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Car: 1973 412 Coupe with stock 1.7L and D-Jet fuel injection previously running great as daily driver. More here http://412coupe.blogspot.com/

Problem: Drove to work the other day and all was fine. Rained all day as usual. Leaving work, car would not fire up. Finally fired up but stumbled terrible for about 5 seconds before stalling. Next day, same but did run normal a few times for 5 seconds then stall suddenly. Repeat starts crank fine, but doesn't fire up.

Recent work: Replaced alternator with rebuilt 70A AL108 alternator and new Bosch voltage regulator (0-192-062-007). Replaced oil cooler seals (had coil disconnected). No problems after work done until other day when all the sudden, no start.

Trouble-shooting:
1. Fuel pressure, tapped off left side fuel rail, gives 30psi cranking, 20psi after cranking -> good pump and regulator.
2. Timing light strobes on each spark wire during cranking -> all sparking.
3. Condensor green wire to ground measures 0.2 ohms; test light flashes connected to negative side of coil when cranking -> condensor not fried, points working.
4. White spark off original black bosch coil wire grounded to case; primary coil measures 2.9 ohms (spec 3.0 ohm); secondary coil measures 9.37 kohms (spec 9.83 kohm)-> coil good.
5. #4 spark plug pulled and found dry after cranking; disconnected cold start valve plug and bypassed fuel line around valve with no change -> not flooded from cold start valve.
6. Fuel pump relay activates pump for a second after key on, then stops. Relay output to pump is 10 VDC while cranking -> good fuel pump relay.
7. CHT sender measures 2.25 kohms at about 50F -> good sender.
8. MPS measures 91 ohms for primary coil (outside pins, spec 90 ohms) and 330 ohms for secondary coil (inside pins, spec 350 ohms) -> injectors should be firing.

Next up, test trigger contacts and injector pulses.

Nothing wrong found yet - please verify my conclusions and suggest other tests to locate problem.

Thanks,
Bill

Try a cylinder pressure test to be sure all is fine inside and you have good compression.

If you have good compression, get a set of Dells and throw away the D-jet.. (sorry, couldn't resist)

It was the trigger contacts. Worn cam rubbing blocks. Replaced with new trigger contacts spare on-hand and fires right up.

Interesting that contacts were opening one at a time by checking continuity between middle and pins of trigger contacts, but due to cam rubbing block wear, the duration of open cycle must have been too short for the ecu to detect. No signal to injector was also verified by checking voltage across injector plug disconnect from injector during cranking. Once fixed, the voltage read about .5 VDC on digital DVM with car running.

Good D-Jet troubleshooting guide here (thank you Paul Anders):
http://members.rennlist.com/pbanders/DJetParts.htm

I'll stick with D-Jet for the sport of it!
Bill

I'll stick with D-Jet for the sport of it!

Too funny! Yeah, I haven't been pushed far enough over the edge yet to convert either.

Travis

Thats not your only issue. Your fuel pressure at no time while cranking or running should drop below 28 psi. This means either that the regulator is leaking or the pump volume is down.
The easy test for the regulator is to run the car. You should have steady pressure at 28-30 psi without more than 2 psi fluctuation...and even that is crappy by my standards. Turn the car off. It should immediately drop pressure to about 23 psi...and no less than 18 psi. It should hold 18 psi for at least an hour....and then slowly leak down to almost nil ver several. If it drops quickly....either the regulator s shot or perhaps even the check/bypass valve in the pump.

In a fixed fuel pressure car with no 02 sensor to correct with you must have rock steady fuel pressure at all extremes. Every fluctuation of 1 psi is between 2.5 and 3.5% of your total fuel mixture depending on set pressure. Your ECU has no control or counter measure for this.

D-jet blows a set of dells away any day....if its properly tuned and in good condition.

Oh...by the way...its doubtful that it was the contacts unless the plug conection is poor....which is common.....or the resistance is very high on one contact set. Ideally the resistance should be no differnt than about .1 ohms side to side. Ideally neither trigger set should be over 1.0 ohms. You can have them perhaps at 1.2 ohms ....if both sets are deaad identical.

Its also common that if your fuel mxture is already off (low fuel pressure will do that).....and the resistance of the triggers are imbalanced....it can cause this.

Another common cause of no injector signal that gets masked as something else and blamed on the triggers is loose ground wire bundles under the plenum. Just pulling the dizzy rattles things around enough under there to make loose grounds work....aking anything you did to teh dizzy seem to fix the problem...when in fact it did not.

I am going from memory......but the trigger gap (gap between rubbing blocks when new) has been posted many times....it is either .923"....or .97"....I will have to look it up in my black book.....but my bet is that unless you ran the triggers bone dry for thousands of miles....they are not worn enough to cause issues.

Also....as long as teh gap is open...the duration of open is set buy the cam....not by the lift of the triggers. If the triggers open at all when the ramp edge approaches.....having worn rubbing blocks will not keep you from starting and running.....in fact....you would be hard pressed to notice any change.
However.....and this is the most common issue with worn rubbing blocks......if the triggers are not opening as wide as they "could".....the oil....or water vapor (you mentioned it was raining) that normally collects on them from the vapors in the dizzy...can still bridge the gap and cause the trigger to not function.

The real key to understanding if the trigger is faulty....is to turn the engine around until each trigger opens....and with a digital volt meter...measure the resistance.

Do two to three cyles of this writing the resistance of each trigger down. If they come back slightly different each time, or miss one or more times, the trigger points are either dirty or oily....or wet.....or corroded....or hace poor electrical crimps. Ray

Thanks for more details Ray.

My fuel pressure was/is solid at 30 psi and dropped to 20 psi AFTER cranking/running so it seems fine. I'll look into pressure drift later.

The distributor shaft was dry when I removed the old trigger contacts and had not been serviced since I bought the car so who knows how long they ran dry. There was some oil residue in the distributor which could have fouled the contact points, but now the resistance between contact sets is 0.3 ohms and 0.4 ohms without touching the contact surfaces since removal (I'm not too sure about the calibration of my DVM, but the main point is that the two sets are close to each other). The distance between the used cam blocks is .925 (I didn't measure the new set). The plug contacts were thoroughly cleaned during the troubleshooting without impact. The car was towed home and garaged for 2 nights without any impact on start up, so moisture probably wasn't it.

I reinspected the FI grounds and did a wiggle test. Tight connections and starts fine after wiggling.

Regardless of the real cause, I'm better prepared to fix it next time

Yep...you are on the right track for trouble shooting. The rubbing block gap actually sounds fine. The closesness of the triggers sounds fine.
It is very common that just removing triggers to clean or inspect changes things drastically. Most of this is due to the connector type that is in the three prong plug. Because the D-jet used miniature male/female spade connectors.....just like their larger cousins you find in your fuse block......eventually plugging and unplugging cause them to not have enough tension in the female terminals to properly grip the male spade. It rattles and conectivity is intermittant.

90% of all D-jet problems are wiring harness related. It sounds that way in your case as well because the triggers appear to spec out ok from what you tell me.

The best thing I could have ever done for dependability isto (a) build a new harness using dual cantilevered L-jet terminals and (b) the most chang for dependability was finding a three prong plug in the junkyard that used l-jet style terminals....for the trigger plug. Ray