Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Customer car towed to my shop. Lost power on freeway got off it stalled and now it's a crank no start. Hooked up Verus pro has a lot of codes but all are low voltage type codes from being crank down to dead and being jump started before being tow in. Cleared all codes. Replaced battery with new. While cranking scan tool shows good cam and crank data pids. Fuel pump in tank is good has fuel all the way to the common rail and injectors. High pressure fuel pump control valve is good.
Ecu requested and actual are good. High pressure actual fluctuates between 4200 and 4700 psi during cranking.
Ecu is not firing injectors verified by low amp clamp around injector solenoid wire.
High pressure fuel sensor on end of common rail has 1.02 to 1.18 volts back probed at sensor signal wire on my Vantage ultra scope. Waveform looks like saw tooth pattern which agrees with pressure readings the Ecu is reporting on data pids.
No codes after cranking.
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
Last edit: 4 years 11 months ago by Chad. Reason: Corrected youtube link.
Sounds like a lot of good testing already done. My first thought is to make sure the fuel and high psi pump is ok. Basically pull the metering valve off of the high pressure pump and check for metal contamination. Also you will be able to smell the fuel and make sure it’s diesel and not gas. Sounds like your cranking pressures are ok but still it’s and easy check to pull that metering valve off. I think it’s 2 t20 or t25 torx bits. The other tip would be to check manifold vacuum while cranking. Diesels don’t produce much vacuum so if you have high vacuum it could be a restriction in the intake. For example the shut off valve could be stuck shut I had that one time and it kicked my ass.
If you unplug the shut off valve it should default to open. And one more thing. If you look at the injectors they should have a vacuum line that runs from injector to injector. There is a pressure retention valve that holds 7-10 bar on the backside of the injectors to help close them.
Always check battery in amp clamp I'm going to put a piece of tape and write that on my amp clamp.
Ecu has injector control, on power and ground side (currant limited 50 volt system).
Checked timing last night pinned cam pump and crank all good. Found a cam and crank waveform it checked out good. High pressure side of system is above Ecu requested. Removed egr pipe from side of head to intake verified egr valve is closed cranked with egr pipe off cranked a little faster but no start. Checked for codes after that and got a p0473 exhaust back pressure circuit fault, that sounds like a sensor problem but I'm going down the plugged exhaust rabbit hole tomorrow. Thx for the input Mr wolf anything else would be appreciated. This thing is kicking my ass off and on for the past 6 days
Today I pulled the o2 sensor after the turbo and checked for back pressure while cranking nothing to speak of doesn't move my vac pressure gauge. Blew air in o2 bung and it exits tail pipe. The p0473 was caused by me when I was checking timing I unplugged the sensor to get it out of my way.
If I unplug the throttle valve the Ecu still has injector control (firing) not a very good run away Strategery by Volks Wagon.
So onto the intake side checked data pids for MAF sensor data is all over the place.
Frequency is 22hz KOEO no where near the 800hz expected. Another mechanic friend in the area his daughter has a 2015 Passat 2.0 tdi I hope the maf is the same so we can swap a known good part. Unplugged maf still crank no start I guess no maf sensor failure strategy built into ECU maybe.
My friend installed the MAF sensor from this car to his daughters car her and her car runs. Unplugged MAF on her car and it will start up and drive around. It's a 2015 Passat tdi 2.0 so that Ecu has a strategy to run with the MAF down. Tommy wolf do you remember looking at a Data pid "injection timing" or (timing advance)?
When cranking the pid displays a negative number like -.98 or -1.0 on my Verus,, Autel, snap onApollos, and BlueDriver. That doesn't look right to me. Seems it should be 2-4 degrees. When cranking has very little vacuum on a gauge. I covered the intake with my hand while I someone crank it and it will pull a over 20". So it has to be moving air. I get this 20hrz 4.87-.1 volt square wave on the 2 MAF sensor signal wires when the sensor sits overnight and I check it the morning the MAF signal wire shows 1.2khrz at KOEO air temp has a 20hrz signal. After trying to start I come back to the scope and both signal wires have the same 5v ref 20hrz square wave 50% duty cycle. Same shape waveform but go slightly out of time with each other.
