Combustion Issue

[Slider15]

I just got back from the garage and found out the combustion in the 4th cylinder of my GTS-t is low. Im going to start with the coil pack and see if that is the problem but that cant be done til Monday. Will driving the car with low combustion cause any major issues over the weekend?

[evilgtr]

Can you provide us with the compression/leakdown numbers to better help us provide advice on your issue ?

[Slider15]

They didnt provide me with any, its a small shop up north so they said they had to check the compression the "old school" way, whatever that means. The mechanic thinks the coil is weak. Im planning on taking it down to an import shop on monday to get it fixed and tuned. The car is misfiring and running rich, just want to know if driving it will hurt the engine, i wouldnt be driving far, just around town and then 45 mins or so to the shop on Monday.

[evilgtr]

I wonder if the old school way is holding his thumb over the plug hole.. Do you have a shop in town where you can buy a compression tester ? they are only about $20 at canadian tire. Hopefully its just a weak coil or plug or something easy an inexpensive. Without accuratly knowing what the issue is its hard to say if its safe or not

[Skym]

Old school way with thumb over sparkplug hole = funny. Rule of thumb.

I would think by what he is saying, mechanic said along the lines of the coilpack is on the way out and not getting complete combustion in that cylinder and has to do it (check the coilpack) the old school way by removing coilpack cover, unplugging coilpacks (or checking coilpack on bench via multimeter), inspecting sides of coilpacks for grey marks, inspecting sparkplugs for fouling. New school way is via shutting coilpacks off via Consult / ECU.

I have driven my car roughly 15+km with bad coilpack to get to a place that had a coilpack in stock (didn't stop in town). Didn't harm engine or turbo that I know of. Just drive off boost if possible where ECU injects less fuel. Also replace oil, oilfilter afterwards, as unburnt fuel in that cylinder could get into oil in sump and affect oils ability to lube, cool engine, turbo. But to be honest, I wouldn't do it again. On a engine in the states (GM? V8) you can shut off 4 cylinders, but I think it also shuts off the injection of fuel on those 4 cylinders.

Compression could be the other cause of the missfiring, which is true if seal around cylinder fails.

[Slider15]

Alright thanks guys, i have to drive it 30 mins to the shop tomorrow so hopefully everything is fine.

[markc32]

youll be fine driving with misfire to get to the shop....usually it kills the cat

[Skym]

It's probably intermittently running on 5 cylinders. When pull sparkplug under faulty coilpack, can see it's gone black and hasn't been firing properly. If dip coilpack in resin? (cover up plug, etc parts before dipping coilpack) or similar it seals the cracks on side of coilpack (coilpacks works like new) where the charge escapes and arcs against mounting bracket (creating the grey marks) and charge doesn't get to sparkplug. It seems to crack along the seal between the two halfs of coilpack.

[Slider15]

Am i am to only change out a single coilpack? How much do stock coilpacks go for? and would it be worth me upgrading if they need to be done? Clearly you can see i am not a mechanic but do like to ask questions.

[Skym]

About questions, it's ok. We were all at that stage, so can relate.

Coilpacks go for reason (find out what caused it to fail). Could be age related due to lots of hot, cold cycles (replace all of them if engine has done over 100,000km) or due to using wrong heat range (stock is NGK PFR5A on RB20DET, NGK PFR6A with intake, exhaust mods) or sparkplug tip gap (stock is 1.1mm and should be roughly 0.8mm) on sparkplugs. Usually if using wrong gaps, heatrange on sparkplugs, 2x coilpacks fail (common) and the rest are ok. From what I can remember, on my car it was 4th, 5th cylinder coilpacks.

Depends where you get coilpacks from. Your options are Yellowjacket, Splitfire, stock coilpacks. Stock is usually the most expensive out of the 3 options. Have a look around the sponsor section of forum and see what they have.

[Slider15]

Thanks Skym for the information and thanks for taking it easy on my ignorance, im looking to learn alot so expect many more questions.

[Skym]

You're welcome.

We are all learning new things everyday, just at different stages in terms of what we know. Even the best in the industry are still learning new things and don't know everything.

[Slider15]

So i took my car in today to get it diagnosed and all of the cylinders were running at 65psi or less. A couple were running at only 30psi. We looked at the coils and they do have some grey spots on them so the mechanic told me to order a set of coils for it and we will go from there but he also said that if that doesnt work then the motor is more than likely ruined. Has anyone else had such a problem?

[Skym]

Was the battery good when he did the compression test (being that low on all cylinders suggests it might be battery related), foot to floor with accelerator pedal???

But anything below 128psi = rebuild time if on all cylinders. New engine is somewhere around 170psi. Cheaper to fit a lower km replacement engine, (check compression before buying).

[Slider15]

The battery is fine, not sure how hard he had the gas pedal down i wasnt there when he did it. Should i even bother trying new coils or does this sound like a major issue?