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Strange 944 Running/ No Start Issues....

 
Old 02-20-2019, 07:24 PM
  #61  
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I would recheck your speed sensor distance to the flywheel . It should be just under 1mm (+=0.3mm ) which is a very tiny gap to get right .
A larger gap would definitely cause the symptoms you describe of starting and immediately cutting out
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Old 02-20-2019, 07:36 PM
  #62  
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Originally Posted by peanut View Post
that is not the most accurate gauge on a car but the most important thing it is telling us is that the engine is not cutting out due to the fuel system suddenly losing fuel pressure .

Good we are getting somewhere.
We can probably assume that the injectors , the fuel pump and the non return valve are not leaking . Same goes for the FPR and damper and the fuel system generally.

Because the car is actually starting and running for a few seconds we can also assume that the DME relay the ECU , the crank position sensor , injectors , and secondary ignition system are also all working ......otherwise the car would not start and run.

So we are now looking for something that would cause one or more of those components to stop working as they should .
Well what I can say for sure is the car starts every single time Iíve tried it. No more endless cranking which is what I was experiencing before. It is worth noting that even though the car only runs for a few seconds, it doesnít run rough or smoke at all. It runs very smoothly and when it dies, it doesnít stumble and die, it dies ineediately. So what would stop it from continuing to run so suddenly?
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Old 02-20-2019, 07:39 PM
  #63  
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I've just told you the most likely one ...the speed sensor . How sure are you that you set it at less than 1mm distance when you replaced it ?

just to explain..The DME will turn off the fuel pump if it does not get a 200 rpm signal from the speed sensor.

The starter circuit overrides this at first and just turns on the fuel pump for starting but if the ECU does not then see a continued 200+rpm from the speed sensor then it will turn off the fuel pump.
Nearly midnight I'm hitting the sack
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Old 02-20-2019, 07:51 PM
  #64  
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Originally Posted by peanut View Post
I've just told you the most likely one ...the speed sensor . How sure are you that you set it at less than 1mm distance when you replaced it ?
the first thing I did was made sure that the sensor could actually touch the flywheel without being gapped properly,
to do so I took a very small piece of painters tape and stuck it on the speed sensor and with the bracket loosely bolted in I inserted the speed sensor and tightened the Allen key bolt that holds it. I then moved the bracket as far down as it would go. If the speed sensor touched the flywheel there should have been some dirt on the painters tape which there was.

I removed the speed sensor and then glued a .091mm thick washer (it was the only thing I could find as close to .08 as possible) to it and again installed it into the bracket fully tightening the Allen key. I moved the bracket as far as it would go and then tightened down the bracket. I then removed the speed sensor and removed the washer and the all of the residue from the glue, and reinstalled the speed sensor.

Thats how I gapped them.

Did I screw something up?

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Old 02-20-2019, 07:55 PM
  #65  
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no that sounds like a perfect job to me !

So if the ECU is seeing the correct engine speed we are going to need to look elswhere.

Just as a simple test you could get someone to start the car whilst you have your ear next to the fuel pump. See if the fuel pump cuts out at the moment the engine dies . If it does it tells us that the ECU is shutting down the fuel pump and injectors for some reason and I suspect it is something to do with the cold start system
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Old 02-20-2019, 07:59 PM
  #66  
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Originally Posted by peanut View Post
I would recheck your speed sensor distance to the flywheel . It should be just under 1mm (+=0.3mm ) which is a very tiny gap to get right .
A larger gap would definitely cause the symptoms you describe of starting and immediately cutting out
I think you hit the nail in the head. The car does idle a little high but I figured that was due to the throttle plate being misadjusted. Sounds like my gap is just a bit too big.
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Old 02-21-2019, 02:31 PM
  #67  
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Originally Posted by peanut View Post
no that sounds like a perfect job to me !

So if the ECU is seeing the correct engine speed we are going to need to look elswhere.

Just as a simple test you could get someone to start the car whilst you have your ear next to the fuel pump. See if the fuel pump cuts out at the moment the engine dies . If it does it tells us that the ECU is shutting down the fuel pump and injectors for some reason and I suspect it is something to do with the cold start system
My apologies peanut I just saw this post today. As soon as I get a chance Iíll have someone fire up the car and Iíll take a listen to the pump. Iíll try to get a good video too maybe that can help demonstrate just how instantaneously the car dies.

I recorded a video yesterday to actually see how long the car runs before it stalls by watching the time on the playback. It literally runs for 2 seconds.

