Losh's VR Ute build thread

[losh1971]

Got the ute back tonight. Mech swapped over the DFI and it went. He didn't find his CAS tester so that didn't get checked. I don't know if the DFI was the problem, since the DFI was swapped when it stalled before and the one that was on there I deemed faulty. However, it worked again a month or two later when I threw it back on. Unless the DFI was on it's last legs and this this week it finally gave up?? I'm not convinced it's the DFI......
Next time I head home I will be packing a spare PCM, because it's one of the three things that could be the no spark problem....

 

[chrisp]

It’s well worthwhile understanding how the ignition system worths as it’ll help you diagnose the fault when it reoccurs.

The DFI module is essentially has full control over the engine during starting. It’s designed to be able to operate at low-voltages than the main PCM. As such, during cranking (and when the engine is below 400rpm) the DFI module is in control of the engine. Lack of spark during starting is therefore something to do with the DFI module, coils, and the CAS. The PCM only provides drive to the injectors (under command of the DFI at this stage). Once the engine is above 400rpm the PCM takes over, but the DFI system still provides the ignition by under the timing control of the PCM.

Checking for spark, or lack of spark, during starting will tell you a lot about which part of the system has failed. No spark is either DFI, CAS, or all the coils (unlikely). The connectors and the harness connecting these are also known to give trouble.

Personally, I wouldn’t rely on mechanics or auto electricians to diagnose intermittent faults unless you have very deep pockets. I think that you are better off reading up on how the system works and how to diagnose it’s faults.

Thus article on the web is excellent - https://easyautodiagnostics.com/gm/3.8L/ignition-module-and-crank-sensor-test-1

 

[Fu Manchu]

Agreed. This stuff can only be diagnosed by a diagnostic interface. Going into the relevant sensors and seeing what their data is. What are voltages. Then looking at the voltage waveforms with a scope if something is not quite right.

It’s professionals not doing this stuff as they should and just parts swapping that bugs me. We can all swap parts. They charge people and nothing is changed. Problem not fixed.

 

[losh1971]

Ok well that makes sense. Good to know it has to be one of three things, DFI, CAS or wiring. The DFI plug and harness had a good inspection when the same or similar thing was happening a year or so ago and it was reported as all in good condition. I'm doubtful it will be the DFI harness. I inspected the CAS harness and it looks in good shape, where as some other parts of the engine harness are not so great (TPS, oil sender and speed sensor plug which was total dodge before I did a semi repair that I'd like to fix better. But so far two or three years on it still works.

 

[losh1971]

Agreed. This stuff can only be diagnosed by a diagnostic interface. Going into the relevant sensors and seeing what their data is. What are voltages. Then looking at the voltage waveforms with a scope if something is not quite right.

It’s professionals not doing this stuff as they should and just parts swapping that bugs me. We can all swap parts. They charge people and nothing is changed. Problem not fixed.

I'd like him to go over it with a diagnostic tool but it was there since Mon 5pm and he used one of my spare DFIs and it started, so he wants to see how it goes. He wouldn't have definitely found the issue tomorrow, as he said he was leaving at lunchtime tomorrow but was hoping he could get it running so I'd have the ute for the weekend. I still think it's most likely the CAS but he didn't want to start fitting CAS' when he managed to get it running with 10min DFI swap. He didn't charge me, but thing is, I could have swapped the DFI after work on Mon and had transport all this week. My hope was he would do a proper diag, but obviously he didn't have time..... It makes me nervous to drive it now though, because I'm not convinced the problem has been rectified.

 

[losh1971]

I personally believe it is the CAS because I have had the same problem a while back. He was the bloke I took the ute too back then and it took a while to figure out the issue and it was then he checked over the wiring, looked at the DFI and plug but he couldn't figure out what the problem was after it broke down three or four times but would normally start again, even if it took a few hours. But it wasn't heat related as it stalled cold as well as hot, like it did this week. I ended up getting the ute running that time after dumping water on the CAS. I then told him what the issue was and he fitted a new CAS and it has lasted almost two years (I think).

 

[Skylarking]

I'm not sure if the sensor is covered in oil but when the oil pressure switch blew oil went everywhere and I assume in and around the balancer seal casing because it was running out with a degreaser for days. Plus the issue mainly seems to have started not long after the oil sender split.

The metallic oily stuff that upsets inductive sensors takes a while to build up and such looks like fuzzy oily muck.

So if your engine was all clean up until the oil sensor pooed itself, it’s not likely your problem, though I’d still look at the cleanliness of the cog that the CAS senses.

Otherwise there was a circuit diagram of the DFI, CAS and other circuits involved in starting that was posted on a thread somewhere (may be earlier in this thread). It wasn’t a huge number of wires involved so should be relatively easy to unpick the existing loom and check the individual wires and connectors for damage.

There was also some video/post somewhere that defined how to add an extra earth wire to the early DFI modules as aluminium oxidation causes all sorts of havoc with the early these modules which were earthed through the DFI body (later ones were earthed through a connector cable going back to the ECU, i think it was).

Simply put, a poor design, lack of documentation on how it is supposed to work and no wiring diagram makes it tough for finding intermittent faults, while the professionals are often lazy and just want the easy $ jobs... so your issue gets very low priority and your car waits until the pro has no jobs on the go...

 

[losh1971]

Might be time I revisit the extra ground strap for the DFI. I tried to buy one from a wreck but no VN to VYs at the wreckers had one. I will buy some cable and make one.
I want to buy a VT DFI mount plate so I can fit the L moulding. Might as well fit the extra ground at the same time.

 

[Skylarking]

Might be time I revisit the extra ground strap for the DFI. I tried to buy one from a wreck but no VN to VYs at the wreckers had one. I will buy some cable and make one.
I want to buy a VT DFI mount plate so I can fit the L moulding. Might as well fit the extra ground at the same time.

You can use any wire to ground the DFI, just make sure you clean the aluminium where it’s attached because aluminium oxide is an insulator... check the other ground strap and if oxide is present, a clean up of the oxide under the strap may helped... then after attaching the earth wire or reattaching the ground strap, it may be wise to paint the attachment point to stop any future oxidation

 

[gtrboyy]

Diagnose CAS just by hearing engine crank over.