Symptoms normal? Speed sensitive rough running
Discussion
I have a stock 400. Sometimes after I have been driving for a bit, I will find that when I'm back in first gear, the car will stumble significantly. If I try to drive thru the gear, power will be flat and boggy until 3500rpm and then it takes off. Alternatively if I quickly short shift to second gear it seems to run much better. Is there an aspect of the ecu or ignition that is knows the car is in 1st gear? Could it be a faulty stepper valve or a vacuum problem, or perhaps a static ingnition problem. I would generally say that low to mid range throttle running is generally a bit choppy where I wonder if I might not be running on all cylinders all the time
Thoughts?
Also, I have a Lucas code reader. Where do I plug that into?
Thoughts?
Also, I have a Lucas code reader. Where do I plug that into?
You need to make sure the basics are correct first so start by checking your dynamic ignition timing using an advance strobe ensuring the distributor is also advancing correctly as you increase engine speed. Check the function of your vacuum advance system, apply a vacuum to the vac advance module while observing the timing marks with your strobe, check the integrity of the vac hose itself and make sure the little nipple it draws air from on the top of the plenum is not blocked. Finally follow the correct procedure for setting your base idle, lots of good first principle base tuning information here
http://www.actproducts.co.uk/2011/lucas-14cux-fuel...
Next look at the ignition side in more detail
1. Fit BPR6ES plugs or better still BPR6EIX instead of the inappropriate B7ECS chosen by TVR
2. Delete the dreadful plug extenders and find another way to protect your HT lead ends from manifold heat, here's my long term proven system
http://www.pistonheads.com/gassing/topic.asp?t=143...
3. Replace your ignition leads with a quality set, I'm a big fan of MSD Superconductors
4. Inspect your distributor cap and replace if you see any carbon tracking, corroded posts or issues with the central sprung carbon brush that connects your coil to the rotor arm
5. Replace your rotor arm if it's not got the name Lucas cast into it or it's red as there are lots of poor quality black after market rotor arms in circulation, the red ones by the way are from The distributor Doctor and are the only after market ones worth having
6. If you have misfires & running issues when hot it may be the coil breaking down, if you choose to replace it buy a Bosch one from a Land Rover spares specialist
7. The ignition amp can also give trouble but as with all the above test the component don't just replace it in the blind hope you'll be lucky & stumble on the problem
Now for vacuum leaks
1. Suspect the crankcase ventilation system, check all hoses especially where they are merely a push fit into a barbed joiner, years of hot acidic crankcase oil mist makes rubber hoses baggy so they tend to leak where no hose clip is used, where a hose clip is used make sure it's properly tight
2. Check all other hoses for cracks & splits, make sure each hose clip is tight, focus particularly on the hoses engine side of the throttle butterfly (connected to the plenum) as these are under full engine vacuum at idle and are most likely to give idle and general running issues. Connected to the plenum are the PCV hose mentioned above in point 1, the brake servo and the carbon canister purge system. Its worth noting only the brake servo has a check valve so any burp or momentary pulse of positive pressure within the plenum when transitioning from on/off throttle can pass up the PCV hose to just in front of the throttle butterfly (atmosphere side) right where the stepper motor is drawing its air in a bid to regulate idle speed ect, these pulses do nothing for drivbility and can be contributing factor to the condition commonly referred to on these pages as "shunting"
3. If you do find and rectify a vacuum leak you will need to repeat the base idle setting procedure
The Stepper Motor
1. Well worth removing and cleaning, it draws its air from atmosphere side of the throttle butterfly just in front of it, the less than ideal air at this point is actually quite turbulent can contain dirty blow by gasses as the crankcase ventilation system shares the same throttle pick-up point (opposite), carbon deposits build up on the stepper tip causing sealing issues
