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Olliedyer97

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Hi guys, me again, a follow on from last post, found another local Land Rover specialist who point my in the direction of fuel pump and pressure regulator being the reason for the misfire and low idle after everything else I’ve replace, replaced them and still no odd, had all adaptive vales reset as well and it’s still horrific, apon further investigation I’ve found the part number on the o2 sensors supplied from a local LR dealer to be fae77350 although they should be amr6244, do any of you know if the fact they’re either the wrong part or a cheaper option for the misfire/poor idle, also to note, when driving if held at a steady throttle ie holding at 30mph, will splutter until you either let off or floor it

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Land Rover don't manufacture the lambda sensors (in fact, like all manufacturers, they don't manufacture most bits, they just bolt together bits from other suppliers), they will be made by someone that specialises is that particular component and given a Land Rover part number. So AMR6244 may be FAE77350, NTK0475 (NGK0475), Walker 250-24512 to name just a few depending on who made it for them. If the plug is correct, it will be the correct part.

What does live data show from the lambda sensors show when it is running rough compared with what it says when running correctly? When you let off the throttle, it will go lean as the injectors are cut off on the overrun to save fuel and give better engine braking, so try to check it when accelerating if it is running cleanly then.

Olliedyer97

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Gilbertd wrote:

Land Rover don't manufacture the lambda sensors (in fact, like all manufacturers, they don't manufacture most bits, they just bolt together bits from other suppliers), they will be made by someone that specialises is that particular component and given a Land Rover part number. So AMR6244 may be FAE77350, NTK0475 (NGK0475), Walker 250-24512 to name just a few depending on who made it for them. If the plug is correct, it will be the correct part.

What does live data show from the lambda sensors show when it is running rough compared with what it says when running correctly? When you let off the throttle, it will go lean as the injectors are cut off on the overrun to save fuel and give better engine braking, so try to check it when accelerating if it is running cleanly then.

Olliedyer97

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Plugs in okay, but did have a code p1190, Oxygen Sensor Heater Type 2 Low Resistance Upstream, On live data they show 0.14-0.61v, fuel trims will also show -25% on both banks, they don’t really change when running, I’ve ordered the new “correct” o2 sensors as was told that the fuel trims are calculated by the o2 sensors and they could throw the other readings out and cause this but wanted to know if anyone else has experienced this

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Assuming your reader is converting the 5-0V reading into an OBD2 compliant 0-1V reading, the short term trims should be changing. When showing 0.14V, the short term trims should go positive (lean mixture so the trims put more fuel in), when showing 0.61V, the trims should go negative.

What are the long term trims showing? If the adaptive values have been reset, they should be showing zero. One thing does spring to mind though. On a GEMS, the adaptive values won't reset unless you have at least a 1/4 tank of fuel in the car so it doesn't reset anything that could have been caused by a low fuel level. How much is in it and have the values all reset to zero?

Olliedyer97

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Gilbertd wrote:

Assuming your reader is converting the 5-0V reading into an OBD2 compliant 0-1V reading, the short term trims should be changing. When showing 0.14V, the short term trims should go positive (lean mixture so the trims put more fuel in), when showing 0.61V, the trims should go negative.

What are the long term trims showing? If the adaptive values have been reset, they should be showing zero. One thing does spring to mind though. On a GEMS, the adaptive values won't reset unless you have at least a 1/4 tank of fuel in the car so it doesn't reset anything that could have been caused by a low fuel level. How much is in it and have the values all reset to zero?

Olliedyer97

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Even with change of o2 sensor readings the fuel trim stays -25%, long term remains the same and short term trims, fuel tank was just above 3/4 a tank when all was reset

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After the reset do all the long and short term trims go to zero? Which is it that is staying at -25%, long or short? What should happen is that the long term trims should be at zero, the short term trims will vary either side of zero going on the output from the lambda sensors. If the short term trims always go one way or the other, the long term trims will alter to bring the short term trims back to moving either side of zero. Whether or not your reader can display it, there is also a figure for AMFR which is a correction added or subtracted from the output of the MAF sensor so that will be read correctly. On my two GEMS cars both MAF sensors give slightly incorrect readings so one has an AMFR of around -2.3 while the other is showing +4.0. When the adaptive values are reset, these reset to zero but will be learnt when the engine is running. The Nanocom allows these to be written in to give a baseline starting point rather than starting from zero

Olliedyer97

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Sorry got confused there I think haha, the short term trim goes straight to -25% within seconds of resetting, my scanner doesn’t show long term, it did on the persons scanner that I had it reset with, although he wasn’t sure about them and said to drive it and see what happens, after the reset I plugged it into the scanner again today for another live reading to see what was happening, maf was 36kg/hr and stepper motor was reading 49 steps although before the reset they were 22.8kg/hr and stepper was at 17 steps, again short term fuel trim remains at -25% idle and under throttle

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Short term trim staying it -25% suggests the mixture is rich and it is trying to correct but that would also suggest that the lambda sensors are showing permanent lean. It might be worth putting a multimeter on the output of the sensors to see what they are actually reading rather than what the diagnostics are showing. Easiest place is on the back of the plug into the ECU, LH bank (bank 1) is on an Orange wire on pin 34 of C507 and the RH bank is on a Blue wire next to it on pin 33. C507 is the red (middle) plug on the ECU. A lean mixture will show as near to 5V while rich will show as near to 0V.

