V8 Range Rover misfire
Discussion
Hi,
For some time my 91 Range Rover 3.9 efi has had an occasional misfire. It didnt bother me much so left it but over the osst few weeks its turned permanent.
I didnt think it was anything serious such as head gasket as it was intermittent. So far i have done the following:
1.Cleaned plugs. (6 anyway as couldnt get last two out). Pulling the leads on these last two made the running worse so think they are ok. Plugs are 4 years old/3000 miles
2. Changed distributor as the ignition module was suggested as possible cause
3. Changed leads
4. Changed coil
5. Checked timing post dizzy change
6. Injection cleaner (Redex).
I dont know what to do next other than compression test and find a specialist in north wiltshire.
Any thoughts or mechanic recommendations?
Thanks
Adam
For some time my 91 Range Rover 3.9 efi has had an occasional misfire. It didnt bother me much so left it but over the osst few weeks its turned permanent.
I didnt think it was anything serious such as head gasket as it was intermittent. So far i have done the following:
1.Cleaned plugs. (6 anyway as couldnt get last two out). Pulling the leads on these last two made the running worse so think they are ok. Plugs are 4 years old/3000 miles
2. Changed distributor as the ignition module was suggested as possible cause
3. Changed leads
4. Changed coil
5. Checked timing post dizzy change
6. Injection cleaner (Redex).
I dont know what to do next other than compression test and find a specialist in north wiltshire.
Any thoughts or mechanic recommendations?
Thanks
Adam
Under what conditions did it misfire?
If the misfire is now permanent, you should be able to find which cylinders are affected by monitoring the header tempts after a cold start.
If the leads are long enough, consider swapping leads between 'good' and 'bad' cylinders to see if the problem follows the lead.
Could also be an injector problem. Not particularly difficult or expensive to get the injectors serviced and cleaned. I'd check that they were all being driven correctly first. You can do that by listening to them at tickover. A mechanic's stethoscope can help with that although with practice you can hear them with the naked ear.
If the problem was initially intermittent it is unlikely to be a worn cam, but it's conceivable. You could do a quick test for that by barring the engine over with the rocker covers off and measuring valve lift.
At that age it would be sensible to replace the plugs anyway.
If the misfire is now permanent, you should be able to find which cylinders are affected by monitoring the header tempts after a cold start.
If the leads are long enough, consider swapping leads between 'good' and 'bad' cylinders to see if the problem follows the lead.
Could also be an injector problem. Not particularly difficult or expensive to get the injectors serviced and cleaned. I'd check that they were all being driven correctly first. You can do that by listening to them at tickover. A mechanic's stethoscope can help with that although with practice you can hear them with the naked ear.
If the problem was initially intermittent it is unlikely to be a worn cam, but it's conceivable. You could do a quick test for that by barring the engine over with the rocker covers off and measuring valve lift.
At that age it would be sensible to replace the plugs anyway.
Edited by GreenV8S on Sunday 12th November 17:53
Worth a read:
http://www.robisonservice.com/servicedep/rover_tro...
As is this:
http://www.carelect.demon.co.uk/rrind.html
You should change the last two plugs - if only to rule them out.
Whilst mine's a 3.5EFi misfires have usually been down to plugs or a faulty temperature sensor. (That said latest issue was a split hose from the plenum to the extra air valve allowing too much air in but was fine once warmed up & the valve closed. Yours hasn't got one of those.)
I have had a couple of ECU's fail - one went very rich with lots of black smoke & the other made the car run as rough as a rough thing. Switching to LPG restored normal running so ruled out the ignition side of things. I do have spare ecus for mine & substitution made the problem go away. Mine is the flapper type which are known for problems but yours should be the hotwire.
They don't like cheapie dizzy caps & DO NOT use a rotor arm that has the metal strip riveted to the plastic. If you want to remove he rotor arm you MUST press down on the reluctor (eight pointed star shaped thingy under the rotor arm) as you pull or will very likely disengage the auto advance/retard mech in the bottom of the dizzy bowl & it may not run at all. Checked by turning the rotor arm with your fingers, Once released it should snap smartly back to its original position.
