where'd the spark go??

#1

My car has decided that it no longer wants to spark. Actually, it had sporatically decided it did not want to start on a few occasions in the past, but would always start after sitting for a while (I guess it just wanted to prove that it was the one in control)! This had only happened a few times, and I hadn’t yet found the problem. I also hadn’t "done anything" to the car that would have caused this, I don’t think. However, it now will turn over but will not start - at all. I’ve traced this down to a lack of spark (fuel pump runs fine & injectors are injecting).

After performing the diagnostic tests in the Bentley, everything seemed to check out ok (except for the DME, which the tests do not cover). The coil gets voltage at post 15 when the ignition is on, the ground is grounded, but the Q&D spark plug test (connect ignition wire to spark plug, hold outer electrode against ground, turn key, watch for spark) was a failure. I went ahead and replaced the coil and pulse sensor, but this did not solve the problem. My rather limited automotive knowledge would lead me to believe that a DME failure would be the most likely culprit. Oh, the cap, rotor, and wires are all < 6 months old, passed visual inspection, and showed proper resistences based on tests in Bentley.

So, to test this I was wondering if anyone would happen to have an extra motronic unit they could send my way to see if this solves the problem. If so, we can work out a price. I’d of course pay postage either way. Please let me know - thanks much!

Also, if anyone has any other ideas as to what might be causing this please let me know that as well.

Thanks much in advance.

Steve

Post edited by: sdais, at: 2006/08/08 17:21

#2

Steve, I’ve got a 153 ECU sitting around. I’ll send it to you and you return it to me at Infineon, cuz you are gonna get this fixed so we can race!

Ship to the same address I sent the calipers?

EDIT: I think you checked pretty much everything. I would check to see that the main relay is working (I think the fuel pump relay next to it is the same kind so just swap and see if you get spark.), but I think if your coil is getting power, then it is probably working fine.

Post edited by: traqrat, at: 2006/08/08 17:57

#3

traqrat wrote:

[quote]Steve, I’ve got a 153 ECU sitting around. I’ll send it to you and you return it to me at Infineon, cuz you are gonna get this fixed so we can race!

Ship to the same address I sent the calipers?

EDIT: I think you checked pretty much everything. I would check to see that the main relay is working (I think the fuel pump relay next to it is the same kind so just swap and see if you get spark.), but I think if your coil is getting power, then it is probably working fine.<br><br>Post edited by: traqrat, at: 2006/08/08 17:57[/quote]

Yep - same address. Calipers were in great shape, by the way.

The main relay powers the fuel relay, which powers the fuel pump, so for the fuel pump to be pumping the main relay must be relaying. I would think…

Steve Dais - the anti-mechanic

#4

Make sure you check the wire that goes from the #6 spark plug wire, across the front of the engine and plugs in to a connector buried on the drivers side. This can cause no spark, also the crank reference sensor can do this, look down on the pass side and see the cylindrical device mountet by the crank pulley by the toothed wheel…this wire can rub and get shorted out and she no go anymore…
Another good spare part to have handy

#5

nasaregistrar wrote:

[quote]Make sure you check the wire that goes from the #6 spark plug wire, across the front of the engine and plugs in to a connector buried on the drivers side. This can cause no spark, also the crank reference sensor can do this, look down on the pass side and see the cylindrical device mountet by the crank pulley by the toothed wheel…this wire can rub and get shorted out and she no go anymore…
Another good spare part to have handy[/quote]

Well, unfortunately the stand-in ECU didn’t do the trick.

Sean - my reading of the Bentley is that the wire that attaches to the #6 plug wire provides timing for the fuel injectors, so the spark plugs would still spark if there was a problem here but the injectors would not inject. I may be wrong. Nonetheless, I tested for continuity & found that two of the three posts in the connector have continuity but the third doesn’t seem to go anywhere (I forget which posts had continuity). I then peeled back the rubber bootie on the connector that this plugs into to see if all three posts were connected to wires - the two outer posts had black wires (one much larger than the other) and the middle post was yellow (same guage as the smaller black wire). Does anyone have a more complete wiring diagram that would show where these wires go?

