E30 problem after compression test&plugs - United Bimmer Community

**ajpoltz** · 04-14-2009, 11:47 AM

Just got a 1988 325 with 134 k and drove it 100 miles and was running well except it idled a little rough at times and after it was driven for 30 min I would hear a buzzing under the car and at the same time if I am heavy on the throttle it felt like it was starving for fuel, also idle emissions were a bit too high too pass. NOW I decided to replace the spark plugs and removed the copper autolite 66 and put in bosch platinum 4037 gapped at 28-30. while all the plugs were out and wires disconnected I did a compression test 1 cyl at a time for 1-2 seconds each. I put the plugs in and it runs very poor with black smoke so i put the old plugs in and still runs very rough.I marked the plug wires and they are installed in correct order. Did I mess something up by doing the compression test ? Thanks for your help.

Big Evil · 04-15-2009, 04:11 PM

For starters the platinum plugs SUCK in these engines. Use the standard copper core OEM recommended plug, they do work MUCH better. Check your cap and rotor, they do wear out. Also the plug wires may look ok but do wear out too. What were the results of your compression test? Black smoke indicates to much fuel, maybe a dodgy O2 sensor or leaking injector (would also cause an HC fail at idle). May be time for a fuel filter and an oil change, doing those right before an emissions test can often turn a fail into a pass. Its hard to mess up a compression test and damage an engine so chances are you have some kind of electrical/mechanical problem in the fuel and/or ignition system.

**ajpoltz** · 04-18-2009, 04:56 PM

I put the old plugs back in and it still runs bad so I must have done something to cause it unless it is a big coincidence.
When I took out the plugs they were wet with raw gas and a couple looked like they may have not fired at all. I guess I'll check for spark next or if anyone has a suggestion it would be helpful. Thanks, Andrew

Big Evil · 04-19-2009, 09:37 AM

Cap, Rotor, Wires and coil. Normal wear and tear parts that need replacing, most likely your problem.

**tkeenan** · 07-03-2009, 07:42 AM

I have the same year e30 that I just bought too. It idles rough and spits black smoke too. Before even driving it, the very least to do is to get a new O2 sensor and clean/new injectors. Fuel filter, stop any fluid leaks with new gaskets. As suggested above, cap, rotor, wires and coil. Replace spark plugs after all that is done to avoid fouling the new ones. Any other suggestions?
Check codes and solve those problems.
check belts for wear.

BigEvil, any idea why the platimum plugs aren't suited for the e30? Brands?
I got Champion iridium because I have a job there, and their logo is cool.

Big Evil · 07-03-2009, 09:20 AM

Yup, platinums and iridiums etc we're designed long after these car were. The e30's use a standard cap and rotor with a single coil. Firing KV is around 15-20 and can only last 1-2ms as a result (and that's actually a LONG time in spark terms for this system). The copper cores they are designed with are of lower resistance which means less voltage is needed to jump the gap so you get a longer lasting spark which promotes better combustion in these engines. Plat's and ir's are of a higher resistance value which mean more voltage is required to initiate spark. This results in a more intense hotter spark initially but it goes out almost as quick as it ignites and leads to poor combustion in these engines. Plat's and Ir's are great if you have say, MSD or some factory version of it, Coil on plug ignition and the like. Those system create more voltage, multiple sparks at idle and can actually handle those types of plugs. Single stock coil running 6 cylinders........not so much. Champion makes copper cores for these cars, use those and then just put the Iridium sticker in the back window :-)

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