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<944> Ignitoin Coil Dead?

Gruppe:

I have an 87 944 NA with a no-start condition. The car sat for 8 months with the PO.

I measured the resistances of the ignition coil at 0.9 ohm primary and 5.72 k-ohm secondary. The specs are 0.4-0.6 ohm for the primary and 5-7.2 k-ohm for the secondary. So, the primary coil is 0.3 ohm over the top end of the spec.

Could this be a reason for no-start?

Thanks in advance!

Neil Deshpande
Old 04-05-2003, 04:36 PM
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Dont know...."bump" Wish i could be more help..as a side note I replaced mine with a msds blaster coil $40....
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Old 04-05-2003, 07:57 PM
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check the DME relay, there is a way to jumper across it (not sure, but someone could provide more info on this), and check to make sure the reference sensors are positioned correctly...

Do you get spark?
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Old 04-05-2003, 08:27 PM
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<944> Ignitoin Coil Dead?

Quote:
Originally posted by ilikemy944
check the DME relay, there is a way to jumper across it (not sure, but someone could provide more info on this), and check to make sure the reference sensors are positioned correctly...

Do you get spark?
The DME relay is fine as the fuel pump runs on cranking and the DME connector pins 5-18 and 5-35 have battery voltage with the ignition on. Reference sensors show correct resistance and looked to be in the correct position, but I have not measured the sensor-flywheel distance. I'll do this later today.

There is no spark. :-(.

Neil Deshpande
Old 04-06-2003, 05:07 AM
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You should have 12v at coil with key on. Momentarily tapping a ground on the green coil wire should produce a spark from between the HV coil wire to chassis. If yes, coil is good. Be careful you don't zap an injector when you do this...it will blow your DME.

If your coil is good (99% of the time it will be good) could be TDC reference sensor problem or DME unit. My problem was the sensor even though the resistance was correct.

When cranking do you get a slight pulsing on the tach? I didn't until I changed out the sensor.

Be sure to clean all connections and use dielectric 'tune-up' grease on them. Big difference.
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Old 04-06-2003, 01:22 PM
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<944> Ignitoin Coil Dead?

Quote:
Originally posted by carsontc
You should have 12v at coil with key on. Momentarily tapping a ground on the green coil wire should produce a spark from between the HV coil wire to chassis. If yes, coil is good. Be careful you don't zap an injector when you do this...it will blow your DME.

If your coil is good (99% of the time it will be good) could be TDC reference sensor problem or DME unit. My problem was the sensor even though the resistance was correct.

When cranking do you get a slight pulsing on the tach? I didn't until I changed out the sensor.

Be sure to clean all connections and use dielectric 'tune-up' grease on them. Big difference.
Which one is the TDC reference sensor? One of the two with rectangular connectors or the one with the circular connector? I don't recall a pulsing of the tach, but I will check this today.

I'll get some contact cleaner for all the connectors and spray that on with an application of dielectric grease.

How can I avoid zapping an injector? Thanks!

Neil Deshpande
Old 04-06-2003, 03:18 PM
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I am betting on the sensors. Your car may have two sensors. I am not sure though.
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Old 04-06-2003, 05:51 PM
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Quote:
Originally posted by carsontc
You should have 12v at coil with key on. Momentarily tapping a ground on the green coil wire should produce a spark from between the HV coil wire to chassis. If yes, coil is good. Be careful you don't zap an injector when you do this...it will blow your DME.

If your coil is good (99% of the time it will be good) could be TDC reference sensor problem or DME unit. My problem was the sensor even though the resistance was correct.

When cranking do you get a slight pulsing on the tach? I didn't until I changed out the sensor.

Be sure to clean all connections and use dielectric 'tune-up' grease on them. Big difference.
OK, I have pulsing on the tach. So, I'm guessing the TDC reference sensor is OK. I had earlier found the speed sensor to be 3 mega-ohm instead of 1 k-ohm resistance, but now it is OK. I'll try and replace that and see if that helps.

I checked and I don't have 12V at the ignition coil with the ignition on. What does this mean? Blown DME? I could get one from a salvage yard on Monday. Thanks!