I also replaced the reference sensor last weekend to see if that was it, but to no avail.

I’m starting to run out of possible culprits, aside from the wires, cap and rotor (all of which are < 9 months old and seemed to pass the resistence tests ok). Anyone have any thoughts on what it could be? Or any tests that might help me find the answer? Thanks much!

Post edited by: sdais, at: 2006/08/15 14:40

#6

sdais wrote:

[quote]nasaregistrar wrote:

[quote]Make sure you check the wire that goes from the #6 spark plug wire, across the front of the engine and plugs in to a connector buried on the drivers side. This can cause no spark, also the crank reference sensor can do this, look down on the pass side and see the cylindrical device mountet by the crank pulley by the toothed wheel…this wire can rub and get shorted out and she no go anymore…
Another good spare part to have handy[/quote]

Well, unfortunately the stand-in ECU didn’t do the trick.

Sean - my reading of the Bentley is that the wire that attaches to the #6 plug wire provides timing for the fuel injectors, so the spark plugs would still spark if there was a problem here but the injectors would not inject. I may be wrong. Nonetheless, I tested for continuity & found that two of the three posts in the connector have continuity but the third doesn’t seem to go anywhere (I forget which posts had continuity). I then peeled back the rubber bootie on the connector that this plugs into to see if all three posts were connected to wires - the two outer posts had black wires (one much larger than the other) and the middle post was yellow (same guage as the smaller black wire). Does anyone have a more complete wiring diagram that would show where these wires go?

I also replaced the reference sensor last weekend to see if that was it, but to no avail.

I’m starting to run out of possible culprits, aside from the wires, cap and rotor (all of which are < 9 months old and seemed to pass the resistence tests ok). Anyone have any thoughts on what it could be? Or any tests that might help me find the answer? Thanks much!<br><br>Post edited by: sdais, at: 2006/08/15 14:40[/quote]
Steve you are right about the #6 wire thing…it is for injector sequencing
have you replaced the main relay…the white one on the L inner fender well.
scary thought but pull the cap and make sure the rotor is going around…

#7

I’ll pull the cap / rotor tonight & check the parts out again. Aargh!

If post 15 on the coil is getting voltage this couldn’t be caused by a faulty ignition switch I wouldn’t think?

#8

You said that there is voltage at the coil,but you may want to double check the coil ground as my repositioning of the ground resulted in rust and a falty ground and intermittent misfire. Heck, you’ve changed the crank sensor (another story in electronics troubleshooting),so I can’t think of any other bases that you’ve not covered. Regards, Robert Patton p.s. It wouldn’t even turn over if the kill switch was faulty, right?

#9

Robert - I wouldn’t think I’d get anything at all if there was a problem with the kill switch. The coil is showing a good ground with the ignition on but nothing with it off.

Does anyone know of a way to test to see if the pulse sender is actually sending a pulse? The Bentley only gives the ohm test, which doesn’t necessarily prove that it’s sending a pulse.

#10

Do you have an oscilloscope?

I think you’re at the point where you need to dig into the ECU and watch signal traces to see what isn’t happening.

Did you do any recent work (even the most insignificant work) on the car before this happened?

#11

Steve - I’m not sure I would give up on the ECU yet. Do you have access to another? If not, I would be happy to send you my spare 173 unit, which I tested and is in good working condition.
Ed

#12

Steve - one more thought - don’t mean to be insulting, but I had a break in continuity in my coil wire from the distributor recently that resulted in no spark. It was an easy, quick fix, but took a while to diagnose. Ed

#13

I guess it doesn’t apply here but here’s something worth mentioning. Robert had a broken crank sensor wire at Road Atlanta and said that he has seen it happen before.

Another thing to put in the spares box.

