Non-Start - Again

[Bow Runner]

The randomness of this car is incredibly frustrating.

I had a non-start problem a a few months ago and would not start for a month then randomly started and began starting fine again (starts easily and runs smoothly), and has done so for the next three months until last night.

I had a non start issue a few months before that when after a good run it then decided to not start when I was miles away from home late at night. In desperation I kept turning her over and finally it fired and started initially a bit rough, but after 30 seconds was ok. God that was a nervous run back home.

It's gone again.

I have tacho bounce up to 4000
I have spark from the king lead
I have tried pulling one of the injectors off to test the charge to the injectors - No joy
I have tried the foot to the floor method when starting and it does fire for a moment then cuts
I've checked all vacum lines in the fuel system
The DME relay is brand new (bought last time it stopped working)

Any ideas?

 

[Monkeythree]

Blocked fuel filter? Try disconnecting the hose from the tank and removing and cleaning the little in-tank filter before the pump. Then refit that along with a new main fuel filter cannister. Treat it as a mini fuel system service and you've got nothing to lose.

 

[Masher]

Clearly a spark and fuel are needed.
Fuel pump working? Fuel arriving at the injectors? Air lock preventing fuel flow?
Electrical earths OK? DME relay (try the old and the new - just because it is new does not mean it works), ECU operating OK (you'll need better jelp than me on how to test)
After this others have found things like crank sensors to be a problem.
Hope something from someone fuels your thoightsand gives a spark of inspiration []
Cheers
Mick

 

[Bow Runner]

I'm thinking it is a faulty fuel pump that periodically sticks.

A blocked fuel filter would mean poor running but the car runs fine normally.

Kicking myself I didn't get the fuel system looked at once it was running again the last time.

If I can get it running again I'll put it in for a fuel pump replacement and filter change. I wanted to put it in for a gearbox oil change anyway.

Annoying. I hate non-running issues as there is no cheap way of getting it to a garage.

 

[Bow Runner]

Update

Checked and tested the fuel pump fuse and all ok
Swapped the DME - no change
Pulled the vacuum line from the FPR and no fuel in it. Possibly a mild smell of gas if you smell the tube but no obvious smell

Looked at the web on diagnosing a fuel pump failure and they do say the car would normally exhibit signs of a wearing out fuel pump before it goes such a cutting out, surging, rough running. I've had none of these.

Looks like I'm going to need to get a fuel pressure gauge to test the fuel rail.

 

[pse_SC]

Have you tried changing the fuel pump relay?

 

[pauljmcnulty]

Have you tried changing the fuel pump relay?

There was a spate of FPR failures a few years ago, it is a weak point.

 

[Bow Runner]

I have tried replacing the DME relay which is the fuel pump relay.

I bought a brand new one before and this did not resolve the problem before. The one I replaced looked pretty new as well so the previous owner must have bought one. I have swapped them back and forth and no difference.

 

[Masher]

I think i hear FPR referrin to fuel pressure regulator. Not that i would know one of these if it hit me on the head []

Cheers
Mick

 

[Waylander]

by the fuel filter under the back of the car is the power lead for the fuel pump, this has a push together connector that gets wet and corroded inside, i had a no start issue on my 68 and it was the connection at fault,

unplugged it squirted it full of switch cleaner plugged it in and out loads of times gave a big squirt of WD40, been fine ever since

 

[peanut]

ORIGINAL: Bow Runner

I'm thinking it is a faulty fuel pump that periodically sticks.

A blocked fuel filter would mean poor running but the car runs fine normally.

Kicking myself I didn't get the fuel system looked at once it was running again the last time.

If I can get it running again I'll put it in for a fuel pump replacement and filter change. I wanted to put it in for a gearbox oil change anyway.

Annoying. I hate non-running issues as there is no cheap way of getting it to a garage.

its very unlikely to be the fuel pump or filter at fault. If the fuel filter was blocked it wouldn't flow sometimes and not others. Same with the fuel pump really.. they either work or not .Fuel pump and filter is one of the most common items indies and owners replace followed by distributor cap, rotor, plugs and leads and finally the crank speed & position sensors . None of which usually need replacement.

As a random intermittent fault it is far more likely to be a bad electrical connection or possibly sticky injector solenoids if the car hasn't been used recently. or a malfunctioning DME relay.

I would recommend that you check the easy things first that don't cost anything.

