No start after replacing both ignition coils

[gearheademporium]

I've owned my 1992 400e since 2015 and it now has around 230k miles. It ran great until recently when my problem started with rough idle, misfiring and lack of acceleration after the engine reaches normal operating temp. It seemed to run a little better after I replaced the set of spark plug wires and non-resistor plugs, caps and rotors, but soon after the same symptom struck again. It was by chance during my troubleshooting that I found the Crank position sensor somehow became loose at the flywheel housing, so instead of just tightening it up, I had the sensor replaced as well. It ran pretty good for a couple of weeks; acceleration was great, no misfiring but still had a slight rough idle.

Last week the symptom of lack of acceleration, rough idle and misfiring returned. Thinking my coils may be the culprit after reading similar situation by other members, I replaced both of my coils today; I also replaced the cam position sensor when I found it was cracked all the way around where the sensor wire plugs into. Reconnected the battery after the job was done and now it would not start.

It cranks fine and at one point appears to want to start but didn't. The only thing I can think of if I did anything wrong was not to label both pair of wire connection to the coils. Could this problem stemmed from having crossed the wiring to the coils.

 

[R129 UK]

Could this problem stemmed from having crossed the wiring to the coils.

Yes, absolutely.

The issue is almost 100% certain to be related to something you did immediately before the problem started.

 

[nocfn]

And you also need to remove caps wipe the interior of them with wd40, as well as remove the rotors and do the same to the area of aluminum that the insulators cover. All of that needs a wiping with wd40. If your caps do not have extra slots yet, you need to add more and deepen the ones that exist, think 10 / 2 position and 5 / 7 at a minimum. multiple threads on this. May also be a good time to run a smoke test - vacuum leaking is common at this age and there are 12-18 different ways to have the leaks.

 

[gsxr]

I've owned my 1992 400e since 2015 and it now has around 230k miles. It ran great until recently when my problem started with rough idle, misfiring and lack of acceleration after the engine reaches normal operating temp. It seemed to run a little better after I replaced the set of spark plug wires and non-resistor plugs, caps and rotors, but soon after the same symptom struck again. It was by chance during my troubleshooting that I found the Crank position sensor somehow became loose at the flywheel housing, so instead of just tightening it up, I had the sensor replaced as well. It ran pretty good for a couple of weeks; acceleration was great, no misfiring but still had a slight rough idle.

Last week the symptom of lack of acceleration, rough idle and misfiring returned. Thinking my coils may be the culprit after reading similar situation by other members, I replaced both of my coils today; I also replaced the cam position sensor when I found it was cracked all the way around where the sensor wire plugs into. Reconnected the battery after the job was done and now it would not start.

What you describe are classic symptoms of moisture in the distributor caps. The issue will keep recurring unless you do 2 things: First, cut additional vent slots into the new caps. And second, eliminate all oil leaks (must be zero oil!) at the caps. The oil leak source is almost always from the intake cam advance solenoid - doesn't look like much, but any trace of oil at the lower edge of the cap will cause problems. Less likely is an oil leak from the radial seal behind the rotor bracket & dust shield, check this to make sure it's completely dry. This thread has all the information you need to know.

It cranks fine and at one point appears to want to start but didn't. The only thing I can think of if I did anything wrong was not to label both pair of wire connection to the coils. Could this problem stemmed from having crossed the wiring to the coils.

Very likely you have the coils backwards. Try that first.

Also, gap the new plugs at 1.0mm (wider than 0.8mm spec). Finally, the cam sensor that was cracked, may be fine. If you replaced it with a cheap aftermarket sensor... consider reinstalling the old one. Don't replace this unless you get a fault code from the LH module for the cam sensor. Details on how to read fault codes are here.


Welcome to the forum!

 

[gearheademporium]

Thank you all for your responses. Before I reattempt to correct this issue, I just wish to ask how to check and ascertain which pair of power wires should be connected to which coil? Appreciate your input again.

 

[gsxr]

Thank you all for your responses. Before I reattempt to correct this issue, I just wish to ask how to check and ascertain which pair of power wires should be connected to which coil? Appreciate your input again.

I'm not sure if there's an easy way to tell, but the wires are usually stiff enough that you'd have to noticeably bend them to attach to the "wrong" coil. I forget if the wires are labeled.

Did you buy Bosch coils, btw?

