VS V6 hard to start, runs rough. Running out of ideas

[jwaye2]

Hi Guys

I know there are a hundred posts about this and believe me ive spent days reading through them but I still haven't found a solution.

Got a VS V6 Auto Statesman that is difficult to start and runs rough. In idle it surges a little, ive revved it up to 4k and it struggles to get to 2k, it smooths out a bit after that and its barely noticeable but the surge is still there. Took it for a drive and even putting my foot down it struggled to get above 2k, may have gotten up there eventually but i ran out of street and didn't wanna push my luck on the main road. I can have it idling for 15 mins, turn it off and try start it again straight away and its just as difficult to start again, hot or cold makes no difference.

Ive checked every injector one by one and they are all working fine, I even put new ones in for good measure.
Every cylinder has strong spark, new coils, leads and plugs
All new filters and fresh fuel, also tested the fuel pump, and pressure reg
All new plenum seals, pcv and vacuum hoses
Got a VS ute that runs perfectly so I did a whole bunch of swapnostics on almost all of the sensors, including MAF
Tested and swapped every fuse and relay, including those not connected to the engine
Checked all plugs for good connections and broken wires
Even tried the spray water/carb cleaner trick all around the intake, manifolds, hoses etc to check for leaks

None of these have made any difference at all and to add to my problems to check for fault codes ive tried 2 different scan tools(one cheap, one professional), even purchased the Envyous Customs AED kit for my laptop and none of them can even detect the existence of an ECU, also tried the paperclip trick to check the engine light flashes and it come up with no codes but this may just be because it cant read the ECU. The weird part is the car does run and start so not sure why it cant read an ECU, surely it wouldn't even turn over at all if it couldn't read it?
Thinking the ECU itself could be the obvious issue ive tried 3 ECU's with matching numbers and two BCM's and had the exact same problem with all of them. No communication and still runs and starts like crap. Ive even checked the Diagnostic plug pin by pin to make sure they all have a signal/earth/power.

The only sensors i haven't swapped yet are the Crank Angle, Cam Angle and Oxygen sensors, though ive unplugged the Oxygen sensors while its running and it made no difference where I thought it would. These are next to look at this weekend if i don't find something else to try.

This is my 6th VS V6 and its the first time ive ever encountered a problem I couldn't figure out, really running out of ideas so im looking for any out of the box thoughts that I may not have missed or not thought of.

Really appreciate if anyone can think of anything that can help.

 

[ephect]

You've done a lot of troubleshooting which is great but will make us helping you a little more difficult, but not impossible.

Grounds, check and clean your ground points in the bay and maybe add another around the ecu.

You've done pin by pin on the aldl port, it's gonna be fun but find a wiring diagram and start checking for continuity from aldl port back to ecu.

Light flashes with a paper clip so it's reading it, but it may have a break in a wire for a scanning tool.

 

[Grimes]

Is this a car you’ve acquired like this, or was it OK one day and then playing up the next?

 

[the_boozer]

How did you check fuel pressure?

 

[jwaye2]

You've done a lot of troubleshooting which is great but will make us helping you a little more difficult, but not impossible.

Grounds, check and clean your ground points in the bay and maybe add another around the ecu.

You've done pin by pin on the aldl port, it's gonna be fun but find a wiring diagram and start checking for continuity from aldl port back to ecu.

Light flashes with a paper clip so it's reading it, but it may have a break in a wire for a scanning tool.

Ive checked the main earths in the engine bay but i haven't checked in the cab so ill check that next.
I was able to confirm each terminal has a signal but not if its the correct signal/voltage, cant find anything to say what it should be.
Ive been able to determine where some of the terminals go with a fair amount of research but not all of them are so easy, this is what ive got below

1. W/Blue - BCM (YB71 pin 4)
5. Black - Earth
6. W/Black - Diagnostic 'test' enable (PCM B3)
9. Red - Gregorys manual says this wire goes to 'PCM A3' but it also splits off to the ABS and BCM but doesn't say what colour or pin
12. Blue - ABS test enable (no pin location)
13. Brown - BCM test enable (no pin location)
16. O/W - 12v Constant Power

Ill check continuity of the ones I know but if anyone can fill in where the others go id really appreciate it.

Is this a car you’ve acquired like this, or was it OK one day and then playing up the next?

Brought the car not running at all, cranked but wouldn't start, previous owner says it sat for about a year because he couldn't get it running but would breifly run with Aerostart, I got it home and determined 2 failed injectors, swapped them out for a couple of spares and got it running but it ran rough like it does now which is what got me started on diagnosing the issue.

How did you check fuel pressure?

With a fuel pressure tester, was all within range, think around 3.2bar at idle. Also swapped the reg from my Ute to double check and same result

 

[lout]

check each injector loom goes to correct cylinder
check each spark plug lead goes to correct cylinder
do a cylinder drop test
do an injector flow test

 

[woteva]

Looks like you have really fired the parts cannon at this one.

I would be trying to get the engine light and ecu connection working first and go from there.

 

[Phillbert]

had similar prob with no thermal paste on DFI,... wouldn't start when did ran rough... Put paste on and bang like new.

 

[Fu Manchu]

When a Crank Angle Sensor becomes faulty, it often happens when it heats. Then when it cools it’s fine. Doesn’t always log a fault code.

I’d run cold water over it when this happens and see if the car starts again.

 

[Grimes]

I’d also try the CAS as Fu Manchu suggests before going too much further. When they go wrong they can manifest as choppy throttle or ‘tacho limiter’ symptoms. Not disimilar to losing all the spark advance in old style distributors.