DIYEFI.org Forum

I just wanted to toss out a note relative to spark checking during operation. I think that feature would be very handy and I would really hope to see it in 2.0.

I'm fighting with my wifes O1 Jetta. About 2 weeks ago it developed a skip, and I'm sure the problem is a weak spark. Figuring out which cyl and why is a different story. Even worse, it's intermittent and may be happening on multiple cyls. When I say intermittent I mean it happens with in 5 minutes, but that's several hundred rotations of the engine, so intermittent.

This is the 1.8T with 4 coils. They sit directly on the plug in the head, no plug wires. VW ran 12V level signals to them and that's it. About 6 months ago or so, cyl 2 had a complete, out of the blue, no warnings, failure. Simply didn't spark at all. I replaced the 4 plugs, the old plugs looked fine (cyl 2 a bit gas wet, but fine) light brown color, no erosion, no carbon deposits, and compression was spot on for each cyl. I was looking for a reason for cyl 2 spark failure. I had to claim the coil simply went junk. Because I felt the coil simply went junk, I replaced all plugs and coils. So I have three good and one bad in the basement, with new equipment in the car.

If I really push it, I can get PO300 (multi miss fire) P0301 (cyl 1 miss fire) P0302 (cyl 2 miss fire) up to P0303. However my wifes driving does skip, but doesn't toss codes. My feel is that the skip is a lack of ignition, not a miss fire. When I drive, the skips cause miss fires on other cyls. I see no reason why timing would an issue, so I believe it has to be a weak spark, not a timing issue. I also see no reason for being concerned about compression, it was spot on 6 months ago. So I'm left trying to figure out why it wouldn't ignite.

So now I'm left trying to figure out how hot the spark is, when I have no tools to figure that out. Perhaps someone has some recommendations. Perhaps I can scope the 12V lines, or measure magnetic flux or something. I know that as soon as I take it out of the bore, it's not the same environment as when it's running so I feel I can't trust it's color when it's on top of the block. I guess I can try, if it's not a nice blue spark, then I can replace it with one of the originals. However, I suspect they won't be blue when out of the bore.

Is it possible to see the missfires by monitoring the EGO output?

The unburnt fuel would cause a spike, rich(???) indication. If you swap in a known good coil on a cylinder then monitor the EGO output on a short drive then try another cylinder and so one for all four coils.

My OBDII tool does allow me to graph the O2 level, and yes I see the bump when it miss fires. I seem to recall the bump started in the up direction, not down. That would seem to match you note. The pulse actually makes is oscillate for a cycle or two. It over shoots in the opposite direction when correcting. I also see the timing bounce around quite a bit, after the miss fire.

I found that the coils on cyl 2 and 4 both had a burn electrical odor to them when removed from the engine. Cyl 2 had a stronger odor. I replaced them with the originals I had left over. A couple months back I replaced all 4 coils when cyl 2 failed completely. I left the plugs the same to try and isolate parts. So far no real change in operation. I guess I'll change the coils around again, and see if that changes anything. However, known good is a bit of a problem. I'm scratching my head about Cyl 2. Perhaps the signals going to it are causing it to fail... Wonder whats going on there.

I used one of the old plugs as a calibrated test gap, and one cyl for an consistent ignition source. I tested each coild this way, and all sparked a nice blue spark. All sparked about the same, so that might indicate the coils are all good, despite the burn smell. Or it indicates, the test setup is fixing the problem while testing. I also tested each coil on their respective cyl with this same plug, and all looked good. Nice largish blue sparks. No white, and not really small.

Even though it has new bosh platinums installed a couple months ago with the coils, I'm beginning to suspect a plug problem. I'm still running some test with the coils, after that the next is to change plugs out and see what happens. If I pull the plugs, I'll check compression again to make sure that a cyl isn't having an issue.

I'd much rather do a test to identify the problem, then replace the part that is known bad. Right now I'm simply a parts changer, not a mechanic. Ugh. If only I had a way to measure how hot the spark was when in the normal environment, I could tell what cyl, and why.

Can you put a scope on the ground wire for each coil pack indipendantly?
And on the input signal?

The input signal will be easier and tell you if the ECU is sending the correct signal.

On the ground wire you might be able to see a ripple for the back EMF (or spark). Not sure how much you will be able to determine from the shape.

That's a hard one. I'm not all that eager to cut the OEM harness, for such a small problem. The wires are individual wires running from the connector to a harness loom. So I could put a current clamp on it to look for some thing. I don't have a small clamp, but I could go buy one. I do have some hall sensors, but that probably won't tell me all that much. I'll have to stew that over. My understanding is that the power transistors are internal to these coil packs. If that's the case, and if I'm getting a back EMF problem, then I would expect to only see it on the ground. Might be hard to separate that signal from the normal current flow.

I'm not getting my next chance to change stuff around, so I'll do that and see where it leads me.

The ground + loop method is how you set timing on the nissan RB engines. They were even nice enough to leave the ground hanging out of the loom in a little loop esp for it. If you can do this it should be sufficient to see what is going on (if there are consistent misses).

Fred.

Well the ignorant parts changer approach appears to have worked. I've now got the three original coils installed, and the best one of the new 4 coils. Hasn't skipped for a couple days now.

I don't want to leave this coil installed, as it has a high failure rate, I'm sure this one will fail, or go sour. Does anyone have a recommended brand of VW coil? The box that these came in notes STI.

All the 1.8t 's have this problem with the coils. Buy the upgraded coil at the dealer.

SFC