Cranking strong but no start on cold engine

[s4BoostKing]

So 6 months ago my car wouldn’t start when the engine was hot. Turned out to be the crank position sensor. 2 months ago I had the exact same problem so I swapped the cps out again which solved the issue. Now just today my car wouldn’t start after sitting overnight. With a cold engine it shows the same symptoms as before. Cranks strong but never shows signs of wanting to start. Is this the cranks sensor again!!!?? Maybe the coolant temp sensor?? I’m getting so fed up with this car I’m afraid of driving it anywhere now and then not being able to start it again.. I have vag com is there something I can look at on the measuring blocks?

[Schtug]

Is it coding for anything currently?

[s4BoostKing]

No codes.. swapped out the cps and coolant temp sensor and still no start. I don’t think I could hear the fuel pump. So I checked the fuse and that was fine but #29 was blown which was for the ECM (engine control module) so I’m getting a new fuse tomorrow. I sure hope this is the issue

[V70R]

What's the amps, 20? Yank your sunroof fuse or something with similar amperage and see if your car starts

[s4BoostKing]

What's the amps, 20? Yank your sunroof fuse or something with similar amperage and see if your car starts

20A yeah. Dang I didn’t think of that. I will in the morning.. after doing some quick research on blown #29 research it’s usually faulty wiring in the coil packs. But about 6 months ago I upgraded to the 2.0 coils so I find that hard to believe that’s the issue

[V70R]

Think of how hot our 2.7T engine bays get and the number of heat cycles they have experienced over nearly 20 years...that's a ton of heat! You may have an electrical issue within your harness as the sheathing that protects the wires breaks down with heat and becomes brittle; hence the no-start condition and blown fuse.

When you go to start your car, keep the driver's door open with the fuse cover removed and turn the key to auxiliary...if you hear a loud pop from the vicinity of the fuse panel, probably have a short in the ignition coils as they receive 12V when the ignition is switched on.

[s4BoostKing]

Nothing worse than tracking down an electrical issue. I just had my car apart for 2 weeks replacing a coolant line to a turbo and now this. Starting to get annoyed with the car

[s4BoostKing]

Think of how hot our 2.7T engine bays get and the number of heat cycles they have experienced over nearly 20 years...that's a ton of heat! You may have an electrical issue within your harness as the sheathing that protects the wires breaks down with heat and becomes brittle; hence the no-start condition and blown fuse.

When you go to start your car, keep the driver's door open with the fuse cover removed and turn the key to auxiliary...if you hear a loud pop from the vicinity of the fuse panel, probably have a short in the ignition coils as they receive 12V when the ignition is switched on.

So I swapped a fuse in there and it blew as soon as the key was turned

[V70R]

Short in the harness. See if you can isolate which coilpack it is- time to grab an ohm meter and start going through the harness.

[s4BoostKing]

Short in the harness. See if you can isolate which coilpack it is- time to grab an ohm meter and start going through the harness.

So could this have something to do with the leak detection pump? Or just coils

[s4BoostKing]

I checked for codes again and sure enough there is 17880 - EVAP Leak Detection Pump P1472 - 35-00 - Short to Ground

[Daveb5s4]

Disconnect the pump and see if it still blows. If the fuse doesn’t blow, your pump is bad.


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[s4BoostKing]

So I quickly checked all the coil wires and they were good and I cleaned the grounds under the coolant reservoir they looked bad. But same issue still the fuse blows as soon as the key is turned. I’ll take a look at the LDP tonight when I get a chance

[ReggieNoble]

Check you 02 sensor harnesses for melted/damaged wires.

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[Schtug]

Start with unplugging the leak detection pump and see if fuse 29 still blows. I feel your pain because I spent between 6 and 8 hours swapping things around trying to track down a short to ground that turned out to be a bad cam position sensor that had shorted out internally. Bitch of it was the sensor was a brand new bosch part and of course you never expect the new part to be bad. The car was coding for anything that used a 5v circuit so it took a while to narrow it down. I was initially thinking the ecu fried due to the amount of codes all at once and also because the car just shut off while driving and wouldn't restart, no blown fuses either. I despise wiring problems.

[s4BoostKing]

Start with unplugging the leak detection pump and see if fuse 29 still blows. I feel your pain because I spent between 6 and 8 hours swapping things around trying to track down a short to ground that turned out to be a bad cam position sensor that had shorted out internally. Bitch of it was the sensor was a brand new bosch part and of course you never expect the new part to be bad. The car was coding for anything that used a 5v circuit so it took a while to narrow it down. I was initially thinking the ecu fried due to the amount of codes all at once and also because the car just shut off while driving and wouldn't restart, no blown fuses either. I despise wiring problems.

