3.9 hesitation and occasional holding back
Discussion
Hi folks,
I’m posting in your section because there are not many examples of my car about - I know it’s a bit of a long shot.
We have just resurrected a neglected 1993 MG RV8 which, I know has basically the same 3.9 EFI engine as many LR vehicles. We only just mot’d it a week ago and taxed it June 1st. We went for its first proper run yesterday - the first in almost 20 years - long story!
It starts well from cold and appears to be on all 8. We drove about 20 miles and when accelerating it sometimes felt like someone had hold of the rear bumper, then without altering the pedal it would take off as expected. Didn’t seem to be misfiring but just perhaps underfuelled. Later we pulled up behind some standing traffic and the revs dropped to around 500 with a definite miss. Thinking it would splutter and die just the cars moved away, I was pleasantly surprised that the revs went back to normal and we went on our way.
I realise it’s early to condemn it until it has a few more miles under its belt (it’s only done 50k anyway)
It has the 5 AM airflow meter 14CUX ecu and most sensors common to the LR
I replaced all of the ignition stuff as a matter of course but this definitely feels more like air/fuel.
Any ideas from the collective?
Ian
I’m posting in your section because there are not many examples of my car about - I know it’s a bit of a long shot.
We have just resurrected a neglected 1993 MG RV8 which, I know has basically the same 3.9 EFI engine as many LR vehicles. We only just mot’d it a week ago and taxed it June 1st. We went for its first proper run yesterday - the first in almost 20 years - long story!
It starts well from cold and appears to be on all 8. We drove about 20 miles and when accelerating it sometimes felt like someone had hold of the rear bumper, then without altering the pedal it would take off as expected. Didn’t seem to be misfiring but just perhaps underfuelled. Later we pulled up behind some standing traffic and the revs dropped to around 500 with a definite miss. Thinking it would splutter and die just the cars moved away, I was pleasantly surprised that the revs went back to normal and we went on our way.
I realise it’s early to condemn it until it has a few more miles under its belt (it’s only done 50k anyway)
It has the 5 AM airflow meter 14CUX ecu and most sensors common to the LR
I replaced all of the ignition stuff as a matter of course but this definitely feels more like air/fuel.
Any ideas from the collective?
Ian
Try here:
http://www.britishv8.org/Articles/Rover-14CUX-EFI....
Throttle potentiometer faulty so intermittent loss of throttle demand hence impression of losing power?
http://www.britishv8.org/Articles/Rover-14CUX-EFI....
Throttle potentiometer faulty so intermittent loss of throttle demand hence impression of losing power?
That’s a great resource, many thanks. I’ll check to see whether there are any jumps in resistance along the sweep of the pot. I have Rover gauge software on my laptop which I bought when we first got the car about 18 months ago but I have since put the USB adaptor lead somewhere very safe! There was so much else needing attention I don’t remember where I put it. When I eventually find the damned thing I’ll see what else seems out of spec.
Thanks again,
Ian
Thanks again,
Ian
Other points to consider.
The RV8 doesn't like pattern ignition parts.
Don't use rotor arms that have the metal strip riveted onto the plastic. Use the ones that are moulded on.
Patterns caps can allow crossfiring. Look for the type that has a lot of shrouding internally & with the 8 outs to the leads shielded on all but the side that faces the rotor arm.
If you remove the rotor arm you MUST press down on the reluctor as you pull the rotor arm - the 8-pointed star thingy under the rotor arm - or you can disengage the auto advance/retard springs in the lower part of the dizzy. Check by turning the rotor arm with your fingers. When released it should return to its original position. If a rotor arm is really stuck then breaking it up to remove it is the best option.
Check the leads aren't touching as this may cause crossfiring. Additional cable clips are cheap enough.
The RV8 doesn't like pattern ignition parts.
Don't use rotor arms that have the metal strip riveted onto the plastic. Use the ones that are moulded on.
Patterns caps can allow crossfiring. Look for the type that has a lot of shrouding internally & with the 8 outs to the leads shielded on all but the side that faces the rotor arm.
If you remove the rotor arm you MUST press down on the reluctor as you pull the rotor arm - the 8-pointed star thingy under the rotor arm - or you can disengage the auto advance/retard springs in the lower part of the dizzy. Check by turning the rotor arm with your fingers. When released it should return to its original position. If a rotor arm is really stuck then breaking it up to remove it is the best option.
Check the leads aren't touching as this may cause crossfiring. Additional cable clips are cheap enough.
Thanks Paintman,
I used the best that Clive Wheatley (MG RV8 man) sells, used standard leads not Magnacor and was careful with lead routing, decent cap and arm. Good tip about the reluctor ring - will check that.
Cleaned the MAF sensor after removing one end cover and making new gasket. Also checked and cleaned the idle air stepper motor which was quite clean anyway and moves OK. I would normally only try one thing at once but I’d like to go to the John O’ Groats Rally on Sunday and time is running away fast. (We are in Orkney, so not too far!)
It quite driveable but I’m sure a new one didn’t misbehave at the price they were back then.
Ian
I used the best that Clive Wheatley (MG RV8 man) sells, used standard leads not Magnacor and was careful with lead routing, decent cap and arm. Good tip about the reluctor ring - will check that.
Cleaned the MAF sensor after removing one end cover and making new gasket. Also checked and cleaned the idle air stepper motor which was quite clean anyway and moves OK. I would normally only try one thing at once but I’d like to go to the John O’ Groats Rally on Sunday and time is running away fast. (We are in Orkney, so not too far!)
It quite driveable but I’m sure a new one didn’t misbehave at the price they were back then.
Ian
Edited by Orcadian on Monday 3rd June 13:14
Thanks for that,
I did check when I replaced all the ignition stuff not long after we bought it but certainly worth another look. The strange thing though now we are actually using it, is that if you gently accelerate to around 3500 rpm (in any gear) it’s slightly holding back but when it hits that point you can feel it surge either on to a full 8 pots or now has enough fuel/air for all.
Ian
I did check when I replaced all the ignition stuff not long after we bought it but certainly worth another look. The strange thing though now we are actually using it, is that if you gently accelerate to around 3500 rpm (in any gear) it’s slightly holding back but when it hits that point you can feel it surge either on to a full 8 pots or now has enough fuel/air for all.
Ian
It may seem obvious, but are the spark plugs OK?
Years ago, Mrs D.R. had a VW Golf that gave very similar symptoms to those you describe. After a £500 bill from the VW garage for loads of new ignition components, the thing then refused to start. VW refused to come and get it so the local garage came round and dragged it away. They returned it an hour or so later with four new spark plugs and running better than it had for months!
Years ago, Mrs D.R. had a VW Golf that gave very similar symptoms to those you describe. After a £500 bill from the VW garage for loads of new ignition components, the thing then refused to start. VW refused to come and get it so the local garage came round and dragged it away. They returned it an hour or so later with four new spark plugs and running better than it had for months!
As it had been sitting around for 2 decades, I replaced all ignition parts with new, including all 8 plugs, leads etc but I do know what you mean and my Honda 400/4 runs better on new plugs - I think this modern fuel somehow gets into the porcelain! No idea how that could be though. By way of an update we have now done close on 200 miles in it and after holding the revs at 4000 occasionally (past the 3500 rpm change point) it certainly seems to be settling down. Many folk have reported that they run rough if left without use. I have also found my USB lead so will check it out with RoverGauge when time permits - we might just have to go the JOG Rally ‘as is’ on Sunday and sort it later without rushing.
Thanks again,
Ian
Thanks again,
Ian
By way of an update,
We had a great run down from Orkney to the John O’ Groats 50th Rally yesterday and the car is now settling down a bit - still not quite there yet and runs well when out on the open road but as soon as we pulled up in traffic it idled roughly for a while before coming back to near normal tickover. Having found my RoverGauge lead and disc, I checked this morning and it has 2 fault codes stored - Lambda sensor on odds (left bank) and idle stepper. I’ve suspected the Lambda since I first checked as the fuel trim changed when it became lumpy on tick-over. Ordered a new one so will report back when fitted. Not sure yet about the stepper as it shows up as 100% when engine not running (shut) and a lowish percentage when running.
Ian
We had a great run down from Orkney to the John O’ Groats 50th Rally yesterday and the car is now settling down a bit - still not quite there yet and runs well when out on the open road but as soon as we pulled up in traffic it idled roughly for a while before coming back to near normal tickover. Having found my RoverGauge lead and disc, I checked this morning and it has 2 fault codes stored - Lambda sensor on odds (left bank) and idle stepper. I’ve suspected the Lambda since I first checked as the fuel trim changed when it became lumpy on tick-over. Ordered a new one so will report back when fitted. Not sure yet about the stepper as it shows up as 100% when engine not running (shut) and a lowish percentage when running.
Ian
Got there in the end!
Replaced the Lambda sensor on the ‘odds’ bank (left) and removed the stepper motor and bunged it in the ultrasonic bath, lots of muck came out even though it looked clean beforehand. Cleared codes, reassembled and went out for a 50 odd mile run and it performs as it should. No hesitation, crisp take up of throttle and a good tick-over when you come to a halt. No codes stored anymore. Just wants using regularly now - off to the Tain Rally next Sunday, about a 200 mile round trip.
Thanks to those who made suggestions,
Ian
Replaced the Lambda sensor on the ‘odds’ bank (left) and removed the stepper motor and bunged it in the ultrasonic bath, lots of muck came out even though it looked clean beforehand. Cleared codes, reassembled and went out for a 50 odd mile run and it performs as it should. No hesitation, crisp take up of throttle and a good tick-over when you come to a halt. No codes stored anymore. Just wants using regularly now - off to the Tain Rally next Sunday, about a 200 mile round trip.
Thanks to those who made suggestions,
Ian
Although it’s really in the wrong section, I felt it important to report the success as someone might experience the same problem sometime. I’m on other sections - Jag, Classic Mini and some other bike stuff and I know how frustrating it is when advice is requested and never acknowledged - it’s important to share and even at 70, every day is a school day! Thanks again,
Ian
Ian
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