runs rough runs smooth runs rough runs smooth

[BobbyWatson]

The Car

• 1993 Holden Commodore Executive Wagon
• VP Series
• V6 engine (says 3800 on top)
• Air conditioning, automatic transmission, no modifications, very factory model car.

The Symptoms

• The engine runs smooth most days.
• It runs rough other days.
• Temperature doesn't seem to be a factor - it can run smooth or rough at any time.
• Never a problem to get it started.
• Can be rough from the get-go, or can get rough while driving... even on the express way.
• Revving the engine can often clear the problem, but sometimes not. It can backfire through the intake when revving.
• I cannot reproduce the problem deliberately. I can start it and get one reaction, shut it down and restart it and get the opposite.
• There seems to be no consistent or predictable pattern.

Two notes. (1) I have not worked on a car for a few years, so I'm out of practice. (2) A few months ago was the first time I saw a Holden in my life, so I'm not familar with the car or its jargon - aka go easy on me with the abbreviations, thanks.

Two more notes. Plugs and wires look good. Computer fault codes come up empty.

I thought this might be a common problem with the model but after reading for an hour or so I haven't come up with an answer yet. Any ideas? Thank you.

[delcowizzid]

do you know anyone with the same model ide borrow there engine computer and try it for a few hours and see if it still does it.or you need to start replaceing stuff to find the issue really new fuel filter etc random sensors and stuff.if you have access to a laptop they can tell yyou a lot more than just the error codes you can see if its a sensor issue

[BobbyWatson]

> do you know anyone with the same model

No. "A few months ago was the first time I saw a Holden in my life" - I'm not exactly widely connected here yet.


> ide borrow there engine computer and try it for a few hours

I'd need a how-to


> or you need to start replaceing stuff

Hit or miss, trial and error, is what I'm trying to avoid.


> if you have access to a laptop they can tell you a lot

I have a laptop. How can this help?


Thanks for the input.

[delcowizzid]

if you make an ALDL cable which is pretty easy ill post a link to a schematic and get a copy of WINALDL free off the net you can monitor the sensors in realtime and see issues like the coolant sensor suddenly going cold is a good one normally makes the car run rough as and comes and goes this is a regular issue and is the ecu on its way out.

[delcowizzid]

What does one need to view error codes from the car computer? schematic for ALDL cable in this thread mate

[crazybiker]

I'm willing to bet it's the ECU (Engines computer) that's shot itself.

That sounds like the exact kinda problems I was having with mine. Tried everything, and then went the ECU and it solved it.

A second hand one from the wrecker should cost you $30 or so

[BobbyWatson]

I found a link on How-to: Make a Diagnostic cable for your VN/VP Commodore which should help, and one too Change a Coolant temp sensor (V8) although it's for a v8 it still gives a hint of what I should be looking for. I found offsite links to many ALDL diagnostic programs but anything commodore-specific is much appreciated. I also found people selling ALDL cables but prices range from moderately expensive to very expensive.

However, I didn't find a link for changing the ECU. delcowizzid, since your first suggestion was to test the ECU with a known good one, it might make good sense to follow that up... the caveat being that used ones may not necessarily be good out of the box - crazybiker, that's a good suggestion... I'll look for what wreckers I can find around here.

[delcowizzid]

WINALDL is the easiest VN-VP software free on the net. to build a cable do it like this 2 10k resistors and a 2n2222a transistor you will need a 3rd 10k resistor as well to put the ecu into diagnostic mode.

[MickT]

Let us know how you go with it. My car is doing the same thing but not backfiring.

[goldvn05]

i also would be keen to find out from you guys, how you resolved it, as im also havign the seme symptoms.

eg.
- intermitent, rough idle and rough drive.
- does rough on both hot days and cool days., then comes good on other days.
- on other thing i noticed, was increased vapour from the exhaust, when it does run rough (as if it was a winter day start up), but it was a normal 20-25 degree day.


lookig forwrd to hear back from you all how you resolved it, thanks

[BobbyWatson]

Well, in my case the verdict is a broken valve spring which was finally detected through a compression test that failed on one cylinder.

[aussieghostrider]

dude I am having same problem !!!

IF city driving car idles really bad and does not accelerate good ... but if engines cold is ok ,freeway and arriving at destination car idles like brand new ..car gets a slight miss when warming up ...

Inlet manifold gasket shot to shit , was told by someone who has done a heap of them said the gasket expands with heat so you get a tight seal so proper air/fuel mixture ... and also theres a water jacket there to keep inlet cool ..the gasket dies in the ass and does not expand like it used to so water in cylinders and air leak ..

I got a quote for $400 ... I am ringing around for a better quote ...

@goldvn05

I was going to say spark plugs or leads or coil pack or stuffed injectors ... but the steam out exhaust is bad sign ..

I was told head gaskets rarely go on VN-VP and the engines are tough as nails .. lol

If you fine you have to add coolant every few months you have inlet manifold leak or headgasket .... I put $100 it be the inlet manifold gasket ..

If you run your cars on tap water and no coolant the first things to start rusting and leaking is the timing cover on right upper side where crank angle sensor wire comes down , and the inlet manifold gasket .. if these become corroded then they rooted and might not be worth fixing unless you can do yourself.

Go to supercheap auto , repco ... they got this stuff called CARGO ... $10 a bottle-->
http://www.derek.com.au/cargo.html

drain cooling system ... add tap water ... add a bottle ... go for a good drive .... leave the stuff in for a day or two ... drain cooling system completely ... leave cooling system dry for 12 hours ... now add coolant and see how you go ... this may help... but eventually time for new gaskets ..