Route the leads as per the manual to avoid crossfiring issues.
If you don't have a workshop manual you should get one. Yours should be covered by the RAVE disc - used to be able to get it for free off the net but is also available on ebay. Work through the diagnostic section.
http://www.robisonservice.com/servicedep/rover_tro...
As is this:
http://www.carelect.demon.co.uk/rrind.html
You should change the last two plugs - if only to rule them out.
Whilst mine's a 3.5EFi misfires have usually been down to plugs or a faulty temperature sensor. (That said latest issue was a split hose from the plenum to the extra air valve allowing too much air in but was fine once warmed up & the valve closed. Yours hasn't got one of those.)
I have had a couple of ECU's fail - one went very rich with lots of black smoke & the other made the car run as rough as a rough thing. Switching to LPG restored normal running so ruled out the ignition side of things. I do have spare ecus for mine & substitution made the problem go away. Mine is the flapper type which are known for problems but yours should be the hotwire.
They don't like cheapie dizzy caps & DO NOT use a rotor arm that has the metal strip riveted to the plastic. If you want to remove he rotor arm you MUST press down on the reluctor (eight pointed star shaped thingy under the rotor arm) as you pull or will very likely disengage the auto advance/retard mech in the bottom of the dizzy bowl & it may not run at all. Checked by turning the rotor arm with your fingers, Once released it should snap smartly back to its original position.
Route the leads as per the manual to avoid crossfiring issues.
If you don't have a workshop manual you should get one. Yours should be covered by the RAVE disc - used to be able to get it for free off the net but is also available on ebay. Work through the diagnostic section.
Edited by paintman on Sunday 12th November 20:10
Some tools would be useful.
Infra red temp gun. point at each exhaust port will show which ones are not playing the game.
Rovergauge...A splendid piece of software that (with a suitable lead) will read what is going on in the ECU and will point at bad temp senders, bad MAF, bad throttle pot, bad lambda etc. Look in the PH TVR classifieds for Blitzracing who makes and sells the leads and will also supply the software and instructions.
Steve
Infra red temp gun. point at each exhaust port will show which ones are not playing the game.
Rovergauge...A splendid piece of software that (with a suitable lead) will read what is going on in the ECU and will point at bad temp senders, bad MAF, bad throttle pot, bad lambda etc. Look in the PH TVR classifieds for Blitzracing who makes and sells the leads and will also supply the software and instructions.
Steve
Thanks for the links - really useful. I shall spend some quality in the office tomorrow reading those!
I’ll take a look at the diagnostic tool too. It might sound stupid but I find anything diagnostic related really daunting. I can do simple DIY stuff but get myself so stressed out with anything else. However, I will give this a go!
Cheers
I’ll take a look at the diagnostic tool too. It might sound stupid but I find anything diagnostic related really daunting. I can do simple DIY stuff but get myself so stressed out with anything else. However, I will give this a go!
Cheers
Just to reiterate the above, all my Rover V8s have been very particular about plug leads & distributor cap. I also found once I replaced, for example, the leads, that this then showed up a weakness in the cap. And the cap needs to be a good one - I tried a cheap generic jobbie and it was no better than the cracked one it replaced.
Plugs - less so - I realised a while back that I was still running the plugs I'd bought it with in 2008 which were some crappy cheap brand - but it never missed a beat on em. Now changed, however....
Plugs - less so - I realised a while back that I was still running the plugs I'd bought it with in 2008 which were some crappy cheap brand - but it never missed a beat on em. Now changed, however....
Harleyboy said:
Thanks for the links - really useful. I shall spend some quality in the office tomorrow reading those!
I’ll take a look at the diagnostic tool too. It might sound stupid but I find anything diagnostic related really daunting. I can do simple DIY stuff but get myself so stressed out with anything else. However, I will give this a go!
Cheers
Don't get stressed by Rovergauge it is very simple. It does not do any programming just shows some readings from which you can apply logic to understand.I’ll take a look at the diagnostic tool too. It might sound stupid but I find anything diagnostic related really daunting. I can do simple DIY stuff but get myself so stressed out with anything else. However, I will give this a go!
