300 i6 Rough idle/oil pressure light, temp and fuel gauge issues
 

Get ready, because this will be a long one! I'm sorry if I seem to be all over the place, but I'll try to keep everything organized.

Issue #1: rough idle/miss. I'll start the story at the beginning. I had finished up the DSII and Edelbrok 500CFM/Offenhauser DP intake conversion about 2 or 3 months before, and had the truck running fairly good (even with my kinda bad tuning skills). It was getting fairly reliable, and I started driving it more, and trusting it more. I had just changed the plugs with new Autolite plugs, and went on a small run (about 30 mins) to pick up a load of lumber with a 16ft trailer. Not a big load (I pulled the same or similar weight when I was still stock), but still enough that I could test the truck out, and see how it pulled. Answer, it pulled GREAT! It was a dream to drive. I swung by tractor supply and picked up a metal gate (not very heavy either) and loaded it up, then headed home. About 8 mins into the 10 min trip home, I head a loud POW from the engine bay. I started slowing down, thinking maybe I was pushing her too hard (keep in mind, this is with a C6 going 65 down the highway), but about 3 seconds later there was another POP, and a second later, POP! The truck started losing power, but not like it was going to die, so I pulled into the local church parking lot, where I could unhook the trailer and have my dad pull it the rest of the way home. As I backed up, I could tell the truck wasn't firing on all 6 cylinders, all the time, but it was still running. I made it home, and it ran fine all the way home (I stayed around 20-40 mph, and even revved it up one or twice, but it never popped, but still missed hard at idle). I get home, and a few days later when I have time, I start the truck up and listen to the tailpipe. When I converted the carb, I went to the EFI manifolds, and also went with a true-dual exhaust, with dual flowmasters (that hurt the pocketbook some). So I listened, and I could hear the left tailpipe had the miss, and by a miss, I mean a pop every now-and then (I'll get a video tomorrow), and somewhat consistently. I checked, and the driver-side tailpipe, is the front 3 cylinders. I start unplugging wires to see which one doesn't make the engine run worse, and the only one that makes any difference (and not even a big difference) was #2. I take out the plug, and sure 'nuff, it has.......issues. (see attached pics)
https://cimg8.ibsrv.net/gimg/www.for...ae873028cc.jpg
Ignore the gap and the top piece being out of wack, I dropped the plug, and bent the top piece back out so I could see it.
https://cimg2.ibsrv.net/gimg/www.for...60f6e9fa85.jpg
https://cimg3.ibsrv.net/gimg/www.for...2e0f4830d9.jpg



So I replace the plug, aaaaaaaaaand it doesn't help. Maybe just a tad, but not very much, as I still have the popping from the driver-side tailpipe. I do some investigating, and find out that the miss goes away (or gets much better) as I raise the RPMs off of idle. I do some more adjusting (mess with the dizzy, the fuel mixtures, although the truck was running fine before this incident, so idk why those would be the issue), but nothing helped. I checked for vacuum leaks with carb cleaner, but got nothing.

SIDENOTE: just to make sure I am not missing something obvious, when I spray carb cleaner into the carb (even if I just barely fog it) it bogs the engine (I have to rev it up to keep her from dieing). I am 99% sure this is normal, but just wanted to check just in case I am losing my mind. Ok, back to the story.

I have checked spark, swapped wires, made sure my mark on the crank pulley was accurate (I pulled the #1 piston to TDC on the compression stroke, and the rotor was just past the #1 wire). I am at a total loss. I am going to check the valve clearances tomorrow, partly because I haven't since I have owned this truck, and partly hope that will help (not sure how, but I still hope!). My only idea of what might have happened is, some of the plug (the park the blew up) might have gotten stuck between a valve, and messed up the valve/seat. I am also going to try to procure a compression tester (the screw-in type, not the kind that has the rubber tip that you hold over the hole and break your arm with), to see if that tells me anything. This truck has blowby issues (that or a completely screwed PCV valve, which I'll also replace while I'm here unless it is outrageous), so I know the rings are on their way (ring job later this year), but that shouldn't cause this issue. I have heard where some parts from some vendors aren't as good as genuine Motorcraft, so here is the list of what I have, as far as ignition. Duralast Gold dizzy off an '82, Duralast ignition module (the silver box), AAW DSII harness from summit (that one REALLY hurt the pocketbook), a set of carquest plug wires, and Autolite AP46 spark plugs (almost new at the time of the blowup). I will take any help I can get. Fortunately, this truck is not my daily driver, so I am not in dire need of it, but I enjoy driving this truck, so I'd like to get her back on the road, while being somewhat reliable.

Problem #2 Oil pressure light not working/blowing emissions fuse.

