Hello, this is my first time posting a thread . I am having a problem with my 1997 f150 4.2 v6. The engine is running rough at idle and while driving. It's running so rough that it vibrates the entire cab of the truck. I found water in the oil when I was trying to fix the problem. I have since had the heads redone and replaced all of the gaskets thinking this was the reason for the rough idling and rough driving. It wasn't; doing this fixed the water in the oil but still I have the rough running engine at idle and driving. I have replaced the EGR valve, plugs and wires, pcv valve, replaced the coil pack, fuel filter and air filter (everything has been replaced with ford recommended parts because I have read that the engine I have doesn't like after market parts). Oh - and while driving the engine vibrates and sound as if it's going in a cycle in a rhythmic sort of way (like a washing machine goes in a cycle) sorry, best way I can explain it. I have come to the end of what I think it is, Does anyone have any ideas? Any help is greatly appreciated & thank you in advice.

 

A miss that bad, that does a rythmic vibration at higher RPM, is often a dead cylinder.

OBD-II codes read? Any particular cylinder misfire codes set? Really best to try to use the PCM's ability to say what it sees that is wrong.

An old-school test would be to find out if there are one or more dead cylinders. Unplug spark plug wire from coil pack, sneak in a small-gauge (like 22 gauge) bare copper wire into the coil terminal and plug boot back on, clip off wire to leave just a little stub sticking out pointing up. Do it for all to-sparkplug terminals on the coil pack.

Then take a length of insulated solid copper wire, 18 gauge or so is fine, ground one end to block, strip off the insulation on the other end for 2-3" or so, wrap the bare part around the shaft of a 1/4" blade regular screwdriver that has a good plastic handle on it.

Start up engine, let it idle. Holding ONLY the plastic handle, bring the screwdriver tip to touch each of the wire stubs one by one, and listen to engine RPM effect while doing so:

Totally dead cylinder - Shorting the spark to ground like this will have no effect on a cylinder that is dead.

Partially dead cylinder - RPM will drop some, not much, while this cylinder's spark is shorted to ground.

Live cylinder - Noticeable drop in engine RPM when shorting this cylinder's spark to ground.

 

That has to be tossing codes, is the CEL on? Don't overlook the use of a vacuum gauge. You can pull the line to the brake booster and hook it up. Simple charts are available on line with a search as to what the meaning is of the vacuum gauge. As mentioned....sure sounds like a dead cylinder. Have you ever done a compression test on each cylinder? You may have a bad valve. A vacuum gauge will point to that. Is the V-6 a pushrod motor?

 

Thank you for your advice, I have OBO II code reader but no codes. CEL isn't on. that's why I have been jumping around. I am going to try the vacuum test and see what happens, and the old school test. thank you again.

 

This is a case for better diagnostics before just replacing parts on hope.
You need a real Scanner to look at live data and spot items out of spec.
A reader won't do.
Since the motor was worked on, is the cam sync properly timed?
What is the fuel pressure?
What do the fuel trim tables look like?
What does mode 6 test 53 look like for cylinder missfire counts?
You can start to see why you can't get a hold of the issue without some basis and no codes.
Codes and CEL are only the first communications with the outside world to be noticed beside drivability.
The system has been designed with wide tolerences such that every small item is not reported causing the owner to be running to a shop excessivly or leaving the vehichle stranded.
With no code you are left with drivability for which you have nothing to go on.
I can't be of specific help, only to reccomend how to go about solving the issues.
If this came to my shop I would be compelled to look at it from this point of view if any sort of results were to be expected.
Good luck.

 

Ok I have some more information. I did the old school test(as directed above) and there was no noticeable deference. The vacuum test was done with the hose from the brake master cylinder hose and was 19 to 20 when cold and a steady 20 after warmed up. As I was pulling the plugs to do the compression test I noticed the new plugs had a lot of carbon build up on them (at least more than you would think new plugs should have on them) and plugs 1,2,3 had more than 4,5,6. I will post some pictures if I figure out how. I don't know if this means anything but thought I would post them just in case.
The compression test is as follows.

cylinder 1 180 dry 185 wet
cylinder 2 175 dry 178 wet
cylinder 3 165 dry 176 wet
cylinder 4 170 dry 180 wet
cylinder 5 175 dry 185 wet
cylinder 6 165 dry 175 wet
is this good or bad?

The tests that I have done are the only tests that I have the tools for but I do have an appointment to take my truck to a mechanic on the 13th but if I can fix it before then I may be able to save money which is a good thing. again any help would by greatly appreciated. Thank you in advice.

 

I think I figured out how to upload pictures, they should be here. from left to right is plug 1 through 6 and each picture is rotated around for a 360 view. the carbon wasn't dry but not completely wet

 

Hmmm...results look good enough. Plugs should be clean though...sounds rich or weak spark....I dunno'.....how dirty are the plugs? But yet the miss is rythmic...like boom...boom..boom....in order like that? Sure sounds like one dead one. Does the V-6 use 1 or 2 coil packs? Is there any chance you have 2 of the wires on the wrong cylinders?

 

I wonder if you pulled one wire at a time and then started it each time if you could find the dead one that way.

 

I just went and looked and the firing order is right 123564. I was also reading one post that said to move 5 to 6 and 6 to 5 so I tried that and it idled a little better but dead died when I tried to drive. Just tried pulling one plug at a time and it started and run the same each time. and sound is more like rooooom rooooom and like cycling in the same pattern each time. the engine has a balance shaft do you think maybe that could be it. when I had the engine apart I noticed I could wiggle it a little. it only has one coil pack.

 

OK , water in oil , heads off . Did you happen to ck the piston travel on all cyl ? Might you have a bent rod ? Water does not compress , rods bend . Just a thought . If vibe was there before and still here .

 

So it's more like a surge than a miss? Does the tach rise high then return to normal in a rythmic surge?

 

yes more like a surge, I don't think a rod is bent because I have had this problem for a at least two weeks be fore I stated looking. at first I thought a motor mont was going bad

 

I dont have a tech gage

 

if it was a bent rod would the cylinder walls be scratched or something like that.