Persistent p0305 code help needed

[Durvyranger]

Hello first post.

I have 1998 3.0 with standard transmission and I had to replace the head gaskets over Christmas due to #6 fouling every few hundred miles. the heads looked fine but I had them redone by a reputable machine shop that has been in business 50 years.

After getting it back together I had a miss at idle that would go away after I got rolling. You could feel it kick-in and was similar to what it was doing on #6 before the head gaskets only now the CEL light comes on with miss in #5instead of #6. And then after 800 miles #5 dies completely (I assume it's #5 from the CEL).

Now over the past two months I have replaced fuel filter, motorcraft plugs, motorcraft coil, NGK plug wires, and most recently #5 motorcraft injector (the original had a broken porcelin tip). A motorcraft cam syncronizer. The compression on #5 is 160 lbs and I don't have the ability to do a leak down. The #5 plug looks fine and is dry. I even switched plugs from good cylinder and ground a spare plug on the manifold and it sparks. I put a stethascope on #5 injector and it's clicking. I put in a new battery.

Now I'm stumped. The local ford dealer says they will charge up to 2 hours to diagnose so with shop fees maybe $250. I'm thinking a scanner might be better money spent but I've never owned one. A local City Garage wants $105 to diagnose but I don't have much faith in them. They tell me they don't have anything to diagnose other than a code scanner and it's all trial and error.

So now I'm at a loss wondering if #5 valve seat came loose, new motorcraft inejector from ebay was defective, the PCM is bad, I have a vacuum leak with no codes, my head gasket leak was just a coincidence and I have the same problem as before, why was my injector tip broken and did I break the repalcement also. Any suggestions on where to go from here.

 

[RonD]

Welcome to TRS

I would retorque the intake on that side, 4, 5, 6
An air leak near #5 could be leaning the mix too much at idle.

Broken injector tip drips fuel at idle so can cause a lean mix in that cylinder.

Floating valve seat would be more permanent or way more intermittent, so always at idle wouldn't fit.

At idle you have the highest vacuum in the intake manifold so if there is a leak that's when the most air would be pulled in.
A clean spark plug on a missing cylinder usually means a lean mix miss, so not rich mix carbon build up or oil fouled from rings or valve guide seal.

Idle is also when the injectors put out the least amount of fuel, so a bad tip would be noticed more at idle.

Bad coil for #5 would most like show a rich mix carbon build up on spark plug.


The bad one would be a steam cleaned spark plug, small head gasket leak, had to be mentioned.
You could do a glove test just to get that off the table.
Any missing coolant?


You can pick up OBD II reader fairly cheap now, there are $30 OBD II Bluetooth readers that connect to smartphone or laptop.

 

[Durvyranger]

Thanks for the reply Ron, no lost coolant and #5 is 100% dead now. Before I remove the upper intake again which is probably inevetable, would a vacuum guage tell me if I have a leak or is it so small to detect. Would a $150 real time scanner help me diagnose a vacuum leak? Maybe the old cigerette smoke test?

 

[RonD]

Vacuum gauge is inexpensive and a very good tool, it can tell you about vacuum leaks but also ring and valve condition

Google: basic vacuum gauge test

However with a dead cylinder it may be hard to get valid vacuum test results.

If you have a compression tester I would pull it out and test 4, 5, and 6
If possible pull out all spark plugs for a compression test, this gives a better test since there is only the one compression stroke to slow down the crank speed.

What does the spark plug look like now?
Swap #4 and #5 plugs.

#1 and #5 cylinder are "paired" on the 3.0l, this means one is at TDC exhaust while the other is at TDC compression.
Since you have a "waste spark" system you can swap #1 and #5 wires on the coil, this would test if there was an internal coil issue, long shot but not 0 shot.

Waste spark means each cylinder gets a spark on every TDC, compression and exhaust.
V6 will have 3 sets of "paired" cylinders, this, of course, balances the engine
3 and 4
2 and 6
1 and 5

Hence the firing order and coil lay out
Any of the "paired" wires can be swapped on the coil

 

[Durvyranger]

Thanks I'll see if I have my old vacuume guage or just buy a new one. It's sleating outside so it will be next weekend before I get around to working on it. I'm thinking vacuum leak at this point and the upper intake covers #5 so it might be hard to get the carb cleaner method to work. Maybe cigar smoke through the brake booster port. If only a lean code would pop up and give me a clue.

