fan928

Hi, (my first post)
I have owned my 1984 928 S2 4 speed auto for near on 20 years and just would like to say that I have appreciated all input from fellow 928 owners over this time. The posts have been extremely helpful to me over the years and enabled me to fix a number of issues, many thanks to all. Now its my turn to ask if anyone is able to offer any advice to fix a specific problem that is really challenging me.

The problem: In October 2017 my car would suddenly cut out now and again. I could find no cause and in fact the car has not had a problem since then, runs just fine. However, yesterday I got the same issue out of the blue. I know it was 29 degrees C but I don’t think that has a bearing on the problem as when it happened a couple of times in October is was cold.

The sequence of events is below to try and explain exactly what happened.

Drove to some shops which is approx. a 25-mile round trip. Started no problem, some traffic along the way and then onto the motorway and gave it a quick blast. No problem, perfect pickup, acceleration etc. The oil OK, water temp throughout the journey just below half way so fine, volts OK. No misfiring or any other issues, perfect.

Returning there was some mild traffic but just kept moving. Approaching a roundabout close to home there was a traffic jam. Slowly moved with the traffic, no problem. Got to my turn to enter the roundabout and it started to hesitate briefly (experience warns me that it is about to die). To try and stop it dying into park and I pumped the throttle a few times to get it to pick up the revs. Looked at the rev counter and the revs were hovering between 200 and 300 and suddenly it cut out. Switch Ignition off and straight back on and it started immediately, rev it a few times to 2,500 / 3,000 no problem, responded at each push of the pedal, great. Backed my foot of the throttle to allow the revs to fall to approx. 500 / 600 and put it into drive. Immediately the revs dropped down and it was struggling to keep turning over, pushed the throttle to try and bring up the revs up. It continued to hesitate but at the same time tried to move forward a few inches (felt like an invisible hand was holding the car back). Moved forward a couple of inches with the engine barely trying to keep going and stopped. Into Park, ignition off and immediately back on, start first time, revved smoothly again to 2,500 / 3,000. Into gear to move off and the revs started to die again, move a couple of inches and stopped.

By now I was blocking traffic behind and was half way out across two lanes and traffic trying to squeeze past in front and behind. Repeated the ignition off and on, revved ok, moved forward a couple of inches and stopped. After about 10 times of repeating the sequence I managed to get around the roundabout and pulled onto the curb. Sat a cursed for a few minutes, started it up and all fine and continued to drive home as though nothing had happened. On the way sat in some more traffic, accelerated when I could, no problems. When home started it a couple of times, revved etc. all OK, perfect no problem. I have since taken it out a couple of times and no problems.

There is no sign of leaks, all leads appear secure, didn’t smell of petrol and any time (i.e. as if I had flooded it when pumping throttle) Temp / volts fine, gear change fine (i.e. you can drop it down a gear or even two and hit the gas and she takes off), everything works. One common thing, this has only happened when in traffic or slowly crawling in traffic (don’t know if that is significant).

I have no idea what this is. It is strange that the car runs just fine for miles then has this problem out the blue and gets over it and is fine again. Is there a valve or something that would play up for a short while and then immediately overcome the problem itself? I don’t understand how it can falter but turning it off and on again it fires up and is fine only to hesitate and die.

I have completed a vast amount of maintenance work on the car over time and kept everything original. It has never let me down and it is in great shape but this has me stumped basically because of its very infrequent nature. Any advice would 'really' be appreciated,
Thanking you in anticipation

The Car:
1984, 928 S2 Euro, 310 BP, 109,000 miles, Rauchquartzmetalic, full black leather, I am the third owner and have the car for the last 20 years, Love it!!!

Speedtoys

When did you last replace fuel pump relay?

Or check condition (overheating, arcing) of fuses, esp fuel pump.

And...seen it happen once...car was perfect, except up the insulation from the 14pin engine harness was death, and that was the runs great...sometimes dies, cause.

Wisconsin Joe

The 'key on, key off' helping it out would lead me towards the ignition switch.

Have you tried wiggling the key to see if this does anything (while it's running normally)?

fan928

Thanks for the input.
I carry new spare type 53 relays and have tried each with no difference. Pump runs fine, car runs fine (apart from when it died). Also a new pump and filter fitted approx. 2,000 miles ago (plus new MAF). When it first started I check all the fuses / wiring (all fine). I also checked and clean all the major ground points and any wire / connections I thought might have a bearing on the problem, all appear secure, nothing loose, broken or arcing. etc. Luckily the wiring has not been messed with by anyone over time so it is basically as it left the factory (as is the rest of the car other than maintenance / new parts where needed). Will look again at the CE board as you suggest to check nothing amiss, thanks

fan928

Thanks Winconsin Joe,
I did check the ignition switch initially but have not done so since the recent problem so will do that again. I did have the pod off a while back to replace some bulbs and checked the wiring then and it seemed OK. I will pull the ignition switch and check again as something may have worked loose, thanks

GregBBRD

It sounds like the engine is "trying" to run, which makes me think it has spark and fuel although the volume of fuel might be an issue.

