Hey Guys, I am new to this forum and have a question about my truck. Bought a 97 ford 4x4 with a 4.2 and 5-speed. Got the truck dirt cheap because of a vibration. When you start it up it it stutters like a fuel issue and after it fires off there is a vibration like it is hitting on 4 cylinders. I have checked the vacuum, spark, compression and fuel pressure and they are all good. When you rev it to 3k it gets really rough. I pulled the plugs and they look rich and the #6 plug is really gassy but when you pull that wire the rpms definitely drop. I ohmed the coil and the primary has around 1.0 ohms resistance and the secondary shows OL on every companion. This has me stumped because you can feel the vibes everywhere and it doesn't really seem clutch related. Scanned it on a Solus and there aren't any codes and the O2s are metering fine. Any help would be great!

 

I would CHANGE the plugs and plug wires and put a bottle of Techron in the gas.

 

The wires are fairly new and ohmed out good, I also put a set of Motorcraft Platinums in it. Ran seafoam through the gas and booster hose. Plan on pulling the upper intake along with the injectors soon as there is a cloudy day. Probably end up getting a complete kit for the injectors and servicing all of them. What is the best way to diagnose a clutch problem? Someone put a clutch in the truck not too long ago and I am afraid they may have warped something!

 

Just because the wires ohm out well doesn't mean they aren't breaking down under load.

 

Yes, I understand that but the spark is good on everyone of them. Just seems if it was clutch related you would feel in in the pedal or something. Hoping maybe someone else has experienced something similar to this. :-)

 

Well, finally dropped the bell housing and checked runout on the flywheel. From what I have read anything inside of .008 is acceptable and the flywheel measured .0012. Also measured runout on the crank and it was .002. Would .0012 cause a hard vibration at idle? Seems possible and I am hoping that is the case! Any insight would be great. Thanks!

 

.0012 is a LOT less than .008 (.0080).

You sure you don't have 2 crossed plug wires? The terminals on the coil pack are NOT in numerical order.

 

If the plugs are gassy like you say and it appears to be running rich, yet you're not showing any codes. Then you pull a plug wire and still no codes. The PCM is saying buh-bye. I'd check with NAPA and see if they have a PCM programmed to your engine and truck. They usually do. It may or may not require new keys, you'll have to ask the NAPA boys. It's a plug and play kinda swap and since you apparently have enough snap to properly get this diagnosis, you have more than enough snap to install a new PCM. Should take about 10 minutes. Depending on which PCM you have the cost can be $169.00 to about $329.00.

 

Meant .012...not .0012!

 

There is no issue with fuel or fire on this truck. That has been confirmed. It is a flywheel/harmonic balancer type vibration. The balancer is in good shape, too.