the coil on each plug thing (electronic vs. physical distributer), and perhaps the smoother ignition has made the computer set back the timing?? I have since replaced the MAP sensor and air filter and noticed nothing new. Perhaps a coincidence of using crappy Maine gas catching up with me? I've run through gas cleaners, used higher octane and whatnot, but not doing anything. Had 83k when I bought it now at 102K 8 months later. Are these plugs just junk? People might argue that they are not worth the money, but would anybody expect to see these symptoms? Should I be looking elsewhere for my troubles? As I said, I'm ready to trash $50 and buy non-Bosch plugs, but wanted to throw it by some of you people first. Suggestions?

 

Not sure about the 3.7 but the plain old copper core Autolite 3923's work great in my 3.9. I tried a few different plugs over the years but none of the other brands worked nearly as well as the 3923. You can buy them for less than $2.00 each at Walmart or for a few cents more per plug at Napa or Advance Auto Parts. There really is no need for platinum, iridium, plutonium, kryptonite/whatever plugs in the Magnum engines. Even Dodge engineers did a study and found the Magnum engines work best with a copper core plug.

Jimmy

 

Dont discount Bosch all together! For our motors yes they are crap. But its is still a good brand for other things, I found that their premium wipers are the best. Beating out the Rain-x fancy longitudes!

Run Autolight 3923's like Silver said, I believe the gap is .035". I have had them in for a little bit now and they are great.

 

problem is that they burn too hot for these engines,
magnums like a cooler copper plug

 

i dont know anyone who has used those Bosch +4 to be happy.

 

I put them on my mazda back in the day, I didnt notice a damn thing. I left them in because it didnt seem to hurt things. Tho I didnt have a forum like this to tell me which is best