'74 2L Starts Then Dies, Never a convenient time... Options

[GregAmy]

Nice beautiful New England Day, heading off to the Manchester CT car show and...car won't start. Cranks, a few cylinders fire, then it dies. I cycle the key and hear the pump running and then stop (as before) and same thing: spits then dies.

I tried cycling the key a few times, with the mindset of building more pressure, and it spits a few more cylinders then dies. Even got it to rev a little bit with a half-dozen key cycles, but always dies.

Only other symptoms is that I noticed the last time I drove it earlier in the week it was dying when I put in the clutch. Was not consistent, only did ti a few times, but that was unusual behavior.

Stock 2L fuel injection, but with cold start and idle air bypass systems disabled; been running fine like this for the several years I've had it.

Checked all the relays, each works with the heater blower. Swapping them makes no difference (which I expected, given the pump cycles with the key). My guess is that however the pump is supposed to continue to run after releasing the key, it's not getting the power it needs (just a guess, I've not gotten under there with a voltmeter to verify). The wiring diagrams are not clear (to me) how that power is applied to the fuel pump relay.

Any way to quickly salvage my afternoon trip to the car show, or am I using my beautiful afternoon to swap the street car onto the lift for extended diagnosis?

40-yr-old electrics, gotta love 'em.

- GA

[GregAmy]

Ok, so maybe this thing isn't worked out yet...

Fuel pump is priming with ignition on, so at least that's resolved. However yesterday I took it for a nice long drive, started/ran fine, no hiccups. However 3 hours later when I went to leave, it started fine (fuel pump primed) but then it kept dying. Thinking it was the lack or AAR and cold start valve, I could kinda keep it running with some throttle, but it was not running smoothly; it would have a random hard miss, and would try to die.

I was following someone to the next stop and it was driving terribly: I mean HARD shutoffs and restarts, not like a dead cylinder miss but like a shut off engine miss. It would die when I came to a stop but would kinda restart, and I could keep it running with some throttle but still not smoothly. As I'm cruising down the road it was HARD shutting off then coming back on, and feeling overall unhappy (like a flooded spark plug) slightly less so with full throttle but it never went away. I thought at one point I was going to have to pull over but kept going, and then...

...all of a sudden it smoothed out. No problems for the rest of the 30-minute trip. Car ran fine and smooth and never stalled again.

Starting up 2 hours later cold, same problem: starting and die, could keep running with throttle but very un-smooth, like a flooded cylinder. I let it warm up for a few minutes and it got better but when I hit the road I got those hard stalls and restarts, and then...

...it warmed up and it was fine for the rest of the trip.

I had these same symptoms that last time I drove the car a few weeks ago, before I replaced the relay plate. I thought it was related to the bad relay plate, that maybe the fuel pump was shutting off. I've replaced the plate and the relay, and it's still there.

I'm stumped, even more so because it seems to be related to the temperature of the engine. Dead cold the problem is not there, partially hot it's there with a vengeance, completely warmed up it's gone.

I've checked the head temp sensor and it's within book range, cold and hot.

Ideas appreciated.

Greg

[BeatNavy]

I've checked the head temp sensor and it's within book range, cold and hot.

Sensor itself may be fine but what's the condition of your wiring harness? I'd look for kinks/breaks that can create open circuit intermittently from CHT to ECU. Inspect the actual connection closely. I have experienced bad CHT symptoms when it was the wiring harness not the sensor itself. One reason I bought one of Jeff's new wiring harnesses...

Like others have said - it sounds electrical - like a connection is sketchy somewhere (CHT, MPS, T1 Sensor, etc.) that's making it either run too rich or completely cutting off (e.g., fuel pump) when it acts up.