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txhokie4life

Crank but no fire

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All voltages on MFI/Start Lock/Ignition/Fuel Pump relays seem to make sense.

 

I also double checked all fuses, both in the kick panel and the main current distribution box.

 

Next is to check Fuel Pressure -- I didn't have the right connector for the kit I bought (murphy's law).

 

Will also check all crimped supply connections for a potential loose wire.  Didn't notice anything from before.

 

I have not swapped ignition switch yet.

 

But as I have assembled and disassembled over the debug, the starting even while jumping was getting worse, 

and not will not start at all -- but the car still cranks fine.

 

Mike

 

 

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Um, sounds more like fuel pressure to me. Still no tach bounce? Have you tried the waekon tester again? If there are sparks but still not fired up, it's very likely fuel related.

If no sparks, given you have the correct voltage on the start lock relay (means immo and DME are happy) and no code, the only thing I can think of is CPS related.

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Posted (edited)

Read the tea leaves wrong -- got a fuel pressure gauge on the car this morning.

 

No fuel pressure KEON or during Cranking.

 

I have a fuel bypass switch to empty the fuel tank.  With that switch i get nearly 4 bar.  So the fuel pump is good.

 

I was getting 12v on 30, 85, and 86 with 87 as 0v on the fuel pump relay.   But I was reading that incorrectly when I said things were good.

 

With the switch, I get ~12v on pin 87, and the fuel pump runs.

 

I ran out of time -- but now I need to go back and revisit some assumptions and revert back to the original DME and 

recollect some data.

 

Mike

 

Edited by txhokie4life

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When should fuel pump relay be running?

 

keon, engine off as well as during starting

or only if CPS gives signal?

 

i was thinking its fuel injectors and spark controlled by cps (indirectly)

 

Btw, I’ve replaced cps

thx,

 

mike

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On a stock 996, the fuel pump (relay) will be run for only about a second when you turn the key to the last position before crank and stays there. Then once engine is running, the pump will keep running.

 

Any sparks when cranking?

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I still haven't found a car with coil on plug that I can access to test on.  So I'm not sure, but I don't think so.

 

I do note that if the pump even came on for a second -- it would pressurize the gauge and it would hold for awhile -- and this is not happening.

 

Wish I could querry the DME and have it tell me what it thinks is going on.

 

Mike

 

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Yes, even running for one second it would produce fuel pressure.

 

Can you tell if the DME activates the start lock relay while cranking? If so, the DME and immo are happy. Of course it still needs the on-going CPS signal to activate the coils/injectors/fuel pump.

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4 hours ago, Ahsai said:

Yes, even running for one second it would produce fuel pressure.

 

Can you tell if the DME activates the start lock relay while cranking? If so, the DME and immo are happy. Of course it still needs the on-going CPS signal to activate the coils/injectors/fuel pump.

 

The StartLock relay is hardwired to VSS.  I might have to figure out if I can tap into the loom to observe the exact signal.

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2 hours ago, txhokie4life said:

 

The StartLock relay is hardwired to VSS.  I might have to figure out if I can tap into the loom to observe the exact signal.

Yeah, pin 66 of the DME. Should supply ground if it's happy.

  • Thanks 1

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Sorry for being offline -- 

 

I had several beach homes in the line of fire of Hurricane Michael -- so I have been a bit preoccupied.

 

I did get the DME sent off and tested -- and its fine -- for good measure -- I had the immobilizer delete performed (it wasn't cheap -- but its a race car and I wanted

to in theory reduce the source of other potential issues).

 

I didn't get a chance to check pin 66 before I shipped it off.

 

I did put the DME back in post modification -- no joy.  No fuel pressure, and when I do do the fuel pump bypass, I get fuel pressure, but no start.

 

I'm headed back out tonite to continue debugging.

 

While I replaced the CPS -- I have not seen tach bounce while trying to start.  I don't know how subtle the bounce would be -- on my old 944, it was fairly obvious.

 

I'm tempted to try yet another CPS, they're not THAT hard to swap out.