Carter

#14

edavidson wrote:

[quote]Steve - I’m not sure I would give up on the ECU yet. Do you have access to another? If not, I would be happy to send you my spare 173 unit, which I tested and is in good working condition.
Ed[/quote]

I sent him a known working ECU and that didn’t fix the problem. :frowning:

#15

Carter wrote:

[quote]I guess it doesn’t apply here but here’s something worth mentioning. Robert had a broken crank sensor wire at Road Atlanta and said that he has seen it happen before.

Another thing to put in the spares box.

Carter[/quote]
Cobetto did too, back at Shenandoah. The routing of this wire is behind the pulleys and it is supposed to clip into a plastic holder that snaps into the timing belt cover. After all the years and timing belt jobs, the clip is usually broken or missing and the cable gets loose and gets rubbed by the pulley. It then shorts to ground. It is a high voltage component that triggers the ignition system based on the crank position.It references off a gap in the toothed wheel.
It would be a good spare part to have for sure.

#16

Thanks to everyone who’s chimed in.

I pulled a plug (again) last night to verify that it still wasn’t sparking (with the outer electrode grounded to the engine). No spark. I did smell gas in the cylinder, so I can check off that the fuel injectors are in fact injecting.

I also turned the key for 1/2 second with the cap off to verify that the rotor is rotating - it is.

I then went back and re-performed all of the tests covered in the Bentley manual relating to the ignition system. The cap, rotor, & wires all had continuity & resistence consistent with specs. The coil also had proper resistence, & voltage at post 15 and at the top post and ground continuity with the ground post with the ignition on. Second, I also re-performed all of the tests relating to the fuel & main relays - all good there. Third, I re-performed the tests relating to the inputs into the DME - all good here also.

I printed out the wiring diagrams this morning relating to the ignition system, which aren’t filling me with any bright ideas. I think I may have to suck it up & take it in to have a ‘real’ mechanic give it a shot (I just play one evenings & weekends).

traqrat wrote:

[quote]Do you have an oscilloscope?

I think you’re at the point where you need to dig into the ECU and watch signal traces to see what isn’t happening.

Did you do any recent work (even the most insignificant work) on the car before this happened?[/quote]

I have no oscilloscope, though I’m sure I could have great fun with one!

#17

sdais wrote:

[quote]Thanks to everyone who’s chimed in.

I pulled a plug (again) last night to verify that it still wasn’t sparking (with the outer electrode grounded to the engine). No spark. I did smell gas in the cylinder, so I can check off that the fuel injectors are in fact injecting.

I also turned the key for 1/2 second with the cap off to verify that the rotor is rotating - it is.

I then went back and re-performed all of the tests covered in the Bentley manual relating to the ignition system. The cap, rotor, & wires all had continuity & resistence consistent with specs. The coil also had proper resistence, & voltage at post 15 and at the top post and ground continuity with the ground post with the ignition on. Second, I also re-performed all of the tests relating to the fuel & main relays - all good there. Third, I re-performed the tests relating to the inputs into the DME - all good here also.

I printed out the wiring diagrams this morning relating to the ignition system, which aren’t filling me with any bright ideas. I think I may have to suck it up & take it in to have a ‘real’ mechanic give it a shot (I just play one evenings & weekends).

traqrat wrote:

[quote]Do you have an oscilloscope?

I think you’re at the point where you need to dig into the ECU and watch signal traces to see what isn’t happening.

Did you do any recent work (even the most insignificant work) on the car before this happened?[/quote]

I have no oscilloscope, though I’m sure I could have great fun with one![/quote]
does the car have the many button OBC? there was some theft deterrent doo dah built in to that thing that would prevent the car from starting.

#18

your symptoms sound like how the car behaves when you jumper two specific wires together in the diagnostic port to get the engine to turn over without actually starting. Don’t know what to suggest beyond that but thought this might trigger an idea.
cheers,
bruce

#19

WE’VE GOT SPARK!

Corroded terminals on the ignition switch were the problem.

#20

Wow, that really is the last place one would check. When are you heading into Sonoma? I’ll be going up sometime Friday and setup.