GeneralDisorder

iTrader: (1)

Background:

I'm running EBL using the stock 86 LB9 spark advance table.

I have verified with 110% certainty that my mechanical timing is dead on. I have verified the balancer marks against true TDC with a piston stop, and I have verified the large-cap module latency with a timing light to 5,000 rpm. Timing chain is new Cloyes double roller.

It is not lean. I have a wideband installed, and datalogs from the EBL show no lean condition. And I always run 93 octane.

This problem was present with the stock 165 ECM also.

I have pulled 10+ degrees of timing out of the whole SA map. It helps, but doesn't eliminate all detonation.

No detonation is present in the logs or audibly when the engine is cold. Which leads me to.....

Could cooling jacket corrosion cause hot spots leading to detonation? Has anyone experienced this?

This car/engine sat for 11 years and the coolant was extremely chunky. It's got so much sediment and scale in the block that NOTHING leaked when I pulled out the knock sensor. I've flushed it half a dozen times and the coolant is greener than it was initially of course, but it's still got so much sediment that it plugs up the overflow bottle hose regularly. There was a lot of corrosion damage to the lower intake - I had to bead blast the pitting, fill it with aluminum epoxy, and block sand for a good seal. It runs good. Pulls hard - especially when it's still fairly cold. The cooling system has never worked *excellent* - I have a 170 thermostat and it does maintain well - though if the ambient temps approach 100 and I try to run the AC it definitely can't keep up. Starts to climb back up to the "normal" 225 range. Otherwise it sits around 185-195.

Now.... I'm more curious than anything as this engine is worthless and getting swapped shortly for a Vortec, but has anyone experienced such a symptom before? I really think that I'm getting insufficient cooling around some of the cylinders, head passages, etc. Leading to hot spots and promoting detonation. I don't have any other explanation for it. The compression is 190 across the board, it burns no oil.....

I'm swapping to a small cap distributor next weekend - needed for fitment with the First Performance intake to be installed with the Vortec. I doubt this will make any difference but on the off chance there's some issue with the existing large cap I'll be ruling it out for unrelated reasons.

GD

LiquidBlue

GeneralDisorder

iTrader: (1)

I mean all of the cooling passages in the block and in the cylinder heads. It's just got a ton of scale and sediment in it. A nice thick layer.

The water pump was new when I swapped to serpentine belt a few years ago.

Pulling block plugs and running cameras is much too heroic for this boat anchor. It's getting tossed into the weeds in the next few months after I line up the intake, a set of injectors, and a few other parts. Next time it comes apart it's not going together again.

I'm just curious if others have experienced something similar. More of an academic discussion on the subject. I can check it out when I pull it and am not driving it every day.

GD

LiquidBlue

LiquidBlue

GeneralDisorder

iTrader: (1)

It's really not burning oil though and no deposits on the plugs so I doubt it's significant carbon deposits.

GD

Orr89RocZ

iTrader: (20)

GeneralDisorder

iTrader: (1)

I can hear it (headers) and it shows up on the knock sensor.

GD

Orr89RocZ

iTrader: (20)

Street Lethal

iTrader: (16)

I can tell you that a few years back, I purchased a used LB9 engine from someone who claimed low miles, and a very strong running engine. Bought the engine, installed it, and immediately noticed it was detonating when warmed up, though it did in fact pull pretty damn good down low. Static compression was well within tolerating limits, was running 93 octane at all times, timing was set to perfection, and it still pinged once warmed up no matter what. Long story short, the former owner altered the timing in the camshaft, realized this during thorough inspection; so increased cylinder pressure coupled with a warmed up engine. Once corrected, the pinging seized.

- Rob

GeneralDisorder

iTrader: (1)

It seems to be most pronounced when I come out of cruise (14.7 target AFR), and get into the throttle after the engine is fully up to temp - especially up a steep hill. I'll get a bunch of detonation between 2500 and 3200 RPM. After that it seems to trail off as more airflow and fuel probably cools the hot spots I guess. If I immediately try to do it again it's either not present or dramatically reduced. I've added as much as 20% more AE and it doesn't help - makes it hesitate. WOT AFR target is 12.5. If I pull timing out of the map I can't hear it as much, but it's still present in the datalogs, etc.

I'm not terribly interested in trying to clean out the passages. I'm swapping the engine for a built Vortec with First Performance intake.

I'll make some datalogs and post them here and maybe someone can see something I'm not seeing. Nothing I have changed in the tune has made the problem go away - that's with the 165 ECM running $6E and the EBL ECM. And I always run 93.... stock 86 timing map. It's got to be related to the condition of this particular engine.

Carbon build up from before I changed the valve stem seals? It's got 165k on it. Original engine.

GD

Orr89RocZ

iTrader: (20)

GeneralDisorder

iTrader: (1)

When I replaced the timing chain I installed it with stock timing. No advance or retard. And this detonation I get doesn't seem consistent enough to be due to mechanical timing. And one would think that pulling 10 degrees out of the timing map would entirely resolve a detonation issue related to timing chain advance, etc.

GD

Street Lethal

iTrader: (16)

Well, you asked if others' have experienced something similar in terms of detonation, so so much for academic discussion. Up until my first post your cam timing was not known nor mentioned. As far as taking ten degrees out of the timing map... which would entirely resolve a detonation issue relating to advanced cam timing, that is an assumption on your part because it resolved nothing with my engine and that was the first thing I did. Engines don't detonate for no apparent reason, it is usually caused by high cylinder temperatures, or pressure. Only so many things will cause this, unless your tune is that far off. I see no datalog, so I cannot say for sure, we can only go by your words alone. In terms of coolant, there are very easy ways to confirm adequate flow, temperatures, and hot spots.

- Rob

GeneralDisorder

iTrader: (1)

True - it is an assumption that pulling out timing would resolve detonation due to an advanced camshaft. But yeah I installed a new timing chain without any additional advance and this is the stock 86 peanut cam.

How would you suggest checking for hot spots in the cylinders? I'm not really sure how to check for that?

GD