Author Topic: Coils and stupid don't mix (Read 5214 times)

Ramblin MAn · « **on:** August 17, 2010, 08:55:09 PM »

So I'm trying troubleshoot a weird spark problem on a guys car so I make up my own coil harness to run straight off the battery. Exactly the same thing happens. First couple pulses light up the timing light and then no more timing light flashes.

So here is where the stupid part comes in. I decide I want to see what happens when I disconnect the ground wire and watch the timing light. So like the moron I am, I disconnect the ground wire wich is an unshielded alligator clip and hold it in my left hand while I have my trusty old school chrome plated metal Craftsman timing light firmly in my right hand. Give the nod to the owner of the car to crank it over and get however many volts these coils produce in a nice steady rythmic pulse across my chest.

F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-F-FUUUCCCCKKKKK!!!!!!!

It didn't stop until I bounced far enough away from the car to pull the hot lead off.

My right arm and rib cage on my right side are sore as hell and it feels like a gorilla tried to rip my arm off. My left side is ok but I'm sure I'll feel it there by morning.

Going by the shit-my-pants-ometer, I would say the coils are fine. The contractions of every muscle in my body were steady and rythmic so I would say the cam and crank sensors are doing their job as is the computer.

What could cause the coils to fire fine on the first couple of pulses and then weaken when checking the spark plugs? I sensed no weakening in spark when I was getting my bell rang. Plug wires?

This is a real stumper. The car starts and runs as long as the timing light pulses and then dies. It acts like the resistance increases as the coils fire. But when the circuit was through my body it all felt nice and strong and steady.

As soon as your done laughing, someone give me a clue.

dkbmxer002 · « **Reply #1 on:** August 17, 2010, 10:16:13 PM »

lol i've accidentally shocked myself a few times, shit sucks.

dude8383 · « **Reply #2 on:** August 18, 2010, 08:31:15 AM »

That was pretty hilarious...I remember getting the same shock when I was checking to see if my friends coil was seated properly. Next thing I know the dude is trying to start up the car and I CAN FEEL IT trying to start. Never do this drunk...I learned the hard way! Haha

Are you sure that its the coils?

In my case the car would start and run but very briefly. Turned out there was rust in the tank and it destroyed my fuel pump. Could it be a failing pump?

Ramblin MAn · « **Reply #3 on:** August 18, 2010, 08:56:40 AM »

I put a fuel pressure guage in line at the fuel rail. Pump takes it right up to 42psi and keeps it there. Volume is good.

It definately "seems" to be spark related. If you pull a plug and rest it on the valve cover, the first two sparks are blinding and then they go wak. They still spark, but are very weak. The plugs come out sooty. I'm going to pull the wires off one of my cars and try it. After that, I've told him we need to pretty much tear it down and trace every connection.

dvmotorsports · « **Reply #4 on:** August 18, 2010, 12:53:55 PM »

I'm done laughing.

Here ya go....

dj91318is · « **Reply #5 on:** August 18, 2010, 05:38:37 PM »

Hello Ramblin MAn,
I'm done laughing! I have had this same problem on other cars, ''Carbon Trail Matter'' it gets more conductive as it warms up, Check for a short in your Plug Wires / Boots, Some times you can definitely see a brownish / gray color it creates.
You can also use a spray bottle with a little mixture of soap and water mix, Do it at Night / in the Dark so you can See the Voltage spark / Jump to a ground while the motor is running and spraying heavily some where along the Spark Plug wires and Boots.
GL & Let us know what ever the problem might have been.

Ramblin MAn · « **Reply #6 on:** August 28, 2010, 09:38:44 AM »

Still have not solved this. I talked the owner of the car to moving it to my buddy's shop so we can work on it in the off hours. I double checked all of the "easy" stuff yesterday like cam timing, compression etc... just for my own sanity.

I tried a known good set of wires, but trying to start it in the dark of the shop with all the lights out may point to a loose wire somewhere so I'll give that a shot.

Unfortunately, the car does not run. It will fire up and immediately die. Like whatever circuit is powering the coils gets weak. I'll be tracing and measuring that today.

Just to clear things up here is the order:
Key on (no check engine light, supposedly burnt out, need to check that too)
Crank engine and timing light will flash two times (two rotations) and then stop.
Stop and repeat, same thing timing light will flash two times and then stop.
As long as the timing light is flashing, the car runs. So it runs for maybe 2 seconds and dies.

So it acts like the coils charge up with the key on and then discharge normally two times before they are no longer strong enough to induce a good pulse. Like the power circuit is being robbed.

However, my bell ringing test showed that with the hot wire connected straight to the battery junction terminal on the firewall, it did the exact same thing.

So, it's like the resistance through the plugs gets too high after two sparks. It's not the wires, and the plugs are brand new.

I'm just not getting it.

DesktopDave · « **Reply #7 on:** August 28, 2010, 07:37:55 PM »

Did you check the primary ground wire off the block? That's the other side of your circuit. Clean up/replace that braided wire. You ohmed out the spark plug wires too, right?

On my old 325 that ground wire was corroded internally - when I broke the grounding bolt loose it sort of dissolved. It was internally frayed and heavily corroded. The M42 coils are much more powerful than the M20 single coil ever was.

Ramblin MAn · « **Reply #8 on:** August 28, 2010, 08:32:11 PM »

This car has so much wrong with it I'm not sure what to do any more.