Olliedyer97

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I will try that tomorrow when I’m work again thank you, am I correct in saying that the fuel trim is done by the o2 sensors? Ie takes exhaust gasses and calculates the fuel/air required?

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Yes, the fuel pressure is a constant and amount of fuel that goes in is dictated by the length of time the injectors are open for. That is taken from the various sensors but primarily the MAF and throttle position sensor and the ECU uses a look up table to decide how long the injectors need to be open for (anything between 3mS and 15mS) under all different revs and load conditions. The lambda sensors are there as a final check so if the fuel pressure is slightly high or the MAF is reading a bit out for instance, the injector pulse duration is varied slightly to keep the mixture correct. That is the short term trim, so a little bit longer or shorter to keep things correct. If the short term trims are always going one way or another, the long term trims change to get the short term trims back to wandering either side of zero.

I recently bought another '98 (a 4.0SE) and had to drive it about 80 miles home. It didn't idle particularly well but seemed fine when being driven until I got within 15 miles of home when it started to misfire. As I had the Nanocom plugged in, I reset the adaptive values which made it much worse. It ran like a dog unless I was flooring it and the report from my missus who was following in my car, it was belching out black smoke (rich), stank of petrol and while the trip computer had been showing 21 mpg up until then, it had dropped to 16 mpg by the time I got it home. That showed a permanent 5.0V (lean) on both banks yet it was running like it was rich and the black spark plugs confirmed this. I found one lambda sensor was dead and the other one had one of the pins pushed out in the connector so it wasn't giving a reading. That is something else you could check, unplug the sensors and make sure all of the pins are there and none have been pushed out of the housing or are bent.

Olliedyer97

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Since our last message I’ve put new o2 sensors in, while watching the live data, short term fuel trim goes to 0% when revved where as before it constantly stayed at -25%, is that good? And will I need to reset adaptive values again?

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As it hasn't been run much since they were last reset, it shouldn't matter and once it has been run for a while they will adapt anyway. Is it staying in closed loop or going open? If in open loop (ignoring the output from the lambda sensors) it will default to zero and stay there. Normally the only time they go open loop is on the overrun or if the ECU has detected something it doesn't like and decides to go to a default fuel strategy which is always slightly rich to prevent engine damage. Your best bet is to try and hold it at 2,000-2,500 rpm and watch the lambda sensor outputs and short term trims. Neither should stay steady, as when the lambda sensor shows rich, the short term trim will go negative until it starts to show lean then it will go positive and it should continue to flip flop between the two extremes.

Olliedyer97

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Goes open loop when revving the goes back to closed loop when dropped back to idle, I’m going to see if I can find a fast live reading as the snap on at work has a bit of a delay before reading update so it’s hard to actually see what’s going on if that makes sense, it’s still very lumpy at idle, and wants to drop below 500rpm when at lights or coming to a stop

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It shouldn't do that, if anything it might go open loop at idle but stay in closed loop under normal running. It sounds very similar to how the 4.0SE I bought was running, that had lumpy idle and would sometimes die when stopping at lights (I was knocking it into Neutral and left foot braking so I could keep the revs up to stop it dying on me). As well as the lambda sensors, someone had turned the plunger on the idle air valve so broken the clip that stops it from rotating so rather than the stepper motor moving the plunger in and out, it was simply rotating. However as you've already replaced that, it can be discounted.

Olliedyer97

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That’s exactly what I’ve had to do previously before replacing a list of parts as long as my arm, Is there a way to test the new stepper motor? I’m just wondering if maybe the new stepper motor could be faulty? Once revved the stepper goes as low as 0 steps but also climbs to as high as 80+ steps, I drove it this morning and cold it was absolutely perfect, it’s now got up to temp, and it’s bouncing all over the shot, ranging from 500rpm to around 700rpm, rough enough it’s making the whole car shake

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It should never go as low as 0, that would suggest an air leak on the intake. When up to temperature it should sit at around 20-30 at idle. It opens up when the TPS shows you've opened the throttle a touch so it allows extra air in (rather than just relying on airflow through the throttle butterfly) to raise the revs. Is the anti tamper plug on the idle adjust missing? That would suggest someone has been in there playing with it. To bring the stepper back into play it needs screwing in to reduce the amount of air that is going in. I don't remember the exact size but it is an Imperial hex key.

Olliedyer97

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Gilbertd wrote:

It should never go as low as 0, that would suggest an air leak on the intake. When up to temperature it should sit at around 20-30 at idle. It opens up when the TPS shows you've opened the throttle a touch so it allows extra air in (rather than just relying on airflow through the throttle butterfly) to raise the revs. Is the anti tamper plug on the idle adjust missing? That would suggest someone has been in there playing with it. To bring the stepper back into play it needs screwing in to reduce the amount of air that is going in. I don't remember the exact size but it is an Imperial hex key.

Olliedyer97

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I didn’t think it was right going as low as zero, and yes the anti tamper plug has been removed as was told that’s how you set up the new stepper motor, I may try and screw it in and see if it changes how it runs