urgent need help two cylinders not working

[cruzn]

I have been experiencing problems with a VR V6 acclaim. Problem is that Cylinders 4 and 6 do not work at all so car runs rough. Also the tacho bounces like crazy when above 2000rpm. Both cylinders have compression of 160psi and the spark plugs smell of unburnt petrol.

I have replaced the following parts with no results;

Crank angle sensor, cam angle sensor, coil packs with dfi modue, ECU temperature sensor, ignition leads, spark plugs, ECU, injectors, MAP sensor and all of the sensors on the throttle body.

[hako]

Check you have the coils placed on the DFI in their correct order as it sounds like you have the firing order mixed up.

[westbad]

Have you checked to see if cylinders 4 and 6 have a spark? did you us brand new coil packs? or 2nd hand? try swapping the coil packs around.. use number 1 and 2 coil pack where number 4 and 6 normally goes and see if that works?? All coil packs are interchangable they just have numbers stamped on them.

[westbad]

Check you have the coils placed on the DFI in their correct order as it sounds like you have the firing order mixed up.

another good point

[cruzn]

The coil packs and DIF module are second hand but i tested them on another VR commodore Acclaim to confirm they were working, same goes for most of the parts i have changed.

Yes the cylinders have spark and injector pulse. The ignition leads are definetely connected to the correct coil pack and cylinder. I double checked with on the other Commodore.

So this leads me to wonder if there could be an internal engine fualt. Could this even be possible even though the cylinders are holding good compression?

[Zuicider]

any water in the oil and visa versa?

[cruzn]

any water in the oil and visa versa?

No traces of water in the oil and visa versa.

[Zuicider]

got a multimeter handy?

[cruzn]

sure do. Car is a VR 11 95 and has travelled 152,000 if that makes a difference.

[Zuicider]

compare the resistance between the coils . 152k worth of km means bugger all if she hasnt been looked after. ive pulled apart both a 400k plus engine and found it to be nicer internally than a 200k engine. did u do any other mods before u came across this problem?

[cruzn]

The car is stock as a rock down to the original hubcaps (except for the headunit). What resistance would be ideal between the coils? (i have tested them on another VR and they worked perfectly but i can happily test the resisitance)

This problem has me stumped. The cylinders have fuel, compression and spark but they do nothing.

What i really want to know is could be an internal engine fualt despite it having good compression?

[Zuicider]

any noise other than the misfire ?

[cruzn]

The engine has what sounds like a slight balance shaft rattle (not that noticable). Has a very, very lumpy idle and the starter motor turns very very slowly (almost stopping) when turning over the engine. And i should should have mentioned that the error codes come up clear.

[Zuicider]

whats the battery like and the brushes on the alternator

[Zuicider]

also have u made sure the hose for the map sensor is good and plugged in well and try swaping the relays around with the efi and shite

[cruzn]

Battery is less then a year old Bosch 380cca. The alternator is near new. When the engine turns over is sounds as though the battery is alomost flat but it is not. (i have tried different batteries, same issue) I must have started it at least 30 times today when i was replacing different parts on the engine. The engine still turns over at the same slow speed.

[cruzn]

also have u made sure the hose for the map sensor is good and plugged in well and try swaping the relays around with the efi and shite

Tried both things today without any change to the problem. I appreciate all the help though Zuicider.

[Zuicider]

hmm its got me stumped, wouldnt think its internal
has to be electrical of some sorts

[Zuicider]

a long shot, but whats the exhaust like??

[Cheap6]

If the compression is good about the only mechanical fault I can think of is a leaking inlet manifold (gasket).

A slow cranking speed could be due to the timing over advanced. The default timing, including at less than 450 rpm, is 10 degrees with the PCM taking over above that speed.

I would have said coil or DFI module but if they've been ruled out/done...

The resistance of the primary side of the coils - across the electrical connector tabs - should be low; ~1 or so Ohms, the secondary side - across the lead posts - 5-7000 Ohms.

Possibly a PCM or an electrical connector fault?

[hako]

I'll buy into this again and say what I said at the beginning - you have somehow stuffed up the firing order of your engine and have plugs firing either early or late. I may be wrong, but from memory your VR will fire on every revolution of the engine. This is different to the later VR and Ecotec engine which fire only when required (once every 2nd revolution). Because the early VR fires every revolution, wiring the plugs incorrectly can still allow the engine to run (roughly)

[Cheap6]

There's no real differences between the ignition systems on all the Buick and Ecotec V6's, right back to the S1 V6.

If the DFI, coils, leads, plugs are OK, I'd be looking at the PCM or the wiring connection between the PCM and the DFI. It's possibly on the EST bypass switching circuits. I've posted a few times re. operation of the V6 ignition system; maybe try a search on "code 42".

Another possibility is an injector fault - you might try swapping the injector positions around and see if the misfire follows the injectors.

The injectors do fire corresponding to cylinder position, 3 at a time, on VR V6.

[cruzn]

Just an update. I replaced the ignition leads again and now cylinder 4 is working. The tacho is working normal now also. Cylinder 6 still does nothing though. The car still has a very, very lumpy idle (like sitting in a electric vibrating sofa) and runs very rough. Does anybody know what three injectors fire at the same time?

[Brett_jjj]

If you have had it running with the engine missing,it might have fouled up the spark plug on that cylinder.

[cruzn]

Just an update. I have replaced the entire engine harness to the ecu as well as the o2 sensor and injectors with no improvements. Does anybody have any other suggestions before i replace the entire engine?