'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]

Thanks for the tips.

I don't think it's the fuel pump itself. I replaced mine a couple years ago with a 2-port NAPA pump/kit I got from Chris (Tangerine) so it's probably OK. Plus, it's correlated to temperature of the engine and there's not a lot of temp change up there (it's mounted under the tank).

Wiring I can certainly understand. One easy trick I can do is run some wire from the power terminal on the pump to an LED in the cockpit and see if I get a flickering light correlating to this problem. If I do get a flickering then I can move the wires back to the replay board, both output and relay control, and try to nail down where the prob may be.

As for the head temp sensor...man, trying to troubleshoot a random problem there will be damned near impossible. Is it correct that the fuel injection shuts off if it doesn't have a good temp reading? If not, what are symptoms of a bad sensor/circuit there? Jeez I hate 40-yr-old wiring. But can't float the cost of a new harness right now.

I have four race weekends in a row coming up*, so this is going to be an October project. Thanks for the advice.

- GA

* LRP Historics (driver observer), SCCA Regional at Palmer (914 race car comes out for the first time), and Mid Ohio SCCA Runoffs (competing). If you're in the area at any of these stop by and say hello, #33 STL Honda Civic Si or orange 914

[BeatNavy]

As for the head temp sensor...man, trying to troubleshoot a random problem there will be damned near impossible. Is it correct that the fuel injection shuts off if it doesn't have a good temp reading? If not, what are symptoms of a bad sensor/circuit there?

No, a bad circuit there is interpreted by the ECU as a cold engine, and it lengthens the pulse for the injectors thinking it's a cold condition. On a warming or warmed up engine it effectively floods the engine and kills it. That's my understanding anyway.

I agree with Phil. Take each component you can think of and test it individually as well as its actual circuit to the ECU. The more suspects you can rule out, the better you can focus on finding the root cause. Test/inspect FI grounds, Trigger Point connections, etc.

Testing the MPS electronically is very simple with an ohmmeter. If you have the vacuum pump, that's an easy enough test too.