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txhokie4life

Crank but no fire

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Spec boxster race car

 

push to start

 

will crank but not start

 

only time it starts is if jumped from another car w/o battery in system

3 different batteries

by passed kill switch, other switches

 

when it cranks, it’ll get to 35-40psi, so starter works.

 

duramatic talks to ecu 

 

immob looks fine (no corrosion)

 

supply and gnd connections look good (tight and clean)

 

if immob unhappy

what what would be symptoms?

 

No spark?  No fuel pump? No fuel injector?

 

does no tach bounce mean anything .. that’s a big hint on 944’s

 

thx,

 

mike

 

 

 

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No tech bounce likely means the crank position sensor is bad but if that:s the case, jump start should not have helped. 

 

The immobilizer is likely fine because otherwise the DME won't allow the starter to crank at all (assume you did not rewire the starter circuit).

 

Have you checked for sparks and fuel pressure?

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23 hours ago, Ahsai said:

No tech bounce likely means the crank position sensor is bad but if that:s the case, jump start should not have helped. 

 

The immobilizer is likely fine because otherwise the DME won't allow the starter to crank at all (assume you did not rewire the starter circuit).

 

Have you checked for sparks and fuel pressure?

 

Changed cps... no delta

 

checked all fuses and relays

 

since it’s a race car with push to start, it might have been wired differently

 

tried to check spark but my test light didn’t fit, attempted wire to close to block, no spark, but that could be bad test setup

 

get fuel kit tomorrow and retry spark test

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Since it's not stock wiring, the typical troubleshooting steps (that assumes certain DME behavior) may not help.

 

You may want to check if you get +12v on your MAF and O2 sensor with key ON engine off (not sure what that corresponds to your system). If not, your engine electronics are not even getting power, which would explain the non bouncing tach.

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Btw, may want to recheck fuses C1 to C4 and E1.

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Thanks -- I will check the MAF VDD

 

I checked all relays and fuses last night -- all good.

 

I have 12.x V at the 40Amp fuse in the back.

 

I get a 430mv drop from battery terminal to starter post while cranking (which seems normal).

 

hoping to do a spark and fuel test tonite.

 

I spoke to the builders of the car -- they suggested that the IMMOB must be happy or there would be no cranking -- so it seems they didn't mess with that any.

 

Mike

 

Edited by txhokie4life

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I use this tool and it works very well on our engine with the limited clearnace of the coils. There are cloned versions that are a bit cheaper. https://www.amazon.com/Waekon-76562-Quick-Variable-Sensitivity/dp/B0021UPE58?crid=W1J35BKWCACE&keywords=cop+spark+tester&qid=1537915077&sprefix=cop+spark&sr=8-1&ref=mp_s_a_1_1

 

Is it cable throttle or e-gae? If e-gas, you may want to do an e-gas recalibration. Then next is still to check for sparks and fuel presaure.

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Will order that -- very nice (and a bit pricey - but worth it)

 

Brought a mechanic buddy of mine out to help -- basically reproduced and confirmed earlier findings.

 

We did attempt to check for spark -- his tool didn't fit well either -- thus ordering above.  It did not appear to have spark during cranking -- but we saw this we think

before it fired up by the other cars alternator route.

 

We did determine that if you remove the immobilizer -- this car still cranks (but does not fire).

 

We found where they stuffed the pill.  Thinking maybe the ignition switch or the little box that detects the rfid info is unhappy.

 

Will grab a spare and try that -- Also sourcing a dme/immob/pill to do a quick swap and test.

 

Mike

 

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BTW, I mentioned the MAF sensor and O2 sensor +12v power because those are the easiest to access in then engine bay (very easy to disconnect and don't affect cranking and firing at all). It may be worthwhile to hook up the multimeter to them and see if they get power during cranking. If not, then the engine electronics basically does not have power to them at all. I've developed the following troubleshooting steps for a stock 996/Boxster to check the two main circuits.

 

With key ON engine OFF, check if the main MFI relay supplies power to the DME and sensors:
o    Unplug MAF and verify pin 2->+12v pin 4->+5v

 

With key ON engine OFF, check if the Ignition relay supplies power to the coils, injectors, and O2 sensors
o    Unplug any O2 sensor and verify any black wire has +12v
 

 

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Went to check Maf voltage but it had a security torx bolt ... really 😞

Didnt have that kit with me

 

swapped dme/immob/key/ring/transponder. .. no change

 

checked spark with waekon... nada

 

ohmed out ignition switch... good, but not 50 which is start pin, however i suspect that’s intentional with push to start.

