ok, just re-read the thread to see what else you'd touched on the motor. I was thinking coolant sensor and wanted to see if you'd replaced it yet. how's the coolant level? any difference if you unplug it (clt sensor, the one for the dme)? how about if you short it at the connector? If you've got a resistor around in the 2-3k ohms range, you can use that to replicate a "good" sensor at room temperature startup.
other random thoughts, got the FPR from the parts car still? I've had one fail before. It's easy to swap and the car should still start/run ok on the higher pressure "i" fpr.
bluej wrote:
ok, just re-read the thread to see what else you'd touched on the motor. I was thinking coolant sensor and wanted to see if you'd replaced it yet. how's the coolant level? any difference if you unplug it (clt sensor, the one for the dme)? how about if you short it at the connector? If you've got a resistor around in the 2-3k ohms range, you can use that to replicate a "good" sensor at room temperature startup.
other random thoughts, got the FPR from the parts car still? I've had one fail before. It's easy to swap and the car should still start/run ok on the higher pressure "i" fpr.
Good tips, I'll try them the next chance I get.
In reply to Tom_Spangler:
keep us updated! I like puzzles 
Do these cars get a signal from a MAF or AFM or some other device to let the fuel pump relay system stay on?
In other words, in alot of mazdas, the fuel pump only runs a short time while cranking OR if the AFM tells teh fuel pump relay that the engine is running. If the AFM is disconnected, it does the exact thing you are experiencing.
Can you put a volt meter on the wires at or near the fuel pump which supplies the engine and see if voltage is constant there or if it is dropping out? If it is constant, you have a fuel system issue. If it drops out, you have an electronics issue.
wvumtnbkr wrote:
Do these cars get a signal from a MAF or AFM or some other device to let the fuel pump relay system stay on?
In other words, in alot of mazdas, the fuel pump only runs a short time while cranking OR if the AFM tells teh fuel pump relay that the engine is running. If the AFM is disconnected, it does the exact thing you are experiencing.
Can you put a volt meter on the wires at or near the fuel pump which supplies the engine and see if voltage is constant there or if it is dropping out? If it is constant, you have a fuel system issue. If it drops out, you have an electronics issue.
My understanding is that the crank position sensors (there are two) perform this function. I have triple-checked my AFM plug, I was hoping that was it. Like the time I left my MAF unplugged on my Miata and drove it all the way to work wondering why it was running like crap. 
Did a bit more investigation last night, unplugging sensors and trying to start it. To review, with all sensors plugged in, it starts, but dies after a second or so. So I tried unplugging these:
The IAC is the top one where the plug goes into the silver cylinder (I assume). With that unplugged, it won't start, but it sort of coughs rhythmically. It's like crank-cough-crank-cough-crank-cough. Hard to describe. It does the same thing if the coolant temp sensor (pic below) is disconnected. If I disconnect the blue plug in the above pic, which goes into the fuel rail or something? It won't start at all, just cranks.
Coolant temp sensor (I assume, it's on top of the thermostat housing).
Coolant level is good, the overflow tank is about half full.
I think the IAC resorts to open (It's a pwm controlling a piston style) when off, so you're getting too much air in that case. The blue plug goes to the cold start injector at the rear of the intake manifold. same conditions w/ that unplugged also points to not enough fuel.
That foremost coolant sensor is NOT the one that the DME (ecu) reads from. It's one of the (multiple) coolant sensors behind the foremost one in the image you posted. See below for what those two foremost sensors are. In the 2nd image below, the DME coolant sensor is the one w/ the blue connector (rearmost relative to vehicle).
You appear to have a second fuel pressure regulator or additional filter in line after the stock one. Looks like it's been there a while. I'd want to know what it's supposed to be doing. Like I said before, if you've still got the stock FPR from the "i" engine, try that in place of the two old (stock and non stock) visible in your pic above. You don't have a fuel pressure gauge around, do you?
bluej wrote:
You appear to have a second fuel pressure regulator or additional filter in line after the stock one. Looks like it's been there a while. I'd want to know what it's supposed to be doing. Like I said before, if you've still got the stock FPR from the "i" engine, try that in place of the two old (stock and non stock) visible in your pic above. You don't have a fuel pressure gauge around, do you?
Yeah, someone has definitely screwed around with the fuel lines on this car in the past. I'll have to dig through my boxes and see if I have another FPR. Though, I was under the impression that the smaller inline things were not pressure regulators, but dampers. An FPR should have a vacuum line attached, and these don't. I think I have two of them.
No, I don't have a fuel pressure gauge, but I think I'll pick one up.
Yeah, I agree that it looks like a dampener, but what's the point of one AFTER the FPR? Unless I'm mistaken, it should just be a straight shot back to the tank. screwy for sure...
