Rover V8 running problem
Discussion
The car is a 92 Range Rover Vogue SE with a 4.2 out of a 94 Range Rover LSE. It is running without cats, without Lambdas, and with a hotwire type air flow meter.
When playing up it wont rev above 1,500 RPM. It will start and idle fine, and will drive fine below 1,500 RPM. If the revs touch 1,500 RPM it will return to idle. It will then run fine, up until you next hit 1,500 RPM. If out of gear you keep your foot on the throttle, it will bounce between idle and 1,500 RPM. If in gear at slow speed you get really violent kangerooring. If it starts at high speed, there is nothing until the engine speed reaches idle due to the car slowing (unless you take it out of gear, in which case, as above). If you turn the ignition off for a few seconds, the problem will clear and it will drive really well until it next plays up (typicaly 2 or 3 minutes later).
It started about 3 weeks ago on my way to the MOT (about half a mile from home). At the end of the test we noticed the plug had fallen off the AFM. Plugging it in made the car run fine for a day or two, when the problem returned. The plug did not seem a very positive fit, so I chopped it off and fitted an old plug I happened to have. This made no difference, and at first I thought it may be because I had not joined the wires very well. I have checked the connections dozens of times since, and am comfident that they are now OK.
At first the problem was intermitent, but now it is virtualy all the time making the car unusable. At first, I suspected that it was worse when the engine was hot or under load, but now it also does it cold and on light load.
Due to the AFM plug (which may or may not have been a red herring), I then swapped the AFM for one off another car, and then, as that made no difference, I have tried changing the following (mostly off other cars, but some new bits have been fitted to):
Coil
AFM (again)
ECU
Dizzy Cap
Rotor Arm
HT leads
Fuel Filter
Fuel pumps relays
spark plugs have not been changed, but are not very old.
Now I have done the easy stuff, I think the time of changing random components is over. I do have a few more things that I "could" do, but would prefer to try and proove them (or at least get a second opinion) before I start. These are:
Ignition Amplifier (but when ever I have had one fail before, it has resulted in the car simply refusing to start).
Fuel Pump on its way out (in the tank, so dont want to change it unless I am confident it is the problem).
Old Alarm / Immobilisor. I was told when I bought the car that it was disconnected, but it does have a dozen or so wires going into it from the loom. I "could" trace all these back in case some of them are the old immobilisor circuits, and the unit is breaking down internaly.
Wiring loom? Is there a break in a wire somewhere? That would be fun to find! Do I change the whole loom?
Distributer? I do have another, but dont really want to risk disturbing the timing unless I am reasonably confident that is the issue.
I dont object to the car going on to a rolling road, other than not having an easy way to getting it to one (none local). Am I likely to gain anything useful by plugging in a fault code reader (which I dont have)? Is there anything that I have missed?
Any (mainly positive & not too sarcastic) comments or suggestions welcomed.
When playing up it wont rev above 1,500 RPM. It will start and idle fine, and will drive fine below 1,500 RPM. If the revs touch 1,500 RPM it will return to idle. It will then run fine, up until you next hit 1,500 RPM. If out of gear you keep your foot on the throttle, it will bounce between idle and 1,500 RPM. If in gear at slow speed you get really violent kangerooring. If it starts at high speed, there is nothing until the engine speed reaches idle due to the car slowing (unless you take it out of gear, in which case, as above). If you turn the ignition off for a few seconds, the problem will clear and it will drive really well until it next plays up (typicaly 2 or 3 minutes later).
It started about 3 weeks ago on my way to the MOT (about half a mile from home). At the end of the test we noticed the plug had fallen off the AFM. Plugging it in made the car run fine for a day or two, when the problem returned. The plug did not seem a very positive fit, so I chopped it off and fitted an old plug I happened to have. This made no difference, and at first I thought it may be because I had not joined the wires very well. I have checked the connections dozens of times since, and am comfident that they are now OK.
At first the problem was intermitent, but now it is virtualy all the time making the car unusable. At first, I suspected that it was worse when the engine was hot or under load, but now it also does it cold and on light load.
Due to the AFM plug (which may or may not have been a red herring), I then swapped the AFM for one off another car, and then, as that made no difference, I have tried changing the following (mostly off other cars, but some new bits have been fitted to):
Coil
AFM (again)
ECU
Dizzy Cap
Rotor Arm
HT leads
Fuel Filter
Fuel pumps relays
spark plugs have not been changed, but are not very old.