Cheers
Example....There are two temp sensors, coolant temp, fuel temp......if the car has not been started and you plug in RG both temps should read about the same and ambient. Logic says if one is reading way off then you have found an issue.
The same sort of simple logic can be applied to all the other readings.
If you want to have an in depth read try http://www.g33.co.uk/pages/technical_fuel_injectio...
Steve
tight fart said:
Have you changed any spark plugs or just cleaned 6 of them?
They aren't that old - maybe 3-4 years. At that point 7 of 8 were changed. 6 are now cleaned.any tips for removal of sticking plugs? Someone suggested WD40 or spraying Coke around them. I have two long extension bars on them to no avail and am nervous about snapping them off. I pulled the plugs off whilst running and each had a negative impact on how the car ran. However, removing all leads one by one seemed to make it run even worse so I was unabble to pinpoint if I had issues with specific cylinders.
Steve_D said:
Don't get stressed by Rovergauge it is very simple. It does not do any programming just shows some readings from which you can apply logic to understand.
Example....There are two temp sensors, coolant temp, fuel temp......if the car has not been started and you plug in RG both temps should read about the same and ambient. Logic says if one is reading way off then you have found an issue.
The same sort of simple logic can be applied to all the other readings.
If you want to have an in depth read try http://www.g33.co.uk/pages/technical_fuel_injectio...
Steve
Thanks - think its worth a go and not expensive to buy eitherExample....There are two temp sensors, coolant temp, fuel temp......if the car has not been started and you plug in RG both temps should read about the same and ambient. Logic says if one is reading way off then you have found an issue.
The same sort of simple logic can be applied to all the other readings.
If you want to have an in depth read try http://www.g33.co.uk/pages/technical_fuel_injectio...
Steve
Arnold Cunningham said:
Just to reiterate the above, all my Rover V8s have been very particular about plug leads & distributor cap. I also found once I replaced, for example, the leads, that this then showed up a weakness in the cap. And the cap needs to be a good one - I tried a cheap generic jobbie and it was no better than the cracked one it replaced.
Plugs - less so - I realised a while back that I was still running the plugs I'd bought it with in 2008 which were some crappy cheap brand - but it never missed a beat on em. Now changed, however....
I changed the leads even though the old ones are only 3 years old. The cap came with the Powerspark distributor and it runs equally badly with the old or new one!Plugs - less so - I realised a while back that I was still running the plugs I'd bought it with in 2008 which were some crappy cheap brand - but it never missed a beat on em. Now changed, however....
Harleyboy said:
They aren't that old - maybe 3-4 years. At that point 7 of 8 were changed. 6 are now cleaned.
Unfortunately it is kind of job no 1 to have them out if you are suffering a misfire, they will/can tell you lots even if they are working correctly.Plus gas/WD40 only work if you can get them moving.
Try both with engine hot & cold & also try tightening/loosening alternately. As soon as you can move them even by the smallest amount get some lubrication in there & keep rocking them in/out and they will come free.
Diesel is as good as anything for penetrating rusty/stiff threads.
Just in case anyone is checking in, i have made some progress! Not exactly fixed it mind you but one of the stuck plugs is out and changed. No impact. The other one has snapped and im waiting to borrow the skills of a friend to try and get it out. Only the ceramic, not the thread thankfully.
Whilst i had it running, i pulled injectors and could tell no difference on one of the cylinders, possibly two so think this may be the issue. I need to get plugs in and then try the injector thing again before getting them off for cleaning.
Fingers crossed the plug comes out!
Whilst i had it running, i pulled injectors and could tell no difference on one of the cylinders, possibly two so think this may be the issue. I need to get plugs in and then try the injector thing again before getting them off for cleaning.
Fingers crossed the plug comes out!
Harleyboy said:
Only the ceramic, not the thread thankfully.
That suggests you may be getting the socket alignment wrong, or failing to support the socket so it is putting a bending load on the plug.In any case, having a broken ceramic should not make the slightest difference to taking the plug out.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff