drive135mph

Alright at long last I found a DME from exactly my car locally and swapped it in this morning. Nothing has changed..... Nothing at all. I confirmed that the injector circuit still has continuity, and 12v at the injectors. At this point I'm looking for something outside the injection circuit itself.
What else could be causing this? Are there any Porsche yodas willing to complete my training and shed some light on this problem?

The local Porsche guy told me reference sensors can do this but wouldn't this inhibit spark as well?

Thanks again.

mel_t_vin

Greg, you have spark, where...at the coil, at the distributor, or at the plugs?

You have good fuel pressure...under what conditions?

Regardless, pressure at the rail guarantees/verifies neither pulse, nor spray, at the injectors. Pull the rail, with injectors attached, and crank the engine.

Got spray?

drive135mph

I have fire at the plugs and indeed through the plugs

I have fuel pressure during cranking.

The problem is that there is no injector pulse despite a new DME, good harness continuity and 12v at he injectors.

any thoughts? This has no stumped the local Porsche specialists in my city.

drive135mph

Ok another possibility bites the dust, The local Porsche tech suggested that my car jumped time... a good thought so I verified my valve timing and it is bang on. Absolutely perfect.

Does any one have any thoughts on what might be going on here? I appreciate the time everyone who has read and posted has put in and I can't help thinking that this is something very simple. As such I am starting to go back over some previous assumptions:

- Good spark: this was tested by resting the plug on the head and seeing that it provided a strong arch, through the electrode and on to the block.
- No injector pulse: Established by plugging a noid light into the injector pig tails and observing the bulb... no flashing
- 12v at the injectors: established by using a voltmeter over the two poles of the injector pigtail and recording the voltage
- No Mass Airflow failure: Had a friend push open the flap in the air meter and attempted to start the car. no change
- Good injector harness continuity: established by connecting an ohm meter to a pole of each injector and it's corresponding pin on the ecu. All injectors had good continuity and no signs of shorting
- Good Reference signal: proved so far by the presence of both spark and tach movement during cranking
- Good engine ground: verified with a volt meter between the head and the intake and the positive battery terminal
- Good DME: though the DME was my original suspect, it was replaced with a "known good" unit and this had no effect at all on my symptoms


If anyone notices anything amiss at all, in my process, I would love to hear about it. I suspect one of my assumptions is wrong because all my tests have proved my car is in good order despite it being in lawn ornament mode...

A Big thanks again to everyone who has posted!

odonnell

If the timing is off by one or two teeth, it will still run but it will be terrible. If its off by more than that, get ready to talk to Lart.

If it was off, wouldn't that significantly hinder compression? The valves wouldn't be seated completely during TDC.

drive135mph

I agree, I really doubted it was off, and I have encountered an number of cars that were a tooth or more off and still "ran". As it happens though my timing is right where Stuttgart intended it to be.

By the way I misspoke above. The injector power was not confirmed across the poles of the injectors but across the head and the injector 12v lead. Sorry

mel_t_vin

Greg, how old are your s/r sensors? Have they been spec'd out at anytime during this troubleshooting session?

Try this...carefully [harness gets brittle with age] disconnect, examine [feel free to clean with electrical spray], and then reconnect one of the sensors. Attempt to start car. Nothing...disconnect, clean, and then reconnect the other sensor. Attempt to start car. Anything?

Nothing...carefully [harness gets brittle with age] pull harness-side connector boots back to examine condition of underlying wires/terminals. My suspicion...one, or both, of your s/r sensor terminals/connectors is degraded.

drive135mph

I will give that a try! As far as I know both sensors are old enough to have seen Hendrix perform

Wouldn't they cripple spark as well as fuel should they fail?

931guru

Bad injector wiring harness.

drive135mph

Ok pulled the pig tails, to the reference and speed sensors and they look good but i cleaned them anyway.... still no joy.

931 guru:
I have good continuity from the plug for the injector back to the dme, is it still possible the harness is bad?

drive135mph

oh also they ohmed out well within spec, leading me to believe they are good to go

drive135mph

Ok odd thing I noticed today that might be clue to someone. I Attempted to start the vehicle after cleaning the reference sensor connections, the car tried to start on the first crank of the key. It sounds like just one cylinder but on the second crank of the key that one cylinder doesn't sound like it's firing anymore.

Any clues anyone?

drive135mph

SO i spoke again with my electrical engineer neighbor and he made a cool point, that possibly when i was ohming out my injector harness, the fact that it was cold caused it to read at a lower resistance than it would when it has had power going to it.

So I tried starting it again and sure enough some cylinders seem to want to try to fire on first crank, but not after. So as such i'm thinking of ordering the Lindsey racing injector harness to test the theory

harveyf

A test that I use for the speed and reference sensor: You need a good digital meter like a Fluke with a max hold feature. Set the meter to AC, a scale > 3 volts. Activate the max hold feature. On your disconnected DME plug, measure across the sensor input pins for the speed sensor. Crank the car. You should find a peak AC signal of around 2 volts. Do again for the Ref sensor. Same deal. I did this last weekend on my car. I got a solid 2.5 volts for the speed sensor and a not so solid 0.5 volts on the Ref sensor. My car starts and runs with these values. As stated in the shop manual, the actual voltage is a function of the starter cranking speed and the distance from the end of the sensor to the moving surface on the flywheel. But no voltage would certainly be a strong clue!

It's a long shot but there are published values in the workshop manual for the DME harness resistance readings for the air flow meter, and the temp sensors. Also tests for throttle position switches. Also tests for voltage at the air flow meter. You haven't mentioned testing those values. Might be time to do so.

I would go ahead and remove, clean, and re-assemble the 2 or 3 ground lugs on the firewall and head/block. Continuity on a meter does not always equal a good ground.

I haven't tried it before but it might be reassuring to check the injectors by grounding the DME harness pin for the injectors manually, just to hear them click/cycle. Basically another way to check the harness. This assumes you are powered up and have 12 volts on the injectors, as you have indicated you have.

I was raised in Lynchburg. It was a sleepy little town. Maybe your car has Rip Van Winkle syndrome

Lecrok

drive, you said you have fuel pressure, was it measured? Too much fuel pressure will cause the injectors not to pulse. Bad FPR. Remove a lead from one of the injectors and see if it starts. I believe it's a Clark's Garage procedure.