Non-start fueling problem?
Discussion
Don't believe this ... went to pick the new car up this morning (3.2 Carrera). My good mate StuB crawled all over and under it for an hour or more, he identified a few jobs that needed doing, nothing majorly serious though, track rod arm bushes, a couple of oil pipes that need replacing, that sort of thing, general wear and tear items. We ran the engine for 15 mins or so, checked the exhaust and various other bits and bobs, turned the engine off and chatted for another 10 mins or so.
Then came the test drive. Turned the key, starter motor spins away merrily, not even a sniff of a catch. The guy had let the fuel run right down to empty. Off he goes and fills it up with a 5 litre can. Still nothing. Not a whiff of petrol hitting the engine.
Owner's first thought - the EMC/ECU type unit under the passenger seat (it has gone before and been replaced).
Me/Stuart's thought - knackered/tired fuel pump.
Anyway - off back to Goole with no car! Not a happy bunny.
Called owner a couple of hours later and he had spoken to his friend who is restoring a 930. He was pretty certain that it is the fuel pressure regulator.
The engine had started first time on the button 45 mins after we had left and it had cooled down. (It started first time from stone cold this morning).
Stuart doesn't think the fuel pressure regulator is likely to fail as it doesn't really have to do that much hence doesn't often break. He reckons it is still the fuel pump.
However, the owner says the pump looks pretty new (although at least 18 months old).
Any ideas/past experiences guys?
A very frustrated Burriana
p.s. On the plus side, Strasse remember the car and confirm it as a good un!
Then came the test drive. Turned the key, starter motor spins away merrily, not even a sniff of a catch. The guy had let the fuel run right down to empty. Off he goes and fills it up with a 5 litre can. Still nothing. Not a whiff of petrol hitting the engine.
Owner's first thought - the EMC/ECU type unit under the passenger seat (it has gone before and been replaced).
Me/Stuart's thought - knackered/tired fuel pump.
Anyway - off back to Goole with no car! Not a happy bunny.
Called owner a couple of hours later and he had spoken to his friend who is restoring a 930. He was pretty certain that it is the fuel pressure regulator.
The engine had started first time on the button 45 mins after we had left and it had cooled down. (It started first time from stone cold this morning).
Stuart doesn't think the fuel pressure regulator is likely to fail as it doesn't really have to do that much hence doesn't often break. He reckons it is still the fuel pump.
However, the owner says the pump looks pretty new (although at least 18 months old).
Any ideas/past experiences guys?
A very frustrated Burriana
p.s. On the plus side, Strasse remember the car and confirm it as a good un!
In the scheme of things the DME relay is nothing and everything for a Porsche. It's likely to go wrong at some point on allmost all 87-89 911's at least, but I think the scope is wider than that. Furthermore it's about the only "pain in the butt" level problem you're likely to get. If the only thing wrong is the DME relay, don't not buy because of it.
Edited to add;
Knock a bit off the price because of it, and then take it to a good auto electrician.
>> Edited by dilbert on Sunday 29th January 00:27
Edited to add;
Knock a bit off the price because of it, and then take it to a good auto electrician.
>> Edited by dilbert on Sunday 29th January 00:27
This is what one of the guys on the PCGB forum said:
[quote 911mot]I had problems similar to yours and it was a simple fix - clean the fuel pump fuse contacts. Corrosion had built up whilst it had been sitting a few months.
So have you checked for spark? DME relays go up the swanny at regular intervals. They crack in the solder. Tapping it lightly with a screwdriver handle is worth a try.
Better explain - if the fuse contacts are corroded it will start ok from cold but once its been running for a while the fuse will warm up and this increases the resistance to the point that the fuel pump cant deliver enough oomph to get it running. Once it's cooled down its ok again. At least that was what was happening in my case.[/quote]
Which seems fair enough, but why do they not just fit a higher rated fuse?
And, if there is a problem with the DME circuit, how can I make sure it doesn't end up damaging the ECU?
Not going to "not" buy the car, but it has set it back a week. I just want to make sure he has at least identified the problem if not totally fixed it.
[quote 911mot]I had problems similar to yours and it was a simple fix - clean the fuel pump fuse contacts. Corrosion had built up whilst it had been sitting a few months.
So have you checked for spark? DME relays go up the swanny at regular intervals. They crack in the solder. Tapping it lightly with a screwdriver handle is worth a try.
Better explain - if the fuse contacts are corroded it will start ok from cold but once its been running for a while the fuse will warm up and this increases the resistance to the point that the fuel pump cant deliver enough oomph to get it running. Once it's cooled down its ok again. At least that was what was happening in my case.[/quote]
Which seems fair enough, but why do they not just fit a higher rated fuse?