Just for giggles, I'd check the positive battery connection where the three big red leads attach. These provide all the power that goes to the relay board and ignition and are famous for being loose and causing all kinds of issues. If the battery ground cable is still original, replace it with the one we make...light years better than the stock cable, which has some serious design flaws.

The strainer in the tanks are widely known to plug up and just have a tiny little area that will allow fuel to pass through. "Loose" dirt and other debris will plug this small area off when the pump is sucking for awhile. And then will not "clear" until the pump is off for a few minutes. We are seeing more and more problems with this.

So, the question is....did you replace or clean the strainer when you did the pump?

After that, look at the things that control the amount of fuel delivered....engine temperature sender for the injection. Connector to the MAF, throttle switch. etc. Speaking of the MAF, did the problems occur before or after the MAF rebuild...not clear from your description. You need to be really careful about MAFs on a Euro engine....there is no O2 sensor to compensate and a "lean" MAF will 'kill" the engine. KILL....MELT....RUIN! You are pretty safe with a John Speake MAF....he's got the calibration down really well. The other rebuilders.....you better be checking the fuel mixture with some sort of a wide band!

How is the crank trigger connector? Cracked and falling apart (like they all do)...or still in good shape without any crack in the plastic? Once the plastic body of the connector cracks, moisture can get in and cause problems.

Pull the coil wire out of the coil and see if it has corroded and turned green. Once the resistance here goes high enough, spark will jump around the boot to the posts on the coil....causing crazy things to happen. (This is super common.)

fan928

Hi GregBBRD, Thanks for your input

Regarding the Strainer, no I didn't touch that when the new filter and pump was fitted. Fuel delivery worked fine once these were changed and so I left it alone.

Turning the ignition of and immediately back on enables the car to fire up first go (i.e. don't have to wait a few minutes for the pump or potentially any debris to move out the way etc.) and rev freely, just when put into gear it struggled to keep the revs up, they immediately start to fall and the engine soon cuts out. Might end up checking it if some of your other suggestions don't improve things.

I did check all connections (in boot, connection to the MAF, ground wires, all of them as per the workshop manual) originally and they were all clean and in good shape. Will check these again (plus coil) given the issue has raised its ugly head again. I find it extraordinary that it starts and runs fine for months (both in colder weather or as it is now in warm weather) without any issue then for a few minutes has a fit only to recover almost immediately and continue just fine for months until it suddenly happens again, very strange...

Taguid

Not really familiar with your year but check fuel dampers and fuel pressure regulator to see if there is fuel smell. If the diaphragm is ruptured more fuel will get into system and possibly run as you have described.

Garth S

Do the dash/pod icons light up and/or flicker when there is an immanent engine stall? This is often another indicator of a failing electrical switch 'half' of the ignition cylinder.

fan928

Hi Taguid,
Thanks for the input, No smell of fuel at any time, cheers

fan928

Hi Garth S,
Thanks for the input.
The lights in the pod stay on as normal, no flickering etc.Only activity is the rev counter that fluctuate and dips down to below 500 and fluctuates there as it struggles to gain some revs. Working the throttle seems to make no difference as she just stumbles on for a while then dies. Turn the key off and immediately back on, start first time, can be revved,(have to let the revs drop as an auto) then into gear to move off and it starts to stutter and eventually dies.Repeat procedure etc. stop for a minute to have a good swear, key on, starts, move off as though nothing had happen. Happy motoring for a couple of months then without warning we are back where we started, This originally happened in October 2017 with three separate occurrences over a few outings and seemed to disappear until the other day. I thought originally it was fuel related (i.e some bad fuel maybe a bit of dirt in the tank) but have filled her up several times and she has driven as she should and been fine, no smell of fuel, misfire etc. strange. Thanks

Taguid

Have you tried putting a vacuum with a mighty vac on the dampers and fpr to see if they hold?

Snark Shark

Aha... now I'm really paying attention as my US '86 might be having the exact same symptoms. I thought my fuel pump relay went bad, but about 1000 miles later the new relay also "failed". Both times when I bench tested the relay it seemed fine. I jumpered the relay, and checked the voltage for the relay trigger with the engine running and that seemed rock solid at 13.6V. Intermittent problems are the worst.

fan928

Hi,
Thought I would do some investigating today, Started her up first time and let her run for a while until she was nicely warmed up (the temperature was on the 1/3 marker). At standstill and in Park revved her up a few times, running sweet. Checked for smell of petrol, leaks, loose wires etc. (wagged key in ignition, hand under the pod, moved wires around etc) all OK.Thought I would try and replicate the problem on the driveway.

Let her tick over and without revs throughout this process put into Reverse, foot off brake, slowly traveled backwards six foot, Braked, into Drive, foot off brake and moved forward six foot (just using the tick over revs). braked / stopped and moved gear lever into Park, pressed throttle coughed and died. I took a 15 second video on my iphone which I will now try and upload (hopefully below) which might give a clue and narrow down the problem further, I am back to thinking this must be related to fuel or?

BTW: Have reduced the size of the video as much as possible to a 3MB .WMV file format rather than the original. MOV file type (which was 37MB so I hope it will play OK)
Thanks in advance for any further suggestions.

fan928

Opps, didn't seem to take the video so will try again