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One Meeelion HP
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Discussion Starter #1
Has anyone had detonation issues with machined heads after a BHG repair do to the higher compression? I have a 94 LS Coupe that had the head gasket done recently by another mechanic. It pings under light load with 93 gas. I dont know how much the heads have been shaved. The car doesn't have a chip in it and the motor appears to be healthy.

Any other suggestions for fixing the problem?

-Matt
 

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Type II King
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1,230 Posts
dame that sucks.. maybe its something wrong with the map sensor
 

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Type II King
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I was gonna say it sounds like maybe something with the knock sensor, I know they are REALLY picky little things, lots of people have run into issues with em when doing head gasket jobs, Ive never seen first hand what a bad knock sensor does, but maybe this is your issue? Are you getting a CEL? I really wish there was a way to datalog our cars and see it in real time.
hmm yea... maybe he hooked the wires to the wrong plug or something
 

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*r**h *eller
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Did the machine shop deburr the head and break all the sharp edges? Just takes one little bit of overheated metal to cause detonation.
 

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you got to think .. when you shave your head what is that doing... it puts the valves closer to the head witch means they will be opening at different times then stock which means your timing is now off if you shaved the heads to much you will need to adjust with cam gears...
 

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One Meeelion HP
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Discussion Starter #6
I was gonna say it sounds like maybe something with the knock sensor, I know they are REALLY picky little things, lots of people have run into issues with em when doing head gasket jobs, Ive never seen first hand what a bad knock sensor does, but maybe this is your issue? Are you getting a CEL? I really wish there was a way to datalog our cars and see it in real time.
The car came in with a bad transmission, 2 broken knock sensors and a CEL with a knock sensor code. The other mechanic broke both of them off during the headgasket repair. The car was pinging pretty bad when the knock sensors were bad. After I replaced them with OEM parts, I no longer have a CEL, but it still has a moderate ping under load and I can feel the ECU pulling back timing. I tested the knock sensor wire harness with an ohmmeter - good. With 93 gas and a healthy motor, the engine shouldn't be pinging under normal operating conditions even with the knock sensors bad, this is why I have suspicions about the milled heads.

I am going to try and swap out the spark plugs (maybe try one step colder?) and if that doesn't work I'm going to make a chip for it with a degree or 2 of reduced timing. I was considering carbon deposits too, has anyone ever heard of using water injection to clear carbon deposits?

LS92Sedan: Real time datalogging is also a dream for me. I have come quite a way in reverse engineering the ECU, but finding time to research my findings is now the problem. In my experiments with ECU chipping, I've found that the ECU will only pull back so much timing. If you jack the timing up too much it will ping, which means that there is a limit on how many degrees it can pull back.

you got to think .. when you shave your head what is that doing... it puts the valves closer to the head witch means they will be opening at different times then stock which means your timing is now off if you shaved the heads to much you will need to adjust with cam gears...
I also considered the timing / geometry issue, I created this thread to see if anyone thats had machined heads has had this problem.

-Matt
 

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How much was taken off the heads ?Have you verified the trigger camwheel is correctly timed?

Chris
 

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I'd say double check the cam timing, also check the EGR pipe for blockage. Although I have my EGR blocked off and my heads are milled about as far as they can be, and I still have never had any pinging issues at all.
 

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Find Em Fuck Em Forget Em
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you got to think .. when you shave your head what is that doing... it puts the valves closer to the head witch means they will be opening at different times then stock which means your timing is now off if you shaved the heads to much you will need to adjust with cam gears...
I wouldn't expect this to be the issue at all. The service spec on the 3.5RL is for a .008" mill. The LS1 guys usually go .010-.015

That really isn't a significant distance, as the altered timing comes from the change in distance between the cam timing gear and crank timing gear.

So unless they absolutely murdered your car I say you're ok from that angle.
 

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One Meeelion HP
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Discussion Starter #12
I ended up taking 3 degrees of timing out of it on the chip, it fixed 95% of the problem but even still, there was some slight pinging - barely audible. The car had to leave the shop today, so I didn't have time to investigate further. From Kenso's response I think I will have to look into this some more, I didn't have the time to start tearing the motor apart.

-Matt
 

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Type II King
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I ended up taking 3 degrees of timing out of it on the chip, there was still some slight pinging - barely audible. The car had to leave the shop today, so I didnt get to investigate further. From Kenso's response I think I will have to look into this some more, I didn't have the time to start tearing the motor apart.

-Matt
well at least they get a chipped ecu haha
 

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Left knock sensor code 23

I recently did a major overhaul of my 93 LS type II, including rings, bearings and heads (machined and valve grind) at mileage 195,000. During my tear down I inadvertently damaged both knock sensors and I got the obvious CEL and both knock sensor codes. I removed intake and replaced both knock sensors. Still had a left sensor code. I removed intake again and double-checked both sensors for any obvious damage or defect and replaced the sensor wiring harness pigtail. I still have a CEL and code 23 after warm-up, along with distinct mis-fire at lower (1500 to 2000) rpm. Misfire can occur under load or in coast mode. The misfire does not always trip the code 23. This condition has persisted for nearly three months since I originally replaced the sensors with Acura OEM. I have verified condition of coils, compression, vacuum, fuel pressure, fuel pump, injector circuitry, etc. Plugs are new NGK legend spec iridium and injectors were cleaned and tested during the overhaul. The other day I found two damaged vacuum hoses that serve the high and low bipass air systems. After I repaired the hoses the CEL, 23 code and mis-fires went away - for a short while. I drove the car three different days for 10 mile trips with no problems. Yesterday, the problems returned. I thought the faulty bipass system and leaking hoses was sending false air to the intake causing lean mixture and misfires. Once or twice during the last 3 months I have also gotten codes 15 and 16 (injector and ignition), but not now. I am stumped again. Your thoughts?
 
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