 

This is where I wish I had not sold my Boxster S -- I could pull the fuel pump relay -- and see just how much the tach bounced.


Mike

 

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The tech bounce should be obvious. I'd say the needle raises about 1/8"~1/4" from the rest position.

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Definitely not the case -- will have to figure out why --

 

I did replace it -- maybe the new one is bad too (unlikely but possible), or there was some issue with the connector/line/etc.

 

Mike

 

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It's entirely possible you have a wiring issue. There are 3 connections - the sensor plug, the X59 connector in the engine bay and the DME connector. When the senor is unplugged, you may want to check for continuity between the sensor socket and the DME pins.

 

You should also ohm out the sensor.

Edited by Ahsai

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Back at it again tonite

 

no tach bounce, no fuel injector firing (mood light)

 

hooked up scope to CPS at dme

i get life.

 

going to noodle on that and game plan for this weekend.

 

one possibility is how does airbag system normally talk to ecu?

 

im 99% sure this has been deleted and circumvented... maybe something there has come loose?

 

mike

 

D06508FA-54F7-4162-B4D8-B996192451AF.jpeg

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Nice meter :)  Is that ~60v peak to peak? The cranking speed looks good. The broken tooth signal is there as well. How about cam sensor signal? 

 

Your airbag theory sounds interesting. Is the thinking srs issue will make the dme disable the engine? The srs system should talk to the dme on one of the K lines. If I rip out my srs module, I expect the engine should still fire up although I never tried.

 

No sparks either, right? Can't think of why the dme is not firing. If the cam sensors signal is not there, there should be error codes.

 

 

 

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Borrowed the o-scope.  Looks like ~8v p-p

 

yep missing tooth looks right and decent crank speed.

 

i haven’t been able to verify no spark ... but I’ve got no fuel injector firing 

 

I was thinking along the lines if not SRS, maybe crash sensor. Roll over sensor, or something like that.

 

i’m running out of ideas....

 

Need to crawl through schematics some more.

 

i guess my only saving grace to my pride is this is proving to be a royal pita and has many folks stunped

 

mike

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1 hour ago, txhokie4life said:

Borrowed the o-scope.  Looks like ~8v p-p

 

yep missing tooth looks right and decent crank speed.

 

i haven’t been able to verify no spark ... but I’ve got no fuel injector firing 

 

I was thinking along the lines if not SRS, maybe crash sensor. Roll over sensor, or something like that.

 

i’m running out of ideas....

 

Need to crawl through schematics some more.

 

i guess my only saving grace to my pride is this is proving to be a royal pita and has many folks stunped

 

mike

I thought it was ~8v p-p too but the scope indicates a 10:1 probe is used.

 

Crash/roll sensor makes sense. If no fuel injector firing, there will likely be no sparks too.

Can you scan the SRS system for fault codes?

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2 hours ago, Ahsai said:

I thought it was ~8v p-p too but the scope indicates a 10:1 probe is used.

 

Crash/roll sensor makes sense. If no fuel injector firing, there will likely be no sparks too.

Can you scan the SRS system for fault codes?

 

Not sure the car still has the SRS (since it's a spec boxter)  --- I'll need to drag the Durametric back out and see what I can talk to -- I did at one point, but I've forgotten.

 

Looking at the schematics -- clutch interlock could come into play as well -- even though the car has been converted to push to start and starter is not controlled by DME.

 

Will have to check that as well

 

Edited by txhokie4life

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Yes, pin 66 as mentioned in one of my posts above. That will tell you if the DME is ready to crank the starter and start the engine.

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On 11/29/2018 at 9:17 PM, Ahsai said:

Yes, pin 66 as mentioned in one of my posts above. That will tell you if the DME is ready to crank the starter and start the engine.

 

Pin 66 is =12v, so it’s not happy

 

Pin 63 remains at 12v, not happy either.

 

The dme was tested fine, and was programmed/modified to ignore the immob.

 

 

mike

 

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