Sensors that can cause turn over but no start
 

I'm wondering if someone knows all sensors that must be functional for the stage 2 MPI & Ignition to come on when trying to start a 996. I've swapped the ignition switch electronics and Crank position sensor. I know the Cam sensors could do this but I'm wondering about all sensors that could cause this. The ECU & Immobilizer have been sent to The ECU doctors and got a clean bill of health. I can turn on the stage 2 Fuel Injection systems with Durametric and hear the fuel pump & a few things in the back running, but when the key is turned it's not coming on. (Starter does & I appear to have spark) I've checked the fuses involved & relays (13 in the front)(1,2,7 in the back), plus the fact that I can turn it on with Durametric kind of rules out no power. I think all 4 O2 sensors may be bad but didn't know if the pre-cat ones might cause the ECU to not turn on Fuel & Ignition because it needs a reading to calculate the mix. Does anyone know if you unplug all 4 O2 sensors would the car still run with a default setting. To clarify, I don't hear the fuel pump at all when the key it turned to on & it does turn over but doesn't seem to even try to fire up. I don't hear fuel injection components coming on but I do get spark at the plugs. Starting fluid didn't fire up either. 1999 996 C2

Any thoughts welcome and appreciated.

Put a fuel pressure guage on the rail and let us know what the pressure is. U can rent the kit from most autoparts stores. U need fuel, air and spark for the engine to run. If u know u have spark then it must be fuel or air....if u have all 3 then its not timed correctly.

The o2s have nothing to do when startng. The computer will go to a defualt value if unpluged and through a code.

Check to make sure you have not crossed up the bank 1 Cam Sensor and the Crank Sensor.......I have seen this a dozen times and it kicks everyones azz

They are right next to each other and will plug in....even though they are color-coded black and white...it is not as obvious as it seems when they are dirty and happens a lot...

When the engine is in the car it is a pain in the azz to test the wiring because these connectors are buried back next to the AOS...so it kicks some azz untill you finally get in there to test the wiring..

Since it won't start with starting fluid, that eliminates FUEL, ....so check these connectors NEXT...

Thanks for the O2S info, I’m sure there’s only residual pressure from running the pump via software. I have ran a long fuel line from the pressure side of the pump so I can see it pump when turned on with Durametric & confirm when trying to start no fuel is pumping, not that I just don’t hear it running.

Thanks, I read about the connectors being swapped beforehand so was very careful to get it right when I did it. Bumper cover, heat shields & mufflers are off the car so it was easy to see and swap out.

Check to make sure you are getting 12v to the injectors, coils, MAF, Vario-cam solenoids, and change-over valves....

They should all power up when the key is turned ON...They get power through some relays and fuses....IF no power, check the fuses first...

Timing?
 

Can someone with a 996 & Duramtric tell me what you see under real time values for Ignition Timing? My ECU is still not happy & won’t turn on the fuel injection when trying to start.
My Durametric shows 78°, not sure if that’s advance but sure it shouldn’t be 78° either way, maybe timing is what the problem is…

Thanks for any thoughts

Please show a picture of the screen that shows 78° . It Sounds very much like a (intake) temp value, though then you wouldn't have written ° but F, I guess.
I have no such picture myself but perhaps searching the pictures in the many durametric threads on here gets you the info you're looking for.

Yes, the temperature values are in Celsius. I will connect the Durametric today and post screenshots of what I’m seeing. Thanks.

https://cimg5.ibsrv.net/gimg/rennlis...31b7f20d85.jpg
https://cimg9.ibsrv.net/gimg/rennlis...4a7c4a4b5a.jpg
https://cimg5.ibsrv.net/gimg/rennlis...16ebb99f94.jpg
https://cimg0.ibsrv.net/gimg/rennlis...935ac02334.jpg
https://cimg3.ibsrv.net/gimg/rennlis...3a05aff38b.jpg
https://cimg4.ibsrv.net/gimg/rennlis...4082107db4.jpg

Durametric won’t report crank angle without engine running. The screen shows 78, that number has no real value concerning timing.

when you try to start vehicle what reaction does your tachometer exhibit ?

Thanks. I don’t see the needle bumping. I have swapped out the crank position sensor though. I’m wondering if the flywheel is rusty or maybe even so rusty that the dual mass part is fused maybe it could cause this. Also I see spark on plug#3 when cranking, haven’t looked at other plugs. Seems to be ECU not sending ground to the fuel pump relay when cranking. But if I tell ECU to turn on the fuel pump it does it.

Ohm test the cps wires back to the dme to check for continuity. Its very weird that u r getting spark but do rpm jump at the dash. May have missed it but can u see rpm with the duremetric when cranking?


Also have u put a fuel pressure gauge on the systen yet? Most autoparts stores rent them for free.

When you see spark, then ecu knows crank position, I.e the cps is working. No other way around it.
Jump the fuel pump relay by connecting terminals 30 and 87 in the relay and see if the engine will then run.
If not check if the injectors receive +12V when ignition is on (haven't re-read the thread to see if you've done that already).

DMS rusted solid won't cause what you describe

I am not sure if engine starts and runs in limp mode when either crank or camshaft position sensor fails. It needs both for sequential injection but with only one of the two signals batch injection would work. It is just a question whether this is implemented on the M96/DME 5.2.2 or 7.4

I have jumped the FP relay, it does come on but still no start. That has me thinking some critical sensor may not be working. The Durametrc seems useless to diag what may be failing. If I go to actual values/ RPMs to see if it shows RPMs while trying to crank it won’t even turn over. I was hoping it could show some realtime errors when it is turning over.

At the FP relay I have 12.4 volts on 30, when I turn key on I have voltage at 86, but no ground on 85 to activate the relay. But when I tell the DME to turn the pump on it does ground 85 and the pump runs. So I think wiring is fine but DME not happy about something & won’t send ground when trying to crank.

Thanks again for suggestions.

I will check injector voltage, been putting it off due to how difficult it is to reach them.