And, if there is a problem with the DME circuit, how can I make sure it doesn't end up damaging the ECU?
Not going to "not" buy the car, but it has set it back a week. I just want to make sure he has at least identified the problem if not totally fixed it.
I can't remember the exact nature of the problem now, beause it's ages since I sorted mine out. From what I remember there are issues with the fuses, especially if you have the "open style" fuse box. The ends of the fuses are plated, and the fingers in the fuse box are unplated copper IIRC. There is a corrosion issue, which you can easily sort out with a fine brass wire brush, and a new batch of fuses.
The fuel pump doesn't last forever, and it's bolted to the underside of the front bulkhead, under the large steel sheet which protects the steering rack. If it's original it has a plastic coated aluminium body, and water causes the case to rot in the end, because of the plastic coating. More particularly the electrical connections to the fuel pump will also be corroded to some extent.
A new one isn't that expensive, and you'll be able to replace the steel sheet at the same time, it'll enevitably be rusty, on all but the lowest milage cars, because it's only very lightly painted.
The DME relay issue, is due to an over complicated circuit for control of the fuel pump.
There are two things that control the "on state" of the fuel pump. The ignition, and the ECU stall flag. When you switch the ignition on the fuel pump should start and it should run until the engine is switched off, or it stalls.
I can't remember the exact details of the circuit, but the output from the ECU that indicates a stall condition eventually fails, and in my case it was intermittent, as verified with a meter measuring the output pin on the ECU.
The DME relay (or one of it's mates) directly switches the fuel pump which is heavily inductive, and very high current. Eventually the contacts in the relay weld themselves closed. The way the circuit is wired, the fault condition causes additional strain on the ECU (as far as I can remember) and the load on the particular pin that drives the relay eventually kills the output on the ECU.
If the DME relay fails, swap it out ASAP, as damage limitation. As I say I can't remember exactly why, but that was the conclusion I came to after a fair bit of poncing about.
If the ECU fails, then you can either replace it (not hugely expensive), or wire out the stall flag control on that circuit. I did the latter, which is not the wisest, but it works, and I don't mind. The problem will not come back, and I figure that if you're gonna die, you're gonna die.
The technically correct solution is to rewire the whole DME circuit, to eliminate the design fault, and replace whatever parts are dead. That's not as bad as it sounds, because all the changes that you would need to make are contained under the passenger seat.
Edited to add;
The design fault being the thing that causes additional failures, as a result of a failure in the DME relay. What should happen is that the DME relay dies, and the car won't work, until you replace it. That's not what happens in practice.
>> Edited by dilbert on Sunday 29th January 13:39
The fuel pump doesn't last forever, and it's bolted to the underside of the front bulkhead, under the large steel sheet which protects the steering rack. If it's original it has a plastic coated aluminium body, and water causes the case to rot in the end, because of the plastic coating. More particularly the electrical connections to the fuel pump will also be corroded to some extent.
A new one isn't that expensive, and you'll be able to replace the steel sheet at the same time, it'll enevitably be rusty, on all but the lowest milage cars, because it's only very lightly painted.
The DME relay issue, is due to an over complicated circuit for control of the fuel pump.
There are two things that control the "on state" of the fuel pump. The ignition, and the ECU stall flag. When you switch the ignition on the fuel pump should start and it should run until the engine is switched off, or it stalls.
I can't remember the exact details of the circuit, but the output from the ECU that indicates a stall condition eventually fails, and in my case it was intermittent, as verified with a meter measuring the output pin on the ECU.
The DME relay (or one of it's mates) directly switches the fuel pump which is heavily inductive, and very high current. Eventually the contacts in the relay weld themselves closed. The way the circuit is wired, the fault condition causes additional strain on the ECU (as far as I can remember) and the load on the particular pin that drives the relay eventually kills the output on the ECU.
If the DME relay fails, swap it out ASAP, as damage limitation. As I say I can't remember exactly why, but that was the conclusion I came to after a fair bit of poncing about.
If the ECU fails, then you can either replace it (not hugely expensive), or wire out the stall flag control on that circuit. I did the latter, which is not the wisest, but it works, and I don't mind. The problem will not come back, and I figure that if you're gonna die, you're gonna die.
The technically correct solution is to rewire the whole DME circuit, to eliminate the design fault, and replace whatever parts are dead. That's not as bad as it sounds, because all the changes that you would need to make are contained under the passenger seat.
Edited to add;
The design fault being the thing that causes additional failures, as a result of a failure in the DME relay. What should happen is that the DME relay dies, and the car won't work, until you replace it. That's not what happens in practice.
