More 3.2 Spark Problems

[IROC]

I spent about 4 hours today trying to figure out why my transplanted 3.2 doesn't have any spark during cranking.

A couple of things I found: 1. I had the 12V lead for the coil attached to a fuse that *didn't* have 12V during cranking. Unfortunately, fixing that didn't solve the problem. 2. Studying the wiring diagrams, I found that there was no signal from the ignition switch going to the DME. This was because I had never hooked up the yellow wire from pin 4 of the DME to the yellow starter circuit wire near the fuse block.

Now, I have 12V at the coil when cranking and the DME is seeing battery voltage thru pin 4 during cranking (just like it's supposed to) . Patting myself on the back I climbed in and turned the key.....

....nothing. Now I have *no* spark at all and my "hard starting but running great when it starts" problem has turned into a "no start and no run at all" problem.

Every single check in the Bentley manual checks out. The only thing that I haven't done is swapped DMEs out to see if that's the problem. Frustration has set in.

Any moral support or suggestions welcome....

Mike

[slakjaw]

check the DME relay it is a 2 poll relay both polls must close to get
coil pulse.


also check to see if you are getting injector pulse.

Kyle
71 911

[IROC]

Originally posted by slakjaw
check the DME relay it is a 2 poll relay both polls must close to get
coil pulse.


also check to see if you are getting injector pulse.

Kyle
71 911

How does the DME relay signal the coil to pulse? Via the DME? Best I can tell, the DME relay only controls the fuel pump and power to the injectors. I have a spare relay, but have not tried it as I checked *all* of the inputs to the DME (by removing the connector). Everything checked out per spec (even the inputs - both ground and voltage - that come from the DME relay).

Basically, everything on the car checks out per the manual, but I have no spark.

Maybe the coil is bad? How do I check that? The Bentley manual conveniently left out the table showing the resistances to verify the coil is OK. It says "Correct values are in Table b". Well, "Table b" is for "Reference or Speed Sensor Terminal Resistance".

Also, I have injector pulse - just no spark....

Thanks,

Mike

[tholyoak]

The circut essentially works like this

1) 12V switched source from ignition closes first set of contacts on DME relay providing switched 12V to the DME and 12V to the low tension side of the coils

2) Upon the DME detecting engine rotation (via the flywheel sensors) it sends a ground to the DME allowing the 2nd set of contacts on the relay to close, completing the circut to the fuel pump and allowing it to run.

3) The same signal that detects engine rotation also sends the signal to the coils to trigger the high tension side (spark) of the coils

So to check things out you should have 12V at term 30 at all times (batt voltage)

term 85 should be cnst grnd very important
term 85b should go to gnd when engine is rotating
(gnd signal from DME)
term 86 should be switched 12V that is present during cranking as I suggested before

term 87b should get 12v when engine is rotating
term 87 should be 12V out to the coil when ignition is switched on (1st set of DME relay contacts close)

I believe these to be correct but this is from memory while sitting here at work so you may want to double check with the factory wiring diagrams

I would start by checking your DME relay gnd (term 85) and double check your flywheel sensor to flywheel gap.

Todd

[IROC]

Todd,

Thanks for the things to check. I have primarily been using the factory wiring diagrams and the Bentley manual (which are both good), but these don't tell me the loic behind what's happening - only how things are supposed to be hooked up.

Thanks a million. I will check this stuff this afternoon.

One additional question - was I correct to connect the yellow wire (from Pin4 of the DME) into the starter circuit? This was not in the original instructions I used to install this engine, but according to the manuals, this port on the DME is supposed to see battery voltage during cranking. It wasn't before (I didn't have this wire hooked to anything) and the engine ran fine. Is that odd??

Thanks alot....

Mike

[tholyoak]

Mike

As I understand it you should have the following DME harness



Located at the bottom center is the part of the harness that interfaces with the chasis, it has been cut in this instance, hopefully yours is intact

There will be a large gauge red wire, this is to run to the battery, provides voltage to term 30 of the DME relay

There are 2 black wires, one runs to term 86 of the DME relay the other back to term 15 of the coil, both these need a 12V switched ignition source on the fuse panel, that is present during cranking

There is a red wire with green stripe, this is the 12V signal from the DME relay (term 87b) that should run to the fuse panel to a 25 amp fuse, and then to the fuel pump, this is the feed from the DME relay to the fuse pump

There should be a black/violet wire from the DME that is the tach signal that you will attach to the tach

There is an additional black wire that is the signal from the DME for the upshift light (pretty sure on this but not 100% positive) regardless you don't need it

Finally there is the yellow wire you speak of from term 4 of the DME. My understanding is it is a 12V source to the DME that is ONLY present in the cranking position on the ignition switch (pos 50), this voltage should not be present when the key returns to the run position. I'm not sure of its function as I don't have the pinout for the DME of a Carrera.

If all the above is correct, the DME harness should be properly integrated.

Todd

[IROC]

Todd,

Yep, this is exactly the way I have it connected...with the exception of the red/green wire. I am not using that as my fuel pump is wired up through the old CIS fuel pump relay/wiring and not the DME relay. My fuel pump runs when the key is in "run" and "start" positions. A friend of mine has suspected this as my problem, but I don't see how this could cause my absence of spark.

I am about to walk out to the shop and check the stuff you sent me earlier. My fingers are crossed.

Thanks,

Mike

[IROC]

Todd, et al,

I checked the stuff above and found that I do not have a ground signal from terminal 85b. Now best I can tell, though, this is irrelevant on my car as my fuel pump is not wired through the DME relay.

