Alarm cause no-start?

[seningen]

Originally Posted by 911monty

I can understand your frustration. So to be clear.

Your car does not ever run (does crank) with battery in system.

Remove battery from system by removing neg clamp from batt post and jump using either the negative clamp or cable connection point on car, using what? a running car or another battery? (13.8 volts vs 12v.)? Either way the alarm module is still in circuit. But car runs every time?

Yes you understand it correctly --

If I use a jump pack, another battery, basically anything but a running car -- it will crank all day -- but not start. NOTE: this was not the case prior to my last track weekend. I did have a similar behavior once before last year, but I charged the battery and I didn't have the problem again. I subsequently replaced the battery and ran an entire race weekend last spring. Fired up many times over the summer, and ran two sessions this past DE weekend. I left the marker lights on and thought I had just run the battery down for my last session of the day, but that's when this mystery mode took over. Charged the battery, no dice. I've run across a case where you kill a battery so badly it creates a dead cell and won't allow you to jump it -- so thats when I did the jump without the battery and determined
it would run. I subsequently have tried 3 different batteries -- including a 1000CA AGM monster -- just to rule out any dumb battery issues.

So summary,
If I hook it up through jumper cables, it will turn ever so slowly, and on the 3rd or 4th revolution -- it fires right up and will run all day long. With or without the battery.
Note the SPB alternator drives ~14.2v.
Anything else, crank but no fire.

I have swapped out the DME/Immob/Key/Signal Transformer/Transponder Coil for a good set -- and no dice.
I've bypassed the kill switch, ignition toggle switch relay.

I have a new ignition switch in hand -- will test it this weekend -- but it ohms out fine, I also have a ignition toggle switch relay on order.

Yes it is a weird one.

I have crawled through the schematics and created this summary page for the main relays of interest.

I have access to the back of the trunk relays -- so I will be probing them this weekend. This will at least let me know if the DME is creating the proper ground paths for the MFI and Start Lock.

I will also be verifying as best I can to see how my SPB is wired relative to this diagram.

I know the DME is getting voltage as the MAF 12v and 5v references are correct.




Whenever I figure this out -- I will have way more intimate knowledge of the wiring and workings of my SPB than I ever really cared to know.

[911monty]

Mike, Since your car is cranking slowly but can run, I would think you have a power delivery issue either due to too small cables or weak ground. Does the car always crank slowly? This can be an issue since the starter is consuming all the electrical power the resulting voltage drop is insufficient to supply the DME to fire users like the fuel injectors, fuel pump and plug coils.

My suggestion would be to temporarily run direct cables from ground post to the engine block and one to the body near the DME. If still no go then a positive jumper directly to the starter then test.

[seningen]

Originally Posted by 911monty

Mike, Since your car is cranking slowly but can run, I would think you have a power delivery issue either due to too small cables or weak ground. Does the car always crank slowly? This can be an issue since the starter is consuming all the electrical power the resulting voltage drop is insufficient to supply the DME to fire users like the fuel injectors, fuel pump and plug coils.

My suggestion would be to temporarily run direct cables from ground post to the engine block and one to the body near the DME. If still no go then a positive jumper directly to the starter then test.

It is a 1999, all spec boxster run the 5.2.2 (97-99) DME (I think thats the number)
I have used a M535 (which is stock to my SPB) and a M531 immobilizer (with the appropriate key/dme that pairs with it)


Clarification:

Via battery or jumped -- she cranks fine -- to the point of 40psi of oil pressure -- cranking is not the issue.

It's only when Amps are limited by the jumper cables does the cranking become very slow -- but it seems as if the higher voltage is sufficient to make the difference because it fires -- at least thats the only way I can make sense of things.

I have checked both positive and negative cables. Even while cranking, I only see a 400mv drop from battery to starter (in battery mode) and a total drop of about 1.5V total (due to load on battery). This seems to be fairly typical.

Note when it does start -- it drops through the jumper cables to about 8.5v! But somehow it seems as if the initial voltage is the key -- but I don't know.

thanks for the suggestions tho -- I might have missed something... (ok clearly I have or I would have figured it out by now)


Mike