Recommended Ignition Coils

dfrost · 06-15-2007, 02:54 PM

I'm going to check my coils when it gets dark tonight, after reading on this forum that coil deterioration may be the cause of the off-idle flat spot that I'm experiencing.

I see that Bosch and Bremi are the readily available brands for similar prices. Any preference on brand?

And I'll also check for vacuum leaks. WD-40 spray has been suggested as a good way to check, listening for increase in idle when sprayed near a vacuum leak.

Jeron · Jeron's Garage

I haven't had a cause to check for vac leaks personally, yet...

I've heard ideas from water mist to carb spray to specialized sprays. id opt for carb cleaner spray over WD-40, since WD-40 will leave residue.

Gene Wilkes · 06-16-2007, 06:11 AM

If you have a coil arching, it will be easy to see in the dark!

dfrost · 06-18-2007, 10:16 AM

Didn't get a chance to do this test over the weekend. Maybe next weekend, when I can watch in the dark (no garage here), then put the cover back on the following AM before I need to use the car again.

So no coil preferences between Bosch and Bremli?

Thanks, Jeron, for the reminder about using carb cleaner for the vacuum test.

Gene Wilkes · 06-18-2007, 10:23 AM

I ended up putting the high performance coils in my 325is.

dfrost · 06-18-2007, 05:57 PM

I haven't seen any references to "high performance coils" from on any BMW part retailers. Which ones are those, and where from?

And quite honestly, our host's price on Bremi coils and plug connectors is so good compared to everyone else, I'll very likely get them from him if needed.

dfrost · 06-21-2007, 12:43 PM

IslandmanPA,

What effects did you notice after changing coils?

Or were you replacing defective coils?

Gene Wilkes · 06-21-2007, 12:49 PM

I had a low speed hesitation that was most noticeable when the engine was cold. When accelerating (5 spd) there was a slight hesitation around 1500-2400 rpms. Was a kind of stumble. The thing that tipped me off to the coils was to look at the engine with cover over coils removed, in the dark! When I manually accelerated the engine I could clearly see arching at two of the coils. This arch was related to the miss. I also installed new plugs. Car runs with no issues now! So basically it was coils, boot and plugs that did the job.

dfrost · 06-21-2007, 04:30 PM

IslandmanPA,

Thanks very much for that response. Those are very similar to my present symptoms that I'm hoping to fix with coils, based on what I recently saw in your response to Dawn.

Did you notice any change in gas mileage after the coil swap? I'd love to get up to the mileage claimed by some here (28-31.5 for E36 325's) , but these days don't see more then 23-25 mpg, even with mostly highway miles.

I'll let you know what my "dark test" reveals after the weekend.

Gene Wilkes · 06-21-2007, 04:32 PM

Yes fuel economy improved! Went from 23 to 27 mpg.

dfrost · 06-25-2007, 12:16 PM

My car has almost identical symptoms to islandmanpa's, except that the stumble/hesitation below 2500 rpm is more evident when the car is warm. It's mild enough that I can't say it hasn't been there all along, or something that has been gradually worsening. Notably, my gas mileage has been dropping recently, down from about 25 to 22 mpg with 60-70% highway miles.

Test results from this weekend:

- No arcing visible at or around coils, at idle or when revved.

- All coils (Bosch) measure 0.5-0.6 ohms resistance between pins 1 and 15 (Bentley says they should be 0.4-0.8 ohms).

- Carb cleaner sprayed around intake boot, intake side hoses, etc. did not cause any change in idle.

- Plugs are NGK BKR6EK, replaced 40,000 miles back.

I had REALLY hoped to see some evidence of a coil problem, so I'd have an obvious culprit like islandmanpa's.

So now I've got a quandary: Should I try new coils in hopes that the existing ones have degraded in some unmeasureable way? I plan to do the plugs at the same time or first, if any of you think they could be the primary cause for my symptoms.

BTW, I've had a Conforti ECU chip for the last 50K miles. Otherwise everything's stock and other engine maintenance items (fuel and air filters, O2 sensor) have been replaced within the last 15K. There's no evidence in the maintenance history going back 140K that the coils have ever been replaced (certainly not in the 60K that I've put on the car).

What would you suggest?

Gene Wilkes · 06-25-2007, 12:58 PM

Start with replacing the plugs! Go from there!

dfrost · 04:00 PM

I replaced the plugs last night (same NGK part number as previous) - no change in symptoms. I'll check highway gas mileage when I drive the car pool tomorrow.

But I did notice that two of the plugs had a dark brown ring around the upper ceramic body, about 2mm high just above the metal portion of the body, and the other four plugs showed lesser examples of the same, just not as dark or high. I looked at my previous plugs (See, there IS a reason to keep these things!) and one of them showed a similar ring.

I suspect that may indicate a breakdown in the plug boots.

I'll probably put in new coils and boots 'just 'cuz.'

Gene Wilkes · 06-26-2007, 02:38 PM

dfrost · 06-26-2007, 03:43 PM

Here's a picture of the plug discoloration (forgot that I had it with me):

http://www.pbase.com/image/81221197.jpg

Jeron · Jeron's Garage

I have 1 2 3 and 6 handy from my last plug change and 2 and 6 have discoloration a little darker than your 3 while look clean 1 and 6 like your 5.

Just remembered hers a pic of 6 4 and another one:
Sparkplug electrodes GONE