Scanned a 2015 Passat at church yesterday and it had the same negative injection timing at start up after it started timing was at zero, if you rev it up a bit the timing would go up to 6 degrees or so then settle back down to zero degrees. So I guess it's normal for vw common rail. The customer wants the Ecu checked any recommendations of a company that can do that ?
No, but it knocks on it a bit. Relative compression 385-400 amps and I scoped the engines built in pressure transducers. Looks the same as a the 2015 Passat that I did some Testing on.
You might want to confirm the injectors actually do inject....
AC-couple the signal from the rail pressure sensor and you will get a recognizable pattern on your scope if the injectors are opening and a pressure drop is taking place. You can check on the 2015 model as reference if in doubt about the signature.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Scoped the rail pressure sensor signal wire, it puts out a saw tooth pattern that coincides with injection pulses and is in the 1.02-1.18 volt signal the 2015 Passat has a similar shaped waveform but lower voltage. The 2015 is a CJAA engine and the ecu requested a lower hp fuel pressure of 3058psi. The 2014 CKRA requested above 4000psi and actual is above that. I pulled the return line off the last injector preretintion valve as Tommy Wolf suggested. fuel comes out of top of the injector in spurts and out of the return line in spurts equal to the other 3 injectors. I did install a vacuum pump to the top of the injector as described in the service manual and the injectors do hold a vacuum. We were under a tornado warning yesterday which came with a quarter size hail warning. The customer called and requested that the car be moved outside of the shop. Im glad he has a sense of humor.
Rory67 wrote: My friend installed the MAF sensor from this car to his daughters car her and her car runs. Unplugged MAF on her car and it will start up and drive around. It's a 2015 Passat tdi 2.0 so that Ecu has a strategy to run with the MAF down..
Most vehicles work like that but as a word of caution I almost got caught out doing the same thing with a 2017 Holden Colorado. It turned out that the 2005 model could run with a bad MAF sensor but the 2017 doesn't even have the ability to report a bad MAF sensor. On top of that the ECU produced a 'built in' 2 g/s when the vehicle was cranked. After blowing air through the MAF sensor live data showed nothing so I replaced it and the problem was fixed. This was after another company had spent $2000 on it. - as a side note
Getting involved in discussions because I have a lot to learn still.
Funny that say that the 2015 could care less if the MAF is plugged in or not it will not throw a code. But the 2014 will code if you unplug it but does not when the data is askew. The MAF seems to function when cold soaked over night. I have KOEO and blown through it with compressed air put it back inline and cranked the engine still no start. Then the signal goes bad after 3-4 minutes of key on. I moved it outside I had to get back on some paying work. It's been ac week here in north west Arkansas.
Rory67 wrote: Funny that say that the 2015 could care less if the MAF is plugged in or not it will not throw a code. But the 2014 will code if you unplug it but does not when the data is askew. The MAF seems to function when cold soaked over night. I have KOEO and blown through it with compressed air put it back inline and cranked the engine still no start. Then the signal goes bad after 3-4 minutes of key on. I moved it outside I had to get back on some paying work. It's been ac week here in north west Arkansas.
It's actually a 2017 that can't throw a code while a 2005 can.
If the MAF sensor is unplugged it only throws a code for air temp sensor, not for MAF sensor which is weird for a newer vehicle. Almost every other vehicle lets the vehicle start with MAF sensor unplugged - not so with the 2017 which is a reminder to never judge the behaviour of one ECU compared to another model, though we can 'guess' based on statistical possibilities based on averages - but never trust it totally.
Getting involved in discussions because I have a lot to learn still.
Where's Tommy Wolfe? :lol:
