87350IROC

iTrader: (2)

I've gone through two since the rebuild in October. Well at least I think its the ECM this time too. All the sudden i have massive audible pinging over 2500 rpm. The problem was fixed last time, December, with a new ECM. What would cause this. Perhaps a bad ground? I had the block and heads repainted and now that i think about it, the ground bolts and threads on the back of the heads are proballly covered with paint. I'm guessing this reduces the grouding quality of those bolts since its not really metal on metal contact. Does that sound about right? What are the important grounds for the ECM, or are they all equally important?

Any other ideas what could be happening? I'm getting tired of fighting the sudden attack of the pings. I guess i really nice to hook it up to the laptop too.

thanks guys
John

Air_Adam

Wrong knock sensor? If a 305 sensor is there, your ECM can't "hear" it knocking.

87350IROC

iTrader: (2)

Nope, original engine. Not to mention before the rebuild i didn't have any such problems. And once i replaced the ecm the first time it corrected the problem.

dimented24x7

iTrader: (2)

What does the SES light do when you have this problem? How does the car run, other then all the detonation when it 'eats' an ECM? Loosing the ecm (burning something major out like the processor) woudl actually cause almost no ign. advance as teh ecm will be in limp home mode. The only advance youd have is from the module so it wouldnt detonate, but instead run like poop. Youd also have a solid SES light at all times. Sounds like it might be time for a new knock module or a new KS.

87350IROC

iTrader: (2)

When i got the detonating the first time after about 3 seconds of pinging the ses light would go on with code 42 & 43. As soon as i restarted the car again the ses light would be off and the car would run fine until it happened again. The car runs fine even with the ses light on, just not very powerful, obviously. This time i have not let it ping for a long period of time with my current ecm so i don't know if the light would come on if i stayed in it. I have not had the ses light come on with my most recent ecm, but i have had audible pinging. I realize they weren't completly wrecked or like you said it wouldn't really run. But for some reason the same function of the ecm has failed twice now. I changed the esc with a different, not necessarily good, one after i had the problem initially. This did not change the problem. As for a new KS, that is a possibility, but the engine shouldn't be detonating in the first place, so that won't really solve the problem.
thanks guys
john

dimented24x7

iTrader: (2)

Sounds like a problem with the knock sensor. Either its grounded or open at times and when that happens, i think the computer retards the timing 15 deg. and sets the code. As for teh code 42, have you changed teh base time recently or taken it in for a tuneup? having an open or grounded wire to the KS or a bad sensor would fully explain the detonation since the computer wouldnt be able to invervine and retard the timing to stop the knock. The problem is definatly not associated with the ecm. It looks like its doing what its supposed to do. When you hear the knock before it sets the code, thats probably the ecm doing the test of the circuit. It advances the timing ALOT and checks for input from the KS. I think it does this twice and if no knock is seen, it sets the codes accordingly.

87350IROC

iTrader: (2)

I don't understand why it would run a test anytime i'm over 2500 rpm and at no other time. Can you explain this? This also doesn't explain why a new ecm fixed the problem before. The KS is hooked up with one wire, right? It goes to the esc module, right? Where is the ground for it?

dimented24x7

iTrader: (2)

The ecm performs the test the first time you give the car moderate throttle loads. It advances the timing untill it sees knock or it peaks out. The detonation may be due to the fact that the timing is overadvanced or some other issue and the reason you hear it is that there is an intermitent problem with the knock sensor, module, or the electrical system that causes loss of the signal.

The circuite for the KS is completed through the engine block. I think you can also have problems if there is alot of external noise or runaway detonation. Those things will saturate the knock sensor and possibly cause a code to be set. Even without the knock sensor, you shouldnt hear much audible knock. Ocasionally on hard acceleration in hot weather you can hear a couple pings on a car without a KS but if its detonating alot then check the base timing for excessive advance and check to make sure the egr valve is fully fuctional. Once youve eliminated the detonation, then see if it continues to set error codes.

87350IROC

iTrader: (2)

well thats why i think its the ecm, because the car shouldn't be pinging in the first place. I have tired timing anywhere from 0 to 12 advanced with similar results. During the rebuild, I had the block painted, the guys who painted the block and heads also painted into the threads, perhaps this is causing a lousy ground.

Also it pings not just the first time but everytime. It has not set a code yet on this current ecm, just audible detonation.

