Untraceable Ping/Knock/Detonation (1 Viewer)

[apc15]

Hi Guys,

I'm at my wit's end. I have tried what seems like everything trying to chase down why this is knocking / pinging / detonating (using all the terms for the searching folks in the future ) and I just cannot get it to stop.

Details:

• '84 FJ60 - 2F rebuilt a little less than 30,000 miles ago by a shop, though finer attention to detail was not paid (he re-used a possible 258k mile fuel pump and it promptly broke the arm off 30 miles into the rebuild -- I was wondering why a brand new rebuild was leaking so badly from the valve cover and I found a 4 cylinder gasket under there).
  • Pretty sure pistons are 0.040 over and IIRC the head was milled as well. I would assume the block was also if the head was done, but see above.
• Engine is completely de-smogged.
  • The only lines running to the intake are the PCV and brake booster. No vacuum leaks stemming from these. I even changed out the old PCV line just in case.
• Speaking of vacuum leaks - I cannot find a single one. I sprayed brake clean all around the base of the carburetor and around the intake and couldn't find a leak.
• Just switched to a City Racer vac advance skinny-cap distributor to try and rid myself of the EGR curve.
  • I can get the knocking to *mostly* stop with timing around 0 degrees, but then the truck runs like garbage, as you would expect.
  • Vac advance not hooked up.
• Running a City Racer Fuji Carb.
  • Spark plugs (NGK 5 heat rating) came out white and crusty.
    • Bumped up (down) to 7 heat rating with no change.
  • Ordered an amazon jet kit that goes up to 240 to try and get rid of the apparently lean running condition-- Installed the 240 on the primary after 200 still knocked -- it is so rich on revs that it smokes and I am still knocking with timing directly in between the line the BB.
• Ran Sea Foam this weekend to try and get rid of any carbon deposits.
• Exhaust (including the manifold) is swiss cheese. It for sure leaks at the union from the 1-2 curve and at the manifold-tail pipe gasket.
  • Refer to above where I couldn't find any intake manifold leaks.

Edit with more:

• This happens even with 93 octane.
• Temp gun on the thermostat housing shows 180-190F.

I'm sure there's more and I will add when I think of them. I've dealt with this practically forever and just lived with retarded timing, but it is frustrating to get nowhere when I'm actively trying to fix it. Please share any insights you may have. Thank you!!

 

[AussieHJCruza]

Do you know how much was taken off the head/deck of the block? Could be that your compression ratio now requires premium fuel or zero timing.

 

[apc15]

That was one thing I forgot! This is all with using 93 octane.

When I still had the stock distributor (again with no advance hooked up, and with a Weber until last month), I put in a little rubber stopper to mechanically stop the advance. This was far from scientific so I don’t know how much, but I was able to run 3-4 degrees of base timing with this.

Now with the new distributor, it is stuck around that 0 point. It is audibly rough at idle though and is generally not happy going anywhere with speed. Still cannot run vac advance at 0 degrees.

If too much was taken off the block and head, my only option would to be to get an untouched head, no? Or a different engine all together?

 

[AussieHJCruza]

So just to confirm, it didn't do this with the old carb or dissy?

Where is the vac advance being connected to?

 

[apc15]

It did do this with the old carb and dizzy. I also richened up that carb and had put in that mechanical stop on the advance armature to get it running with minimal knock, though not none. Vac advance is capped off on the carb.

I got this setup in hopes that it would be a loosely "stock" correct setup for a non-EGR engine.

 

[Skreddy]

With everything else that was apparently done wrong on the engine; the cam could be out of time with the crank.
Are you sure your sound isn’t just exhaust leaks if your exhaust is that bad?

 

[apc15]

1. The cam timing - I suppose that is a possibility. The thing generally runs well except for this issue, though. I can pull the timing cover if nothing else solves the issue. Thinking about it though - If it was off in either direction, wouldn't there be less mixture getting into the cylinder and therefore less pressure? Via intake valve closing too early or too late and pushing some back out?

2. Exhaust leak - This definitely crossed my mind and I haven't completely ruled it out yet. But it really really sounds like knock. The volume is load and ignition timing dependent. Which I suppose again could be the exhaust. -- The plugs I took out though were pretty gnarly looking and I stuck a borescope down into the cylinders and the tops of the pistons have also seen better days. I will try to get a video later and maybe you guys can be the judge of the sound.

——————————
Pictures:

Cylinder 3 was the worst looking

Old plug after I wire brushed all the crud off

Initially looked more or less like the 3rd pic

 

[Pighead]

When I still had the stock distributor (again with no advance hooked up, and with a Weber until last month), I put in a little rubber stopper to mechanically stop the advance. This was far from scientific so I don’t know how much, but I was able to run 3-4 degrees of base timing with this.

You can fiddle with your mechanical advance curve, no need to get rid of the big cap dizzy

 

[Skreddy]

1. The cam timing - I suppose that is a possibility. The thing generally runs well except for this issue, though. I can pull the timing cover if nothing else solves the issue. Thinking about it though - If it was off in either direction, wouldn't there be less mixture getting into the cylinder and therefore less pressure? Via intake valve closing too early or too late and pushing some back out?

2. Exhaust leak - This definitely crossed my mind and I haven't completely ruled it out yet. But it really really sounds like knock. The volume is load and ignition timing dependent. Which I suppose again could be the exhaust. -- The plugs I took out though were pretty gnarly looking and I stuck a borescope down into the cylinders and the tops of the pistons have also seen better days. I will try to get a video later and maybe you guys can be the judge of the sound.