Now I have done the easy stuff, I think the time of changing random components is over. I do have a few more things that I "could" do, but would prefer to try and proove them (or at least get a second opinion) before I start. These are:
Ignition Amplifier (but when ever I have had one fail before, it has resulted in the car simply refusing to start).
Fuel Pump on its way out (in the tank, so dont want to change it unless I am confident it is the problem).
Old Alarm / Immobilisor. I was told when I bought the car that it was disconnected, but it does have a dozen or so wires going into it from the loom. I "could" trace all these back in case some of them are the old immobilisor circuits, and the unit is breaking down internaly.
Wiring loom? Is there a break in a wire somewhere? That would be fun to find! Do I change the whole loom?
Distributer? I do have another, but dont really want to risk disturbing the timing unless I am reasonably confident that is the issue.
I dont object to the car going on to a rolling road, other than not having an easy way to getting it to one (none local). Am I likely to gain anything useful by plugging in a fault code reader (which I dont have)? Is there anything that I have missed?
Any (mainly positive & not too sarcastic) comments or suggestions welcomed.
sarcastic....or maybe not.
Take it to someone who has the ability to diagnose.
Fault code readers have limited use. A proper diagnostic scanner in the hands of someone who actually knows how to use it would make a lot more sense.
But you seem to be changing stuff, with no real logic or reason for doing so.
So no matter what you do, it will not rev over 1500rpm ? parked, driving, whatever ?
could be as simple as a lack of speed signal, or brake light switch. But without a proper inspection and diagnosis, its impossible to tell from afar.
Although at 92....modern type diagnostics might be quite limited.
Take it to someone who has the ability to diagnose.
Fault code readers have limited use. A proper diagnostic scanner in the hands of someone who actually knows how to use it would make a lot more sense.
But you seem to be changing stuff, with no real logic or reason for doing so.
So no matter what you do, it will not rev over 1500rpm ? parked, driving, whatever ?
could be as simple as a lack of speed signal, or brake light switch. But without a proper inspection and diagnosis, its impossible to tell from afar.
Although at 92....modern type diagnostics might be quite limited.
Edited by stevieturbo on Monday 2nd August 22:59
stevieturbo said:
sarcastic....or maybe not.
Take it to someone who has the ability to diagnose.
Fault code readers have limited use. A proper diagnostic scanner in the hands of someone who actually knows how to use it would make a lot more sense.
But you seem to be changing stuff, with no real logic or reason for doing so.
So no matter what you do, it will not rev over 1500rpm ? parked, driving, whatever ?
could be as simple as a lack of speed signal, or brake light switch. But without a proper inspection and diagnosis, its impossible to tell from afar
I agree with you. The local garage said "main dealer", but they are neither interested in old cars, or modified cars.Take it to someone who has the ability to diagnose.
Fault code readers have limited use. A proper diagnostic scanner in the hands of someone who actually knows how to use it would make a lot more sense.
But you seem to be changing stuff, with no real logic or reason for doing so.
So no matter what you do, it will not rev over 1500rpm ? parked, driving, whatever ?
could be as simple as a lack of speed signal, or brake light switch. But without a proper inspection and diagnosis, its impossible to tell from afar
The logic for changing the parts was that since I had them, and they were "easy" then if it was one of these then I could identify it from that. It will be going to an independant specialist once I can work out how to get it there, but in the mean time I thought I would post here just in case I had missed something obvious.
1500 rpm sounds about where the overrun fuel cut off might work from. I don't know how this is triggered on your particular car but something in that circuit might be the cause, possibly a throttle position sensor failing or a faulty microswitch to indicate closed throttle on the butterfly spindle.
I'm guessing the hot wire flowmeter is indicating airflow properly but the TPS or microswitch is telling the ecu the throttle is closed. Below the cutoff rpm this will have no effect but above it the ecu switches off the fuel supply because it thinks the engine is on the overrun. The revs then drop and the fuel comes back on again until you hit the limit rpm once more.
I'm guessing the hot wire flowmeter is indicating airflow properly but the TPS or microswitch is telling the ecu the throttle is closed. Below the cutoff rpm this will have no effect but above it the ecu switches off the fuel supply because it thinks the engine is on the overrun. The revs then drop and the fuel comes back on again until you hit the limit rpm once more.