I haven't read this entire thread so..............take it with a grain of salt. If it's starting up for just a second and immediately dies I'd be looking at having the injectors cleaned. Had this happen to my Alfa Milano. Swapped in some cleaned injectors that had been sitting for about 2 years. The cold start injector would give it enough gas to start but that's it. Swapped back to my old injectors and it would start right up and stay running. Doesn't take long for injectors to get stuck.
Also, pull a couple plugs to check again. I'd like to make sure it's not flooded/flooding. Can you smell gas? If that "dampener" or the FPR is blocked, that could be flooding it out, or the overpressure could be locking out the injectors. Might also explain the dual dead fuel pumps.
If you do want to have the injectors cleaned or just replace them, here's a very cheap outlet that I recently used.
http://www.mepeh.com/
http://www.r3vlimited.com/board/showthread.php?t=266477&highlight=injector+cleaning
A bit more experimentation. I unplugged the cold start injector again, tried to start it and got the "crank-cough" routine again. So I think dbgrubbs is right about it providing enough fuel to start it, because without it, the car doesn't start. I did manage to dig out the FPR from my parts car and I installed it. It had no effect. I then removed the fuel damper that was after it inline, and that had no effect. Still starts for a second, then dies. When I pulled the old FPR, a fair amount of fuel came out of the rail, so I know it's getting some fuel, at least.
Checking for blockages, I tried pulling the lines off the Tee where the fuel supply line goes off to the rail on one side and the cold start injector on the other, but I couldn't get it off and ended up pulling the Tee apart. So I need a new one of those before I can experiment further.
So, I know the rail is getting fuel, and I have switched out or removed the things that could block fuel from leaving it. I guess it could be my injectors, but what are the odds that all of them, or even most of them, got clogged up when the car wasn't running? Now I'm starting to wonder if there's another blockage in the return line somewhere.
After a long break for various vacations and other summer-related stuff, I got back at it last night. Replaced the broken tee and checked the return line by pulling it off the fuel sender at the tank and blowing some compressed air into it. It's fine, and I got a fine mist of fuel all over the front of the car.
So, I don't know. Near as I can tell, the fuel system checks out 100%. It will pump fuel into a container while I'm cranking from any of the hoses under the hood. It is getting spark. I think I'm ready to punt, put the thing back together the rest of the way, and take it to a shop. Either that or push the berkeleying thing into a lake. 
Tom_Spangler wrote:
So, I don't know. Near as I can tell, the fuel system checks out 100%. It will pump fuel into a container while I'm cranking from any of the hoses under the hood. It is getting spark. I think I'm ready to punt, put the thing back together the rest of the way, and take it to a shop. Either that or push the berkeleying thing into a lake.
I decided to go with option "A" above. It's mostly all put back together and on the trailer. Tomorrow it goes to Steve's European in Waterford:
bummer, but sometimes it's worth to play the "skip ahead" card on a project when you hit a roadblock.
Progress is progress. Hopefully this will be the hump that gets you over the roadblock and you'll be fired up to have a running car back
Update: It finally runs again! Poorly, but it runs.
Quick overview of what's happened the last few months. I took it to Steve's, they did a thorough diagnosis and told me my injectors were probably clogged or damaged. This is not surprising since the original fuel tank was loaded with crap. They did install my exhaust and aligned the car for me, but I decided to replace the injectors myself.
Obviously, this took me a while, between family and house priorities, and my general lack of motivation with winter approaching, I worked on it in fits and starts. The upper intake had to come off, which was a surprisingly PITA job. I bought some injectors from a forum member for $30 that supposedly came from a running car and put them in. Finally got it all buttoned up today.
After cranking for a minute or so, it fired up. It's not running well, it sounds like it's missing, down at least one, maybe two cylinders. So, maybe those injectors I got aren't all working, or maybe I developed another ignition problem in the 3+ years it's been since it last ran. I don't know, my next task will be to diagnose that, then I need to do the timing belt and other front-of-the-engine stuff.
First can you pull the ht leads one at a time to see which one is missing (ie it doesnt gert worse when pulled). Then check that that injector is working. I know it's really tough to swap the injectors, but can you swap the plugs to see if the falt follows the injector.
Adrian_Thompson wrote:
First can you pull the ht leads one at a time to see which one is missing (ie it doesnt gert worse when pulled). Then check that that injector is working. I know it's really tough to swap the injectors, but can you swap the plugs to see if the falt follows the injector.
If only it were that easy. 90% of the rail is buried under the upper intake, and it's tight under there. I can't even unplug them without removing the upper intake again.
The M20 is not an easy engine to work on.
In reply to Tom_Spangler:
OK. At least pull the leads one by one to find out which one or how many are miss firing or not firing and if it's constant.
OK, I give. I'm never going to finish this car, and I've already spent more time and money than I wanted to on it. Time for someone else to finish it up. It's for sale. Look for a thread tomorrow.