A while back, I noticed that my oil pressure light would not come on when I turned the key on, but didn't start the truck. I did the usual, grounding out the wire on the switch, and it did nothing. I then changed the bulb, and that did nothing. I checked the fuse box cover for anything related to the oil pressure, or even the cluster, nothing. I replaced the ignition switch (I checked my diagrams, and the power light supposedly goes through there, and I was having issue with the switch anyway, but was too lazy to replace before now), but that didn't work either. I then notice on the back of the printed circuit, that the pads where the bulb socket for the oil pressure light bulb, are worn out. Since my fuel gauge wasn't working as well (we already replaced the sender and checked the wiring in between) and the pads where the connector made contact were coming off, I ordered a new printed circuit from LMC for the models without gauges. I get it in, install, and nothing changes (except my fuel guage moves somewhat now). I then whip out my trusty test-light, and find out that there is good ground at the connector for the instrument cluster, but no power for the light. I do more checking in my diagrams, and notice where the wire for the light goes into the fuse panel. I noticed before, and checked for a oil pressure light fuse, or anything cluster-related, but found nothing. I then go through and check every fuse, and find that the emission fuse is blow. I think nothing of it, since I deleted all the emissions from this truck (what little were left when I got it), but out of habit, replace it anyway. All of a sudden, my light works again!!!!!!! I feel like a first-class idiot and newbie. I turn off the key, and go get a drink of water, come back and start the truck to move it out of the garage, and notice that the light doesn't come on again.... I checked and the fuse blew again. I replace with a fuse slightly bigger, and it blows again. Also, I now notice my fuel gauge shows a quarter of a tank (I am pretty sure I have more, but still need to check), and the temp guage pegs all the way out when I first turn the key on (it takes a bit to get there, but it always goes all the way to the right). I now am pretty sure I have a short somewhere in the vast mess of wires behind the dash, and something screwed up with the fuel gauge/temp guage (I unplugged the temp sender, and that didn't affect the gauge). I was going to (or told myself I was going to) take off the top of the dash at some point, and fix the droop in it, and clean everything back up while I'm at it. I now and afraid I have to take the ENTIRE console, dash, I mean EVERYTHING out to find this one wire. I am a stickler for having things look stock, or if not stock, look like they could be factory. So I won't go the route of adding a mechanical gauge (just yet, I might add one in addition to the light, after I rebuild the engine), and I NEED to find and fix this wire. My question is, does anyone have ANY IDEA where this bare wire/short could be, or where to start looking? I have a dedicated shop now, so I have the space and time to tear into it, but I'm in no particular hurry, so I want to research all I can before I tear into the console/dash area.



I really appreciate anyone taking the time to read through this, as I know it is extremely long. I will take any advice/help I can get.

Thanks everyone,
Josh

Problem #1. Continue on with the compression test. See if the one with the broken plug is low now.

Problem #2. You can check the temperature gauge just like you did the oil pressure light. Ground and unground the sending unit wire for the temp gauge with the key in run, the gauge should swing back and forth. If it does, your sender is bad.

After that nice long post, you didn't say what year truck you have. I took a guess that thought the 85 diagram may work and looked here, Fuse Panel & Circuit Protection - Gary's Garagemahal (the Bullnose bible) but didn't find a emissions fuse.

Besides the missing center electrode, I'm curious about the damage at the 2:00 position in your first picture. There's a little gap on the outer shell. Is that a chunk of carbon missing? Or is that metal missing from the outer shell itself? And for new plugs, it seems like a lot of carbon build-up, too.

I agree with your idea to do a compression test. As you mentioned, I wonder if that missing electrode piece got caught under a valve. A compression test will quickly show if something is wrong.

1.This is normal.

2. Do a compression test, wet and dry. Also spin the engine with valve cover off and observe valves. You can even do this while its running for a short time.

--What is an "emissions fuse"? Does this power the computer or the emissions light? Did it power purge solenoids etc? I have never heard of this.

--How did you connect temp/oil sending wires when you converted to duraspark? these are actually part of the ignition wiring loom so maybe you made an error there.

So, an Executive Summary would have something like: You did a DS2 + EFI manifolds + dual exhaust swap but it's still not running correctly, it sporadically backfires through the carb & exhaust, correct?

You investigated & replaced a single spark plug, what do its neighbors look like? A lean condition can cause backfires, look at ALL of your spark plugs.
Don't use a spark plug you dropped as a primary method of diagnosis, that can be misleading.

The water temperature gauge is red/white and the oil pressure gauge is white/red; they both run from the connector at the back of the gauge cluster -> through the firewall to a connector on the driver's side wheel well under the hood -> to the sending units on the engine. You definitely have a short circuit somewhere in the Temp gauge circuit... my first thought is that you should look at that connector under the hood on the wheel cover, the ignition system connects in that very same spot and you were just here, you very well could have messed this up somehow.

1985 EVTM here: Fuel Tank Selector & Gauges (Gas) - Gary's Garagemahal (the Bullnose bible)
Page 98 has the dash gauges

Thanks for all the help guys. I got so caught up in providing as much detail as possible about my problem, I forgot the basics.

1984 f150 4X4 stepside, 300 i6. I did nothing to the harness on the truck (I just unplugged everything on the carb, and original distributor). I got the wiring harness from American Autowire, and connected my ignition module, the distributor, and the coil together. The only wires I ran directly to the truck, were to the starter solenoid (for power while cranking) and to the truck for keyed power. I did nothing to the the OEM harness, except disconnect it from the carb, and the dizzy. I haven't even removed/cut the connectors off (for this very reason). Everything was working fine after the conversion, even the oil light, and temp gauge (the fuel gauge hasn't worked since I bought the truck). So I assumed it was something that happened recently.

