Intermitant Cutting Out

[avante101]

Hi
I have a 1987 2.5 8v n/a 944 which has developed a new way of winding me up. In general it starts easily, has a rock stead idle and runs really well. However at the weekend it cut out and would not re-start for 10mins, then it started and ran perfectly for 5 mins and then cut out again. At this point I called the recovery man and got trailered home.
When it cut out the revs would fail away until it stopped, pumping the accelerator made no difference. The first time it cut out I replaced the DME relay at the roadside and checked connections to speed sensors on bell housing and also connection to AFM on intake. All seemed okay.
When I got it home it started fine and ran perfectly...
I am planning to change the fuel filter as a precaution, and probably get new HT leads, coil and dist cap as I dont know when the were last changed. The coil especially looks quite old.
Does any one have any other suggestions?
Many thanks in advance.
Barnaby

 

[peanut]

if it generally starts ok and runs ok I would suggest you don't buy anything yet . Its a natural reaction to replace all of the HT stuff but that is rarely at fault.

I would suggest you check the fuel delivery and fuel pressure as it sounds more like a fuel delivery problem than a HT electrical fault . An HT fault would tend to give you coughs, stutters and possibly backfires rather than a sudden cut out

. If the FPR (fuel pressure relief valve )is not maintaining sufficient pressure in the fuel rail that would cause an intermittant cut out as you describe. Next time it cuts out pull off the the vacumn pipe from the FPR and check for fuel.

Also next time it cuts out open the fuel tank cap and check for sucking air which would indicate a blocked tank vent.

The other thing you could try is the 3xway DME bypass in place of the DME relay. If it then runs ok that would suggest a DME/ECU electrical/sensor fault.

 

[alwigley]

My guess would be that the engine had just reached operating temperature when it cut out, and restarted once it had a chance to cool which is the classic symptom of a fractured coil lead - normally the high tension side from the coil to distributor cap, but sometimes the low tension leads running to the coil can also get internal breaks in the cable which separate under heat, and return to normal when cooled down. Similar problems with plug leads can cause a car to start running on 3 cylinders, then recover once cooled down.

If you have access to a spare set of leads, I would try replacing them and see - there are a few nice chaps on this forum who can probably lend you a set for fault finding purposes as I gather they can be pretty expensive to replace. Also carefully check all connections to/from the coil.

Would second the other suggestions from Peanut, although I have had different experiences with lead failure. When you say that the revs fall away, is it gradual or sudden ?

Sorry Peanut - not trying to disagree with you (perish the thought of disagreeing with my elders.......[]), but have seen similar failure on various vehicles over the years. Does that earn me a cheeky young upstart footnote as well ?!

 

[pauljmcnulty]

Second for the FPR, heard of it more than once and it seems to be the last thing to get either checked or changed.

 

[peanut]

ORIGINAL: alwigley


Sorry Peanut - not trying to disagree with you (perish the thought of disagreeing with my elders.......[]), but have seen similar failure on various vehicles over the years. Does that earn me a cheeky young upstart footnote as well ?!

[][][] don't worry i'm not in my zimmer yet lol[]

.Intermittant faults are the worse...It could be anything really but it definitely sounds heat related doesn't it !

Long distance diagnosis is always a bit difficult and is very dependant on the op giving all the relevant details .

Pity we couldn't put together a Nationwide response team of PCGB forumers that could go to the aid of other 944 owners within their area.

 

[alwigley]

Have working replacement coil & FPR from trying to trace an intermittent fault on mine, so PM me if you need.

 

[avante101]

Thanks guys, next time it happens I will investigate the FPR. I am based in west cornwall and I have a good local indy who I should be able to borrow a coil and leads from.

 

[avante101]

Hi Again,
It has just done it again and left me on the side of a dual carriage way for 10 mins. It seems to be following a pattern now:
Starts and runs fine until I get to where ever I am going. If I stop for more than 10 mins or so it will cut out within 1 min of restarting.

I also noticed that when I was trying to re-start the tacho needle was staying completely still and not bouncing, so today I am going to pull the speed sensors off and test them as per Clarkes Garage.
Cheers

 

[Mike_Pollock]

Yes thst sounds like sensors - would chevk wires in particular as appears heat related.
Good luck
Mike

 

[peanut]

I had exactly the same thing happen on my Lux 10 years ago. Damned if i can remember what I did to cure it.
I'd make a frequent trip to the bank in the next town without problem .It would get me there then refuse to start 5 minutes later.

I'd have to leave it 15-20 minutes to cool down before it would restart every time.

It could be due to any number of things including the AFM but my guess is you have a fuel pressure /delivery problem.

Next time this happens I would :-
1. Check you have a spark when the engine is hot .
2. Check that the tacho needle jumps slightly on cranking.
3. Pull the spark plugs and check for fuel .. ?

