97 SHO Rough Idle and Growing Repair Bill

[jwinhulsen]

Good morning, everyone. Hopefully some of you can offer insight into my car's problem, as my mechanic is having difficulty to say the least.

I have a 97 SHO, 95,000 miles. Since about 85,000 it has been rough idling while stopped and in gear (serious shaking). Misfire in Cylinder #4 light has come on twice, and I finally had the coil pack replaced in that cylinder. Also had all sparkplugs replaced, MAF Sensor cleaned, and Injectors flushed....and its still rough idling.

My mechanic has a hard time if the "service engine" light isn't on and there is no "code" to guide him. I have heard several statements regarding our vehicle types:

1) Only Ford Motorcraft parts should be used, otherwise issues will arise.
2) Similar problems with others required all coil packs and plugs to be replaced, then the car runs like new.

Any ideas, comments, sugguestions. I am really at a loss and my repair bill keeps growing. I need to be able to drive this vehicle for another 100,000 miles.

 

[SHO#7]

I see that this is your first post, so welcome.

First and foremost, I hope that your cams are welded. If not, now is the time to get this done. Or the missfire will not be a problem any longer.

If you have a vibration and your mechanic can not figure out what cylinder is at fault, I would recommend that you go to Ford and have them perform a cylinder balance test. That will pinpoint what is going wrong, provided it is a coil going south.

Good luck

 

[SHOZ123]

As far as the coils go there is only one manufacturer out there for them. Go to Murry's Auto parts for the cheapest price by far. And with a warranty. I would at least get 4 new ones and put them in the back. Keep the old ones for swapping out in the front if the problem persist. They seem to be very fragile regarding cracking of the plastic housing.

I would only use the Motorcraft plugs. They are around $4 each. AGSF32FMF4 If you have Bosch +4s now then this may be the problem.

 

[Ian Macoomb]

If you're paying labor to replace coils it would be a good idea to get them all done at the same time. I've got a theory that the coils don't like to be touched. The simple act of removing the coil from the plug may damage the windings on the secondary side. A number of people have had coil troubles shortly after a plug change or cam weld.

Call around to the local autoparts stores and get prices. I've found that the Napa store here gives me the best price (about $75 US). And like Paul said, they're all made by the same company since the market is too small for multiple manufacturers. The coils I get from Napa come in a Napa Echlin box but have a Motorcraft sticker on the coil itself. Others have reported similar stories from other suppliers.

 

[97V8SHO]

I would only use the Motorcraft plugs. They are around $4 each. AGSF32FMF4 If you have Bosch +4s now then this may be the problem.

Why only motorcraft plugs? I put denso iridiums (same thing as NGK) and it seemed to pick up in top end some. I got thoughs for $17 for a box of 4...gotta love Auto Zone's stupidity because they're normaly $17 a plug.

 

[Mr Anonymous]

Why only motorcraft plugs? I put denso iridiums (same thing as NGK) and it seemed to pick up in top end some. I got thoughs for $17 for a box of 4...gotta love Auto Zone's stupidity because they're normaly $17 a plug.

NGK and Nippondenso (a/k/a Denso) are two completely different companies, and make two completely different iridium spark plugs.

Unless you're running nitrous, the iridium plugs are a waste of money (although if you did get Denso and not NGK plugs, you did get a heck of a deal). Spark plugs are generally not a performance enhancer unless you are going from a old school copper plug to a newer design platinum.

The factory Ford plugs have proven time and time again to be the most reliable choice for both the V6 and V8 SHO's. Quite frequently, we have customers with a persistent misfire that they have had no luck in isolating, often after installing 8 brand new coils. As soon as we remove the aftermarket plugs and install Motorcraft FM's, voila no more misfire!

jwinhulsen, from the sound of it you've exhausted all of the normal course of diagnostics, the next step I'd recommend would be to schedule an appointment with your local Ford dealer for a cylinder balance test (also often called a power balance test) on their WDS machine. Expect to pay about an hour labor for this (probably anywhere from $60 to $100). Unfortunately, Ford is pretty much the only resource for running this test, but it's usually pretty accurate at determining which cylinder(s) isn't contributing its equal share. It may still not tell you exactly why the cylinder isn't contributing, but it's going to be either a coil, plug, injector, or wiring harness problem. Cylinder 4 is notorious for wiring harness problems due to melting and shorting.

 

[97V8SHO]

I read somewhere that Denso makes NGK, I belive that's what it siad. If I'm wrong, my bad.