Unplugged the electrical connector to the leak detection pump. Tried to turn it over and fuse #29 blew instantly. So I guess there’s a short in the coils which I already checked or the O2 wires which I’ll check now.. I was half pissed off just getting the fender liner out

[s4BoostKing]

I hooked up my vag com and am looking st a few things; oxygen sensor heating, oxygen sensors, evaporative emissions, and catalytic converters all failed readiness.. so maybe the problem does like with the O2 wiring

[s4BoostKing]

When I unplugged the LDP the only code I had was P1473 Evap leak detection pump OPEN CIRCUIT.. then when I reconnected everything the code went back to P1472 Evap leak detection pump SHORT to ground.

[Schtug]

When I unplugged the LDP the only code I had was P1473 Evap leak detection pump OPEN CIRCUIT.. then when I reconnected everything the code went back to P1472 Evap leak detection pump SHORT to ground.

Unplug the ecu, unplug the LDP, then check for short to ground on pins 25 and 80. There's nothing else tied into the LDP circuit.

[s4BoostKing]

Unplug the ecu, unplug the LDP, then check for short to ground on pins 25 and 80. There's nothing else tied into the LDP circuit.

I’ll give that a shot tomorrow when I have the proper tools.

Other similar post have fuse #34 control engine unit also blowing which is 15A.. but I just checked mine and that is not blown..

I checked all the O2 wires and they all look good but I’m gonna try unplugging them one at a time tomorrow and see if fuse #29 blows.. I’ll do the same thing with the coils after that.

I’m not electrically inclined and good with the tools that’s why this is turning into a nightmare

[s4BoostKing]

Still don’t have a multimeter and not much time on weekdays to work on the car. But I was able to unplug each O2 sensor one at a time and try to start the car and the fuse still blew for all of them. I ran out of fuses but I’m doing the coils tomorrow one at a time

[Schtug]

Still don’t have a multimeter and not much time on weekdays to work on the car. But I was able to unplug each O2 sensor one at a time and try to start the car and the fuse still blew for all of them. I ran out of fuses but I’m doing the coils tomorrow one at a time

Just a reminder, unplugging a sensor or device doesn't rule out the possibility that the wiring going to it is shorted out. You really need a multi meter. Christ, even the ones harbor freight gives away for free will get the job done. Lol

[s4BoostKing]

Finally got a good multimeter and will begin diagnosing tomorrow. I know what to do for the coils but I was wondering how to test for a short to the O2 sensors. It’s 4 pin but I’m not sure which are what

[LJS]

Assuming you have Bosch sensors---
The (2) white wires are for the sensor heater
The black wire is the sensor signal wire
The grey is the sensor ground

[s4BoostKing]

So I can test a short to ground to either of the white wires to the ground? Or test both?

[s4BoostKing]

Sorry for the stupid questions but should I replace the fuse or pull it out when measuring the resistance of the coil pins??

[s4BoostKing]

Okay so I used the multimeter to check the resistance in the coil connectors. Every single one of them has .5 ohms from the #1 12v pin to the #4 ground pin(or any ground on the car I got the same reading).. I also get the same reading with a new fuse in #29 and also without one.. I get a solid continuity reading on each coil connector between the first pin and ground as well obviously. From what I learned in the last few days there should be no continuity or resistance between the 12v pin and any ground with the fuse pulled. So every coil connector is shorting to ground??? I followed the coil wires into the harness and into the ecu nothing looks bad visually. Where to now????

[s4BoostKing]

Some side notes. The fuse doesn’t pop when I take the fuel pump relay out. The relay had burn marks on the bottom of all the tabs. Could this be the culprit??? Also the coil pack connector under the oil cap had some oil inside of it, I’m going to clean it out and leave the connector unplugged overnight to dry out. Could this be why I’m seeing the resistance in the coils when I shouldn’t be?

[s4BoostKing]

So I cleaned the fuel pump relay tabs, cleaned the coil pack connector, and did a ecu reset.. fuse doesn’t pop and car starts up right away and runs like a dream. Not sure what the actual issue was. But I measured the resistance on the coil pack connector again and now it was 1 ohms from the #1 12v pin to ground. Does that sound normal?