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SDS Timing Wierdness!!


Nigel

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Just a regular diode then? I don't think you ment to say "reversed biased" in that case' date=' which would be a Zener. I've got lots of regular diodes kicking around. So, it would have to be the white stripe (I always get cathode and anode mixed up) to the solenoid terminal. Makes sense...

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"Reverse Bias" does not solely apply to a Zener. You reverse bias a Zener because it has a very low reverse breakdown voltage, and you can use this for voltage regulation.

 

A reverse biased regular diode simply has voltage applied across it such that it does not flow current. In the case of back-EMF protection on a relay, the diode does nothing when the relay is energized. However, when the relay is shut off, the coil tries to keep it's current flowing (current through a coil cannot change instantaneously), the result of which is a large negative voltage spike. In this situation, the diode becomes forward biased, and limits the 'spike' to it's forward bias voltage, usually about 0.7V.

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Thanks Tim. I hauled out my electronic devices theory text and read the section on reverse-bias condition. I'm up to speed now :wink:

 

I guess I probably don't need knock sensing with 94 octane pump fuel and 7 psi of boost, but I've never tuned an engine before so I don't have any experience to fall back on. I've read the SDS manual several times, and everything else I can find on tuning, so I'm well acquainted with the theory of it all. The experience is building with practice.

 

I have an EGT gauge with the probe mounted just before the turbo, but I don't find it all that helpfull. How am I supposed to know what my peak temperature should be without running the car on a dyno (which I eventually hope to do)?

 

Nigel

'73 240ZT

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Guest Zcarsmakemyheadhurt

You only read the EGT at WOT other than that its all over the place so don't depend on it to tune drivebility. Push the timing way up at low boost and use race fuel when tunning hi boost. Enjoy.

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:frown:

 

I got the latest chip from SDS and I installed it along with two filter caps on the board. I took the car for a spin and I'm still seeing occasion knock sensor activity at full throttle. I went to go out again to try some new settings, and I notice what sounds like an occasional miss while it's idling. I don't know if was there before or not, because it's very subtle. But I decided to investigate further.

 

I reved up the engine to 2000 rpm and held it there to see if it would be more obvious. Sure enough, instead of getting a constant vrooooooooooom, I get vrooom, vrooom, vrooom, vrooom! I see the air/fuel ratio guage spiking lean in time with cycling engine note. Upon further investigation, I noted that the fuel pressure, which normally pulses in time with the injectors, pauses with the cycling engine note. The period is roughly around 1 second.

 

I listened to each injector while it's doing this, and it's not obvious that one is cutting out. Disconecting one injector at a time also shows nothing conclusive. The cycling is also not 100% repeatable. Some times I can rev it up and I can only detect an occasional miss. Other times, it's like clockwork.

 

WTF is going on! :fmad:

 

On the plus side, I fixed the rpm error from the fast idle solenoid shut of with a diode. :-D

 

Nigel

'73 240ZT

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On a whim, I checked the plugs last night, and once again I have 4 that look normal (in fact they're bordering on carbon fouled), and two that are white (with a bit of depositing on what I'm guessing is the shadow side of the electrode). I had checked the plugs earlier in the day before I did all the testing as described in my previous post, but I guess there hadn't been enough time for the deposists to build up on the 4 and burn off on the 2.

 

And once again, the white plugs correspond to the 2 questionable injectors (ones that I had been told flowed as well as the others). I moved these 2 injectors to different cylinders than they had been in before (cylinders 3 and 4 instead of 1 and 2), so I don't think there's any question that these two injectors are not flowing as well as the other 4, despite what the injector rebuilder said (if they actually bothered to test them).

 

I still can't quite figure out how this would translate into the symptoms I described, but I'm going to ditch these two injectors and try to find some more.

 

Nigel

'73 240ZT

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I got my two spare injectors cleaned and I installed them this morning. The miss at idle seems to be gone but I'm still getting this... I don't know what to call it exactly. It's like power to the injectors is momentarily being cut off when I hold engine speed in the 1750 to 2250 RPM range. I see a lean blip in the air/fuel ratio, the EGT blips lower as well and the engine briefly stumbles. Fuel pressure pauses on the low side of the range it normally fluctuates at. It'll do this repeatedly every 1 to 2 seconds.

 

I've crimped off all the vacuum lines to see if it's getting a gulp of air from somewhere, but I could find nothing. Disconnecting the vacuum line on the pressure regulator does nothing. Manifold pressure is constant. RPMs don't fluctuate. Duty cycle and ignition timing are constant.

 

I need some ideas on how to troubleshoot this!

 

Thank you to all who reply!

 

Nigel

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SOLVED!!!

 

:D

 

I can't believe this. Hours of head scratching and it turned out to be something stupid. I had reached a point where I was grasping at straws, and so I replaced my plugs and removed the filter caps from the ECU that SDS had given me. Of course, that made no difference. So I was sitting in the car reving it up 'till it stumbled, trying to think of what was wrong. I noticed that it seemed to always cut out by around 2000 rpm on the tach. Could I have accidentally set the RPM FUEL CUT at 2000...? Nope. Damn.

 

So I was thinking, what else causes a fuel cut. Manifold Pressure... it's set to 8.5 psi. That's not it... Throttle position...? That's it! Throttle position! I had noted that the engine would only cut out if I reved it up slowly. So, I watched the TP value when the engine was stumbling, and sure enough, it was the same value that I had entered for TP FUEL CUT!

 

Typically, when you rev the engine up, you pass through the value almost instantly, so it's never an issue. But just by chance, I reved the engine up slowly enough (just opening the throttle a crack) that it was staying on that value. :bonk:

 

Un-freaking-believable! :2thumbs:

 

Nigel

'73 240ZT

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