 

[gearheademporium]

Yes, I picked up both Bosch coils from FCP Euro.

 

[R129 UK]

What you describe are classic symptoms of moisture in the distributor caps.

Dave - for my own understanding, isn't the warm starting issue also potentially the crankshaft position sensor too?

 

[gsxr]

Dave - for my own understanding, isn't the warm starting issue also potentially the crankshaft position sensor too?

A failing crank sensor typically manifests as the engine running normally (no misfires), then dying and refusing to restart until the engine (and sensor) cool down. It should start & run normally when cold. This can be confirmed by measuring CKP resistance, should be 800 ohms or so cold, slightly higher warm/hot. When the engine refuses to start, CKP resistance will be either infinite/open, or very high (thousands of ohms).

The OP stated the car had "misfiring and lack of acceleration after the engine reaches normal operating temp". Assuming this is 10-15 mins after a cold start, that would be the classic problem with secondary ignition, where the additional vents/slots and elimination of oil contamination should cure the post-warmup misfire.

 

[R129 UK]

A failing crank sensor typically manifests as the engine running normally (no misfires), then dying and refusing to restart until the engine (and sensor) cool down. It should start & run normally when cold. This can be confirmed by measuring CKP resistance, should be 800 ohms or so cold, slightly higher warm/hot. When the engine refuses to start, CKP resistance will be either infinite/open, or very high (thousands of ohms).

The OP stated the car had "misfiring and lack of acceleration after the engine reaches normal operating temp". Assuming this is 10-15 mins after a cold start, that would be the classic problem with secondary ignition, where the additional vents/slots and elimination of oil contamination should cure the post-warmup misfire.

Yes, my question about the crank position sensor was "in a vacuum" and not related in any way to this thread specifically. Thanks.

 

[emerydc8]

When I did coils years ago I noted which part number goes where under the ABS tray so if you go to autohausaz and find where it actually states which is which (left or right) then you should be able to tell from the attached parts diagram. IB = inboard which is closer to the engine.

 

[gsxr]

When I did coils years ago I noted which part number goes where under the ABS tray so if you go to autohausaz and find where it actually states which is which (left or right) then you should be able to tell from the attached parts diagram.

Yup! The coils are electrically the same, but the terminal location relative to the mounting bracket is rotated 90° between them. Pretty sure you can't install them backwards, at least not easily.

I had originally thought he got the high-tension lead backwards, which also should be checked.

 

[emerydc8]

The 000 158 58 03 (000 158 64 03) is the left right coil according to www.mbpartsource.com. Attached.

So it looks like the coil closest to the engine is for the left right (passenger) bank as confirmed below by @gsxr.

 

[gearheademporium]

The coils are of different configurations relating to the terminal locations and I replaced the coil one at a time. Its just I failed to label the power wires so could not recall which wire or set of wires goes to which coil. I'm curious as to why incorrect routing of these wires would result in no start?

 

[gsxr]

So it looks like the coil closest to the engine is for the left bank.

Yup!
Coil closest to engine goes to passenger side bank.
Coil closest to fender goes to driver side bank.

 

[R129 UK]

The coils are of different configurations relating to the terminal locations and I replaced the coil one at a time. Its just I failed to label the power wires so could not recall which wire or set of wires goes to which coil. I'm curious as to why incorrect routing of these wires would result in no start?

If I understand you correctly, you could have the firing order different than the expected layout resulting in a spark at the wrong time in terms of engine timing.

 

[gsxr]

The coils are of different configurations relating to the terminal locations and I replaced the coil one at a time. Its just I failed to label the power wires so could not recall which wire or set of wires goes to which coil. I'm curious as to why incorrect routing of these wires would result in no start?

If the power wires to each coil got reversed or otherwise incorrect, the ignition may not fire at the right time.

Did you replace the cam sensor at the same time? Or did the engine start normally after the cam sensor swap, but then won't start after replacing coils only?

 

[emerydc8]

I took pictures of the two wire leads going to each coil and if I recall there was a smaller-holed terminal and larger so you couldn’t mess that up. As for whether the wires went to the left or right coil, are they not labeled?

 

[gearheademporium]

If the power wires to each coil got reversed or otherwise incorrect, the ignition may not fire at the right time.

Did you replace the cam sensor at the same time? Or did the engine start normally after the cam sensor swap, but then won't start after replacing coils only?

