3.0 liter, #3 misfire

[94RoadkillRanger]

So, how do I start? 1998 Ranger 2WD, EXT-Cab 3.0 with automatic. It has a misfire. I was driving down the interstate and at some point hit the gas when the road opened up from slow traffic, the engine revved high in my opinion and i took my foot off the gas quickly. Maybe I never pushed it that hard before. Now it shakes on idle, but runs good on the road.

 

[94RoadkillRanger]

A year ago I bought it with a #2 misfire and fixed it by replacing the injector and spark plug. I pulled codes and came up with left bank lean, right bank lean, and #3 misfire. Spark tester said that I was getting spark. Noid light said that I was getting a signal from the computer. And the compression test read 130psi. So, I replaced all 6 plugs this time and the #3 injector. But I still have a misfire. Also, the engine had a hard start. I replaced the fuel pump assembly and the hard starts are gone but I still have a misfire.

 

[94RoadkillRanger]

Another thing...it started making a whirling noise at slow speeds. After I replaced the Sensor & Syncronizer the whirl went away. Engine runs good but shakes on idle.

 

[94RoadkillRanger]

Keep thinking of stuff...The reason I replaced the injector was because during idle, I pulled the electrical connector and did not notice a difference in the way it ran. I also tore the plug wire on #3 while checking the cylinder and so I bought a set and replaced #1, 2 and 3 wires.

 

[Rearanger]

I'd start by looking for vacuum leaks.

 

[94RoadkillRanger]

OK - vacuum leaks. I disconnected the battery on one of my repairs and lost the codes. The next day the misfire #3 came back. So, I'll try propane around that area especially, including the intake manifold.

 

[6herald6]

This sounds very familiar to me. My '05, 3.0l had the continuous misfire problem about 3 years ago and I went through all the relatively simple problem checks that you did. Of course, it turned out to be THE worst case problem: valve seat recession. Two cylinder heads + labor cost $,$$$.$$! And now... the problem is back!

Fred

 

[94RoadkillRanger]

So, I spend 16 minutes blowing propane and nothing. Replaced the remaining spark plug wires #4, 5, 6. Last night, with assistance, trany in gear, brake on, with more shakes and more propane (using 3' of 3/8 hose) still nothing, except for the #3 misfire.

@ 6herald6 - so you had good compression with that?

 

[94RoadkillRanger]

Four wires to the coil pack, power and three grounds I suppose, which is a wasted spark setup. So, if coil pack was bad then should also miss on #4. Removed it; visual inspection of coil pack: no cracks, 0.5 ohms on the three primary windings, 12k ohms across the three secondary windings. Should be good, replaced it anyway for $30 new. Yep, still misses.

Removed upper intake manifold, inspection: no cracks. Saw what looked like a bad spot on bottom of upper intake. Replaced gasket with thin layer of sealant both sides, all back together. Still misses.

I suspected maybe clogged fuel rail at the end (where #3 lives). Pulled rail from injector, gas poured out, again, as it did when I had replaced the injector earlier.

Now I'm thinking maybe a broken rocker, with a permanently closed valve.

 

[JP02XLT]

What does the plug look like?

JP02XLT

 

[94RoadkillRanger]

Plugs brand new. Old plug was clean, only had 10k on them.

 

[JP02XLT]

So the plug has no color to it after it has been ran? pull the plug and check the coloring on it

Just because the plug is new means nothing.

JP02XLT

 

[94RoadkillRanger]

The exhaust has puffs out of the tailpipe, but no smoke. In park I slowly revved the engine and could still feel and see the miss at higher RPMs, but it drives OK. So, I pulled the #3 injector wire to prevent raw fuel from dumping into the catalytic and drove two miles. It definitely runs better plugged in; injector reconnected.
I pulled all six spark plugs and they look the same on the threads. However, the ceramic below the gap is brick red on all six and I took pics this morning.
Game changer! While the plugs were all out, did another compression test:
1) 160psi
2) 175
3) 70
4) 165
5) 170
6) 175
The lean codes are gone, with the P0303 remaining.
I suppose the thing to do next is connect an air hose to #3.

 

[JP02XLT]

Cyl 3 with only 70 psi is an issue, either a burnt valve, or something holding the valve open, These heads are well known for having a valve seat issues, or cracks.

The coloring on a plug on an engine running properly is going to be a light tan near the electrode tip and generally gets a shade darker into the plug, The Red color is almost always due to additves in the unleaded fuel, still considered normal due to the fuel

Have a look at this plug read chart http://www.autolite.com/media/11838/plugtips.pdf
You have an issue on cylinder #3, and unfortunately will likely have to tear that head off to figure out & fix the problem.

JP02XLT

 

[94RoadkillRanger]

Connected up air to cylinder #3 at TDC, only heard air through tailpipe. Rotated engine 360, stopped at 60, 120, 180, 240, 300 degrees along the way and heard and felt air coming out tailpipe at every stop. Head is on order, already have right head gasket, bolts, other gaskets, oil, filter, coolant, thermostat.