Neil Deshpande
Old 04-06-2003, 06:10 PM
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<944> No-Start Contd.

Gruppe:

I put in a new speed sensor, the one that had a too-high resistance earlier, but was OK now. The old one was a bit frayed and the wire strands were breaking so I'm not unhappy that I put in a new one. The reference sensor wiring, etc., was OK. I measured the voltage out of the sensor to be around 0.2V during cranking. The new sensor was the same as the old one.

However, still no start. No 12V at the ignition coil primary with ignition ON or while cranking. DME?

This is frustrating, but I'm getting to know the car well and when it runs it will be all the more satisfying for the hassle before.

Neil Deshpande
Old 04-06-2003, 06:57 PM
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Re: <944> No-Start Contd.

Quote:
Originally posted by neildeshpande
Gruppe:

I put in a new speed sensor, the one that had a too-high resistance earlier, but was OK now. The old one was a bit frayed and the wire strands were breaking so I'm not unhappy that I put in a new one. The reference sensor wiring, etc., was OK. I measured the voltage out of the sensor to be around 0.2V during cranking. The new sensor was the same as the old one.

However, still no start. No 12V at the ignition coil primary with ignition ON or while cranking. DME?

This is frustrating, but I'm getting to know the car well and when it runs it will be all the more satisfying for the hassle before.

Neil Deshpande
OK, I measured the voltage between coil +ve and battery -ve and coil +ve and cylinder head (ground) and found 11.88V. So, the coil is getting the 12V with the key at "ON".

I was measuring across the coil primary earlier, but they are nearly at the same voltage with the coil resistance being so low. Silly me!

I'm going to operate the coil manually by making and breaking the green wire's contact as suggested here. Will post results back.

Neil Deshpande
Old 04-06-2003, 07:14 PM
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Your coil readings are probably not out of spec enough to cause zero spark. Have you checked the coil wire, cap and rotor?
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Old 04-06-2003, 07:30 PM
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<944> Testing Ignition Coil.

Quote:
Originally posted by Roger Hall
Your coil readings are probably not out of spec enough to cause zero spark. Have you checked the coil wire, cap and rotor?
Roger:

I figured the same. The spec is 0.3-0.6 ohm and I'm getting even 0.7 ohm in my measurements.

I carried out the following test. Connected coil +ve and measured the voltage between it and battery -ve at 11.88V. Then connected the high voltage wire to a spark plug at one end and the coil at the other and set it against the strut bearing nut (previously measured at 11.88V from battery +ve). Then I connected the coil -ve (green) intermittently and tried to get a spark between the plug and the bolt. Nothing.

Any idea what this means? Operating the coil manually thusly should yeild a spark, no?

Neil Deshpande
Old 04-06-2003, 07:34 PM
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I am not sure about the exact process. Have you tried taking the coil wire out of the distributor and holding it near a ground less than 1/2 an inch away? I purchased a spark gap meeter at a local auto parts store for about $3. It has a clip and a bolt. Attach the clip to a ground the coil wire to the bolt and screw the bolt in or out to mesure the distance a spark will travel.

Here are a couple of thoughts

Do you have one or two reference sensors. Think some models have one on the flywheel and one on the cam gear.

Also I belive that the resistance and the gap on the reference sensors needs to be checked.

Battery voltage should be over 12 volts. More like 12.7 volts.
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Old 04-06-2003, 08:34 PM
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Quote:
Originally posted by Roger Hall
I am not sure about the exact process. Have you tried taking the coil wire out of the distributor and holding it near a ground less than 1/2 an inch away? I purchased a spark gap meeter at a local auto parts store for about $3. It has a clip and a bolt. Attach the clip to a ground the coil wire to the bolt and screw the bolt in or out to mesure the distance a spark will travel.

Here are a couple of thoughts

Do you have one or two reference sensors. Think some models have one on the flywheel and one on the cam gear.

Also I belive that the resistance and the gap on the reference sensors needs to be checked.

Battery voltage should be over 12 volts. More like 12.7 volts.
Roger:

2 sensors - one reference and one speed. Both are the same part number. I guess there are two toothed wheels on the flywheel, one with many teeth and one with one tooth. Both sensors check out good on resistance (1 k-ohm). Gap should be OK as it has not been touched since the car was running. I will check it though.

