Discussion
'92 4.3:
After cleaning/fixing numerous dodgy connections and miscellaneous lash ups I really thought I'd got this licked. Did over 1000 miles including 100 on track towards the end of last year without a hiccup, then I took the car out for the second time this year yesterday and in approx. 50 miles had three instances of loss of power/stalling.
I have replaced:
plugs
shrouds
leads
coil
(dizzy cap and rotor arm newish and look good)
coolant temp sensor
all relays (inc. 'special' metal ones in loom in footwell)
all fuses
vacuum advance tubing
I have also:
checked or remade all engine bay electrical connections
cleaned and remade all earths
cleaned fuse box connections
checked ECU connector and wiring
remounted ignition module (to the side of the dizzy) with heat conductive paste
Symptoms are:
Engine warm, running absolutely superbly, then suddenly loses almost all power. If I dip the clutch the engine stalls. If I floor the accelerator the engine will just about keep going, but there is a smell of fuel. On the third occasion I pulled over and the engine did not stall but was certainly not running on all 8. And it was not revving cleanly. As I engine braked there was a pop (unburnt fuel?). The car, follwing a Mark Adams set up, does not normally pop and bang.
In each case of power loss, the preceding driving conditions were different. On the first occasion I'd been following a slow-moving que (40mph) at part throttle for about 6 miles. When I finally got to overtake I had all the power I needed until the problem occured approx. 30 secs later. The second time, I had a clear road, a good run of accelerating and braking out of/in to corners and then on a trailing throttle, suddenly felt engine braking as the power went. Third time was a cruise, detected rough running and then foot to the floor gave little response. I don't remeber jolting the car over a bump or anything each time.
In each case the car the restarted and ran fine. Dashboard instruments behaved normally (I don't remember the tacho needle dropping).
Having replaced the cheap stuff and being pretty confident about the general wiring I'm starting to think the most likely candidates are the ignition module or the signal pick-up in the distributor - but surely then the tacho needle would drop?. At least I'm pretty sure it's a spark problem, not a fuel one.
Any ideas? Before I start replacing components (£££)? If only it'd break down for good I could take it somewhere, but if I do that now it'll no doubt behave impeccably...
After cleaning/fixing numerous dodgy connections and miscellaneous lash ups I really thought I'd got this licked. Did over 1000 miles including 100 on track towards the end of last year without a hiccup, then I took the car out for the second time this year yesterday and in approx. 50 miles had three instances of loss of power/stalling.
I have replaced:
plugs
shrouds
leads
coil
(dizzy cap and rotor arm newish and look good)
coolant temp sensor
all relays (inc. 'special' metal ones in loom in footwell)
all fuses
vacuum advance tubing
I have also:
checked or remade all engine bay electrical connections
cleaned and remade all earths
cleaned fuse box connections
checked ECU connector and wiring
remounted ignition module (to the side of the dizzy) with heat conductive paste
Symptoms are:
Engine warm, running absolutely superbly, then suddenly loses almost all power. If I dip the clutch the engine stalls. If I floor the accelerator the engine will just about keep going, but there is a smell of fuel. On the third occasion I pulled over and the engine did not stall but was certainly not running on all 8. And it was not revving cleanly. As I engine braked there was a pop (unburnt fuel?). The car, follwing a Mark Adams set up, does not normally pop and bang.
In each case of power loss, the preceding driving conditions were different. On the first occasion I'd been following a slow-moving que (40mph) at part throttle for about 6 miles. When I finally got to overtake I had all the power I needed until the problem occured approx. 30 secs later. The second time, I had a clear road, a good run of accelerating and braking out of/in to corners and then on a trailing throttle, suddenly felt engine braking as the power went. Third time was a cruise, detected rough running and then foot to the floor gave little response. I don't remeber jolting the car over a bump or anything each time.
In each case the car the restarted and ran fine. Dashboard instruments behaved normally (I don't remember the tacho needle dropping).
Having replaced the cheap stuff and being pretty confident about the general wiring I'm starting to think the most likely candidates are the ignition module or the signal pick-up in the distributor - but surely then the tacho needle would drop?. At least I'm pretty sure it's a spark problem, not a fuel one.
Any ideas? Before I start replacing components (£££)? If only it'd break down for good I could take it somewhere, but if I do that now it'll no doubt behave impeccably...
The fact that you smell fuel seems to indicate that this is an ignition fault. As far as I can see the only things you haven't replaced are the ignition amplifier and the points. Ignition amplifier could give symptoms like this and is relatively cheap and easy to replace so I'd be inclined to give that a try.
GreenV8S said:
The fact that you smell fuel seems to indicate that this is an ignition fault. As far as I can see the only things you haven't replaced are the ignition amplifier and the points. Ignition amplifier could give symptoms like this and is relatively cheap and easy to replace so I'd be inclined to give that a try.