2. There's little point in cleaning the stepper motor if you don't clean it's housing too, to do this you'll need to remove the plenum
3. Follow the procedure for re-setting the stepper motor
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
4. Land Rover created a completely closed loop system of hose work where both the PVC system and the stepper motor share the same point of passive mild vacuum just in front throttle butterfly, this was for emissions. However, its asking an awful lot of the poor old stepper motor to accurately regulate idle speed when it's drawing on this dirty turbulent air, air that can swing rapidly from positive to negative pressure as the throttle is opened and closed. The stepper motor is just an ECU managed air bleed valve and a rather old tech crude one at that, as such it would work a lot better if it was drawing clean still air at atmospheric pressure rather than the dirty turbulent air just in front of the throttle butterfly Land Rover forced it to work with. People who fit an after market ECU tend to use the more accurate Bosch PWM rotary idle valve and plumb it so it's drawing clean still air at atmospheric pressure from the engine bay, this is a massive improvement on the Land Rover system. In my opinion people still on the 14CUX can learn from this, experiment by disconnecting the stepper motor hose from the steel pipe just in front of the throttle butterfly (the rear one of the two), leave it free to breath in the engine bay with a little filter fitted to stop dirt being ingested by the engine, now use a bung to completely seal the steel pipe and go for a test drive
The Uncomfortable Truth
There's a whole lot more to look at than the areas, systems and components I've listed above and diagnosing such issues is not something you can really expect to conduct over the internet, forums are extremely helpful but the uncomfortable truth is they seldom deliver the magic bullet solution to a complex problem.
You need the patient in front of you and good knowledge, you also need a systematic approach because your issue could be caused by an huge number of potential faults and its highly likely you actually have more than one issue. For example the car may well drive acceptably with a small vacuum leak or a slight/intermittent ignition misfire, it's not until you combine the two faults that you notice a significant reduction in idle quality and or drivability.
While there are a multitude of faults that could potentially be causing your poor drivability issues the above should help get you started and I hope my rather incomplete list leads you to your problem, what I've tried to do is point you in the direction of a few (more likely) areas to focus on initially but your success in finding the problem will be measured by your ability to work systematically using logic.
Avoid trying to fix the car by simply replacing components in the blind hope you'll be lucky enough to stumble on the fault or faults, be systematic and test each component to prove to yourself it's either working correctly or not. This approach will save you a lot of time and money and is how professionals fault find, its also why professionals are way more successful at finding faults than amateurs who adopt the "guess and replace" approach.
I'd wish you good luck but as we've already established luck has little to do with diagnosing and resolving mechanical & electrical faults, however I genuinely hope my contribution helps steer you towards locating & resolving your issue. I'll end all this by saying if at any time you feel the above might be a little beyond your skills there's absolutely no shame in recruiting the help of a professional, a good TVR specialist will find the problem way quicker than most and will likely save you money in the long run
Dave
http://www.actproducts.co.uk/2011/lucas-14cux-fuel...
Next look at the ignition side in more detail
1. Fit BPR6ES plugs or better still BPR6EIX instead of the inappropriate B7ECS chosen by TVR
2. Delete the dreadful plug extenders and find another way to protect your HT lead ends from manifold heat, here's my long term proven system
http://www.pistonheads.com/gassing/topic.asp?t=143...
