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Discussion Starter · #1 · (Edited)
SOLVED!! - 1.8T AWM Engine cranks+has fuel but no start! Help!!

Hi all,

I've had a good couple months and a couple thousand miles out of my Passat since fixing it initially.
Now, suddenly, she won't start. There's a strong crank and she's getting fuel, but no catching/firing.

Some background to help.
Initially when I bought her, the ECU wiring was corroded to pieces, previous owner swapped out the ecu and left it like that.
I bought it, connected the wires properly and had the 'new' ECU married back to the car (instrument cluster and such) so that the immobilizer would stop kicking in after the 3 seconds. The 'marrying' was done at VW along with the coil pack recall.

Since then, I've been driving it pretty much every week day to school (around 12 miles each way) and where ever else + couple 150 mile round trips around various places in Florida....

Then today, I came home, reversed on the drive and shut the car off as usual. A couple hours I am ready to leave to go elsewhere and it cranks but won't start!!


Also, if it's related, I have a CEL for 02 sensor and misfire.
And the Park/Rev/Neu etc thing on the red display highlights all the gears - instead of the one you're in - but very rarely 1/20 drives, it would work properly.



Any help would be greatly appreciated. I will start digging around tomorrow morning........

Brad
 

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Discussion Starter · #2 ·
To add to this, unusually as mentioned in the OP, the gear selection display is working perfectly every single time?
It shows the gear I'm in each time I turn the ignition on and works.... are there any sensors associated with this that would prevent iginition?
I also swapped out the ignition switch, no difference however.
 

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Discussion Starter · #3 ·
After looking around I've found the fuel relay is working and the fuel pump is pressurizing the system.
Still cranks but no start
 

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Discussion Starter · #4 ·
Quite surprised no one has chimed in here, but for any with similar problems now or in the future I'm sure the solution will be handy.
So after replacing the Fuel pump relay (372) in the drivers footwell I started to get #29 Fuse (ECM) blowing with the ignition on.
Some research brought me to this site....
P0688 and blown fuse #29

And the problem was in fact my coil pack wiring shorting. However, a couple months ago I had replaced the plugs going to the coil packs and I have now found that the heatshrink around the connections was melting and the coil pack wires were shorting, causing the blown fuse.
After re insulating the wires and refitting with a new fuse, all is well, started straight up.
Of course, this is not a common problem as it is my connections that were shorting, but as seen from the thread it is common for the same shorting problems to occur with the standard wiring crumbling. The error code which showed up on a scan was p0688 ECM Relay load circuit:Open Circuit.......I think?

Whilst during my troublshooting I noticed that the ECM relay (429 - can be 428) would close upon ignition but never open back (break ECM circuit) unless the battery was disconnected, unless maybe it opens after a long period of time. Hopefully that is the case.

I suspect this was also causing my random misfires at idle and maybe even the lack of power around 35/45mph(4000rpm in 3rd)


Hopefully this will help someone else
 

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I hadn't responded to your posts because I couldn't understand what you were trying to say,
I was in the process of asking you to explain some points when you posted your 4th post.


It appears the White/Black wire that connects from the relay to the ECU pin T121/21, may now have a partial short to ground.
Or the relay or ECU could be faulty.


NOTE: Something strange happened with this post; I edited it soon after posting. Today I noticed it had reverted to the original post,
I clicked the edit button to change it back and the edited version came up so I saved it and all seems OK.
 

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Discussion Starter · #8 ·
Okay, I see
I don't see how a short in the Relay power wire would cause it to stay shut?
The relay shuts upon ignition and as far as I know it doesn't open back until the battery is pulled.
Is it 'supposed' to shut the circuit off when ignition is off or would it do so after some time. I have heard all sorts about these VW's, some powering the fuel pump to prime the engine as soon as the drivers door is opened and so on....
 

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Okay, I see
I don't see how a short in the Relay power wire would cause it to stay shut?
The relay shuts upon ignition and as far as I know it doesn't open back until the battery is pulled.
Is it 'supposed' to shut the circuit off when ignition is off or would it do so after some time. I have heard all sorts about these VW's, some powering the fuel pump to prime the engine as soon as the drivers door is opened and so on....
Don't believe everything you hear.

I was referring to the trigger wire, NOT the power wire which is Red/Green and/or Red/Grey.

The relay should always be off when the ignition is off.

Please read posts carefully with an open mind.
 

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Discussion Starter · #10 ·
Okay, I tested the relay itself by powering it up and checking it works as it should, and it does.
So like you say, I guess I must look for this short which is keeping the relay shut.
But how would this short be happening only when ignition goes on, and then staying without ignition? Seems weird
 

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Check post #5, I'm not sure which version you have been using.

A partial short could draw enough current to hold the relay closed but not pull it closed.
Remove the relay and disconnect the relevant plug from the ECU, What is the resistance between the White/Black wire (that connects from the relay to the ECU pin T121/21) and ground ?

If not open circuit, find and repair fault in that wire; otherwise the ECU is faulty or staying on, could be corrosion between T121/21 and adjacent pins or case.
 
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