Over fueling when cold start up
Discussion
Hi Guys, a little help needed please.
Have recently replaced the HT lead set with a ceramic type to replace the plug extenders which were starting to cause issues, a fresh set of plugs BPR6ES which is what I have always used.
Everything was perfect on test run out and very pleased, however did notice the rev counter was a bit unstable – before the lead and plug change it was perfect.
Now have a problem with over fueling when cold start – very lumpy and wants to stall with the slightest use of throttle – once a bit of temp comes up runs fine. Occasionally if sat for a few hours although slightly warm it stalls and very difficult to start.
Thinking of changing the temp sensor, but would have thought a faulty one would cause problem over total temp range.
Now thinking that the changing HT leads may have started another problem, with the tacho a bit bouncy on the move perhaps getting some interference and upsetting the ecu.
Any input very welcome.
Have recently replaced the HT lead set with a ceramic type to replace the plug extenders which were starting to cause issues, a fresh set of plugs BPR6ES which is what I have always used.
Everything was perfect on test run out and very pleased, however did notice the rev counter was a bit unstable – before the lead and plug change it was perfect.
Now have a problem with over fueling when cold start – very lumpy and wants to stall with the slightest use of throttle – once a bit of temp comes up runs fine. Occasionally if sat for a few hours although slightly warm it stalls and very difficult to start.
Thinking of changing the temp sensor, but would have thought a faulty one would cause problem over total temp range.
Now thinking that the changing HT leads may have started another problem, with the tacho a bit bouncy on the move perhaps getting some interference and upsetting the ecu.
Any input very welcome.
What are the HT leads? The bouncy tacho is a symptom of uncontrolled discharge of the coil when the HT lead resistance is too low. Magnecore blue and red leads are bad for this. If the car is misfiring, it will over fuel as unburnt mixture is picked up as a lean mixture, so the ECU will chuck in more fuel.
Thanks Mark for your comments
The leads are from RaceTech made up for the Rover V8 with 8mm resistive lead and ceramic cap.
Should have said before am running non cats with the non cat map, do not have misfire just this very bad lumpy start up which clears maybe 3 / 4 mins with temp.
After a run out with car running fine can park up for a few hours and sometimes have difficulty in restarting (catches then dies) sometimes had to take out pump relay, initial start ok then dies with no fuel, put relay back in and starts ok, replaced both pump relays just after lead change because one failed and pump would not prime.
Actually just thought that some relays keep running so maybe this may be problem and leads red hearing ? Relays form Powers so would have thought ok
The leads are from RaceTech made up for the Rover V8 with 8mm resistive lead and ceramic cap.
Should have said before am running non cats with the non cat map, do not have misfire just this very bad lumpy start up which clears maybe 3 / 4 mins with temp.
After a run out with car running fine can park up for a few hours and sometimes have difficulty in restarting (catches then dies) sometimes had to take out pump relay, initial start ok then dies with no fuel, put relay back in and starts ok, replaced both pump relays just after lead change because one failed and pump would not prime.
Actually just thought that some relays keep running so maybe this may be problem and leads red hearing ? Relays form Powers so would have thought ok
Running green takes any misfires or lambda correction out of the equation. The next culprits would be AFM or water temp sensor. The water temp is easy to test as its the same device as the fuel rail sensor, so you can unplug them both and do a resistance check on a cold engine as see if the resistance is the same. Afm voltages can be tested with a volt meter at idle as below, about quarter way down the page. Another thing to check is the AFM CO trim voltage, as if this is high it will over fuel horribly. Typical trim voltage is around 1 to 1.4 volts, turning the screw clockwise makes the engine run richer.
http://www.g33.co.uk/pages/technical-fuel-injectio...
It wont be relays causing the issue for sure- as they simply switch the pump on and off.
http://www.g33.co.uk/pages/technical-fuel-injectio...
It wont be relays causing the issue for sure- as they simply switch the pump on and off.