Yah I did replace the cam sensor at the same time. Would it make any difference? I replaced it due the plug terminal had completely separated from the body of the sensor.

 

[gearheademporium]

I took pictures of the two wire leads going to each coil and if I recall there was a smaller-holed terminal and larger so you couldn’t mess that up. As for whether the wires went to the left or right coil, are they not labeled?

There were no labels on the harness. One of the removed coils appear to be OEM and the other was a Bosch, so I guess the PO must have replaced one of them before I took ownership. I'll try swapping the 2 wires to the smaller terminals later today and will advise the result. Thank you all for the input and guidance.

 

[gsxr]

Yah I did replace the cam sensor at the same time. Would it make any difference? I replaced it due the plug terminal had completely separated from the body of the sensor.

Measure the resistance of the cam sensor, compare old to new. What brand sensor did you install? I believe a faulty cam sensor can cause a non-start condition. Not 100% positive though, never tested this by disconnecting the CMP to see what happens.

There were no labels on the harness. One of the removed coils appear to be OEM and the other was a Bosch, so I guess the PO must have replaced one of them before I took ownership. I'll try swapping the 2 wires to the smaller terminals later today and will advise the result. Thank you all for the input and guidance.

I'm not sure it's a good idea to only swap 2 wires. With the coils removed, the wires usually hang in the air in place, due to the insulation hardening. If you didn't have to bend or yank on wires to make them fit onto the new coils, they may be wired correctly.

You said you replaced 1 coil at a time, but you must have removed all 4 wires (and both high voltage leads) at the same time, right? When I hear "one at a time", I think that means the other coil was still wired up and there was no way to mix up any wires.

 

[gearheademporium]

Measure the resistance of the cam sensor, compare old to new. What brand sensor did you install? I believe a faulty cam sensor can cause a non-start condition. Not 100% positive though, never tested this by disconnecting the CMP to see what happens.



I'm not sure it's a good idea to only swap 2 wires. With the coils removed, the wires usually hang in the air in place, due to the insulation hardening. If you didn't have to bend or yank on wires to make them fit onto the new coils, they may be wired correctly.

You said you replaced 1 coil at a time, but you must have removed all 4 wires (and both high voltage leads) at the same time, right? When I hear "one at a time", I think that means the other coil was still wired up and there was no way to mix up any wires.

The new cam sensor was a Hella brand; surprisingly, the wiring to the coils weren't all that stuff as most had stated. I'm getting ready to tackle this shortly and will report back in a couple of hours? Fingers crossed. Thanks again to all for the responses.

 

[gearheademporium]

Happy to report after rerouting/swapping the 2 wires going to the smaller stud on the coils, the engine fires up immediately. Note to self, need to label wires from now on. What misled me to incorrectly connect the wiring was I assume the wire coming out of the loom on the inboard side should go to the inboard coil but not so. I now need to put everything back and go on a test drive.

 

[nocfn]

There are few jobs I hate - 124 coil replacement, wire replacement and Cap/insulator ongoing care. Other than that, she is MX free

 

[emerydc8]

There are few jobs I hate - 124 coil replacement, wire replacement and Cap/insulator ongoing care. Other than that, she is MX free

A stubby 10 mm ratcheting wrench is a must-have for the coils.

 

[gearheademporium]

A stubby 10 mm ratcheting wrench is a must-have for the coils.

I found loosening the 3 ABS isolator mount bolts and gently propped the unit up offered good clearance to use a regular geared box wrench to remove the aft mount bolt for the outboard coil, as the forward mount bolt just needs to be loosened and left in place as a guide. I also had loosened and moved the horn out of the way.

 

[emerydc8]

I hadn’t considered loosening the ABS isolator mount bolts. Good idea. I dropped one of the coil side mount bolts into a black hole and it jammed against the ABS riser and inner fender. It was easier just to replace the bolt after an hour of fishing for it.

 

[gearheademporium]

Just wish to give a big thanks to you all who had generously offered helpful tips that I'd like to say my M119 now runs like a champ again. No more misfire, rough idle or lack of power. I was somewhat skeptical about the condensation buildup inside the distributor caps until I pulled them off to have a look. Yup, the pics are of my old caps. The right cap had a heavier moisture buildup than the left. I'll be replacing the insulator on the right due to 2 small hairline cracks in the near future.