I took a set of jumper cables and clamped one end to the DME case and the other to the negative post of the battery and viola! I have good strong spark now. Only now, it's obvious that it's erratic as my last girlfriend (I miss her so) and the car acts no different. Instead of steady pulses once every second the timing light flashes away with no hint of a pattern.

We put on a different wiring harness today with absolutely no change.

We have used two different sets of crank and cam sensors with no change.

Open the door and there are no interior lights. Turn the key to the run position and interior lights come on.

It's a real mess because I don't know if any of the sensors or wiring are known (by me)to be good or not. On top of that, the car apparently never ran for any of the last two owners. The last owner did the motor swap into this car and couldn't figure out the problem and then the current owner got it off ebay a while back. I didn't realize the car had all these issues until today because I thought it was merely a bad cam sensor ( and may still be) and said borrow my spare and see if it helps. Then started finding all of these other weird issues.

Correct me if I am wrong, I should be able to hook up a known good harness and computer and as long as all the sensors are good, this thing should fire right up regardless of the body electrical issues, is that correct?

dj91318is · « **Reply #9 on:** August 29, 2010, 07:58:24 AM »

Ramblin MAn - I wish I had the answer for you. It has Spark at Plugs? = Good.

Your Fuel Pump, Unhook the hose to the F.P.R. and fill up a container Glass preferred to see if you see any contaminants that might be mixed with the gas,Water/Rust. And your Fuel pump connector they get cooked / toasted and can cause the pump to cut in and out. = Bad Pump / Relay / Connection.
GL

DesktopDave · « **Reply #10 on:** August 29, 2010, 08:29:52 AM »

Quote from: Ramblin MAn;95987

This car has so much wrong with it I'm not sure what to do any more.

I took a set of jumper cables and clamped one end to the DME case and the other to the negative post of the battery and viola! I have good strong spark now. Only now, it's obvious that it's erratic as my last girlfriend (I miss her so) and the car acts no different. Instead of steady pulses once every second the timing light flashes away with no hint of a pattern.

That is odd. The DME can run down to 7vdc - it has to fire when the starter is cranking. What's the battery condition? Is it draining from some sort somewhere?

Quote from: Ramblin MAn;95987

We put on a different wiring harness today with absolutely no change.

We have used two different sets of crank and cam sensors with no change.

Open the door and there are no interior lights. Turn the key to the run position and interior lights come on.

I'd ignore that door light problem for now, it might be a bad door switch, loose wire or something else trivial.

Quote from: Ramblin MAn;95987

It's a real mess because I don't know if any of the sensors or wiring are known (by me)to be good or not. On top of that, the car apparently never ran for any of the last two owners. The last owner did the motor swap into this car and couldn't figure out the problem and then the current owner got it off ebay a while back. I didn't realize the car had all these issues until today because I thought it was merely a bad cam sensor ( and may still be) and said borrow my spare and see if it helps. Then started finding all of these other weird issues.

Correct me if I am wrong, I should be able to hook up a known good harness and computer and as long as all the sensors are good, this thing should fire right up regardless of the body electrical issues, is that correct?

You're absolutely right about the harness. The motor wiring harness in this car is totally separate from the body harness and should fire the car up. Check the car grounds...especially the engine strap, engine relays and the DME grounds. Some of the sensors (crank, cam, AFM) have floating grounds in the DME case and must be intact. If they pick up signals from the rest of the car you'll never get the car to run right.

FYI, you can get a good body harness from any post-87 car, they're all pretty similar. It's not as agonizing to replace it as you'd think, maybe a weekend project. Toughest part is pulling up the carpet, it must weigh 100 pounds.

The e36 M42 engine harness might be similar to the e30 model, I'm not 100% sure of that. Seems like a BMW thing to do, though.

Ramblin MAn · « **Reply #11 on:** August 31, 2010, 08:50:25 AM »

Well we are at the component replacement stage of the game now. The owner is looking at getting new crank and cam sensors, but I want to try new coils first. Since I have an m42 powered e21 I was thinking I would try to find the COP coils at a junk yard for my car and let him "have" mine.

Did anyone ever put together a list of cars that had coils that would work? I don't know what cars to look at.

Nevermind, found this on realoem

Part 12131748017 (Ignition coil) was found on the following vehicles:

E31: Details on E31
E31 840Ci Coupe

E38: Details on E38
E38 740i Sedan
E38 740iL Sedan
E38 740iLP Sedan

E39: Details on E39
E39 M5 Sedan

E52: Details on E52
E52 Z8 Roadster

dj91318is · « **Reply #12 on:** August 31, 2010, 01:09:21 PM »

How long did the car sit? Maybe an injector problume leakey O-Rings / Rust in the ingestors / F.P.R. Get a can of starting fluid and gige lite sprays where you thing intake air can seep in when the motor is warm/cold a big leak will stall engine, a irratic run will indicate a small leak. GL

DesktopDave · « **Reply #13 on:** August 31, 2010, 01:33:35 PM »

Be careful buying used coil packs - grab spares. From what I've heard BMW went through several producers, and still might not have the problem with dying packs sorted.

I'll bet you can find compatibles on other makes too. My Mom's Lincoln LS has packs that look awfully familiar...

locknload · « **Reply #14 on:** September 10, 2010, 03:37:59 PM »

You said it has received a motor swap, which reminded me of this:
http://www.m42club.com/forums/showthread.php?t=7757
Your symptoms don't match, but that doesn't mean it's not the problem. It may be worth the few minutes it takes to check. Personally, I think your coils/wires/plugs are fine. Maybe a DME swap would help narrow it down if you're sure the grounds are all functioning properly.