Intermittent cold start - cranks but no fire

[RedB5S4]

Been a little while guys but I'm still kickin'. Need some help diagnosing an intermittent no start issue. Some days the car will run fine, other days it just cranks and cranks but will not start.

What I know:
- There are no codes. Scanned it multiple times, nothing.
- Pretty sure this is isolated to cold starts. Once the car has been running/warm, it fires right up.
- I have fuel. There's pressure at the rail and the plugs are wet when I pull them.
- New plugs. Spark is there sometimes, I'm assuming other times it is not.
- The tach is not reading anything while cranking. It doesn't move.
- There is an audible clicking noise while cranking. Thought it was the FP relay but then thought better of it since I know I'm getting fuel.

I've read that no tach reading while cranking is a hallmark issue of a faulty crank sensor, but since I'm not getting any codes, I'm coming here for comfort. I have a new coolant temp sensor and CPS on the way, but this has got my feathers ruffled.

Advice, suggestions, insults - all are welcome

Thanks!

[LightningLou]

When you try cranking and no start, then stop, and try cranking again what happens? I have seen this issue before, but only on e85 for whatever reasons. What fuel and pump are you running?

[RedB5S4]

It just continues cranking. I can stop and start again as many times as I want with the same result. Fuel pump is an 044, 93 oct tune by Daz.

I should also say that this could be a starter related issue, as it does seem to be on its way out. Won't engage the flywheel all the time, but if I let the car roll a little bit it will catch and crank. Just putting that out there.

[Tjtalan]

Have you checked to make sure you're getting crank signal when it's not starting?

[Zba]

If it cranks continuously you can rule out a starter.

"Doesn't engage"? What do you mean by this? Starter goes "whIIIIZZZZZZZZZZZZZZZZZZZzzzzzz"?

[Austonwerner4]

Sounds like a bad crank sensor

[RedB5S4]

Have you checked to make sure you're getting crank signal when it's not starting?

Not yet, I need to check this tomorrow. If I'm not getting any signal, that's surely the crank sensor, correct?

If it cranks continuously you can rule out a starter.

"Doesn't engage"? What do you mean by this? Starter goes "whIIIIZZZZZZZZZZZZZZZZZZZzzzzzz"?

Pretty much. I can hear the starter spin, but it's almost like it's not engaging the flywheel - engine doesn't turn over. When this happens, I can cycle the key and/or let the car roll a little bit and it will grab and crank. Once it's engaged, it just cranks continuously... So I'm with you, I think the starter can be ruled out, otherwise it wouldn't be cranking at all.

What about ignition switch?

Sounds like a bad crank sensor

That's my thinking, but there are some curious issues that I'm not sure about. I'm going to check to see if I'm getting any crank signal at all via VC and go from there. If there's no signal then it's gotta be the crank sensor, if I am getting signal then it's gotta be something else.

I'm thinking CPS, ignition switch, fuel pump/relay, in that order. I just don't know why I'd be getting fuel if the pump or relay were bad. Don't think fuel is the problem.

[Tjtalan]

Not yet, I need to check this tomorrow. If I'm not getting any signal, that's surely the crank sensor, correct?

.

If you don't have any RPM signal when cranking it's definitely a crankshaft position sensor. It also sounds like the solenoid is failing in your starter, probably going to need a new starter soon.

[RedB5S4]

If you don't have any RPM signal when cranking it's definitely a crankshaft position sensor. It also sounds like the solenoid is failing in your starter, probably going to need a new starter soon.

OK, that's what I thought. And if I have RPM signal via VC but not on my tach?
Aware of the starter going out, but it's fine for the time being. I don't think it's related to the no-start issue in any case.

[Tjtalan]

Don't overthink it yet. The engine only spins at about 200 RPM when motivated by the starter. I don't know if the cluster would even register crank signal that low. Check tomorrow and go from there, good luck.

[RedB5S4]

Don't overthink it yet. The engine only spins at about 200 RPM when motivated by the starter. I don't know if the cluster would even register crank signal that low. Check tomorrow and go from there, good luck.

Yes but I've confirmed that the tach should at least move while cranking. Pulled the fuel pump fuse on a buddy's car and it was visibly reading RPMs. Will check tomorrow nonetheless and update with my findings.

[Tjtalan]

Well then everything is making sense. The cluster gets RPM signal from the crankshaft sensor. So if your sensor is bad the tachometer Would not register while cranking.

[RedB5S4]

Ok, so the tach is still not registering anything while cranking, but VCDS is. Which tells me that it might not be the crank sensor.

Any other ideas? I'll put the new crank and coolant sensors in just to be sure, and I'll put a gallon of gas in it JUST in case the sender is bad. I'll also check for spark again. If I'm not getting spark, which I'm assuming I'm not, I'm not sure what else it could be. New plugs, R8 coils, and ICM deletes. Ignition switch would probably not be cranking. Not sure what else would be preventing it from getting spark.

[Tjtalan]

Back to basics, spark and fuel. One is missing find out witch one and go from there.

[RedB5S4]

I have to say, after all my years of owning a B5, I've never felt like this much of a noob.

GUYS WHY ISN'T MY CAR RUNNING?!
CPS




... I think I may have found my problem.

[Yuppie]

Speed sensor wire ripped apart?

[RedB5S4]

The connection was sitting on the driver's side downpipe apparently, melted together. Had to splice another connection into the wiring harness and voila, she fired up on an almost dead battery lol. Crank sensor was the ticket.

[Tjtalan]

I have to say, after all my years of owning a B5, I've never felt like this much of a noob.

GUYS WHY ISN'T MY CAR RUNNING?!
CPS




... I think I may have found my problem.

That will do it haha. Its weird it still had signal, glad you figured it out.

[RedB5S4]

Yeah I think 1 or 2 of the wires may still have been in tact somehow... So it was getting signal in VCDS maybe but the wire that tells the plugs when to fire must have been toast. That's the only reasonable explanation I can come up with anyway. Not getting tach readings is usually a tell tale sign of a bad CPS though, so I can't say I'm too surprised.