The battery was over 12V, but has come down a bit since I've been cranking the car w/o recharging the battery. I'll likely set it to recharge again tomorrow evening.

Neil Deshpande
Old 04-06-2003, 09:42 PM
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Have you opened the distributor cap to see it's condition..and the rotor is turning and not loose?

Also as I said earlier when I momentarily was tapping a ground on my green coil wire it produced a spark from between the HV coil wire to chassis (hold about a 1/16 of an inch away from engine metal and not near any wires). If yes, coil is good.

Tom
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Old 04-07-2003, 01:41 AM
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While trying to solve my 'hot starting - no spark' problem, I replaced the battery cable clamps, removed & cleaned (w/dielectric tune up grease) ALL the connections to the battery and starter, and added a ground strap from the negative battery terminal that engine to firewall copper strap connection. All my electrical stuff seems to work much better. You may really need to do this at some point.

btw, the speed sensor shuts off the fuel pump (for safety) when RPM drops below 200.
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Old 04-07-2003, 01:52 AM
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Quote:
Originally posted by carsontc
While trying to solve my 'hot starting - no spark' problem, I replaced the battery cable clamps, removed & cleaned (w/dielectric tune up grease) ALL the connections to the battery and starter, and added a ground strap from the negative battery terminal that engine to firewall copper strap connection. All my electrical stuff seems to work much better. You may really need to do this at some point.

btw, the speed sensor shuts off the fuel pump (for safety) when RPM drops below 200.
OK, I just realized I used the ignition coil -ve wire to ground out the -ve terminal, but that wire is likely going to the DME and interrupted at this point. I'll have to repeat that test of the coil this evening by grounding it directly.

Also, I could not find the firewall ground point at all. I looked for it on the firewall directly behind the fuel rail. Nothing. I did see the engine ground (two bolts) on the engine near the firewall though. I've had ground trouble on my BMW 325 iS (poor ground strap connection) so I understand this. Any ideas on where the firewall ground might be? Thanks! I guess I could measure the voltage drop between engine and chassis during cranking to deterime the quality of the engine ground connection. Right?

Yes, I think the BMW Motronic shuts off fuel at 300 RPM. Or, rather waits for 300 RPM to supply it.

Neil Deshpande
Old 04-07-2003, 04:39 AM
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I believe the green wire is the 'pulsing' ground from the DME.

Pull it (green wire) off the coil and be sure you have 12volts now at both terminals on coil. One from the terminal supplied fromthe key 12 volts...and the other feeding though the coil to where the green wire was connected.

Now manually pulse the coil terminal with a ground. If it gives you a spark, see if you are getting the 'pulsing' gound from the DME green.
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Old 04-07-2003, 04:57 AM
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I had a similar problem.. after checking the DME relay (purchased a new one, then used the "paper trick" to modify the old one) verified that I was getting fuel from the pump. Checked Coil, Spark to plugs, Belts(just in case..) Plug wires, Cap , rotor, fuel delivery and all were ok. Had it towed to my Mech and it turns out my coil was in spec, but still not enough voltage to ignite the Bosch Plats I was running. New Coil and back to OEM Bosch Coppers and it's running like a champ.
Keep in mind-- mine is a daily driver and just quit one day with no warning.
If its been sitting it could be bad fuel, varnish buildup along the fuel delivery system, or junk in the gas tank.
Good Luck!!
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Old 04-07-2003, 08:21 AM
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<944> Ignition Coil Dead?

Quote:
Originally posted by carsontc
Have you opened the distributor cap to see it's condition..and the rotor is turning and not loose?

Also as I said earlier when I momentarily was tapping a ground on my green coil wire it produced a spark from between the HV coil wire to chassis (hold about a 1/16 of an inch away from engine metal and not near any wires). If yes, coil is good.

Tom
I did the test. The coil does spark from HV terminal to ground, but weakly. About 1/16" is all it'll handle and with a very weak spark. The spark on the LV side when I remove the connection to ground is much higher!

Neil Deshpande
Old 04-07-2003, 05:33 PM
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