Thanks both - looks like that's the next step then. I bought a 'spare' from an auto jumble for 50p last year, so I might try that (although it might be no better!). Thing is, the original is all black, the 'spare' is black except the outer face which is white. Connections/dimensions identical. Can it hurt to try it?
Also I disconnected various things to try to replicate the symptoms. To my surprise when I disconnected the airflow meter the engine still ran normally and even revved with the throttle. Is that right?!?!
griffter said:
To my surprise when I disconnected the airflow meter the engine still ran normally and even revved with the throttle. Is that right?!?!
Should have kept running in 'limp' mode which will be rougher and less tractible than normal mode. You'd need to reset the ECU to restore normal operation afterwards.
david beer said:
My last Griff behaved the same, it would suddenly go "rich", it was the air flow meter, i moved it to the air box and it never happened again.
Interesting, can you explain in a bit more detail? I guess you moved the AFM from the wing to the plenum, or something like that?
Higgins23 said:
I have exactly the same thing happen on a 95 500HC. Car is fine 95% of the time but all of a sudden it starts acting up and stalling. The problem then goes away onlyu to resurface a couple of weeks later. it never happens on the highway, only when driving slowly around town.
My latest theory is that electromagnetic interference from the ignition leads upsets the pulse from the ignition amplifier to the coil. The coil then doesn't create the voltage necessary, or when required, for each spark - so the engine starts to run rough or dies. The engine restarts on the key because the interference has gone. Sometimes the problem resolves itself as the dying coil voltage redcuces the interference - but by then the engine may be flooded and struggling - and hence the smell of fuel.
It's just a theory...based on the fact that Land Rover upgraded the 2 pin ignition amps to 3 pin and provided a shielded lead to link the dizzy to the coil, where the amp is mounted near the coil.
I'm currently juggling the advantages of an off the shelf remote-mount upgrade from Rimmers vs DIY...
Hi Peter
i simply extended the wires and placed the meter direct to the air filter box, by moving pipes around you do not need anything else. Althoug my under bonnet temps were a lot lower than normal, i guess the damage had already been done in the 5years before. Did not have a code reader then so do not know if it would of shown so. As long as postage is covered, i could lend it out if required, Griffter.
Interesting, can you explain in a bit more detail? I guess you moved the AFM from the wing to the plenum, or something like that?[/quote]
i simply extended the wires and placed the meter direct to the air filter box, by moving pipes around you do not need anything else. Althoug my under bonnet temps were a lot lower than normal, i guess the damage had already been done in the 5years before. Did not have a code reader then so do not know if it would of shown so. As long as postage is covered, i could lend it out if required, Griffter.
Interesting, can you explain in a bit more detail? I guess you moved the AFM from the wing to the plenum, or something like that?[/quote]
My guess would be the ignition module, I believe the original has white on one side (and the lucas symbol embossed in the corner) I bought a 3rd party one which was about £20 and has worked fine for the last 6 months (much to everyones non-recommendation) if it goes again I would buy an original part, think they are about £45. Well worth changing, dont know if i would risk the autojumble thing??
Lig.
Lig.
I haven't come across interference problems on the LT line to the coil before, but the line carrying the same signal to the ECU is vulnerable to interference from the HT leads. This can cause the ECU to get confused over the actual engine speed. The signal line is normally a single black wire running from the ignition module, along the top of the near sie rocker cover, under the throttle and unto the passengers footwell. There's a resister in series with this close to the footwell end. It's worth physically arranging the HT leads and this signal wire to make sure they don't run close to each other.
lig said:
My guess would be the ignition module, I believe the original has white on one side (and the lucas symbol embossed in the corner) I bought a 3rd party one which was about £20 and has worked fine for the last 6 months (much to everyones non-recommendation) if it goes again I would buy an original part, think they are about £45. Well worth changing, dont know if i would risk the autojumble thing??
Lig.
You're right - I got my wires crossed
- original is white-sided, spare is all black. I've sourced a (allegedly) Lucas spare so I'll go with that.GreenV8S said:
I haven't come across interference problems on the LT line to the coil before, but the line carrying the same signal to the ECU is vulnerable to interference from the HT leads. This can cause the ECU to get confused over the actual engine speed. The signal line is normally a single black wire running from the ignition module, along the top of the near sie rocker cover, under the throttle and unto the passengers footwell. There's a resister in series with this close to the footwell end. It's worth physically arranging the HT leads and this signal wire to make sure they don't run close to each other.
I think perhaps the LT interferance thing is a bit misleading. When mounting the amplifier away from the distributor, the signal from the distributor is LT - and unamplified. Presumably then it's more susceptible to interferance which would explain LR providing a shielded link lead in the remote mount kit. May not be a problem with amplified LT signal.
I know the signal to ECU lead you mention. Is it worth trying to shield it? I'm sure I've seen steel braided sleeve somewhere for shielding otherwise unshielded wires, but can't for the life of me remember where.
I know the resistor you mean as well - maybe worth changing just in case...
Thanks again.
Gassing Station | Griffith | Top of Page | What's New | My Stuff