I checked compression on all 6, and here are the numbers: #1:155, #2:105, #3:145, #4:130, #5:135, #6:130. #2 cylinder is the one where the plug blew. It is definitely lower, but I'm not sure if that is low enough to cause my issue. I checked while cold, after the engine had sat overnight, at around 60 degrees ambient.

That is correct Ctubutis, but it only backfires/misses on the driverside tailpipe, and not the carb (the driver-side are #1, #2, and #3 cylinders). It misses slightly on the passenger side also (#4, #5, and #6 cylinders) but not near as bad. I just assume that is because it's an old/worn out engine. I checked the other plugs, and #1,2,3 are dark, but only brown. #4,5,6 are black. I assume this is because the back half is running too rich, and the front too lean. Next time I run the engine, I'll adjust the carb with that in mind. I'll also disconnect the connector on the fender well (I see 2 round ones, so I'll get both), clean them, and see if that helps anything.

KR98664, I think that was a chunk of carbon, but I'm not sure. Like I mentioned, my tuning skills are lacking, but I had gotten the truck set at around 10/11 degrees BTC, and the carb adjusted where there was plenty of power, and she idled great (I know that doesn't mean it's tuned right, but that worked until I could find someone who knew what they were doing, to tune it, or learn better myself).

About the "emissions" fuse. I was using the diagram in my haynes manual, and that's what they called it. I finally found the original fuse panel cover (someone stuffed it under the seat), and it actually called it the "warning lamps" fuse, so that makes complete sense. I just don't understand why Haynes called it "emissions". But either way, whenever I replace it, it blows again within a minute, so I'm assuming the power wire that feeds that light, is shorting somewhere. But I wonder......I still have the original printed circuit. If the LMC one had a bad trace (and they all look fine to me), and shorted the wires, it would continue to blow the fuse, and maybe the original problem, was just an old fuse blowing (like they do). After I fix the running issue, I'm tearing into that one.

About the temp gauge, I unplugged the wires off of the sender on the thermostat housing, and that didn't change it. I haven't grounded them out, but assumed since it was getting no power, it would just fall back to the cold side.

I am going to take off the valve cover, and check the clearances, and if they are bad off, I'll recheck compression. If not that bad, I'll watch the valves moving while running, and see how they look (I just gotta move some hoses and wires off of the cover first).

Again, thanks for all the help, and I hoped I haven't missed anything!

I've learned alot about this truck over the 2 or 3 years I've had it, but I still have a ways to go.

I don't have access to a 1984 diagram right now. Does this 1985 look the same? Fuse Panel & Circuit Protection - Gary's Garagemahal (the Bullnose bible) It says the warning light fuse is #18, 15 amp. Is that the same position in your truck? I would think they would be close to the same.

There should not be "wires". There should be 1 wire. I think you are looking at the computer temp sensor, not the gauge sensor. The gauge sensor will have a single wire going to it.

Adding to what Franklin2 said... the 1984 had a sending unit located in the thermostat housing with two wires. This provided input to the computer, not the gauge or idiot light.

The temperature sending unit [for the gauge] is a single wire and is located under the exhaust manifold under the #6 cylinder [nearest the firewall].

Thanks guys, I found the sender, but am waiting to test it until I can hook the battery back up. I found a bare wire coming off of the starter solenoid when I was moving wires to take the valve cover off, so I'm going to get a connector and replace that wire, then hook the battery back up, and test. I also found out that the valves are not adjustable unless you replace push-rods. By just looking, the valves seem to be fine (none are obviously too lose), so I think I'll leave them. But that still leaves the question...what is the miss? is the compression on #2 low enough to cause my problem? Could a piece of that plug have gotten stuck between the valve and seat, and therefore hurt my compression? I don't think it's the tuning, since it was running fine before the plug blew up. I just am not sure.

That part of the plug that broke off would not get stuck to hold the valve open and if it did you would have 0 compression.
That part is small so it may have held it open for stroke and then be pushed out.

You can try a little oil in that low hole and see if the number comes up.
A leak down test would tell you why it is low.
Now you don't need the leak down gauges but an air hose screwed in the plug hole, that hole on TDC and turn the air on and listen.
Is air coming out the tail pipe? bad exh valve / seat.
Is air coming out the carb? bad intake valve / seat
Is air coming out the oil filler or breather cap? bad rings

I don't know what plugs you are running but I would replace them all with a different brand. If you had 1 come apart the others may do the same.
Dave ----

The valve & seat are pretty hard so cant see it getting hurt from that piece but anything can happen I guess.

Do you have an extra air hose fitting & welder? If so knock the center out of the junk plug in the pictures and weld the fitting to it.
Sometimes if you have a screw in compression tester that has a 2 part hose you can fit an air fitting to it.

As for PSI good question? I have never don't a leak down test so never thought of it. Maybe start at 25psi?
Maybe someone knows?
Dave ----