Stringy

Hello Guys,

My 1999 996 C4 suddenly lost power yesterday on my way home from work.
I was on the motorway, around 65mph, suddenly no power - no response to accelerator.
No lights that I remember, but then I was getting to a safe place.
Car is transported and pushed into back into my garage.
When I try to start, just a glimmer, but immediately stalls.
Recently idle has been dodgy when up to temperature, but that lately improved, if that could be a clue.

I've had a search of the forums, but can't find how I should start to diagnose.
I have a Foxwell Porsche specific scanner.

Can anyone advise, so I don't waste too much time.
Thanks in advance.

Stringy

Some more info, after using the scanner:
DME faults
P0130 O2 sensor ahead of cat bank 1
P1115 O2 sensor heater ahead of cat bank 1
P1119 O2 sensor heater ahead of cat bank 2
P0154 O2 sensor ahead of cat bank 1

Also, on the dash, the oil level check is counting down from a very large number 58:41 - see pic.

De Jeeper

Ignore the oil pressure counter. It does dump things with the motor not running.

Looking at your faults i would check 3 things.

1. Pull the air box and do a through inspection of all the wiring of the o2 harness and main harness. Mice love to eat it.

2. Pull the front o2 sensors and see if she runs. It almost looks like the cats r cloged because those codes should not prevent the car from running.

3. Check your fuel pressure. Testers r free to borrow from most local parts stores. Actually do this 2nd as its easier then pulling the o2 sensors

U did say motoway....not that it matters but r u accross the pond?

Your car has a throttle cable so it should be a little easier to diagnose. Other numbers we may need r short term fuel and cam deviations if u have a good scanner.

Stringy

Hello De Jeeper.
Yes, I am in the centre of civilisation known as England.
Thanks for taking the time to respond.

The car is a C4, so fly by wire. My scanner shows me pedal positions moving, and throttle potentiometers moving with pedal too. I can't hear any moving, but I presume that means the throttle is opening ok.
I could check if I removed the air box.
I wonder if the fuel pressure can be accessed by my scanner. I engaged some fuel pump relay and heard some gurgling from the front.
Let me give you some 'actual values' - I have no idea what they mean.
O2 sensing bank 1, 1.00
ditto for bank 2
O2 sensor voltage ahead of cat bank 1, 0.4V
ditto bank 2, 0.45V
Cat temperature 50 degrees C (it is around 7C today)
O2 senor resistance ahead of cat bank 1, 0.0 Ohms
O2 sensor heat ahead of cat bank 1, 4.37V
ditto bank 2, 4.36V

Whatever has happened has caused DME codes on faults on both banks - what could be common?
DME relay? (Where is that on a cabriolet, I wonder?) Do the readings above look plausible.

Thanks so far...

Mike Murphy

I know fuel pumps often fail on restarts, but maybe that’s the first thing I would check here (fuel pressure). Sometimes the fuel pump issue isn’t a locked rotor, but instead, the fuel line comes off the pump.

Stringy

Thanks Mike.
Would such a fuel pressure loss cause those DME codes?
I'm fairly sure those codes were not present when I scanned a little while ago chasing my low idle problem.

De Jeeper

Low fuel pressure can cause a lean condition which in turn can set an o2 code. Usually the heated o2 code is set at startup so its a little weird. I did have a issue with an intermintant o2 heater curcuit that cause an sai pump fault but thats not whats happening here.

Fuel pressure itself is not monitored and must be tested with with an external gauge. There is a schrader valve in the fuel rail that is capped. Thats where u hose screws in.

We can rent/loan these kits at most parts stores for free.

https://shop.advanceautoparts.com/p/...ce=1&gclsrc=ds

Mike Murphy

I ran out of gas last year and had all sorts of codes - misfires and such, and then a check engine light stayed on for a good day after. I don’t think they were cat codes though.

Stringy

Thanks guys.

Yesterday I checked that the throttle was opening - it did.
I am wondering too, if I ran effectively out of fuel. The gauge says 1/2.
I disconnected - waited - reconnected the battery and it still read half.
Is it true that the level is predicted below a certain point.

Re the fuel pressure. What should the pressure be?
I can see the fuel filter, where is the schrader in relation to that please?

I mentioned that when I enabled the final? fuel relay via scanner, I heard a load of gurgling from the front.
Is that normal? I have read of problems with the in-tank fuel lines perishing.
I had in mind to add a few additional litres of fuel, in case the tank is actually empty or a broken tube only picks up above a certain level.

I'm picking up on your comment that O2 sensor codes should not prevent the car from starting.
If I sprayed some 'engine start' would that prove anything fuel wise.

Thanks again for comments so far.

De Jeeper

If it fires in ether then its a fuel issue. Orange cap is the schreader valve.

https://rennlist.com/forums/996-foru...-pressure.html

Stringy

The extra couple of litres of fuel has not made a difference.
I have a can of engine start, which I'll try tomorrow.
Then I'll look for a way to test the fuel pressure; for that I'll probably have to buy something..

Stringy

An update today.
When I topped up the fuel yesterday, I tried to start it two or three times - is that enough for the fuel to get to the right places if I had run out?

Today with a spray or two of 'engine start', it started, and to my surprise continued to run unaided.
Could it be that the extra fuel did fix it, but I didn't try for long enough?

I'll try removing a more fuel than I put in, and see if it stops again.
Is there a good way to remove fuel? I have a very thin pipe and diaphragm pump which I have used successfully in the past - but it is slow.

Do 996 fuel gauges go wrong? Could the fuel tank pipe perishing thing cause it not to supply fuel below a certain level?

What I don't want is an intermittent problem.

De Jeeper

Its a simple test....your fuel pump is failing or u have a bad in tank hose. If u dont want intermintant failures find the root cause and fix it. I highly doubt its the gauge unless u added about 18 gal of fuel u were not empty.

These pumps work well for empting the tank.

Mike Murphy

The tank calibration is a thing for sure. There is a procedure for it, and it’s not super easy.

One thing you could do is fill the tank completely, then disconnect the battery for 5-10 mins while shorting the cables cables together (no battery).

The downside of doing this right now is that if you fill the tank, now the tank needs to be drained to fix any fuel pump issue.

Then other thing to think about is if your car has an external fuel filter or not. My 99 C2 has one outside the tank on the car, but many cars have a filter built-in to the fuel pump inside the tank. If yours is external, you could replace the filter and see how much junk or fuel comes out. But I suspect C4S might have the filter in the tank.

Stringy

Hi Mike, my fuel filter is external to the tank. I can see it near the coolant expansion tank.
I'm struggling to find a video to show me how to get to the fuel pressure test point.
I know De Jeefer provided a picture, but I don't know how to access it.

My fuel removal via filler with thin pipe failed to pick up any fuel.

Guys, do let me know if you think I'm wasting my time with my fuel level hypothesis.
If not I may try draining 5 litres via the fuel filter.

p.s. For the C4 with its front transfer box, is the fuel tank access under the battery?