Super rich plugs fouled

[Dave WM]

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...

 

[Zed Head]

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 September 8, 2016 by Zed Head

[Dave WM]

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.

[siteunseen]

Unplug the cold start valve and see what it does.

[Zed Head]

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.

[Dave WM]

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.

 

 

 

[Dave WM]

guess I should do a compression test to rule out a valve that may be not fully sealing.

[240260280z]

Usually it is the coolant temp sensor wiring going high resistance/open

[Dave WM]

that was my 1st check Blue, it was right on the money at least at the bullet connector, I did not check a the ECU pins, So yes maybe a wiring issue but seems ok now with the replacement ECU.

[Dave WM]

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.

[Dave WM]

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?

[Captain Obvious]

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!