2-3 cylinders down.Any answers?

[SVR]

Any ideas? HSV started missing and now will only run on 5 and sometimes 6 cyls;
New o2 sensors,comp; ok,plugs new,injectors ok,fuel pump and pressure and flow ok,good spark,EFI shows no trouble codes,but Bank 2 only shows around .1to .15 volts Bank 1 as normal,ie .3 to.9V.Tried different PCM.
Bank 2 fires on 1 not 2 or 3 and occasionally 4.Bank 1 all 4.
Anyone experienced this problem as I am now struggling with it.

[joecar]

Plug wires.
Coil packs.
Subharness to coil packs.

[GMPX]

There is a common 12V between the coils and the Injectors (on a VX anyway, LHS is green wire, RHS is red), perhaps you are losing this, also check the common GND on the coil packs (pin A on the coil pack bulk connector) seems something shared between cylinders on that bank is messing with you.

Good Luck
Ross

[SVR]

Thanks for input guys but still no success.
Swapped coil packs over ,no change,so leads,coil packs and harness ok!
Checked common GND on coil packs A to PCM connections 1 and 40 on both banks.cont: ok.
Checked 12v supply to coil pack and injectors Red and Grn.full 12v supply with ign on. WHERE now i wonder.
As i previously said every mechanical aspect fully checked out.It must be electrical, but where :?:

[GMPX]

What state are you in?.

Cheers,
Ross

[SVR]

United Kingdom

[Delco]

You need to narow it down to if its spark not firing on those cylinders and injector not working on those cylinders then follow through depending on what you find.

[SVR]

I must be missing something really obvious because all plugs fire,each one seen to spark,and each injector energises,ie,with lovolt test lamp and tech 2 shows each working.EFI also confirms,so with no mechanical problems!!!! do not know where to look now.

[GMPX]

United Kingdom

Ah, I forgot that HSV's were sold in the UK.
I was going to recommend someone in Aus but that's not good.
Anyway, I really have no other suggestions, something like that fault I'd need to be at the car with a scope, that's about as far as I could go.

Cheers,
Ross

[tuff]

You said that the injectors are firing are you sure there not clogged?How many miles on the car and what kind of mods have you done.On those cylinders that are not working are the plugs the same color as the rest?When you drive the car do you feel the cyl missing Or does it happen only under a load.

[SVR]

Changed the whole set of injectors with a set of known perfect ones.Car done 27000 miles.Supercharged with a whipple and been no real problem,until now.On right bank the #4,6,and occaisionally 8 cyls; do not run at all.ie starts up and runs on 5 and sometimes 6,even if you try out on road under normal driving conditions.
The engine is mechanically in very good condition.Plugs spark ok on 4,6,&8 when engine running.
EFI Scan shows when connected and engine not running a IAC of 140 and HO2S11 at 0.2v while HO2S21 (the problem side) only .05v,when running at op;temp HO2S11 normal ie,.20 to .90v whereas HO2S21 remains constant at about .10v and IAC no lower than 134.No Vac leaks. :(

[tuff]

Did you check your ground wires on the back side of the drivers side head.Just a thought at this time.

[SVR]

Yes,All Earths OK.

[joecar]

Have you tried changing the HO2 sensor(s)...?

[tuff]

Are your plugs gaped right.I see your supercharged and if the gap is to big it can blow out the spark.Im a nitrous guy and i set my gaps at .28.The weird thing is that you don't have a SES light on so that kind of rules out an electric problem i beleve the pcm would pick that problem up.Im suprised you don't pick up an engine missfire trouble code?

[SVR]

This is the mystery.New H02 sensors fitted.Plugs gapped to .035".
Not a sign of trouble codes with EFI.Asked a mate who has access to GM Tech 2 to do a scan.Not a single fault code seen.I thought I was reasonably good with motors but this fault has got me completely baffled.
What is also confusing is that the IAC reads 134 when it used to come down to around 20.IAC has been relaced.

[joecar]

Have you actually observed spark from plugs at offending cylinders...?
(remove plug, ground it's body, have assistant start engine while you observe spark;
look for big fat blue arc that makes sharp crack sound, not wimpy faint weak arc that makes soft tick sound;
you may want to use jumper wire with large alligator clips to ground plug;
don't get zapped, it's uncomfortable at best;
CAUTION: keep yourself and your tools away from the pulleys).