Edited by blitzracing on Tuesday 4th September 11:19
So you're saying the issue appeared immediately after you changed your leads 
Sorry to state the obvious, but my money would be on HT leads
Try reinstating your old leads and see if normal service is resumed
The pulse that drives your tacho is a very sensitive signal and your ignition system produces a very high voltage, a bouncing tacho needle is therefore a classic sign that one or more of your leads is shorting, it's no coincidence the bouncing rev counter and the cold start issue coincided with the change of HT leads.
Remember, electricity will always find the easiest route to earth, if your leads are shorting to the block or cross firing between leads you can usually see this easily by running the engine up in the dark, you will however need a pitch dark environment to see it, you will likely hear a tick as the spark jumps to the block too.
It's worth noting the ACCEL ceramic leads come into the UK as universal set, RaceTech will crimping the distributor ends on to suit the Lucas dizzy cap before sending them out, if the crimping work wasn't good on one or more of the leads this will give the issue you describe.
I very much doubt your engine is over fueling, whats likely happening is the fuel present is not being burnt because you have a weak or missing spark on one or more cylinders, I suspect this is because a lead or two is shorting to the block. During cold start your injection system throws a huge amount of fuel at the engine, if the spark isn't strong enough or its missing altogether combustion will either be incomplete or nonexistent on one or more cylinder. As the engine warms less fuel is needed so the injection system reduces the injector durations dramatically, at this point a weak spark may be sufficient to provide complete combustion of the reduced fuel present which is why your engine comes good when warm.
Also keep in mind the other very voltage sensitive component that can be effected is your idle valve (stepper motor), unlike the tacho bounce which is staring you in the face the behavior of your stepper motor is invisible without plugging in your laptop and using the Rover Gauge software. If your stepper motor is being affected by your new leads this can compound the issue as not only is your ECU trowing in a tonne more fuel on cold start it also opens the stepper motor to let in a lot of air too, if this isn't happening the car will very easily flood as the air fuel ratio will be even richer.
I'd try the pitch dark check for shorts first, you'll see the sparks for sure if it's dark enough and the leads are shorting, then to finally confirm this is the source of the problem refit your old leads and try one cold start to see if the problem disappears.
https://www.youtube.com/watch?v=vOgBRTCPpys
Sorry to state the obvious, but my money would be on HT leads
Try reinstating your old leads and see if normal service is resumed
The pulse that drives your tacho is a very sensitive signal and your ignition system produces a very high voltage, a bouncing tacho needle is therefore a classic sign that one or more of your leads is shorting, it's no coincidence the bouncing rev counter and the cold start issue coincided with the change of HT leads.
Remember, electricity will always find the easiest route to earth, if your leads are shorting to the block or cross firing between leads you can usually see this easily by running the engine up in the dark, you will however need a pitch dark environment to see it, you will likely hear a tick as the spark jumps to the block too.
It's worth noting the ACCEL ceramic leads come into the UK as universal set, RaceTech will crimping the distributor ends on to suit the Lucas dizzy cap before sending them out, if the crimping work wasn't good on one or more of the leads this will give the issue you describe.
I very much doubt your engine is over fueling, whats likely happening is the fuel present is not being burnt because you have a weak or missing spark on one or more cylinders, I suspect this is because a lead or two is shorting to the block. During cold start your injection system throws a huge amount of fuel at the engine, if the spark isn't strong enough or its missing altogether combustion will either be incomplete or nonexistent on one or more cylinder. As the engine warms less fuel is needed so the injection system reduces the injector durations dramatically, at this point a weak spark may be sufficient to provide complete combustion of the reduced fuel present which is why your engine comes good when warm.