My problem is no spark, and contrary to the above post, the coil is not fed any signals from the DME relay. The only thing the coil sees is 12V from the fuse block (which I have, both during "run" and "start") and there is a green wire from pin 1 on the DME that sends a "pulsed voltage" signal to the coil. That's it - there is no connection with the DME relay. I still think the DME relay only powers the fuel pump and oxygen sensor.

Now, I would have to say that my potential problem is the a problem with the signal from the DME to the coil, but I just checked that and I have voltage during cranking. Now, the Bentley manual says I should have "pulsed voltage", but I simply saw the needle moving around during cranking, so it's hard for me to say if that is what I'm supposed to see or not.

I also checked my speed and reference sensors and their resistances checked out per spec. I have not checked these with an oscilloscope (yeah, like I've got one of those laying around...), but last week when the car was still running, it would start with the reference sensor connected, but it would not start with it disconnected, so I assumed it was functioning properly.

Help me!!! This is driving me nuts!!!

Mike

[tholyoak]

Mike

My mistake on the coil voltage, as I stated it was from memory at work, you are correct that the low tension side of the coil gets 12V switched ignition directly (as I correctly stated in the second post)
The DME sends the pulsed signal to the hight ension side of the coil via the green wire which is converted to spark

The fact that you are not getting ground is important regardless of the way you have the fuel pump hooked up (personally I would hook it up correctly, removing the red CIS relay from the circut, but that is a personal choice I guess. I'm pretty sure the DME cuts out the fuel pump as part of its rev limiting function

Anyway, if the DME is not throwing the ground to term 85b then the DME is not sensing engine rotation and will not send the ignition signal to the coil and would be why you have no spark and if the fuel pump were hooked up as it was in the 3.2 Carrera you would not have the fuel pump running

This raises the question why?
Is your battery fully charged and your starter in good shape?
The engine must rotate at some minimum speed in order for it to 'sense' rotation, if the engine turns too slowly it will not detect engine rotation, therefore you need a strong battery and starter. i also vaguely remember that if the voltage upon cranking drops too low due to current draw of a poor condition starter( 9.5 volts rings a bell but again just my memory here) the DME will also not send the ignition pulse to the coil.

I would start with the battery and starter and double check the sensor gap is 0.8mm

Good luck
Todd

[tholyoak]

Mike

After a little reading I found out what the yellow wire from the starter circut does

In order to send the ground to 85b of the DME relay the DME needs to see the rpm sensor producing pulses and starter cranking voltage, therefore it needs the yellow wire input in order to close the 2nd set of relay contact to power the fuel pump

If either of these signals are missing, the motor can
still be bump started as after approx. 1 second of rpm pulses and crank position pulses occuring together the fuel pump is switched on despite the cranking voltage being missing.
The fuel pump remains on as long as the rpm is above 300 rpm.

The way you have the fuel pump hooked up, this wouldn't have an effect.
This would explain why in your 'instructions' you talk about it is not hooked up. since using the CIS fuel pump relay to still power the pump obviates its use

Seems to still suggest that your DME is not seeing the pulses from the sensors

Todd

[IROC]

Todd,

I think I am aggreeing with your assessment of the problem. The DME is not sensing the rotation of the engine for some reason. I checked the reference and speed sensors and their respective resistances are correct. The engine started (albeit after some cranking) and ran perfectly fine up until Saturday when I started messing with it. One thing I found Saturday was that I had the 12V to the coil wired to a fuse on the fuseblock that only saw 12V during "run" and not "start". I assumed that was my problem, but after moving that one wire, I get no spark at all now. I am going to switch it back the way it was this afternoon and see what happens...

Obviously, the DME was sensing rotation prior to Saturday. My battery is in good shape (it's new) and the engine is cranking with plenty of speed.

Thanks for all of your help on this - figuring out this engine management system logic is difficult when you're just staring at wiring diagrams. I have learned alot over the last couple of days though.

Mike

[BGCarrera32]

Just curious, when you crank your engine is your tach flutterring/functioning?

[IROC]

Originally posted by BGCarrera32
Just curious, when you crank your engine is your tach flutterring/functioning?

I haven't noticed, actually. I will let you know this evening.

Hmmm....if it is, then obviously the DME is sensing some rotation, right?

Mike

[slakjaw]

dosent the dme have to see engine rotation to fire the injectors

you said you have injector pulse.

Kyle

[IROC]

Originally posted by slakjaw
dosent the dme have to see engine rotation to fire the injectors

you said you have injector pulse.

Kyle

Yeah, the thing ran fine (started hard) until Saturday when I started troubleshooting. The *only* real thing I have done that is drastically different than the configuration the car was in prior to this weekend was hook up the yellow wire (12V during starting) to pin 4 of the DME.

I'm going to disconnect that wire today and see if it starts. If it does, then I am just going to throw my hands up as that makes no sense.

Thanks for all the comments.

Mike

[IROC]

Originally posted by BGCarrera32
Just curious, when you crank your engine is your tach flutterring/functioning?

Just checked it - no tach movement. I think it is obvious now that either the DME is not sensing rotation (bad reference or speed sensor) or that the DME is bad and it is not telling everything else (tach, coil, DME relay) that the engine is rotating.

Coincidentally, I talked to the guy I bought the engine from about this problem last week and he told me that this same DME suffered a failure with very similar symptoms when he owned it. Car stopped running and would crank and crank without starting. It ended up being a broken solder joint in the DME.

Maybe this same joint failed again?

Thanks for everyone's help.

Mike