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Super rich plugs fouled


Dave WM

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took the Z out, odd rough idle, that was new, start down the street, can't hold idle stalls out finally get it started and nurse it home. Pull the plugs super carbon fouled, cleaned them, try starting again very hard to start, would not idle then dies.

fuel pressure check, 36 psi during cranking, so at least the FPR and fuel supply/returns are providing the correct static pressure.

Spark looks good and strong.

thinking it maybe a stuck open cold start, I remove it to see if it fires (should not its hot) it does not but the car runs fine with a massive air leak at the cold start hole. plug it up and the engine dies. So clearly its running rich. The only other diagnostic I run is the water temp sender. It test ok about 360ohms (hot engine).
 

Decide to cut to the chase, swap in a spare ECU, starts right up. runs fine. So the plan is to open the old one up and look for any obvious looking failed parts. I sure am glad I had that spare ECU...

 

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Spare parts are cool.  Can't have too many.  I had a similar situation but I was testing my spare.  It was bad itself and killed the engine dead.  There's actually quite a bit on this forum about the rich ECU problem.  There was a guy called Night Train or Mad Dog (Boone's Farm maybe?) who suggested re-flowing all of the solder at the connector pins.  He said that wiggling the connector cable while driving could fix it temporarily.  Other people kick the ECU to knock things back in to shape.

In my case, I replaced the transistors and that fixed it.  There seems to be more than one cause.

Edit - I also have a spare known-good ECU, and ignition module, behind the seat.

Edited by Zed Head
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well I will assume the most likely suspect would be the one that handles the most power so I will start with checking the power transistors to see if something has shorted out. Problem is all the plugs were fouled, I would assume that would be something up stream of the power transistors since IIRC each one fires 3 injectors so with all the plugs fouled both would need to be defective. With out a schematic and a LOT more info on how to diagnose it seems unlikely that I could trace the issue down.

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He removed the CSV entirely and nada.

That's a good point about two transistors.  Maybe I replaced mine for the wrong reason and the problem is still there.  My dinking around might have moved something.  Although if one transistor is sticking its injectors open there might be enough fuel to go around.  I replaced the transistor because I thought the symptoms were similar to bad ignition modules and also thought that's why they failed.  But I could be wrong there also.  Sometimes I just try stuff and it works, but the reason why may be unclear.

Can't remember if the transistors are split n to two and four like the dropping resistors or if it's three and three.  It's been discussed before.  I think that CO knows.

There are so many things that add injector open time.  Any one of those circuits could be bad, I'd guess.

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I checked them (the TO-3's) took two of the legs out of circuit, tested somewhat leaky but I don't think that is wrong for power transistors. were megs here. The tested exactly the same. I have some other T0-3 power transistors so will test to compare. I did see what looked like a carbon path between two traces, could not really get a good conductivity test on it. Put it back together will try tomorrow.

New problem. while testing the fuel pressure I get 36 with no manifold vacuum, it starts fine and seem to run ok, but the FP only drops to 30psi. I have not checked the vacuum (need a new gauge, will get tomorrow) but should be interesting to see what the idle vacuum is. The FPR is working as I goose it the pressure comes up. Further complication on the vacuum, the AC idle up/vents stopped working, lose of vacuum. If I bypass the check valve and go directly to the vacuum tank it works but seems the restriction of the check valve is too much.

All this is pointing a vacuum issue. Removing the valve cover cap causing the engine to stumble, same with the dip stick, but disconnecting the brake boost had little effect but not like you would expect. very odd.

I did remove the PCV valve, cleaned it up and reinstalled (seemed fine) I wonder if I could have cracked the pipe to it? but that was at least a week ago and it was fine until last night.

I can't hear any whistling or other obvious sounds of a leak. I am going to buy a cigar (don't smoke) and see if I can blow smoke into it and find a leak.

 

 

 

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hooked up my AC gauges, about neg 17-18 PSI so I guess the vacuum is good, could not see any movement in the needle but maybe that is because I used AC gauges (damped?). I should have check the vacuum AT the vacuum tank, I checked it at the nipple that feeds the line to the vacuum tank.

I wonder if the FPR is working right, seems like my fuel PSI should have been closer to 20 than 30 with that much manifold vacuum.

I will go on with the compression test just the same.

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More thoughts, using an aftermarket pump (90psi) seems like it would put more of a burden on the FPR to return excess fuel thru the return line. I don't really know how to test the stuffiness of it (maybe that is in the FSM, seem to recall something on checking "stuffiness"). Anyway the lines are orig to the car, could be stuffy, I blew them out and they do pass air but still with the increased burden of the fuel high pressure fuel pump could this cause a limit to the max pressure regulation?

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I doubt that it's the ECU. Bad connection (at the ECU) on the water or air temp sensors or the AFM. I once had a very rich condition and after poking around a little, I realized that I had disconnected my AFM to take some readings and had forgotten to reconnect it. I was surprised the motor ran at all.
 
But as for the ECU internals, the two output transistors drive in banks of three each and the bases of the output drivers are tied together so they both actuate at the same time.
 
