BMW M5 Forum and M6 Forums banner

1 - 4 of 4 Posts

90 Posts
Discussion Starter #1
What a Day. Im so F&^% pissed its not funny.

It all started like this. My s38b36 91, Bog Stock 180,000 Kms full service history (in my hands for less that 1 year). I thought i might take it down and dyno it to see what kind of power its making before i apply some very light mods, mainly exhaust (muffler and cat) related. Obviously i will be able to measure the difference then.

It came up with this.

2 Things.

1. The guys could not believe the power this thing makes. 3.6l, stock standard, almost 20 yrs old and 180kms. 186KW at the wheels = 250 rear wheel HP. Remember this car is standard, nothing done to it whatsoever.

2. He could not believe i had not melted a piston given how lean the car was running looking at the air fuel ratio above which should basically be a straight curve, without spikes.

** Ok so i start shi**ng myself.

Get home, let the engine cool and immediately crack open the spart plug cover and pull a plug out. Guess what?

Bosch 5YDDC - 0.8 gap, used on e36 m3.

S38b36 should be running bosch 6YDC with .6m gap.

** This car was came with receipts from a so called specialist bmw place in Sydney, Australia. Im not going to reveal who they were, but you cant imagine what i want to do to them.

Questions i need answered from you guys in the know:

1. First thing tomorrow i getting correct plugs and changing them. Driving the car felt smooth enough, i would never have picked this without the dyno. What is likely to be the noticable difference with the correct plugs?

2. What potential damage could i have done already with the m3 larger gap plugs?

3. Once plugs are correct, im planning to lacate a workshop with a scanner who can read the O2 sensor and Air mass meter numbers and check if they are ok. Does anyone know the best way to test these readings and what they should be. Bentley and other Do not state testing on the s38 engines.

4. Im having the injectors tested and cleaned next week.

5. What are the chances the m3 plugs are causing it to run lean, and nothing else? 99% ?

6. If im still lean, i guess it's time to look at air leaks and etc. What else can be added to the list?

All help much appreciated guys! And i must really stress, my car drove beautifully, i would have never have known this ever! until either going onto the dyno or 2, melthing a piston. I suggest you ALL have yours checked!

Am i overreacting? Thx Again guys

115 Posts
There is nothing "wrong" with the plugs that were in there, they are simply one step colder than the stock plugs. Less prone to pre-ignition on a hot, hi-po engine, though more prone to fouling. Gap is only critical if you are having issues with spark blow out (which would feel like bad hesitation or stuttering) at high load, which doesn't seem to be a problem with your car. Power looks and sounds smooth, so in other words, no harm done by the plugs.

The AFRs, while unsteady, are at a safe level for the most part. So check things that affect mixture, as you have planned- O2 sensor, AMM, clean/balance injectors, check for vacuum leaks, exhaust leaks, etc.

And relax:)
1 - 4 of 4 Posts