Also keep in mind the other very voltage sensitive component that can be effected is your idle valve (stepper motor), unlike the tacho bounce which is staring you in the face the behavior of your stepper motor is invisible without plugging in your laptop and using the Rover Gauge software. If your stepper motor is being affected by your new leads this can compound the issue as not only is your ECU trowing in a tonne more fuel on cold start it also opens the stepper motor to let in a lot of air too, if this isn't happening the car will very easily flood as the air fuel ratio will be even richer.
I'd try the pitch dark check for shorts first, you'll see the sparks for sure if it's dark enough and the leads are shorting, then to finally confirm this is the source of the problem refit your old leads and try one cold start to see if the problem disappears.
https://www.youtube.com/watch?v=vOgBRTCPpys
lancelin said:
Coor, id like to know peoples thoughts on plug lead resistance. My car ran like rubbish with low resistance leads!
That's a rather sweeping statement... What spark plugs were you using, and what make were the leads?As long as you're running resistor spark plugs BPR6ES ect you really shouldn't have an issue with low resistance plug leads, assuming that is they're good quality leads. If they were Magnecors I wouldn't call them good quality, expensive yes.... good quality not so much
I've been running a set of MSD Super Conductor HT leads for years, these are not only exceptional quality they also have the lowest resistance of any leads available. As long as you've got those essential resistor plugs MSD Super Conductor low resistance HT leads work absolutely brilliantly as proved my tens of thousands of hot rodders that use them in the States, over the pond they are well accepted as the best leads you can get.
Issues caused by HT leads being low resistance is a red herring, on the other hand..... issues with Magnecors are common
Problem is in this case we have no lambda feedback to make it run rich, so your only option is a misfire, thats dumping un burnt fuel into the exhaust so it smells rich. The real telling would be to pull the plugs out- if they are jet black and sooty its rich, if they are washed clean its likely to be a misfire.
I had the same issue with mine. Swapped out the rubbish extenders for new standard HT leads with woven heat shields, resistive spark plugs, new rotor arm, new ignition amp and new distributor cap. Also used the lead separator's to run the HT leads in the best way possible.
It totally changed the engine and it has been running perfectly since. I would agree the over fuelling I had was actually due to lack of ignition than any fuelling issue itself. I tried to use what I felt was the best quality parts I could get as well.
It totally changed the engine and it has been running perfectly since. I would agree the over fuelling I had was actually due to lack of ignition than any fuelling issue itself. I tried to use what I felt was the best quality parts I could get as well.
Thanks Guys for all the comments, which has lead me to the problem.
Because the car ran well once up to temp, did not have any missfire or issue, only when cold, this situation was not straight after changing the leads but came on a little while later just after the pump relay packed in.
So with all the advise started to go through in a logical way to find the issue and now solved.
The ceramic plug caps are quite difficult to push over the plug as they have a very tight o ring at the entry, they also do not engage with a positive click, all making it difficult to know it is fitted correct.
The cap can be pushed all the way down over the plug until it feels fine, then after a couple of mins the cap will start to creap up the plug, perhaps due to air pressure trapped in the cap, will look for a solution to stop this happening.
So there we have it, the connection to plug being problem, when cold not enough volts to ignite all the fuel and causing power to bog down.
The leads are well made as expected for the price, but do not feel totaly satisfied straight out of the box.
Because the car ran well once up to temp, did not have any missfire or issue, only when cold, this situation was not straight after changing the leads but came on a little while later just after the pump relay packed in.
So with all the advise started to go through in a logical way to find the issue and now solved.
The ceramic plug caps are quite difficult to push over the plug as they have a very tight o ring at the entry, they also do not engage with a positive click, all making it difficult to know it is fitted correct.
The cap can be pushed all the way down over the plug until it feels fine, then after a couple of mins the cap will start to creap up the plug, perhaps due to air pressure trapped in the cap, will look for a solution to stop this happening.
So there we have it, the connection to plug being problem, when cold not enough volts to ignite all the fuel and causing power to bog down.
The leads are well made as expected for the price, but do not feel totaly satisfied straight out of the box.
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