What else can I tell you..... The output transistors are NPN Darlingtons. That might explain any strange readings you got when testing them. I can't tell you the individual values for the built in resistors on the bases, but I did measure the total and write that down somewhere. I reverse engineered the output stage, but it's so simple that I have no doubt you would be able to do it yourself by the time I find my notes. I'll race ya!
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I have not tried putting it back in to see if messing with it may have fixed it. I have been focused on the AC, seems like It must be the check valve, I have 16-17 on one side and nothing on the other, so the vacuum bottle never gets pulled down. For now I just stuck a piece of tubing to join the two "S" lines together so my AC idle up and ducting servos all work again. I would like to try disconnecting the return line and feeding it into a gas container just to see if my theory of a stuffy return line could be influencing the fuel pressure. I am liking the idea of just popping for the OE pump that uses a built in regulator that limits the output to 45 psi (think that is what I read).

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Haha! Thanks for the laugh!

Pull the connector off the ECU and take some measurements. I'd start there. Well actually I'd start by wiggling the WTS, and AFM connectors...

And for checking the sensor resistance measurements, I just posted a chart that should help:
http://www.classiczcars.com/forums/topic/56146-280z-efi-temperature-sensor-vs-resistance-chart/

 

Edited by Captain Obvious
Added chart link
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6 hours ago, Dave WM said:

Decide to cut to the chase, swap in a spare ECU, starts right up. runs fine. So the plan is to open the old one up and look for any obvious looking failed parts. I sure am glad I had that spare ECU...

Brass tacks and all that (whatever that means, I've never really known).  Dave had a problem, he swapped ECU's and the problem went away.  In the interest of avoiding distraction and unnecessary excursions maybe re-installing the "bad" ECU would be worthwhile.  If the problem follows the ECU, it's the ECU.  Right?  Just saying...

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ZH that's the plan for tomorrow put the old one back together after mussing with it, other than the small carbonized looking junk I cleared off the one trace, no other action taken on it. I did try going back to it when I did the 1st swap, and the problem returned so I know it was ECU related. The only question now is did the action taken have any effect. I am REAL glad I had the extra ECU, typically that is the last place I would go to, and it prob would have driven me nearly mad checking all the usual suspects.

Edited by Dave WM
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started car cold with replacement ECU, started right up ran fine.

replaced ECU with the one that was a problem yesterday (still cold car), started right up ran fine.

Left the replacement in, will drive car later and get up to full temp, then try the swap again.

Anybody know what the two white wires that come out of the wire harness right at the 35 pin connector (they have bullet connectors) is for? I looked at the FSM and saw something that maybe it, control and checking term? two white wires that appear to go to the ECU pins 11 and 26. Nothing about them that I could find. 

update on 11 and 26 Search and found Capt O had mentioned injector signal test points on an earlier thread.

Edited by Dave WM
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Pins 11 and 26 internally connect to the open collector outputs of the two output transistors through 1.5K resistors. So you could put a scope on those two pins while the ECU is running instead of probing the injector connections directly. I believe them to be test connection outputs to check the operation of the ECU.

You could also wire those pins to +12 and disconnect all the injectors and view the output signal as a clean square wave without any noise from the injector impedance. In other words... Instead of pulling the transistors up to +12 through the injectors, you can disconnect all the injectors and pull the transistor collectors to +12 through that 1.5K limiting resistor. Then you could scope the injector pins to see a clean square wave drive signal. Good for bench testing and may have been used for Datsun's ECU tester modules.

About the white wires though. Interesting because I don't have any white wires with bullet connectors. In fact, my harness doesn't even have pins 11 and 26 populated.  The ECU has pins there, but the corresponding harness positions are empty. I wonder if they put those white wires on the earlier 280's and then decided that things were reliable enough that they didn't need them anymore on the later years.

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I will confirm the wires I have are indeed connected to the 11/26 pins on the 35 pin connector (just a continuity check from the bullets back to the connector) the wires exit from the connector right above where the wire harness goes into the socket, just hang there covered by the kick panel. Going to get some new plugs as well so I can do a check of the fuel mixture, I cleaned the old ones up, but not well enough to evaluate the air/fuel mix since they stained so dark now.

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I found my notes and here's what the output stage looks like:
outputs_zps9fwwbmsv.jpg

Note that I didn't have a Darlington symbol handy that included built in base resistors (and I didn't feel like creating one), so I left those two built-in resistors out. I can tell you, however, that the total resistance of the two of them is 2.7K Ohms total.

 

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Put some new plugs in it, seems fine now with the replacement ECU. Will try the old one later. Still wondering about the fuel pressure, the plan now is to get some fuel line, enough to take the return line and feed it safely into a gas container. That would eliminate any "stuffiness" on the return side. See if that effects the fuel pressure. I will prob still end up popping for the OE pump just to take the strain off the rest of the fuel system.

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I wonder if you have the wiggly connector issue.  There's a fair record of sporadically bad ECU's out there.  I'll see if I can dig some threads up.

Here's one.  The guy hasn't been around for a while.  http://www.classiczcars.com/forums/topic/34229-280zzx-ecm-tech/

Some wiggle the connector comments - http://www.zdriver.com/forums/280zx-s130-forums-77/resoldering-ecu-31290/

Of course, all of these people and me included could just have been doing random things and the act of taking the ECU apart and putting it back together was what "fixed" the problem.

 

 

Edited by Zed Head
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