 

orderded an ignition switch anyways... they’re cheap and good to have as backup.

 

there is a 4 pin connector in the lights switch wiring bundle that’s dangling...  gray, yellow/white, brown, black/yellow if I remember right

cant find home for it, or in wiring diagrams

 

i do have supply voltage on the 40amp fuse

 

Mike

 

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No need to remove the MAF sensor! Just disconnect its electrical connector and check the pins on the connector like I described. If no voltage there, you will need to trace the relays below the parcel shelf.

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That connector wouldn't budge -- thus I went to the forums and they suggested removing the MAF itself then accessing the clip that allows you to unplug 😞

 

I did separately check the relays on a bench and they were fine -- but will check the MAF anyways.

 

M

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Ah I see. Is the 40amp fuse the one for the SAI pump? If so, it's connected directly to the battery +ve terminal so having 12v there really doesn't tell you whether the DME gets power.

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Ok, 

got access to the maf

equiv of Keon-ignition off

have 12v and 5v ref

 

all 3 relays in the back are tested good

the two #1 & #2 are warm, and have 12v on 30 with relay out.

same for the black relay.

 

ordered ignition switch, should be here Thursday.

 

mike

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Any error codes on the DME?

MAF having voltage means the DME has power. Is it easy yo get to any O2 sensor connector? If it is, you also want to check for +12v on any black wire. The coils and the injectors are on the same circuit.

 

Any tach needle bounce while cranking?

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Have you verified the Waekon tester on another running car?

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8 hours ago, Ahsai said:

Any error codes on the DME?

MAF having voltage means the DME has power. Is it easy yo get to any O2 sensor connector? If it is, you also want to check for +12v on any black wire. The coils and the injectors are on the same circuit.

 

Any tach needle bounce while cranking?

 

No codes

When I try to do live values, I was getting software errors and no valid values.

I did get basic info like running hours, overruns, DME #, etc.

I was unsuccessful to get to connect when it actually was running off the Cayenne -- I can try that again.

 

No tach bounce

 

I should be able to get to the o2 sensors.

 

Haven't confirmed Waekon, I'll try that as well.

 

Wish there was a LED or other indicator that said -- yes I am happy with the immob/key pill etc.

 

I'm waiting on the ignition switch.

 

Mike

 

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On a stock car there is a starter interlock relay that is powered by the DME that activates ONLY if the DME and immo are happy. Since your car had been rewired, not sure where that wire is connected to now. Alternatively you can find out the corresponding DME pin.

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Posted (edited)

Looks like it's pin 66 of the DME, "Actuation start lock". It supplies GROUND voltage (close to 0v) when the DME and immo are happy.

Or pin 85 of the start lock relay - relay #7 - yellow/violet/brown wire.

 

See the diagrams in the last post here.

Edited by Ahsai

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Thank you for your help -- I REALLY appreciate it.

 

I was fiddling around with those relays last night and noted one pin at 1V.

 

I was running a bit blind -- (knowledge wise) so I wasn't being meticulous about what was what -- next time I'll make some notes.

Believe the other pins were at 12v -- so that suggests it was energized -- now was that the DME or some wiring hack, who knows.

 

I'll add it to the list to confirm.

 

Mike

 

 

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Posted (edited)

Been crawling through the wiring diagrams.  This should be able to give me a game plan for probing.

I have access to the backside of the top 3 relays easy enough -- should be able to get

some good diagnostic information from them.

 

<corrected diagram below>

 

Edited by txhokie4life

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You may want to retrace your diagram above. Pin 85 of the ignition relay should be ground and pin 30 should be connected to fuse C2 directly. Fuel pump relay pin 86 should connect to start lock relay pin 86.

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11 minutes ago, Ahsai said:

You may want to retrace your diagram above. Pin 85 of the ignition relay should be ground and pin 30 should be connected to fuse C2 directly. Fuel pump relay pin 86 should connect to start lock relay pin 86.

 

Correct -- I can't even read my own notes 🙂

 

Basically MFI closes (87) to supply power to the Start Lock, Ignition and Fuel Pump and other relay coils.

 

Of course it will be interesting to eventually figure out how my SPB is wired.  But at least I know how the system should work.

 

I will remove the diagram above and include this one -- so no one following is led astray.

 

Mike

IMG_8051.JPG.thumb.jpeg.d43748cf53b4170c4ee2c940da8bbdae.jpeg

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Yes, it looks good now and agree with your explanation as well.

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