[tuff]

How about bad fuel?I think i ran out of ideas. :(

[Scoota]

By any chance would you have cracked the spark plugs on the affending cylinders when you replaced them? Very common symptoms.
I have had a customer with simallar problems as you are having, turned out to be cracked valve spring retainers. It wasn't an LS1 although it could be worth a check.

Cheers Scotty.

[SVR]

Thanks a lot guys but I think we are all running out of ideas on my problem.If anyone has any other suggestions most welcome and WHEN I do resolve this problem I will post the result here.Might be a little time but rest assured I will crack it. :evil:

[tuff]

Did you do a compression test or a cylinder leak down test? Just to make sure you don't have a burnt or bent valve.I thought you said your vac or iac were screwy maybe your leaking off cyl presser into the intake.I wish i was there to take a look. this stuff bugs me. Keep me posted if you find something.

[joecar]

SVR, how did you determine that cylinders 4, 6, 8 are not working...?

[SVR]

Compression test done and well within OEM spec:Nothing mechanical wrong with engine.Valves inspected etc;
4,6,8, not working by(a)lift off plug leads and no different.(b)lift of injector plug leads and no different(FUEL PROBLEM) (c)feel the pipes from 4,6,8, headers and cold at startup,whilst 2 is very hot!!!

[Delco]

Compression test done and well within OEM spec:Nothing mechanical wrong with engine.Valves inspected etc;
4,6,8, not working by(a)lift off plug leads and no different.(b)lift of injector plug leads and no different(FUEL PROBLEM) (c)feel the pipes from 4,6,8, headers and cold at startup,whilst 2 is very hot!!!

You need to look at the basics , a engine only needs compression , spark and fuel to run.

I would try and move the problem to a different cylinder one thing at a time , swap injectors around and see if that helps , swap coil/lead/plug to a different cylinder until you can find what is causing the issue.

heat gun on the pipes is a real good indication of how each cylinder is running.

[joecar]

...(a)lift off plug leads and no different.(b)lift of injector plug leads and no different(FUEL PROBLEM)...
Narrowed down to either no spark or no spray or both.

[Delco]

...(a)lift off plug leads and no different.(b)lift of injector plug leads and no different(FUEL PROBLEM)...
Narrowed down to either no spark or no spray or both.

Lifting the leads of wont tell you anything other than to narrow down to a cyl.

If it is a dud lead/coil/injector/harness as if the cyl is down it will not matter what output you turn off it will still be down.

[joecar]

...(a)lift off plug leads and no different.(b)lift of injector plug leads and no different(FUEL PROBLEM)...
Narrowed down to either no spark or no spray or both.

Lifting the leads of wont tell you anything other than to narrow down to a cyl.

If it is a dud lead/coil/injector/harness as if the cyl is down it will not matter what output you turn off it will still be down.

But it does point to either or both as a starting point:
if no spark, then start at plug and work back, testing or swapping until the reason is found (...the reason has to exist...);
if no spray, start at injector and work back... same thing;
may even be a bad pcm output driver or broken harness wire;
important point: must be able to [visually] verify each step in sequence.

[Delco]

I noticed on another forum you have a racelogic traction control , possible it is cutting the injectors out to those cylinders ( or limiting their output)

[SVR]

Now in the process of going thro traction control harnes to confirm no breaks,shorts on whole loom,wiring to abs etc.

[Delco]

Now in the process of going thro traction control harnes to confirm no breaks,shorts on whole loom,wiring to abs etc.

Has this combo been running properly with the blower etc in the past ?

[SVR]

For 2 years,with no problems at all

[ForcedC5]

what were the last changes made just prior to this happening. Any flashing or OS changes?

When I first upgraded my 2000 to a 2002 it ran fine for a week and then ran like crap. This with tunes that it ran just fine on. I went back to my old flash and it all symptoms went away. I've since gone back to the 2002 and it runs good ( a few inconsistencies but it runs good).

[SVR]

Yes,i have done a few reflashes,but still same fault with 2 different pcms tried.