vt shuddering problem - plugs? leads? coil pack? help please..

[pulling my hair out]

Yep, I think so...



I'm looking at a tuned ECU from Ebay, and will be picking up a coolant sensor this afternoon and changing it over Easter as it is due for an oil change now anyway. Have read that could be a cause of issues; I think **** it, I have done just about everything else! $20- from Veales I may as well. New genuine leads going on it too.

I just had it in a mech workshop and he put a scan tool on it, no codes that he could find, fuel pressure goes up to 40psi and settles 30-35psi. Manifold vacuum is in the green of his gauge so not an issue, knock sensors were kicking in when it was shuddering so we thin that the computer is massively retarding the timing at some point of acceleration as it thinks its knocking, yet we cannot figure out how.

When cruising around my car goes just fine, idles fine, but when rev it in neutral or I have to go up a hill or overtake and put my foot down a bit further, it shudders and backfires etc... if I knock it back to 2nd, it will take off like a rocket.

Could it be a fuel curve, because I don't usually plant my foot and it has to re-learn fuel settings? FAAAAAAAARRKKKK

Yep IDENTICAL symptoms as my VT 11 got 300 000ks on the clock now had it since it had 49 000ks on it so I totally know its history! I'm starting to think its programmed in it somewhere to play up to get you to replace it ! maybe a conspericy theory!! Im waiting for a cam angle and crank angle sensors to turn up and I will try that but dont hold much hope. I also looked at the ECU on Ebay but I believe that it will have to be introduced to the BCM with a tech 2 tool before the car will start ! will be expensive if that don't solve it !!!

 

[CapnCarnage]

Ok, so as my fuel pressure was reading a little low at ~35psi (not the new fuel sender units fault, as we blocked the return line with a clamp and the pressure shot up to 100psi), so i just picked up and installed a Genuine BOSCH 3.5bar (50Psi) fuel pressure regulator.

Unfortunately, this has not completely removed the surging / knock-retard nor backfire-under-heavy-acceleration issues.

Removed the battery terminal and the computer re-learned the tune, which has helped a little in drive-ability. I think it will continue to re-learn the long term fuel curve for a while.

Next up is to try a tuned PCM, and some Iridium spark plugs...

 

[pulling my hair out]

Ok, so as my fuel pressure was reading a little low at ~35psi (not the new fuel sender units fault, as we blocked the return line with a clamp and the pressure shot up to 100psi), so i just picked up and installed a Genuine BOSCH 3.5bar (50Psi) fuel pressure regulator.

Unfortunately, this has not completely removed the surging / knock-retard nor backfire-under-heavy-acceleration issues.

Removed the battery terminal and the computer re-learned the tune, which has helped a little in drive-ability. I think it will continue to re-learn the long term fuel curve for a while.

Next up is to try a tuned PCM, and some Iridium spark plugs...

Retarted timing is a good way to discribe the symtoms, mine is the same, under a quick rev in neutral it gives a shudder before the revs start to increase or when you want slight acceleration but only if it is in top gear, everything is fine once it kicks back a gear and gets some more revs up, as you say it seems to have retarted timing but only momentarily.
I was thinking about the knock senors too, but why would it be so sparatic and be fine when the revs increased? you wold think it to worse as the revs increased.
I'm temped to take it to a EFI auto-electrian specicalist to see if they can pin point the cause but I'm dreading what they are going to charge me

 

[pulling my hair out]

Ok, so as my fuel pressure was reading a little low at ~35psi (not the new fuel sender units fault, as we blocked the return line with a clamp and the pressure shot up to 100psi), so i just picked up and installed a Genuine BOSCH 3.5bar (50Psi) fuel pressure regulator.

Unfortunately, this has not completely removed the surging / knock-retard nor backfire-under-heavy-acceleration issues.

Removed the battery terminal and the computer re-learned the tune, which has helped a little in drive-ability. I think it will continue to re-learn the long term fuel curve for a while.

Next up is to try a tuned PCM, and some Iridium spark plugs...

Ok, so as my fuel pressure was reading a little low at ~35psi (not the new fuel sender units fault, as we blocked the return line with a clamp and the pressure shot up to 100psi), so i just picked up and installed a Genuine BOSCH 3.5bar (50Psi) fuel pressure regulator.

Unfortunately, this has not completely removed the surging / knock-retard nor backfire-under-heavy-acceleration issues.

Removed the battery terminal and the computer re-learned the tune, which has helped a little in drive-ability. I think it will continue to re-learn the long term fuel curve for a while.

Next up is to try a tuned PCM, and some Iridium spark plugs...

is yours a manual or auto?

 

[pulling my hair out]

re- 80kph shuttering problem:- finally took the VT to an auto-electrian to have a scan tool put on it to look for any answers regarding the dreaded 80kph shutter in top gear (auto-transmission). As exspected cost me nearly $400 and they found nothing!!!!! I had to drive it for them as they said they could not get the car to fault. when I got it to shutter while they had the scan tool connected they could check that the knock, cam, crank, O2, TPS, EGS, coolent sensors were all working satisfactory! Oh Great ! The only comment that they could come up with that there is a solenoid in the auto-transmission that engages and locks up the torque convertor that MAYBE ????? hesitating to actuate on acceleration an has suggested that I should take it to an auto-trassmission specialist for further diagnosis! **** more money that may not come up with an answer to solve it. anyone else got any ideas apart from burning it !!!!

 

[devilly]

middle of exhaust system the part that's got spring loaded bolts are check here.have a feel around the engine back and anywhere vacuum lines are you may find and air leak.at least you know it ain't sensors so go with something small.on idles and aircon on does it do anything different.

 

[CapnCarnage]

is yours a manual or auto?

Auto

 

[CapnCarnage]

middle of exhaust system the part that's got spring loaded bolts are check here.have a feel around the engine back and anywhere vacuum lines are you may find and air leak.at least you know it ain't sensors so go with something small.on idles and aircon on does it do anything different.

At idle mine has a miss, I rev it a bit and it will hesitate and stutter, aircon on and it has very low power and the hesitation/stutter is more prevalent. Plant the foot hard and it will backfire.

 

[devilly]

At idle mine has a miss, I rev it a bit and it will hesitate and stutter, aircon on and it has very low power and the hesitation/stutter is more prevalent. Plant the foot hard and it will backfire.

i had that happen at one stage trying to remember how i fixed it.i think i moved the injectors around a little while it was idling and found one that when i moved it changed the idles of the motor.so too much fuel was getting in and making it back fire.i then changed out my tps throttle position sensor and haven't had the problem since.

 

[CapnCarnage]

OOOOOOOOOOOOOOOKkkkkkkkkkkkkkkkkkk....

Last night swapped out brand new NGK BPR6-EFS15 plugs (same as what was in there, only brand-new...) and also brand-new original GMH metal heat shielded leads (had the MAX300 set in there, which were new last service, less than 6 months) and it seems to have fixed my issues right up... gave her a caning on the way to work today and it seemed to be going 100% now... no more hesitant shudder, no backfiring, gear changes strong and much more torque.

Thanks for all of your help guys