If you make a 3x wire bypass and the next time the engine doesn't start fit it in place of your DME relay it should supply power to your ECU, Fuel pump, Injectors, sensors .This will bypass your DME relay and eliminate the DME relay being at fault.
You should now be able to hear the fuel pump running continuously. You can also check that you now have 12v at the injectors .

If the engine still fails to start then I would suggest that you check the fuel pressure relief valve FPR and do a fuel pressure and leak down test which is very straightforward and and easy job to diy.

It wouldn't hurt to remove clean and remake all of your earth connections listed in the electrical section of the Haynes manual especially around the bulkhead area and under the dash near the fuse relay box which earths the DME relay and ECU .check all the immobiliser connections also as Jon says they are the most common cause of non starting cars towed into his garage .

 

[ChasR]

Do you have a spark at the plugs or not with them earthing to the engine? If you were closer I have a device which can check for this.

If that is working my next port of call would be a fuelling issues. I should not suggest this but does the car start with Easy Start? If so you almost certainly have a fuelling issue, but it is best to check for this first before taking a lottery as to what part will fix it.

 

[Bow Runner]

ORIGINAL: Waylander

by the fuel filter under the back of the car is the power lead for the fuel pump, this has a push together connector that gets wet and corroded inside, i had a no start issue on my 68 and it was the connection at fault,

unplugged it squirted it full of switch cleaner plugged it in and out loads of times gave a big squirt of WD40, been fine ever since

I'm going to check this out as its certainly a new area to look at.

 

[OLD_ian]

When mine had it's long standing hot start problems it was the crank sensors. After replacing those it had a very occasional problem, but replacing the wires leading to the sensors fixed it properly.

 

[Masher]

Distributor cap, leads and coil are areas to consider. Relatively cheap and the root of many an issue.
Mick

 

[Bow Runner]

Well I have now checked the distributor and that is ok. I have also checked spark to the plugs and that is ok.

Given that the car does show signs of firing after being left for a while I think it's most likely to be the Fuel Pressure Regulator.

I think I'll get a new one anyway as the one I have looks original.

 

[George Elliott]

Good luck with that Bow Runner,

Just looking at the irregular nature of the symptoms, I would immediately think electrical. Intermittent electrical problems are quite common on these cars if not used constantly in my experience.

The areas are earth connections as mentioned above, AFM connector (vital signal source to ECU) Crank sensors (ditto). All easy to check, cost nothing to check.

The reason for the irregular behaviour is heat/cold, damp, battery voltage, corrosion resistance in old electrical connectors, all affecting the situation in varying levels, some outside the threshold where it works, some-tmes not.

Lovely spec btw

George
944t

 

[Bow Runner]

Still no progress.

I was going to buy a fuel injection pressure tester but I am aware that the testing point on the porsche fuel rail is an unusual size. Would any normal testing kit fit this or would I need to get an adapter if they are available?

I know lindsey racing do a fuel pressure gauge that fits onto the rail and includes the correct adapter. No real need to have one on there permanently but if its the only way of getting a correct adapter.

I'm going to try the DME bypass and also do some testing on the connectors. Any guidance on what to do. I have a multimeter.

I tried the car again yesterday and it starts to fire then dies. Then no firing at all.

The car ran fine the day before it failed to start and when it runs it runs with no issues. Quite spritely in fact.

 

[peanut]

Fitting a DME relay bypass is a diagnostic test.Its not a random suggestion .
Once you fit the bypass the results of that test can narrow down the search and possibly pinpoint the source of the problem.

We cannot see your car and are totally dependant on the information you provide us with []

There have been numerous detailed past threads about carrying out fuel pressure tests if you do a search.
All you need to do is remove the threaded nut from the test point (take care to retain the large ball bearing ) and push a bit of garden hosepipe on the fuel rail spigot. Shove a £5.00 tyre pressure guage in the other end and tighten them up with some jubilee clips.

You are looking for around 2.5Bar for a 2.5 lump and 3.0 Bar for a 3.0Lt.
If it holds that pressure whilst cranking the engine then check how long it holds that pressure when you switch the engine off. (check the leakdown figures in your manual . )
Its not rocket science . Any fluid or air pressure guage will do that will fit in the end of a bit of garden hose.You do not need to buy expensive guages and 2Kg of brass fittings ,pipe and adaptors!

 

[Bow Runner]

Right a DME bypass and fuel pressure test later I think I've identified the problem. No fuel pressure whatsoever. It's either a duff fuel pump or some failure in power to the fuel pump.