Help!!!! '93 M5 runs rough/stalls when warm.

[m3driver97]

I started checking out the ignition components and the cap and rotor had 'normal' wear. I am replacing them (cap is on order, rotor and plugs are on hand). What's interesting is that the plug gap on all the plugs was .044-.045"
instead of the .024" gap specified for this engine. I'm sure that replacing them will make a noticeable difference.

The plug wires all fell in the range of 5.5-6.0K ohm so I believe that they are OK.

Does anyone know the coil specifications for the S38B36 engine?????

I checked the ignition coil and it looks very clean (no corrosion). However the Bentley manual has no resistance specs for the S38B36 coil.

What has me puzzled are the ignition coil readings.

The Bentley coil specs for the M20/M30 are:
-- coil primary (between 1(-) & 15(+) are 0.50Kohm
-- coil secondary (between 15(+) & 4 (center tower) = 6.0Kohm

The Bentley coil specs for the M50/M60 are:
-- coil primary (between 1(-) & 15(+) are 0.4-0.8ohm
-- coil secondary (N.A. in specs column).

I measured 0.75 ohm between 1 & 15 (coil primary)
I measured 8.5K ohm between 15 & center tower

These might be right for the S38B36 (M5) coil, but I don't know the specs.

Hate to throw away the money on a new coil if I don't need to.

Anyone know the specs for the coil on this car..??

[m3driver97]

Hi everyone,

Just wanted to post the results of my repair activities in case anyone else runs into this type of scenario.

Sorry for the delay, but it took over 2 weeks for Pelican to provide all of the parts that I had ordered from them and then to compound the situation I ended up out of town almost 2 weeks.

I ended up doing the following to the car:

-- Checked/replaced all small vacuum hoses under the hood
-- Cleaned ICV but it was almost spotless inside before I started
-- Cleaned oil separator assembly and replaced O-ring & drain hose
-- Replaced valve cover breather hose
-- Replaced Cap/Rotor/Plugs with all Bosch parts (dist & cap had some corrosion but no moisture)
-- Replaced O-rings between throttle bodies and plenum
-- Replaced main relay and fuel pump relay
-- Cleaned all pluggable connections with and applied dielectric grease
-- Checked resistance & condition of plug wires and coil and they were OK
-- TPS checked per manual and measured 0 ohms at both idle and WOT
-- CPS (Crankshaft Position Sensor) checked out per manual
-- IAT sensor (in MAF box) checked out per manual
-- ECT sensor checked out per Bentley manual
-- Tightened all grounding lugs I could find under hood and rear seat
-- Fuel pressure checked out per manual

Bottom line, there were only 3 or 4 things that I am pretty sure were involved with the problem.

1. The upper ICV hose was totally loose where it connected to the center throttle body. This would be the prime candidate for a significant vacuum leak. Might have been from previous maintenence by FO.

2. The oil separator drain hose was rock hard and broken where it connects to the dipstick tube and was replaced.

3. Orifice in dipstick tube where oil separator hose connects was plugged solid. Cleaned out with appropriate sized drill bit.

4. Plug gap was 0.042 instead of nominal 0.024

So far, the car is running fine after all this work. I still plan to replace the O2 sensor as the records don't indicate that it has ever been changed.

Thanks again for all your input and areas to check out. MUCH easier to see what's going on with the engine when the plenum is removed.

Regards, Brent Dann

[VentoGT]

Thanks for the follow up Brent. My cap and rotor were toast when my car was running rough, water in the rotor, bad points, etc. Glad you got your problem figured out.

[Brandon J]

So it looks like basic maintenance did the trick huh. Also, don't forget to check if the resonance flap is working. One last thing, sometimes it is difficult to check the wires. One technique to check for bad wires and cross firing is to remove the plug wire cover, turn off the light in the garage, and run the car through the rev range. Any cross firing is easier to see when it lights up in the dark.

Good Luck,

[BillionPa]

fyi coil specs should be .5/6000, so you are running at about 70% ignition power.

[stu1]

Thanks for posting the results - I was fairly sure it was some closed loop thing, not even thinking about vacuum leaks when warmed up.

Cheers,
Stu.