Lifted head, hg failiure or something else?

My car has started to act strange, with it pinging like crazy at totally random rpms when on full boost. Its a b21 block with a 398 head and an elring gasket with the stock headbolts.

Timing map has not changed, nor has the ve table. It started pretty sudden, it would start pinging randomly at different loads/rpms. It drives totally fine, but when it hits full boost it will sometimes ping, sometimes blow out the spark or just run like garbage. Afr's are unchanged, except for when it misfires.

Octane booster didn't help, retarding the ignition from 20 to 12 degrees at full boost didn't do ****, adding more fuel didn't help (just made it blow out the spark even more).

It will not pull as hard as before in the top end, and sometimes the coolant temp will rise a bit and take a long time to reach normal levels again (normal temp is around 155F, it will rise to about 190 and then fluctuate quite a bit before slowly returning to normal).

I'm not really loosing any coolant that I can see, there is no excessive pressure in the coolant system, no oil in coolant or vice versa. The problem only manifests itself after repeatedly hitting full boost. No signs of trouble under normal driving

I've ordered a new hg, but is there other things I should look into that can cause these problems?

Distributor?

Timing is controlled by vems, so if the distributor shifted somewhat it wouldn't really make any difference (like on lh2.4 cars)

My 740 behaved this way when I cracked my head, small crack, boosted and ran ok, but acted weird & random like you are talking about. I was able to diagnose with leak down test, although thought it was blown hg at first, until I pulled the head and saw a good hg to my dismay.

Redblocks don't generally lift heads.

Have you done the basics? Compression and leakdown tests? Used a block tester in the radiator reservoir?

How's the condition of everything else? Distributor cap/rotor, plugs, injectors clean, fuel filter clean, etc. Have you checked fuel pressure?

This sounds more like a maintenance thread than performance.

You also didn't specify what car you have and how the (I assume) megasquirt conversion was accomplished. Have you checked timing? What's your ignition setup?

Do you have a wideband on it? Is that showing anything weird? If you're having some intermittent fuel flow issues causing some lean running, it could cause pinging.

EDIT: Derp, I missed that line first read throu.

I've had some very mild HG failures before. Cometic's don't just blow out in a big way, when they leak it's usually pretty subtle. But it isn't those symptoms, it jsut starts to blow coolant out when you thrash it hard.

propav8r said:

Redblocks don't generally lift heads.

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That's why I'm asking. I don't know what happens when a 30 year old head (and bolts) is subjected to high boost over time. And since the problem only seem to happen on boost I'm a bit confused..

Have you done the basics? Compression and leakdown tests? Used a block tester in the radiator reservoir?

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No leakdown test, but compression is good. No HC in the coolant.

How's the condition of everything else? Distributor cap/rotor, plugs, injectors clean, fuel filter clean, etc. Have you checked fuel pressure?

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cap/rotor, plugs, injectors, fuel filter and fuel pressure are good/correct. Afr's/datalogs are not showing anything wierd (except for when I add too much fuel and it misfires because of it).

This sounds more like a maintenance thread than performance.

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If a moderator sees this, please move the thread

You also didn't specify what car you have and how the (I assume) megasquirt conversion was accomplished. Have you checked timing? What's your ignition setup?

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It's a 740, with a b21 block, 398 head, 90+manifold, stock radiator/cooling system with 152F thermostat, deka 60lbs in the k-jet holes, triggering of a 60-2 flywheel with stock volvo lh2.4 sensor, vems controls an accel ultracoil directly. Using stock block mounted lh2.4 distributor. BCR8ES plugs. No trigger errors in the logs, and locking timing to 10degrees shows 10 degrees on the front of the engine.



The reason I started thinking it was something to do with the hg or head (instead of a tuning problem) was because of the coolant temp increasing and fluctuating before settling back to normal after driving it off boost for a while.

Drove arond a week or so, it finally started drinking some coolant....

Looks slightly broken

I see no issue here

So, was it pinging because the head gasket was letting go, or did the head gasket let go because it was pinging? Guess you won't know until it's back together.

Don't know what caused what. Replaced the cps and got rid of some strange trigger errors before the hg went, but the gasket might have been hurt already. It's back together, replacing a headgasket on these agricultural machines isn't rocket science and only takes about 1.5 hours