>> Edited by dilbert on Sunday 29th January 13:39
on a 3.2 i would roll all the fuses in the fuse box to make sure they all contact well and spray some wd 40 over them all, then the red and black relays in the same box need to be pushed fully in as they vibrate out, then go to the dme under the seat as pointed out and apart from the obvious checking for spark so on go to the crank ref sensor, these can be quite problematic
best of luck
best of luck
In order of simplicity.
1 clean the ends of the fuses, (continental "bullet" type), with some 180 grade wet & dry. Also clean the corresponding contacts on the fuse board. No use just spraying WD, you actually need to clean everything up.
2. Have a bit of a wiggle of the fuel pump relay (round & just above fuses). Possible even swap for a "non essential one".
3. Check DME relay. (black oblong next to ECU under passenger seat). Bolted down with a 10mm nut. Undo the nut and pull the relay to the back of the seat, (move seat forwards at this point). Pry off the plastic cover and you should see 2 solenoids. Place Relay back in holder (only goes 1 way with a plastic pin at one end). Crank engine over and manually make sure both the solenoids are closed. There are normally 1 or 2 dry solder joints (you`ll see a crack running all round the joint if you look carefully). You could re-solder the joints and replace asap.
4. If that doesn`t cure the problem take the car to a good specialist. Don`t waste your time pissing into the wind on the advice of some internet "experts". It could be loads of things. Engine speed sensor, fuel pump, ecu, any of the fuel injection sensors, battery earth, poor compression, etc, etc and you`ll wate time effort and money trying to locate the fault possible doing more harm than good.
I hope it isn`t but the poor engine compression is possible and that would be a very big bill so go steady. As I said when you came round for a chat you`re buying a very old car and you need to be something of an expert to guarantee getting it right. You aren`t, (and I mean it in the nicest way !). Hopefully 1. 2. or 3. will cure the problem.
Henry
1 clean the ends of the fuses, (continental "bullet" type), with some 180 grade wet & dry. Also clean the corresponding contacts on the fuse board. No use just spraying WD, you actually need to clean everything up.
2. Have a bit of a wiggle of the fuel pump relay (round & just above fuses). Possible even swap for a "non essential one".
3. Check DME relay. (black oblong next to ECU under passenger seat). Bolted down with a 10mm nut. Undo the nut and pull the relay to the back of the seat, (move seat forwards at this point). Pry off the plastic cover and you should see 2 solenoids. Place Relay back in holder (only goes 1 way with a plastic pin at one end). Crank engine over and manually make sure both the solenoids are closed. There are normally 1 or 2 dry solder joints (you`ll see a crack running all round the joint if you look carefully). You could re-solder the joints and replace asap.
4. If that doesn`t cure the problem take the car to a good specialist. Don`t waste your time pissing into the wind on the advice of some internet "experts". It could be loads of things. Engine speed sensor, fuel pump, ecu, any of the fuel injection sensors, battery earth, poor compression, etc, etc and you`ll wate time effort and money trying to locate the fault possible doing more harm than good.
I hope it isn`t but the poor engine compression is possible and that would be a very big bill so go steady. As I said when you came round for a chat you`re buying a very old car and you need to be something of an expert to guarantee getting it right. You aren`t, (and I mean it in the nicest way !). Hopefully 1. 2. or 3. will cure the problem.
Henry
Thanks for all the advice guys.
The owner is getting an auto-electrician round to source the problem so fingers crossed that we find which bit of the electrical maze it is!
I think someone on PCGB forum said that one of the first things you should do on the older cars is find every fuse, relay and electrical contact you can and clean and/or replace, purely as a preventitive measure.
He is going to deliver down to me next weekend and if Strasse can fit it in it will be going straight in there for a full service and check up
The owner is getting an auto-electrician round to source the problem so fingers crossed that we find which bit of the electrical maze it is!
I think someone on PCGB forum said that one of the first things you should do on the older cars is find every fuse, relay and electrical contact you can and clean and/or replace, purely as a preventitive measure.
He is going to deliver down to me next weekend and if Strasse can fit it in it will be going straight in there for a full service and check up
Unfortunately this is not feasible with the car being in Darlington.
That's why I had a thorough inspection done on saturday and, from the various bits and pieces that require work have negotiated a lower purchase price to cover this. I also spoke to both Charlie and Dave at Strasse who know and remember the car as being a good one.
That's why I had a thorough inspection done on saturday and, from the various bits and pieces that require work have negotiated a lower purchase price to cover this. I also spoke to both Charlie and Dave at Strasse who know and remember the car as being a good one.
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