——————————
Pictures:

Cylinder 3 was the worst looking

Old plug after I wire brushed all the crud off

Initially looked more or less like the 3rd pic

View attachment 3992620

View attachment 3992622

View attachment 3992623

Is it smoking? That looks to me like either running pig rich or burning a lot of oil.
I’d be having a chant with whoever built the engine.

 

[apc15]

Not actively smoking besides when I intentionally make it rich (with the 240 jet). Does consume a bit of oil though... And more than it drips I think. But nothing crazy, maybe a quart or a little more in between oil changes.

Unfortunately engine guy is across the country in Arizona (long story) and it's been 3 years. The distance was the main reason I didn't pursue anything when I found the other things. He did put a new camshaft in it when he rebuilt it. He said he had to look everywhere for it-- I wonder what it actually ended up being. Naive me didn't think to ask because I assumed it would be correct (lessons learned). Are there cams that would fit but would be drastically incorrect enough to cause this??

 

[SteveH]

I would think a hot engine compression test is seriously in order. You should see 150-ish PSI for a stock engine at your elevation.

 

[apc15]

Good point, Steve. I will do that tomorrow and report back.

 

[apc15]

The results are in... The middle two cylinders are sad (remember how I said Cyl 3 looks the worst). The rest are above the 150 mark. They were probably higher when the rebuild was new.

165
160
110
135
165
165

---------------
I went back through my notes app and actually do have a test I ran about 6 months after the rebuild. They were indeed higher lol.
185
185
180
165
175
185

----------------

Not sure where to go from here. Pistons are obviously still black after the Sea Foam from the borescope pictures. Maybe try running more of that? Is there a thicker head gasket available to try and relieve some of that extra compression?

 

[Skreddy]

Was this a test on a hot engine with throttle wide open and all plugs removed?
Have the valves been adjusted/checked recently?

I wouldn’t worry about those 165’s. Compression test numbers do not equal compression ratio. I’d be more concerned with the 2 lower numbers and for that, I’d check valves, then do a leak down test or at minimum, put air pressure to each cylinder with that cylinder at TDC on compression stroke (both valves closed) and you’d hear air coming out A) intake (bad/not seating intake valve); B) exhaust (exhaust valve issue); or C) crankcase/pcv/head oil drain holes, which is fine if it’s minimal as the air should leak past the rings. If it’s blowing like crazy compared to other cylinders, then it’s rings. Only need like 20-30 psi for this test and hold it from rotating the crank. Can do it with an air blow gun and a rubber tip to seat against spark plug hole.

 

[CruiserTrash]

My vote is on a slow-leaking head gasket failure between cylinders 3&4 and an exhaust leak that sounds like pinging. Two problems for the price of one. Engine autopsy - or at least removal of the head - is going to tell the story here I think.

The mis-timed cam is an interesting theory. the 3F cams, which were available after the 2F cams were discontinued were only 4 degrees advanced versus the 2F cam, but that wouldn't be enough to cause pinging with 93 octane fuel I don't think. To get the came more advanced, somebody would need to fill the woodruff key notch with weld and cut a new key slot. The chances of that happening seem very slim. But again ... you never know.

 

[Skreddy]

My vote is on a slow-leaking head gasket failure between cylinders 3&4 and an exhaust leak that sounds like pinging. Two problems for the price of one. Engine autopsy - or at least removal of the head - is going to tell the story here I think.

The mis-timed cam is an interesting theory. the 3F cams, which were available after the 2F cams were discontinued were only 4 degrees advanced versus the 2F cam, but that wouldn't be enough to cause pinging with 93 octane fuel I don't think. To get the came more advanced, somebody would need to fill the woodruff key notch with weld and cut a new key slot. The chances of that happening seem very slim. But again ... you never know.

Unless the machinist put the cam in off a whole tooth, or more. If the cam were too far advanced, it’d be building cylinder pressure too early on the compression stroke. If the cam were too far retarded, it’d be pushing some of that mix back out the intake valve, depending how far advanced or retarded it was.
Too much advance and detonation will erode the head gasket too. I’ve seen a few poorly desmogged (or smogged but not functioning) 2F’s running advanced timing and a bad gasket between cylinders 3 and 4.

Pics of the engine could be helpful. We saw a recent post where the 2F was desmogged but the EGR tube was just open.

Another note here is the fuel pump arm breaking off. How did you get the broken piece(s) out and was it installed without the spacer and that’s why it broke?

 

[CruiserTrash]

Unless the machinist put the cam in off a whole tooth, or more. If the cam were too far advanced, it’d be building cylinder pressure too early on the compression stroke. If the cam were too far retarded, it’d be pushing some of that mix back out the intake valve, depending how far advanced or retarded it was.
Too much advance and detonation will erode the head gasket too. I’ve seen a few poorly desmogged (or smogged but not functioning) 2F’s running advanced timing and a bad gasket between cylinders 3 and 4.

Pics of the engine could be helpful. We saw a recent post where the 2F was desmogged but the EGR tube was just open.

Another note here is the fuel pump arm breaking off. How did you get the broken piece(s) out and was it installed without the spacer and that’s why it broke?

Yeah could be a tooth off on the timing gears. Interesting...