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Old 05-09-2008, 12:59 AM   #1
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Default Knocking when cold

If you have ever driven a miata with VVT this will be a bit easier to explain, but here I go:

When I normally cold accelerate with the stock ECU with constant throttle, it is a little sluggish until it hits like 3500 and then it jumps. I believe this has something to do with the VVT system, but I may be wrong.

With the MS cold accelerating under constant throttle, I hear what I believe is knock until it gets to that same point around 3500 and it seems to stop knocking.

Now to make it even more strange, I only hear the knock when it is cold. I used to run a more advanced spark table (knocked at cold and fine when hot), which felt really great, and now I am running a retarded 96-97mspnp map, which is more conservative before retard, it still knocks cold and feels slower hot.

Any ideas? I want to be able to run the advanced timing, but not at the cost of knock...

edit: I drive a 2001 for the record.

Last edited by compy; 05-09-2008 at 01:05 AM. Reason: more info
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Old 05-09-2008, 11:28 AM   #2
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My spark table:
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Old 05-09-2008, 12:00 PM   #3
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Your timing map looks pretty conservative to me. But since it's only doing this cold, and not hot, I think we can ignore that table. Is it possible that you may inadvertently have some ludicrously high numbers in IAT/Clt Related Ignition?

You're absolutely certain this is detonation, and not some mechanical noise? Hell, my transmission pings when it's cold and I'm accelerating below about 2,500 RPM in 3'rd.
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Old 05-09-2008, 12:11 PM   #4
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Not quite sure how the IAT/CLT got setup but it looks like this:
Add 1 degree every: 65F
When below: 140.0
Max allowable added: 4.2
Pull 1 degree of ignition retard every 50F
when MAP above: 60KPA
and IAT above: 105F

What do you think? I think I'm just going to turn it off.
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Old 05-09-2008, 03:02 PM   #5
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I think those are some really bizarre values, and I support your turning it off for the moment.
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Old 05-09-2008, 04:40 PM   #6
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Turned it off and still had same knock result. I'm pretty sure what I am hearing is knock. Seems to get louder with RPMs. Symptom of knock? The pretty concrete reason I think it is knock is because it never happened until MS started doing timing.

Maybe I can erase the "add degrees" and jack up the ignition retard and make it so it retards the timing while car is cold.

It is just so strange to me that it goes away once it warms up. I would figure if it was too advanced cold, it would be too advanced hot. It certainly is getting enough fuel since it has the warmup enrichments and such adding fuel while its cold.
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Old 05-09-2008, 05:09 PM   #7
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Well, check the logs. Is it in fact more advanced when cold? Find a pair of datapoints which are at the same RPM and MAP, one hot one cold, and compare the advance.
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Old 05-09-2008, 06:50 PM   #8
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I'm pretty sure since the iat/coolant related ignition settings are turned off, it doesn't do anything for it anymore. So the timing table would be the same all around?
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Old 05-09-2008, 07:03 PM   #9
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VTCS. what're you doing with it?

aaaaaaand

are you using the stock ECU to do anything?

details on the install please.
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Old 05-09-2008, 08:51 PM   #10
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Its a parallel install, MS does the fuel and timing. The rest is handled by the stock ECU.
I am currently running ms_extra high res. Custom built pcb3.0.

Let me know what else you need to know to help solve.
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Old 05-10-2008, 01:20 AM   #11
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find the VTCS solenoid and un plug it. it's the small valve with the vac line on the intake manifold near the firewall... not the EGR, the small one. unplug that when the car is cold and try driving it and see how it is.
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Old 05-10-2008, 01:46 PM   #12
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Ok. Will unplugging it have any adverse reactions? If not I will try today.
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Old 05-10-2008, 01:55 PM   #13
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not adverse, but it may not run well cold.
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Old 05-11-2008, 09:53 AM   #14
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does your obdII scanner show you when you have knock?
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Old 05-11-2008, 05:32 PM   #15
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I know the knock sensor circuit has an OBD code, but I think it is only for when it is not working.
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Old 05-14-2008, 08:12 PM   #16
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Y8's was correct. Unplugged the solenoid as suggested and the noise went away. Does this indicate it was knock? What now?
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Old 05-15-2008, 11:22 AM   #17
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hard to say. try blowing through your nose with it plugged and tell me what the noise is--cuz that's about what was going on. the VTCS butterflies were closed and obstructing flow.
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Old 05-15-2008, 06:29 PM   #18
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Guess I will have to figure out how to open them then =o.
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Old 05-15-2008, 07:19 PM   #19
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they really only help with cold start. worst case, you put them on a switch or figure out how to set them to < 1500 rpm AND < 60C coolant temp.
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Old 05-15-2008, 09:27 PM   #20
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Do they only stay closed when cold then since the issue goes away when warmed up? It's just weird to me that switching over the timing made the issue develop. I would think the stock ECU would still do it's job of opening and closing them. If it isn't knock that I hear then it wouldn't bother me that they do not work, but I don't want to damage my engine. I had to send my knocksense back to be repaired, so I'll have to wait until I get it back to confirm it. I'm surprised nobody else has had this issue (and resolution) with the megasquirt.
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