3. Replace your ignition leads with a quality set, I'm a big fan of MSD Superconductors
4. Inspect your distributor cap and replace if you see any carbon tracking, corroded posts or issues with the central sprung carbon brush that connects your coil to the rotor arm
5. Replace your rotor arm if it's not got the name Lucas cast into it or it's red as there are lots of poor quality black after market rotor arms in circulation, the red ones by the way are from The distributor Doctor and are the only after market ones worth having
6. If you have misfires & running issues when hot it may be the coil breaking down, if you choose to replace it buy a Bosch one from a Land Rover spares specialist
7. The ignition amp can also give trouble but as with all the above test the component don't just replace it in the blind hope you'll be lucky & stumble on the problem
Now for vacuum leaks
1. Suspect the crankcase ventilation system, check all hoses especially where they are merely a push fit into a barbed joiner, years of hot acidic crankcase oil mist makes rubber hoses baggy so they tend to leak where no hose clip is used, where a hose clip is used make sure it's properly tight
2. Check all other hoses for cracks & splits, make sure each hose clip is tight, focus particularly on the hoses engine side of the throttle butterfly (connected to the plenum) as these are under full engine vacuum at idle and are most likely to give idle and general running issues. Connected to the plenum are the PCV hose mentioned above in point 1, the brake servo and the carbon canister purge system. Its worth noting only the brake servo has a check valve so any burp or momentary pulse of positive pressure within the plenum when transitioning from on/off throttle can pass up the PCV hose to just in front of the throttle butterfly (atmosphere side) right where the stepper motor is drawing its air in a bid to regulate idle speed ect, these pulses do nothing for drivbility and can be contributing factor to the condition commonly referred to on these pages as "shunting"
3. If you do find and rectify a vacuum leak you will need to repeat the base idle setting procedure
The Stepper Motor
1. Well worth removing and cleaning, it draws its air from atmosphere side of the throttle butterfly just in front of it, the less than ideal air at this point is actually quite turbulent can contain dirty blow by gasses as the crankcase ventilation system shares the same throttle pick-up point (opposite), carbon deposits build up on the stepper tip causing sealing issues
2. There's little point in cleaning the stepper motor if you don't clean it's housing too, to do this you'll need to remove the plenum
3. Follow the procedure for re-setting the stepper motor
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
4. Land Rover created a completely closed loop system of hose work where both the PVC system and the stepper motor share the same point of passive mild vacuum just in front throttle butterfly, this was for emissions. However, its asking an awful lot of the poor old stepper motor to accurately regulate idle speed when it's drawing on this dirty turbulent air, air that can swing rapidly from positive to negative pressure as the throttle is opened and closed. The stepper motor is just an ECU managed air bleed valve and a rather old tech crude one at that, as such it would work a lot better if it was drawing clean still air at atmospheric pressure rather than the dirty turbulent air just in front of the throttle butterfly Land Rover forced it to work with. People who fit an after market ECU tend to use the more accurate Bosch PWM rotary idle valve and plumb it so it's drawing clean still air at atmospheric pressure from the engine bay, this is a massive improvement on the Land Rover system. In my opinion people still on the 14CUX can learn from this, experiment by disconnecting the stepper motor hose from the steel pipe just in front of the throttle butterfly (the rear one of the two), leave it free to breath in the engine bay with a little filter fitted to stop dirt being ingested by the engine, now use a bung to completely seal the steel pipe and go for a test drive
The Uncomfortable Truth
There's a whole lot more to look at than the areas, systems and components I've listed above and diagnosing such issues is not something you can really expect to conduct over the internet, forums are extremely helpful but the uncomfortable truth is they seldom deliver the magic bullet solution to a complex problem.
You need the patient in front of you and good knowledge, you also need a systematic approach because your issue could be caused by an huge number of potential faults and its highly likely you actually have more than one issue. For example the car may well drive acceptably with a small vacuum leak or a slight/intermittent ignition misfire, it's not until you combine the two faults that you notice a significant reduction in idle quality and or drivability.
While there are a multitude of faults that could potentially be causing your poor drivability issues the above should help get you started and I hope my rather incomplete list leads you to your problem, what I've tried to do is point you in the direction of a few (more likely) areas to focus on initially but your success in finding the problem will be measured by your ability to work systematically using logic.
Avoid trying to fix the car by simply replacing components in the blind hope you'll be lucky enough to stumble on the fault or faults, be systematic and test each component to prove to yourself it's either working correctly or not. This approach will save you a lot of time and money and is how professionals fault find, its also why professionals are way more successful at finding faults than amateurs who adopt the "guess and replace" approach.
I'd wish you good luck but as we've already established luck has little to do with diagnosing and resolving mechanical & electrical faults, however I genuinely hope my contribution helps steer you towards locating & resolving your issue. I'll end all this by saying if at any time you feel the above might be a little beyond your skills there's absolutely no shame in recruiting the help of a professional, a good TVR specialist will find the problem way quicker than most and will likely save you money in the long run
Dave
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