Carbon deposits won't raise compression any appreciable amount but they retain enough heat to ignite the fuel charge early which is what causes knocking. Since you have now blown the head gasket you'll soon find out if carbon buildup is you problem but based on the above info that would be my suspect.

 

Are you certain this work was done correctly? If the truck didn't have this problem before the timing chain was changed then the logical conclusion is the work created the problem.

 

Unfortunately I won't be repairing this engine. I'm gonna put the 300 from my '89 F150 into this 94, as I have a 6.9 Diesel going in my '89 F150.

I was going to fix it, but just incase I find a whole lot more than just a blown head gasket.... i'll just swap them.

But Since i'll have to pull the '94 300, I'll still the head off and have a look inside, cause I am curious my self.

 

I'm NO EXPERT but there are some things that could cause a "lean" condition.

Obviously......... an O2 sensor.
Poor block grounding, ground points, battery cables and connections.
Oxidized or corroded connectors and/or pins and recepticals
Poor PCM ground(ing) and circuits
PSOM not calibrated for current tire size
Failing in-dash tank selector switch
Inferior quality/failing fuel regulator
Exhaust leak pre-O2 sensor
Vacuum leak pre-combustion

Those are some things I have chased and corrected on my truck.

My 94' with a 4.9 averages 15-17 mpg and since I'm a grandpa', I drive like one.

Bob

 

Would a lean condition cause me to get really ****ty mpg?


Your mpg's is what mine should be getting! Exact same truck, mines a shorty truck, reg cab short bed.


I do have a small exhaust leak (manifold) as also under load, only takes a light load, you can hear a ticka ticka ticka ticka. You can also hear it cruising along if you turn the radio off. It's hard to hear, but I can hear it if i'm listening for it.

 

John,

Some random responses...

If the mixture is lean enough to cause misfire and knock, then yes, it will really hurt your mileage. I'm not talking just a little lean though, I'm talking "somethings pretty screwed up" lean.

You said you hadn't done a compression test. When I talk about compression causing knock I'm not worried about bad rings or valves causing a lack of compression. I'm talking about someone swapping a set of 10:1 pistons into it. Probably not an issue.

I don't know about the 4.9 six, but on my 460, my 302 and my Jeep 258 six, all had the sheetmetal pointer slightly to the passenger side of center. IF (big if) you are looking at the wrong pointer, I'm about 95% sure that being off in that direction would retard your timing, not advance it. So while I'm surprised that the pointer is to the drivers side, I don't think that could cause this problem (the driver does sit on the left in Canada, correct? )

What you're talking about does sound like knock. Knock is always worse under heavy throttle, and always worse at lower rpm (same load at lower rpm means more throttle, plus more rpm tolerates more spark advance without knock)

Conanski is right about the carbon deposits. They retain heat and make hot spots that can ignite the mixture. Knock (or more technically, preignition) is when the fuel/air mixture starts burning in multiple places rather than just the spark plug. This causes multiple flame fronts to crash into each other, which is not a good thing. Anything that raises heat and/or pressure (pressure raises heat) in the combustion chamber will lead to knock.

 

Very interesting for sure!

If it matters any, the old super worn out plugs I removed from this engine when I got it, though it seemed to run good with them (to my surprise, judging how bad they were), were burnt in color, orangish, pitted and blistered white insulator, and the electrode looked glazed and the tip was melted and pitted on some of them.


The fan had ate a chunk from the radiator when I got it, and it was elaking there under pressure, and it was running hot (though not overheating), so god knows how long it's been like that.


I pulled a couple plugs out a while ago for inspection when I was checking everything out, and working out the bugs problem by problem, and the new ones I put in 4-5k miles ago seem to be doing good, normal in color.

 

I'm still caught up with this.
My 94' 300 has the pointer on the PASSENGER side of the engine.

Dampners have been known to slip, but, two different locations to set the base timing on the same truck ????

And another possible cause for running lean ????.........Since the capacitors in the PCM's are prone to failing/leaking, it isn't out of the realm of possibilities that a leaking or failing capacitor(s) in the PCM are having an "effect" of the performance of your truck.

Just my take ........

Bob

 

Well now..... hahaha get ready to laugh at me guys!


Some pics will confirm here.


This is what I went by,



And now that my fan clutch spun it self off and fell on the ground that same night I blew the head gasket, looking down, I found what I SHOULD of used to do timing on the passenger side of the block.





Man.... wonder how bad my timing is. lol What the heck is those numbers for on the drivers side?

 

I'm not sure about the 4.9's harmonic balancer, but I know of on the 5.0's a lot of them had a rubber isolator built into them. A lot of times the balancer would "slip" and cause it to spin around in relation to the crank shaft, not enough to imbalance the engine, but enough to make your timing marks off. IF this was possible for the 4.9, you COULD be advancing the timing way passed 10 degrees. Because it sounds to me like it's pinging like a SOB due to being too far advanced.

 

But if timing was to far advance, it would ping all the time with RPM's going up. Mine only rattles under load.

 

Not necessarily. On my truck I advanced the timing pretty far, can't remember exact number. But it would idle fine and under light acceleration it drove good. If I had a good load on it or accelerated hard it would ping really bad. Backed the timing off and haven't heard it ping since.

 

It could be that under lighter loads the knock sensor can pull the timing back far enough to stop the knock, but that it just runs out of range when it's loaded down. But I'm still twisted around on how timing to that side of the engine makes the timing too advanced. Engines turn CW as you look at them from the front. The timing mark being way over there when #1 fires means that #1 is past TDC when it fires. After TDC is retarded, Before TDC is advanced. So I'm confused there. A slipped dampener sounds like something to check out too.

 

Well, my only explaination would be that John may have been using a mark on the dampener/harmonic balancer that was close to where he thought the "correct" degree guage was, on the DRIVERS SIDE, and then adjusted his timing using that "close" scribe mark on the dampener/harmonic balancer as his timing mark.

I really shouldn't be answering for someone else though..........

Bob

 

I re-did my timing last night. I set it at 10 deg as it was sitting at 6 deg. Woke the truck up in the whole rpm range. I fiddled with it a bit more and went up to 14 deg. It didn't ping at all just cruising or idling but under load she started to tick. I finally settled at 12 deg and it seems to be very happy there.