Sudden no start on my 3b swap with VEMS. Need help!

[maverick]

So I'm nearing completion of my 3b swap into my 80q, running on a VEMS plug and play which ran the engine in my 200. I got the car to a point where it would start and idle nicely, but hadn't taken it for a test drive yet. In an attempt to turn the car around in the driveway, I started it and backed up, drove it about 10 feet, then it died suddenly and wouldn't restart. I assumed I flooded it or something, but it continued to not start, and never started again. Turns out it's not firing injectors or coils. I pulled out my laptop and did an output test on coils and injectors, both of which worked correctly. I tried to take a trigger log, but I'm not positive I trust the results. I hadn't really used the trigger log much, but the first time I tried(before this incident) it gave me what looks like a nice clean log with spark events.


Currently, I am usually getting absolutely nothing in my logs, or occasionally just the primary trigger alone, no secondary showing. Never sparks, never squirts.


I verified I have power and ground at my cam position sensor. (cam position is secondary, correct?) I verified the cam position sensor is functioning properly, and I verified it is getting a clean strong signal all the way to the connector at the ecu. Why would my VEMS be showing zero trigger action when my cam sensor is most definitely functioning? And why is it showing no signal from either most of the time? I verified my engine speed sensor is generating a nice AC voltage at the back of the ecu connector as well. Pretty frustrated at the moment and could really use any advice about the trigger logs from anyone with some experience.

[audifreakjim]

Looks like your flywheel sensor is fine. Is it using audi trigger? Do you have the same flywheel as before? You might need to modify the reference pin on the flywheel. Weld a larger pin on it.. With Audi trigger it uses this as the secondary I believe.

[maverick]

I'm actually not sure. Being a plug and play unit it was all set up before it shipped. I used this flywheel for about a year on my last swap. I don't think the size of the pin is the issue. I mean it was working for a week every time I started it and now it will not sputter at all. Whatever the issue is, it happened suddenly.

Are you saying the flywheel teeth counting VR sensor is my primary and the timing pin is my secondary? I was under the impression the cam was the secondary... like I said it was all setup before it shipped and I never had to mess with any of that so I'm woefully ignorant.

[audifreakjim]

Looks like it is all three. I have never used audi trigger so not sure what trips the secondary trigger in the logs. I suspect it is a combination of crankhome and cam-hall aligning. Just like factory.
VR 135 crankteeth input (EC36/27 or motronic pin)
VR crankhome 1 tooth input (EC18/12 or motronic pin)
and cam-HALL input (1 pulse per cam rotation). (EC36/13 or motronic pin).

[pilihp2]

....shot in the dark.
Did the pin break?
Is the hall sensor still good? Either one of those will cause no secondary, and no spark

Secondary Trigger event happens when hall sensor is in window and when the secondary crank sensor sees the flywheel pin at the same time. If they're out of sync, or one isn't working, you get no secondary trigger

[Grillage]

As Phil said above, the secondary trigger requires both the cam sensor and the crank sensor when you use Auditrigger.

it doesn't look at all for the crank pin sensor unless the Cam sensor sees the "window". This keeps the crank pin sensor from looking for the pin and reading interference when it's not in range. When the Cam sensor is in the window the Crank sensor looks for the pin.

So you've either lost your Cam or Crank Pin sensor or they aren't in alignment with each other any longer. I had problems on my V8 swap where the flex of the timing belt pulled the two out of sync but that won't stop it from running.

I don't know what would have caused it to die. The loss of the secondary wouldn't do that.

[pilihp2]

I'm pretty sure the secondary is required to stay running on VEMS. It's not necessary on factory motronic except for startup, but VEMS it always looks for that secondary

[Grillage]

When I'd lose mine on the V8 it would give me a "less Sec Trigger" error but never died. Never even sputtered or anything. That could be because it was reading again pretty quickly though. I don't know what would happen if I unplugged it while it was running.