Next I would fit a fuel pressure gauge to the fuel rail and start the car from cold .Note the fuel pressure when running. It should, from memory, be about 2.5bar (3bar for 944S2)
Run the car until hot then switch off and leave for 10 minutes or so to replicate the usual no-start condition.

Check the residual fuel pressure on the guage which should be at least 1.5Bar
If the pressure is lower theres your problem right there.......... lack of fuel pressure during hot start.
This could be due to leaking injectors or a fuel leak on the fuel line somewhere or a leaky non-return valve in the fuel pump or a leaky FPR (fuel pressure relief valve

Fit the 3x way DME bypass cable in place of the DME relay (see Clarks Garage Workshop manual) so that the pump runs continuously and try a hot start . If you still cannot get full fuel pressure on the gauge then you need to check all the places I mentioned for leaks.

If the fuel pressure is good and the residulal pressure is ok and you can smell fuel or have wet plugs then you could have an over-pressure situation when hot . This would most likely be caused by a sticking FPR valve. This would show on the fuel pressure guage if you have one fitted .
Alternatively the next time you have a hot no start situation try pulling off a fuel injector electrical connector to one of the injectors and starting the car . If it then starts the culpret is likely to be the FPR

 

[Neil Haughey]

I had a similar problem on my 968, wound me up for a long time as it seemed to have it for more than a year. Problem was when sat in heavy traffic or idling for a long time the engine would eventually start misfiring and if really bad cut out. In my case it was HT related, I had a duff lead so replaced all the leads then noted that it could still happen a little so replaced the coil. Car ran very different with the new coil and had/has almost telepathic throttle response since but don't know for sure if its cured.

The case above sounds different though.

 

[avante101]

The speed sensors tested OK on the multimeter, so I am inclined to agree with with Peanut that it is fuel pressure related. A check on on Clarkes backs this up as well.

Thanks guys, I hope this sorts it! Love the car but it has had lots of niggley problems which I think were due to it standing for a couple of years before I got it.

 

[pauljmcnulty]

FPR is very often the cause, just for some reason it tends to be one of the last things people look at. I'm not technical at all, and can only base this on what feedback I get, but I'd say FPR is as common as DME relay failure now. Rotor arm being close behind, along with leads.

 

[peanut]

There seems to be an ever increasing instance of no start problems with our cars and I'm rapidly coming to the conclusion that it more often than not is due to several factors including
1. lack of preventive maintainence
2. Age and general deterioration of components
3. Poor electrical connections due to oxidation of terminals
4. lack of regular use

A chain is only as good as each and every link.
My S2 has twice given me a no-start problem. The first time took me a couple of months to solve.

The Bosch Motronic Engine Management system is a complex system with a huge number of components and is not easy to fault-find despite some excellent guides at Pelican, Clarkes garage etc When i get the time I intend to draw up a comprehensive flow chart for diagnosing a 'no-start' condition on Bosch Motronic Engine Management systems which will also include some unlisted problems related specifically to component age and irregular usage plus some common intermittant issues and preventative maintenance suggestions.

 

[Mike_Pollock]

FPR is one of those things - years ago I had a Lancia HPE iE with the same Bosch system and when it went wrong the FPR was the LAST thing in the diagnostic book!
Mike

 

[AntB]

Had exactly the same simptoms on my 2.7 lux earlier this year. Failed on a dual carreage way and spluttered to a hault. Wouldnt restart immediatly - but give it 20 mins it restarted and then conked out again within miniutes.

Resolution - replaced both Speed Reference sensors (well GT One did) and she has been as good as gold since.

 

[morris944s2john]

Next time the car refuses to start for a while, do some diagnostics while it is in the fault mode.

Have someone turn the engine over while you check for a spark, if there is a spark at the plugs, then it may be a fuel problem, If no sparl, ignition.

If there is a spark at the plugs check for fuel pressure, then check the voltage going to the fuel injectors while cranking. No voltage means the CPU has an intermittent fault and need s replacing. This was the only time I have a break down and no start fault on my S2.

 

[pauljmcnulty]

FPR is one of those things - years ago I had a Lancia HPE iE with the same Bosch system and when it went wrong the FPR was the LAST thing in the diagnostic book!

Perhaps it was never expected that the FPR would be an issue when the book was written? Much the same way that the service schedule doesn't mention the cam chain on the S2, or the fact that the plastic pad gets brittle after 20 years.

I was thinking about this tonight. I've not had an enquiry that had the obvious answer "replace the DME relay" for at least a year now. It used to be almost a weekly conversation. I guess that people have either changed theirs, or carry a spare, based on the years of nagging. Wish it worked at home. [&o]

Peanut, a diagnostic guide aimed at the cars in their present form would be great. Faq is ready and waiting. []