Mr_John111

Hi all

Looking for some guidance regarding tests I have carried out so far and any suggestions for possible further tests or solutions.

Ok the story so far:

Got the car, was sluggish to start after being stopped for a while. But it eventually started and ran well.

Investigation of the fuel rail (removing the plug) led to no fuel coming out so took this to mean either FPR faulty or check valve in pump allowing fuel to bleed away. Replaced both and full correct fuel pressure now seen and fuel leak down is not a problem now. Gauge confirms 30+ psi even after standing overnight.

Great!

However.... This now leads to a new problem, the car cranks, starts properly (and will rev) but after 10 seconds dies. After dying it won't start until left for a while (or bizarrely if the DME relay is swapped- I have 2, one brand new and one that appears to work ok)

I guess/sense that somehow the DME is not getting a signal it needs from somewhere within the 10 seconds and is shutting down the injectors (in an 8v it needs a signal from the speed sensor?)

I search the Internet and find out about 'tach bounce' which I'd not noticed before ( but to be fair I wasn't looking for it) but it was not happening so that makes me think of speed and reference sensors (or to be more accurate the crank sensor and the hall sensor on the cam as this is a 16 valve engine like an S2)

My rudimentary electrical knowledge gets the multimeter on the crank sensor plug and sees resistance in the correct range between 2 pins. However when plug reconnected could not see the same resistance at pins 47 and 48 on the multi plug into the DME ECU. (Possible break in the loom?)

With the hall sensor, when I went to the connection I found it brittle and cracked with wires exposed so remade the plug. This did now lead to tach bounce (progress??) but still the same result, will dies after a few seconds.

When I checked the pins of the hall (cam) sensor I get no resistance between any of the pins. (But I can find no 'specs' for this ) is the sensor faulty and would this cause my problem.

Have a friend with an oscilloscope who I will ask to come round to see if there are signals coming from each sensor.

If it is not this has anyone any suggestions?

Thanks in advance

John

Mr_John111

Having remade the connection for the cam sensor the car now doesn't start at all.

I'll try disconnecting it and see if it starts.

Perhaps it's worse to have a faulty sensor attached than not?

Can anyone confirm that there definitely should be some resistance measured between the pins on the sensor ( in the same 600 - 1600 ohm range as per the other sensor.

If that I the case then the fact I can find no resistances at all confirms that the cam sensor is broken? Do you agree?

Cheers

John

AlphaOmegaPower

I think your DME relay was the original problem from what it reads like.

Mr_John111

So why when I swapped DME relay for a brand new one it made no difference? (and still doesn't?)

John

951bo

Id b looking at an alarm as being the problem. Clarks garage has the bypass if you'd want to try it.

Mr_John111

Thanks, I'll have a look but I don't think it has a factory fitted alarm (there is an after market Cobra alarm but it also appears disconnected)

Does anyone with a 16v engine and a multi meter mind checking the cam hall sensor for a resistance? I get nothing on any of the pins ( and think this is the route of my problems)

Thanks in advance

John

odonnell

Is the sensor getting 12v and a ground? That's what 2 out of the 3 wires are for it.

Mr_John111

Ok so I changed the hall sensor on the cam and the problem has subtly changed.

Starting from cold the car will start and idle.( seemingly indefinitely rather than cutting out after 10 secs) I did get a whiff of fuel from the exhaust - too rich?

But now it won't rev, it gets bogged down and dies.

When it gets warm it then won't even idle smoothly.

My thoughts now are TPS and temp sensor. If temp sensor, presumably when warm it is just running too rich?

Mr_John111

When it gets warm it then won't even idle smoothly. It will start but only if you floor the throttle and then it will run happily at 3-4000 rpm

joes

The hall sensor even unhooked will not effect the starting of the car. It does effect sequencing of the injectors and gives the DME info from the knock sensors for timing retard for knock. from the previous posts looks like you have fuel. the easiest way to check the flywheel pick up is with a 1.5V LED. Connect at the DME or at the end of the plug at the firewall. That is probably where the problem is.

odonnell

Another sensor it could be is the O2 sensor. I'd put my money on the DME coolant temp sensor though, if it's never been changed. It sounds like a classic case of way too much fuel enrichment.

Mr_John111

Thanks for the suggestions, in my own mind I have eliminated the crank sensor, the car starts and runs. If I disconnect the crank sensor it dies. I have the right resistance across the pins as per clarks garage and hooking an oscilloscope shows a wave form.

The temp sensor was low cost so have bought one, if I connect it without disturbing the old one, that should confirm one way or the other?

I.e if the old one is broken in such a way that it is causing too much enrichment then the new one doesn't need to read any temp to avoid this?

As a UK car I'm not sure if it has an o2 sensor?

John

ramius665

With the camshaft hall sensor disconnected or non-functioning, the DME will pull 5* of timing but the engine will still run. The S models don't have a variable potentiometer for the TPS but it's possible there is a heavily worn spot just off the idle switch which is causing problems with the DME seeing throttle input. I'm not sure what the DME's default response is to a lack of throttle input but I imagine it would be a return to idle map and not the WOT map. Replacing the DME temp sensor is a good way to ensure the DME is using the cold start idle enrichment but if it fails it should cause the DME to run in full-enrichment all the time. I would check the TPS for functionality to confirm it is properly working.

odonnell

Even with the idle switch not engaged, the car will still hold a solid idle. For a while I intentionally did this when I had a 1983 DME installed... because the idle switch would cut fuel when suddenly engage and the engine would cut out for 1/2 a second which was annoying.

UK cars won't have an O2 sensor, correct, must have missed your location.

Mr_John111

RESOLVED

Turns out it was a fuel delivery problem.

The hose from the tank to the pump was collapsing. Fuel pressure was fine but not volume.

Replaced hose with new one from Porsche (had a certain stiffness ) and all is well

Thanks for all of your suggestions

John