m30 engine that won't run

[Headshrinker]

I’m about to give up so if you have any idea’s, I’m desperate!

I have an 1991 BMW with an m30 engine (actually in a 735i, but I’m cross listing in hopes of better visibility), with 200k miles on it. It began running rough and finally will not run at all. The plugs were fowled (black and wet with fuel). Spark plugs and injector tests indicate erratic firing while cranking, dim flash then bright for a couple of seconds then dim again.

Here’s what I’ve tried/tested/replaced so far:

Cap & rotor
Plugs
Wires (tested, not replaced, all are ~6k resistance)
Injectors (fire as described above)
Fuel pressure is between 40 and 45 lbs and holds well after cranking
Ignition coil
Reference sensor
Air flow meter
Injection ECU
Idle control solenoid
Fuel tank is full and gas does not smell varnished

I have not replaced plug wires as I do not have a spare set around (I’m more of an early big 6 guy, I have two e28s and an e24) but I do have some concerns about the inductive pickup on wire #1. It looks fine, but if it failed, could this cause the care not to start? My other sources have indicated that this pickup is not used my the ECU, if this is incorrect let me know.

Any assistance would be greatly appreciated.

Lisle

[Bill R.]

i would suspect the coil or the crank position sensor, if you already replaced them both did you set the gap on the reference sensor and have you rotated the engine while watching the reference sensor to see if perhaps the harmonic damp has gone bad and there's too much runout on the crank pulley meaning the gap gets larger and smaller at the sensor as you rotate... As far as the induction loop on the plug wire goes, it is used on your car but it will not keep it from starting and running. . Your engine has what they call semi sequential fuel injection, meaning that your injectors normally open in 2 groups of 3.... 1,3,5 open then 2.4.6 open the next revolution. This is done to control injection a little more precisely for emissions. It uses this induction loop as the sensor to determine where it is in the firing order. When it fails it goes into a mode where all the injectors open simultaneously but they only stay open for half as long since this way they open every revolution. This doesn't measure fuel quite as precisely but most people haven't been able to tell any difference in how it runs.

I’m about to give up so if you have any idea’s, I’m desperate!

I have an 1991 BMW with an m30 engine (actually in a 735i, but I’m cross listing in hopes of better visibility), with 200k miles on it. It began running rough and finally will not run at all. The plugs were fowled (black and wet with fuel). Spark plugs and injector tests indicate erratic firing while cranking, dim flash then bright for a couple of seconds then dim again.

Here’s what I’ve tried/tested/replaced so far:

Cap & rotor
Plugs
Wires (tested, not replaced, all are ~6k resistance)
Injectors (fire as described above)
Fuel pressure is between 40 and 45 lbs and holds well after cranking
Ignition coil
Reference sensor
Air flow meter
Injection ECU
Idle control solenoid
Fuel tank is full and gas does not smell varnished

I have not replaced plug wires as I do not have a spare set around (I’m more of an early big 6 guy, I have two e28s and an e24) but I do have some concerns about the inductive pickup on wire #1. It looks fine, but if it failed, could this cause the care not to start? My other sources have indicated that this pickup is not used my the ECU, if this is incorrect let me know.

Any assistance would be greatly appreciated.

Lisle

[Headshrinker]

Bill,

I happen to be in the middle of upgrading the injection system on my 1980 euro 635CSi from an early 1990’s Haltech system to that of a 1991 735i. So, I have a complete ignition/injection system lying in my garage that came off of a running car. This facilitated my testing/swapping parts to ensure each of the components I listed are actually functioning. The coil was included in this group. However, I have not actually turned over the engine and watched for run-out on the crank pulley. In fact, now that you mention it, it seems as if the gap between the sensor and the trigger wheel was a bit wide. I’ll check for run-out and if it looks good I’ll narrow the gap some and see if that takes care of it.

Thanks for the advice,

Lisle

[Bill R.]

Bill,

I happen to be in the middle of upgrading the injection system on my 1980 euro 635CSi from an early 1990’s Haltech system to that of a 1991 735i. So, I have a complete ignition/injection system lying in my garage that came off of a running car. This facilitated my testing/swapping parts to ensure each of the components I listed are actually functioning. The coil was included in this group. However, I have not actually turned over the engine and watched for run-out on the crank pulley. In fact, now that you mention it, it seems as if the gap between the sensor and the trigger wheel was a bit wide. I’ll check for run-out and if it looks good I’ll narrow the gap some and see if that takes care of it.

Thanks for the advice,

Lisle

[Headshrinker]

As it turns out the sensor was not bad, but the woodruff key was sheered and the crank pulley was slipping. The crank pulley nut is missing allowing the pulley to turn intermittently. I really appreciate you suggestion of looking for an out of round trigger, otherwise I might not have found it. I ran into this once before with a 2002, but discovered the problem when the charge light would come on.

I think a lower cover crank seal and new key and nut/washer and it should be good to go.

Thanks again,

Lisle

[Bill R.]

it worked loose allowing the crank damper to work back and forth enough to shear the key...I've seen this on a lot of other cars but not on an m30 before...

As it turns out the sensor was not bad, but the woodruff key was sheered and the crank pulley was slipping. The crank pulley nut is missing allowing the pulley to turn intermittently. I really appreciate you suggestion of looking for an out of round trigger, otherwise I might not have found it. I ran into this once before with a 2002, but discovered the problem when the charge light would come on.

I think a lower cover crank seal and new key and nut/washer and it should be good to go.

Thanks again,

Lisle

[632 Regal]

I remember he had quite an ordeal after his sheared and trashed the crank...

[Headshrinker]

Thanks Bill,

I installed a new front main seal, Key, wave washer and nut, and used locktite just to be sure it stays put. Car runns good, but is whining pretty bad, I'll have to see if it's the water pump or another accessory. It sat since the end of June so who knows. It runs again so I feel better. I just never thought to look at the crank pully.

Thanks again for the assistance,

Lisle Hites

[winfred]

i've sold a few hubs but never seen a bad one myself, the old 80s 4 and 5 cylinder mercedes diesels **** their ballencers off all of the time and they have two good sized keys

it worked loose allowing the crank damper to work back and forth enough to shear the key...I've seen this on a lot of other cars but not on an m30 before...