I did swap plugs and even went back to my original coil. Tested the coil by holding the wire an inch or so above the coil and the spark jumped.

 

[Durvyranger]

UPDATE: Incase anyone has this issue in the future, I hate reading threads that suddenly stop without an ending. I took the truck up to a chain called City Garage and the manager said they had a $28K diagnostics machine that would determine the issue. Within an hour i get a call and it turns out it was #1 missing NOT #5 like the CEL indicated. Then the light bulb went off and I remember placing the old plug from the blown #6 in there since I forgot to get a replacement and was eager to get it started. The plug was only 3K miles old but had some discoloration and contaminates that I tried to clean off with carb cleaner. #1 was easist to get to if i needed to repalce so that is where it went and I made a mental note that if issues on #1 came up I knew what it was. I also told him that I had repalced the syncro and he asked if i used the tool. I didn't. They called back again and said they would repalce the spark plug and adjust the syncro for $378 and guarantee it would not miss, I was so sick of messing with this I agreed. I suspect they had already repalced the plug and had it running fine. This seemed excessive for what would take me 30 minutes but I was happy to get this three month ordeal over and move on to other things. Also, several people said my freshly refurbished heads were bad which had me worried I was going to have to junk the truck since another head repalcement was not an option.

So if you get a miss code for one cylinder don't trust the code 100%. I concentrated all my effort on # 5 when that was not the cylinder all along. When he told me #1 I knew instantly what the issue was. Now I'm wondering what level of scanner I would have had to buy to detect this issue. The diagnistics was $105 and the syncro adjustment was $210 the plug was $35 shop supplies $26 plus tax was $378.

 

[RonD]

Thanks for the update

#1 and #5 spark at the same time, share the same coil.
One will be starting power stroke when the other is just starting intake stroke when both spark plugs fire, this continues for every rotation of crank shaft.

The mis-fire 30x code is usually generated by info from the CKP(crank position) sensor, the computer monitors milli-second time between pulses on the crank rotation, if there is a delay then that one cylinder didn't add power to the crank, so mis-fire is detected.
There are other codes if coil mis-fire issue is detected.
Computer would have to be pretty F*ed up to confuse #5 and #1, they are on opposite sides of V6 firing order.

With the one coil and 2 spark plug setup, waste spark system, the spark plugs are wired in series, so one plug/wire can effect the other.
My guess would be #5 was missing as was #1 intermittently, both caused by #1 plug.
Electricity always travels on the path of least resistance, so #1 plug was both lower and normal resistance at different times, starving spark from #5, the resistance changes based on heating and cooling.
So computer did see #5 missing it was just not correctable without repair of #1.

The synrco wasn't an issue in the mis-fire.

DTCs are pretty general even when they look specific.
But yours is especially interesting, sorry it cost so much to fix

Thanks for the heads up

 

[Durvyranger]

Ok, I spoke with the mechanic again and he said the syncro was out 180 degrees. At first I had my doubts but now that i think back, I set the syncro with the heads off and #1 at TDC with the timing marks on the balancer and a visual on the #1 piston. What I failed to realize was that it was TDC on the exhaust stroke not the compression stroke this made the computer think it was #5 missing not the actual #1. At the end of the day this guy was able to figure out what I couldn't and fix it within a couple of hours. Money well spent.

 

[6.2]

yeah those misfire codes are tricky. i scanned my truck with two different code readers and they both said a different cylinder (shared on coil though) so i knew it was one or the other. I replaced all my plugs and wires anyways since they needed it.

obd2 scanners can be helpful, but not always 100% accurate.

glad you were able to get it all fixed up. shitty it ended up costing you a nice chunk of change, but well worth it in the end.

 

[Durvyranger]

If i had just repalced the #1 plug like i should have i would have never known the syncro was out 180 degress since both plugs fire at the same time.

 

[6.2]

This is true! Sometimes misinformation can be helpful.



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