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Abrupt hot no-start 700 1990

posted by  Will740turbo on  Wed May 11 00:28 CST 2016
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last visit: Wed Oct 22 16:09 CST 2014
[RELATED]

I've got an unexpected and sudden no hot start. 90 740T.

Drove around all day, no issues. Haven't had any issues at all in the last several years.

Last night, I was working on getting some new battery cables ready to install. I noticed one of the larger (maybe 8awg) leads to the positive terminal had some heavy corrosion, and poked at it a little to check for voltage drop between the alternator terminal. I didn't make any changes other than to add a 3/4 of a quart of oil. The new cables are a long story, but they've been sitting around for ages, unneeded; I was just looking for something to fix.

Two things that were different today from other days:
1) It was warmer than it has been regularly and I drove about 30 miles. This happened after the car sat for about an hour and a half and the engine was still nearly warmed up.
2) I drove with the headlights *off* 90% of the time. I almost always drive with them on constantly. I did this because of a low-voltage under load issue I'm just beginning to look into.

I ran the car (LH2.4) through its self-test procedures modes 2 and 3. The crank sensor registered and the throttle switch did too. I can feel the fuel/hear the fuel pumps prime, and I can feel the RSR click on. In mode 2, it fires the fuel injectors without issue.
I backprobed a LED light into one of the injectors and found that it does NOT pulse when cranking. This seems rather odd. As for spark, the car fires and starts and runs for a few seconds on starting fluid.


My first suspect was the RSR, FI relay, and ignition amplifier. I have a spare ignition amplifier to try tomorrow and the RSR/FIR appear fine and to be working. Again, it seems very odd that the injectors weren't pulsing.

My real fear, if it's not the ignition amplifier, is that either leaking AC voltage from a failing alternator diode set or some other oddity damaged the FI computer. It's parked at a friend's house for the night.

Cheers!

PS I hope it's not this. I really don't want to re-open the ECU connectors: https://www.brickboard.com/RWD/index.htm?id=918069





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