[maverick]

Well, the car wasn't tuned yet, and it didn't have any intake plumbing, so it's possible the car simply stalled and I was unable to restart it.
This morning as per Marc's suggestion I jumped the hall sensor. That means the ecu always sees the window and will always look for the timing pin. He said it will start 50% of the time(random chance of starting on the compression or exhaust stroke) I tried many, many times. No coughing, no sputtering, no fuel, no spark. So that eliminates a few things. It eliminates the cam sensor as faulty as well as a syncing issue.(I was hoping I forgot to tighten down my dizzy, no such luck). I pulled out the VR home sensor and checked for metal filings. Nothing on it. I'm beginning to suspect the timing pin, however I ran this flywheel for a year and I beat the crap out of it. It seems odd that it would fail at 2mph in my driveway.

The other thing I'm concerned about is that this log I posted with only the primary is not what it usually shows. It usually shows zero data. No primary or secondary trigger at all. I think I got 2 logs with primary trigger out of maybe 15 logs. The other 13 show zero trigger data no matter how long I try to start it. It makes me think I can't really trust the results. Anybody have more experience with the triggerlog? Does it sometimes just not work for some reason?

[pilihp2]

Ive never had triggerlogs not work. Even if it gets only primary, it gets something.
Check grounds for trigger sensors, check connections. Sounds like poor wiring connectivity somewhere or something electrical

[maverick]

Well I still haven't figured it out. Here's what I have done: I verified all wiring for all three sensors. All three have good grounds with no excess resistance. Al three have good continuity between the sensor signal wires and the ecu connector. I measured the crank speed and timing pin at the ecu, they both are generating a consistent AC voltage. The Cam sensor has good voltage at the sensor and good continuity to the ecu connector. I used an led to watch the signal from the hall effect switch. It flashes as it should. Since apparently the ecu doesn't look for the timing pin until the window lines up in the distributor, I plugged in a spare distributor and line up the window manually. Still no secondary triggers were generated while cranking. No spark, no fuel.(I also tried with the window NOT lined up, just in case.) That should eliminate any sync issue like a dizzy that moved.
So it really seems like my sensors are all working as they should. I emailed Marc and he asked me to send a log of the car while cranking. I tried, but I think the ecu loses communication whilst cranking. Not sure if that's normal or not. He said there are a couple analog input chips which could be damaged. Let's hope not. Anybody else have any ideas? It's quite frustrating.

[carl]

Try re-flashing firmware, could be corrupt, also some versions are not as signal friendly either, on others engine starts later. Have you tried topping off the battery and cranking without plugs in cyls? Could be you have a weak signal at low rpm requiring you move the sensor closer and/or add weld blob to pin.

Have you really checked that the timing pin is still physically there and vr is sending a signal? There's a specific way to measure the tdc pin signal, the pulse is so quick, you'd need a led, oscilloscope or maybe a really fast polling voltmeter with peak hold.

[88a5tq]

My 3b was in poor condition due to cylinders missing material and exposing the top piston rings to the chamber. As a result it had a hard time holding idle and I ended up stalling the car at a stop sign. seconds before that, while doing donuts, the cam drive gear seized that drove the distributor and gear snapped off the 7a cam. car wouldn't restart as the dizzy wasn't driven any longer. Another separate occasion I had a no start due to firmware corruption on the VEMS ecu after an update. These guys are giving solid advice on here. carry on

[maverick]

Sorry guys, I neglected this thread. I figured it out. It was in fact my timing pin. I hooked up an oscilloscope and saw my signal was there, but weak. After a pin repair, the car is starting consistently and running well. It's on the road now with about 100 miles on the clock and no issues to speak of. Thanks for all the help!

[pilihp2]

Shoulda pulled the starter and just looked

[PRY4SNO]

Thanks for the update, Mav. I like threads like this, full of diagnostic info. Plus you followed up on the solution. Helps a ton when a guy goes to search similar issues later.

[88a5tq]

Was the pin missing or you just needed to enlarge it?

Edit after rereading your most recent post it looks like you just needed to enlarge it possibly.