ECU relay (labeled 30 in plastic box on firewall near brake master cylinder). $20 part.

 

Worth a try.

 

One other quick question... if the ECU was not getting power due to the relay not working, would the rpm gauge still show the engine speed while cranking? It's not much, but it does register the speed the engine is turning over. Wouldn't the RPM gauge be run off a signal through the ECU? If so, if the ECU is not getting power due to the relay failing, how would the rpm gauge still be working? Or is it powered another way? Thanks

 

Your fuel pump may be overheating and on its way out. Connect a fuel pressure gauge to the fuel injection manifold and check for pressure when this condition occurs.

 

This may be what is happening. I'll look at the fuel pump idea too.

 

Well, did it to me again. Fuel pump is running, the rpm gauge moves up a little while cranking.

Does the rpm gauge get its signal from the crank sensor, or from a cam sensor?

This thing acts like a gm product when the crank sensor is going out. Heats up, quits sending a signal, cools off it then will send signal again.

Crank sensor go out on these 1.8s?

 

Well, did it to me again. Fuel pump is running, the rpm gauge moves up a little while cranking.

Just FYI, but I have seen many fuel pumps fail in such a way that they make noise but don't produce enough pressure to run the engine. Very often, the problem temporarily goes away after the pump cools off.

 

Wouldn't you know it? Had time today to see if I could figure whether it's a fuel problem, or electrical problem. Drove the car most of the day so far and hasn't acted up once. In town and out of town about 60 miles so far. Have a trip this weekend, but not sure about trying to take the Passat. We'll see.

The other day it quit after 20 miles and waited an hour before it would restart. UGH! Gonna have to start drinking.

 

That's what I'm leaning towards is the fuel pump. I was hoping it would act up today since I had time to actually work on it. Thanks for the heads up though.

 

If indeed your only code is random misfires, then your car probably isn't missing a sensor signal, or ECU power. With 200K miles, change the fuel pump. They wear out, and sometimes you get lucky and get advance warning, like you have been getting. Sometimes you don't, like when mine just quit cold-turkey on the freeway, with a mile of no emergency lane due to construction going on. Fortunately I was doing 80 when the tach dropped to zero, and was just able to coast to safety, but it was a nail biter.

 

Against my better judgement, we had to make a trip in the car this weekend. Drove almost 400 miles round trip and the car ran fine. Always started, never acted up. Did not get a chance to put in a fuel pump. Go figure. Thanks for the suggestions on what to do and look for, but now have another car and will either sell this one or scrap it out.

 

Thought the new fuel pump had my problem solved, but the car would not start again today. Shut it off, came back out and it wouldn't start. Cranks fine, just no spark. Fuel pump is running and making good pressure, but when it won't start, it has no spark. While cranking the RPM will come up, then drop to nothing when you stop. So do I go ahead and loiok at replacing the crank sensor any way? Acts much like some GM products when the crank sensor gets hot and won't let the engine start.

 

That won't help if there is no crank sensor fault code. I'd check the power and ground at the coils, with a DMM, when it won't start. Pull one connector from a coil and probe the appropriate contacts with the meter set for Volts, looking for battery power, with the negative meter lead touching grounded metal. Also check the resistance between the ground pin and the grounded parts, such as the intake manifold, using the Ohms selection. If those are good, then you want to see a firing signal getting to each coil from the ECU.

 

I'll get out my meter and scan tool tomorrow and see what I can find. Would not start at all today. Cranks fine, but does not fire. Can't complain too much, only gave pocket change for the car four years ago.

 

If it's an ATW, and the fuel pump is working while cranking, and the ignition is not working while cranking, I would expect the CrPS is working and,
I would suggest you check the Motronic Power Supply Relay, it is controlled by the ECU and supplies power to the coils.

What engine is it ?

 

So I need to see if I'm getting power to the coils, and if not, look at or replace this relay? I'll check this out when I get back home from church. Thanks.

 

After a week of not starting I finally got the crank sensor put in and it fired right up. Runs good again. Guess I'll see how long this works.

 

Well, no start again. And checking the wiring at the coils reveals no battery voltage to any of the coils. The fuel pump does run and has good pressure. I'm not getting spark because it isn't getting power to the coils. Where is the "Motronic Relay"? Thanks in advance.

 

If you want answers, please answer questions.

What engine is it ?

 

1.8 Liter ATW engine. Sorry, I posted the 1.8 in my initial post here, but did not put the ATW. I'll try to remember it makes a difference. Thanks for the help.

 

I'm not sure exactly where it is, but I expect it is the same relay as mentioned in post #2.
It supplies 12V through fuse F29/20A to the coils, and (a secondary supply) to the ECU. It is activated only while engine is turning.

ECU power supply relay | Location in ECU Box

 

Thanks, then that may be the relay under the hood by the ECU. If so I replaced it and still no fire to the coils while the engine is turning over. Guess I better start looking at the possibility of a blown fuse. Thanks again. Anyone else with ideas let me know. Ordered a manual on this car and should be in soon.

 

Is this F29 fuse located on the drivers side fuse box at the end of the dash?

 

Yes.

 

Well.... no power to F29 fuse whether or not the engine is cranking over. So for grins and giggles I supplied 12 volts to the fuse and the car starts and runs. Remove the 12 volt jumper and it will start a couple of times then won't until you supply the fuse with 12 volts via a jumper. Hopefully my book gets here so I can see how this fuse is supplied.

 

Check fuse 29 holder contacts, and Red/Grey wire to the "Motronic/ECU Power Supply Relay"
If the relay you replaced has 2 Red wires, a White/Black wire and a Red/Grey wire connected to it, that will be the "Motronic/ECU Power Supply Relay"
The fault is almost certainly a bad connection, in the relay or its socket, or the fuse or its socket, or the Red/Grey wire between the fuse socket and relay socket.

 

I'm beginning to believe it is the socket where the fuse goes. I noticed some corrosion on some of the fuses. You can wiggle the fuse box around a bit and it will finally make contact and start. So I'm gonna start there. I'll see if I can unbolt the box and turn it some so I can see behind it. Thanks for the suggestion on which fuse to look at.

 

If it is a faulty socket, with it unbolted drill 2 holes through the socket, run the wires through and connect an inline fuse holder.
That way, you keep it tied to the F29 position.