1997 4.2 170,000 miles cylinder 5 miss issue im lost i have spark fuel and compression i dont know where else to look

 

Is it a code in the computer, or and actual miss that you can feel and/or hear? If it's an actual miss, it could be the plug wire, the plug, or the coil pack. Just because you have spark at idle with the hood up, doesn't mean it's strong enough under load to properly fire the cylinder.

 

When does it miss? One common cause is several EGR ports plug up so most of the EGR flow goes to one cylinder, causing that cylinder to misfire. I've not been in this engine, it may not be that way. As a first pass, disconnect the vacuum line from the EGR valve (the vacuum valve up above and to the left of the thermostat). If it quits, you have plugged EGR ports.

 

code in the computer tells me cylinder number 5 checked voltage in th plug wire while running changed plugs around has compression egr ports cleaned out last year when i changed intake gaskets

 

unplugged vacum line to egr valve still no change. time for a new truck?

 

May be time for a trip to the Ford service dept.

 

But is it simply a check engine light, or an actual miss that you notice while driving. I still lean toward the coil pack, the wires, or maybe even the crank position sensor. If that cylinder still has good compression, it's gotta be the ignition system, or something that tells the ignition when to fire, or a fuel problem.

 

it is a check engine light it is a dead cylinder you can hear it in the exhaust you can feel the shake in the engine and when i drove it you can tell its dead v6 not enough power for a full size truck and dead cylinder that much worse

 

relax. I would get a manual first and see what condtions can set this code. I don't think the knock sensor can tell you which cylinder is dead (it might be able to, but I'm not an engine computer guy, I'm a suspension one). I would lean towards a bad part in the ignition.

Try this, pull the plug wire and ground it to something and crank the motor. Then shut her down and pull the plug. Is it wet with fuel. If not then the injector is not firing. If it is, then swap the plug with another one, then the wire...and go one doing this until the code is set for another cylinder. I't mostlike just the wire.

Also, look down the hole for the plug. Sometimes water will get in there and short out the plug wire. Clean it out and see if the problem goes away.

 

dona all that ive checked out every possible solution i have freinds that are mechanics 1 dones driveabilty diagnosis every one is stumped by this so far

 

1. Verify spark with a spark tester ($6). This is different from testing with wire 1/2" from ground (doesn't verify boot) or with plug grounded (no pressure during firing event means far less KV required).

2. Now verify spark with plug pulled and grounded. Or better yet, put 1 new plug in it. Plugs can have internal problems with opens and grounds also.

3. Verify fuel flow. Several ways, one is to pull the injector and watch it. Another is a injector drop test with a scan tool. Smelling, feeling, seeing fuel on plug isn't good enough. It has to not flow when not commanded also. If you pull two, you can visually see if they flow the same. Plug holes with something that won't get ingested, like your thumbs.

4. Running compression test. Should be 30-40 psi at idle, should jump up to 140 or so if you snap the throttle. Static compression isn't always useful. Don't need a leakage test for a miss. If running compression, it should fire.

5. Verify both valves actually open. Compression tests do NOT tell you this. Have to pull the valve cover.

6. If the EGR passages were all plugged except #5 and the EGR valve didn't close, pulling the vacuum line off wouldn't help. Disconnect the EGR metal tube from the passenger exhaust manifold, or break it elsewhere, and PLUG it. If you don't plug it and the EGR valve isn't closing, you'll have the world's largest vacuum leak. Or pull the manifold and clean it, I wouldn't if I didn't have to.

7. Pinch the EVAP hose, oh skip that, it wouldn't affect just one cylinder. On most engines EGR wouldn't either but it sure does on this one.

8. Verify spark timing for that cylinder, fuel timing could be off 180 degrees and not hurt. I've never heard of this, but you never know. Oh hell, skip this too. If it's that outlandish, it's haunted.

My guesses, (1) no spark under load. (2) EGR flowing and blocked to most cylinders. (3) partially plugged or leaking injector.

If you really have mechanic friends, get them to look at the aggregate fuel trim (add short and long term fuel trims together). For most misfires, if very, very high trims (positive 20% or more) the injector is plugged. If less that 8-10% either way, no spark or mechanical (compression/valve) problem. If it's running and you pull the injector connector and the fuel trim doesn't change or changes less than 10%, it was the injector.

Good luck, wish you were down here in Columbus, I'd love to know what's up!

 

found my cure removed blue oval replaced with a nice gold bowtie never run better before in its life

 

I'll bite, the bowtie may have been the principal fix, but did you do something else at the same time?

 

gm 502/502

 

I kept getting a #4 misfire code on my computer. I changed plugs and wires, but it kept coming back after a while. Took my truck in last week to get the infamous defective stock upper/lower intake gasket replaced and guess what the mechanic showed me - a blow-out on the lower gasket on the #4 exhaust port. Apparently it was dripping coolant into the cylinder and causing the misfire when I started up in the morning, but ONLY on the days that the engine stopped with the #4 exhaust port open on that chamber.

Problem fixed!

Good luck,
Dan