Also I did have a friend help me smoke test the intake yesterday and Iím happy to report that no smoke came up from the intake, or any vacuum lines. But I wonít rule out the possibility of unmetered air entering somewhere.

I donít want to sound overly excited but she fires every time I crank her over which is a promising sign. Iím optimistic that after this last bug is sorted sheíll be back on the road. Iíll report back once Iíve verified whether or not the pump is shutting down.
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Old 02-21-2019, 03:12 PM
  #68  
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that is really good news Jacob because as I said previously that has to mean that everything is functioning exactly as it should or it would not start up like that.

I still think it is the speed sensor that is at fault. If the ECU doesn't see 200+ rpm engine speed it will immediately shut down the fuel pump.
This is why i keep saying to you FIT the 3 wire bypass in place of the DME relay. A 3x wire bypass will force the pump to run and should over-ride the pump shutdown by the ECU

If the engine then runs normally you'll know that it is the speed sensor gap or a break in the wires somewhere between the sender coil and the ecu.
Do you actually know how to make and fit a 3x wire bypass ? if not I can send you a picture how it is fitted .

I still think you need to check the speed sensor gap and check continuity of the wires and connectors from the speed sensor back to the ECU connector

IMPORTANT. do not under any circumstances use a multimeter on the actual ECU terminals to test anything. The ECU works on tiny voltages and a multimeter could send a voltage through some voltage sensitive circuits and damage a component.
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Old 02-21-2019, 08:13 PM
  #69  
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Post a link to the video
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Old 02-22-2019, 02:25 PM
  #70  
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Okay guys! Back with results of the 3 wire bypass test.

With the fuel pump jumpered using the bypass the car cranks but does not start. The pump does turn on and the pressure does build.
With the relay reinstalled afterwards the car once again starts right up.

Heres the video:

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Old 02-22-2019, 02:44 PM
  #71  
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I'll jump on the Peanut bandwagon and blame some sensors;

This gap looks pretty good, doesn't it??


It caused this when fully reassembled:

I did everything including use the digital oscilloscope at the DME to ensure the pulses were there.
Replaced the sensor and ... all fixed.

Edit: Video at 8 seconds shows the car dropping to ~210 RPM. If it dropped lower -- it wouldn't have started at all.
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Old 02-22-2019, 02:50 PM
  #72  
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Ugh hahahahaha. Iíll take a definitive answer over not knowing Iíll at least say that much. Is there anyway I can do this without having to take the intake completely apart again?
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Old 02-22-2019, 02:57 PM
  #73  
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Originally Posted by Jacob AbuKhader View Post
Ugh hahahahaha. Iíll take a definitive answer over not knowing Iíll at least say that much. Is there anyway I can do this without having to take the intake completely apart again?
Remove the intake?! No no. I popped in new speed and ref sensors without removing anything -- just a step stool and leaning in from the side.
You may have to un-cable tie some things and shuffle them around.

I remember cutting my hand up really good on some of the cable ties and stuff in there, but it should be doable. The sensors anchor to the top of the engine with a removable clip - once that's out of the way, it's almost straight down. Just put a towel over the fender so you don't leave scratches..
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Old 02-22-2019, 03:01 PM
  #74  
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Originally Posted by indes View Post
Remove the intake?! No no. I popped in new speed and ref sensors without removing anything -- just a step stool and leaning in from the side.
You may have to un-cable tie some things and shuffle them around.

I remember cutting my hand up really good on some of the cable ties and stuff in there, but it should be doable. The sensors anchor to the top of the engine with a removable clip - once that's out of the way, it's almost straight down. Just put a towel over the fender so you don't leave scratches..

Ahhh got it. Will do. Was your sensor bad? Or did you just have to readjust the gap?
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Old 02-22-2019, 03:06 PM
  #75  
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Originally Posted by Jacob AbuKhader View Post
Ahhh got it. Will do. Was your sensor bad? Or did you just have to readjust the gap?
I fought with the gap for about a week. Everything on scope looked at min tolerance. ( I think I was looking at Clark's garage for reference measures.. can't find the pics. )
Sometimes rotating the sensor seemed to help - but you can't screw it down that way as it doesn't line up with the hole. With no screw, as soon as I'd move the car, it'd move out enough or rotate back causing it to stall out, etc.
When I replaced it - no readjustment needed. Plug and play fix. No more flutter. Starts every time.
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