Edit. I just went out to hook up the laptop and it went into ALDL 1000rpm idle mode, but didn't give my any data. This may be related or not.

dimented24x7

iTrader: (2)

If your concerned about the grounds, remove the ground straps (both in the rear and pass side one at the front) and the terminals for them and sand the mating surfaces on the heads and clean up the terminals and put it back together. Not exactly the easiest thing to do but it should take care of the grounds. Also make sure the ground strap that leads to the firewall is in place as well.

Next thing would be to check what the timing is. Unhook the bypass connecter over the heater box and set the base time to whats called for by the label on the underside of the hood. After that, reconnect the bypass connector and restart the motor. Check to see what the timing is at idle. Itll be something like 16-18 degrees or so. At 2000 + itll come up to around 30-35 degrees of advance. Hard to say exactly since it depends on the calibration in the ecm but it should do something like that.

After that, check the fuel pressure at idle and under laod. Should be something like 38 psi but I dont know the stock tpi pressure off the top of my head. If the engine is going lean under load from loss of pressure or crummy injectors, itll start detonating.

After that check to make sure the EGR isnt clogged. Clogged EGRs will cause detonation.

Finally check the wiring for the EST circuit and make sure its all intact.

Also want to check the KS by running the engine above 1000 rpm and hitting the block around the area where the KS is and make sure the ecm retards teh timing. Youll see the timing retard momentarily each time the block is struck. If it doesnt do this, consider replacing the sensor.

Try to check this stuff first so you dont needlessly replace parts. Not saying the ECM isnt faulty, but you should eliminate everything else first.

As for the engine rebuild, what was used as the base? The stock longblock? Reaching here but maybe he used smaller 58 CC heads for the rebuild?

87350IROC

iTrader: (2)

I have a question for you. I was just looking at my machine shot recipt. And I noted they shaved the stock L98 iron head .01" I didn't remember them doing that. What size combustion champer does that give me? Is there an equation somewhere on the net for this. I also have KB 4 valve relief flat tops. However i don't know thick my head gasket is. What is the stock thickness, i will use that to calculate what maximum compression would be.j
I still don't think this is the root of the problem, but it is something to look at. The reason i say this, is because there was a period of several months where it didnt' ping and ran nice.
thanks
JP

Vader

What is the casting number on the heads you are using?

87350IROC

iTrader: (2)

They are stock iron L98's. They are 083.

dimented24x7

iTrader: (2)

Well, you have the right head for your application. Its unusual that the problem is intermittent. I guess the only way to find out the cause is to eliminate things one at a time untill the cause is found.

87350IROC

iTrader: (2)

I've just picked up a new problem. Or perhaps its is related. While checking the timing for the hundreth time i heard a little taping. Like a loose rocker noise. I think maybe, it is the same noise just getting worse. So maybe my noise wasn't really pinging, and the computer didn't pick it up. So i pulled off the valve cover and one of the rockers was off center on the valve. Also it has been a while since i've done valves, when the valve is closed, should the rocker be loose enough that i can easily twist it with my hand? I'm taking off the TPI manifold anyway to port match it to my new AS&M runners so I should easily be able to get the valves adjusted at the correct position. One other thing, i'm going to take a picture of my stock pressed in studs and post is here so see if they have pulled out at all. Or do you know far they should stick out of the head? I made the mistake of keeping the pressed in studs when using the ZZ4 cam.
thanks again
JP

Vader

If you have a straightedge, you can check the heights of all the rocker studs. Just lay the straightedge across the tops of the studs. High studs will be readily apparent.

If you have a pulling stud, screw it. Then screw the rest:
Rocker Stud Replacement

A rocker that is off the valve center is NOT a good thing on an '87-later SBC. The self aligning rockers shouldn't walk around. Since you mentioned that the engine is all stock, you should still have SA rockers. They need to be inspected closely - especially the one that was "flopped". You may also have a bent push rod or rocker stud causing the rocker to walk.

If the head was shaved 0.010", the static CR should have only been increased from about 9.54:1 to 9.77:1. That also depends heavily on the replacement gasket you installed. If you still have your part numbers, check the gasket compressed thickness. A standard FelPro .041 gasket would have "corrected" the CR right back to stock specs.

87350IROC

iTrader: (2)

I bought a "master kit" from sealed power. Then i added, changed, and removed to get my current setup. Unfortunatly i can't find specs on what comes in the kit. One would think since it is a stock replacement head gasket it would be the wedge style, but i don't know. This was my first engine build and i have learned a lot from it already. So you are saying with a stock gasket + KB 4 valve relief pistons + shaved heads = 9.77-1? Not a bad number. Yea, i was suprised to see the SA rocker off center. Makes me wonder, i will check the rocker and take a pic and post it. I checked the pushrod, it looks straight.
JP