Edited by Pumaracing on Tuesday 3rd August 06:55
My first swap would have been the ignition amp. Unlike your experience I have had them fail in many different ways including happy to run at idle and a little above but no pull or higher revs.
Borrow or find an inline fuel pump and fit it in the engine bay to eliminate fuel supply as the problem.
Steve
Borrow or find an inline fuel pump and fit it in the engine bay to eliminate fuel supply as the problem.
Steve
Pumaracing said:
1500 rpm sounds about where the overrun fuel cut off might work from. I don't know how this is triggered on your particular car but something in that circuit might be the cause, possibly a throttle position sensor failing or a faulty microswitch to indicate closed throttle on the butterfly spindle.
I'm guessing the hot wire flowmeter is indicating airflow properly but the TPS or microswitch is telling the ecu the throttle is closed. Below the cutoff rpm this will have no effect but above it the ecu switches off the fuel supply because it thinks the engine is on the overrun. The revs then drop and the fuel comes back on again until you hit the limit rpm once more.
Some models do have an overrun facility. Vacuum valve (at back of plenum) and a relay mounted near the MAF. The relay cuts the ignition signal to the ECU which then cuts the fuel pump.I'm guessing the hot wire flowmeter is indicating airflow properly but the TPS or microswitch is telling the ecu the throttle is closed. Below the cutoff rpm this will have no effect but above it the ecu switches off the fuel supply because it thinks the engine is on the overrun. The revs then drop and the fuel comes back on again until you hit the limit rpm once more.
Edited by Pumaracing on Tuesday 3rd August 06:55
Easy test for this is to rig a bulb across the fuel pump relay and see if the fuel pump supply is cut at any stage.
Steve
If by chance its fuel cut off, you just need to test the throttle potentiometer, as this controls the cut off point. Your ECU will have fault codes stored in it from when you disconnected the AFM, so first you need to unplug it for 30 seconds to reset it. Then beg, borrow or steal a fault code reader and plug it in, and see what code you get after the fault has reoccured. It wont pick evey fault condition up, but this sounds bad enough to throw a code.
Manual download at the top of the page here:
http://www.g33.co.uk/fuel_injection.htm
Manual download at the top of the page here:
http://www.g33.co.uk/fuel_injection.htm
Edited by blitzracing on Tuesday 3rd August 13:00
Steve_D said:
Some models do have an overrun facility. Vacuum valve (at back of plenum) and a relay mounted near the MAF. The relay cuts the ignition signal to the ECU which then cuts the fuel pump.
There still has to be a butterfly position sensor for fuel cutoff or the ecu doesn't know if the engine is on the overrun or not. Plenum vacuum isn't sufficient to indicate this precisely.Pumaracing said:
Steve_D said:
Some models do have an overrun facility. Vacuum valve (at back of plenum) and a relay mounted near the MAF. The relay cuts the ignition signal to the ECU which then cuts the fuel pump.
There still has to be a butterfly position sensor for fuel cutoff or the ecu doesn't know if the engine is on the overrun or not. Plenum vacuum isn't sufficient to indicate this precisely.If this switch could not detect the difference between tickover and over-run then the system could not work.
Steve
Steve_D said:
Pumaracing said:
Steve_D said:
Some models do have an overrun facility. Vacuum valve (at back of plenum) and a relay mounted near the MAF. The relay cuts the ignition signal to the ECU which then cuts the fuel pump.
There still has to be a butterfly position sensor for fuel cutoff or the ecu doesn't know if the engine is on the overrun or not. Plenum vacuum isn't sufficient to indicate this precisely.If this switch could not detect the difference between tickover and over-run then the system could not work.
Steve
Edited by blitzracing on Wednesday 4th August 12:51
Steve_D said:
Pumaracing said:
Steve_D said:
Some models do have an overrun facility. Vacuum valve (at back of plenum) and a relay mounted near the MAF. The relay cuts the ignition signal to the ECU which then cuts the fuel pump.
There still has to be a butterfly position sensor for fuel cutoff or the ecu doesn't know if the engine is on the overrun or not. Plenum vacuum isn't sufficient to indicate this precisely.If this switch could not detect the difference between tickover and over-run then the system could not work.
Steve
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