Engine hunts when hot

[blitzracing]

LenChim said:

blitzracing said:

Even though RoverGauge only reads trim to 3400 rpm, you can still pop a meter on the lambda output to get a passenger to read the voltage directly. It should cycle between 0 and 1.2 (or so) up to 3400, then stick at around 1.2 volts or slightly over to peak RPM. If you are running out of fuel it will drop to 0 volts. Problem is a bad misfire also looks like a lean mixture, so the results may not be that different. If you want to diagnose HT faults, and old style Crypton tuner is the way to go where you can monitor the HT wave forms. Shorts show as low HT, and open circuits show as higher voltage spikes. Mind you it may cost you as much to diagnose as swap all the suspect bits out. Its a pity Gunson used to do a brilliant HT tester with a simple LED bar display for the HT voltages, that tells you a lot, but have long since been out of production.

OK Christmas is over so I have made the plug assembly's to go in line to check the lambda out put and ran the test today. The outputs were good once the engine had warmed up. On the road the at constant speed they seemed to cycle ok, decelerating and accelerating but at about 3300RPM they switched off zero volts.
So the question is were do I go from hear? I don't have a Crypton tuner, as I said I have replaced the HT leads but they are tied together. I did take the cap of the dizzi and clean it and look for cracks, tracking lines etc. It does not sound as though it is misfiring. I have rechecked the fuel pressure its ok, also when revved hard but I can not test it under load (no rolling road).
Any suggestions.

The lambda switching you describe is correct- it drops to zero on the over run as there is no fuel going in- BUT it should not drop to zero as the RPM increases the voltage should rise to around 1.2 volts at 3400 and stay there to peak RPM. If it does drop to zero, the engine is running horribly lean or misfiring really badly. Lean running can be a blocked fuel filter, poor fuel pump supply voltage (or connections)or crushed fuel line. Checking fuel pressure is tricky, but can be done by removing the valve from the pressure point take off,(serp engine only) and attaching a fuel line to an oil pressure gauge that you can lodge under a wiper blade so you can read it inside the car under load. Fuel pressure should be 2.5 bar at full load and RPM.

[LenChim]

[quote=blitzracing]

The lambda switching you describe is correct- it drops to zero on the over run as there is no fuel going in- BUT it should not drop to zero as the RPM increases the voltage should rise to around 1.2 volts at 3400 and stay there to peak RPM. If it does drop to zero, the engine is running horribly lean or misfiring really badly. Lean running can be a blocked fuel filter, poor fuel pump supply voltage (or connections)or crushed fuel line. Checking fuel pressure is tricky, but can be done by removing the valve from the pressure point take off,(serp engine only) and attaching a fuel line to an oil pressure gauge that you can lodge under a wiper blade so you can read it inside the car under load. Fuel pressure should be 2.5 bar at full load and RPM.

One question, it may be stupid but could the lambda sensors be wired back to front?

[blitzracing]

Not easily- it is possible to short the heater wire to lambda output, this puts 12v on the ECU input, that will make the ECU think the mixture is rich, but in this case both the short term and long term trim is stuck at 100% removing fuel in RoverGauge. If the short term trim is moving, the probes are working. One thing I will say is loss of fuel pressure or lean running under load wont cause hunting RPM or a misfire at low RPM when the fuel requirement is low, I don't want you to chase faults that may not be there, as the results are so inconsistent. If you think you have a misfire, just try melting a cable tie onto each exhaust header on a warm engine, as its less likely to melt on a cylinder thats not firing correctly.

[LenChim]

blitzracing said:

Not easily- it is possible to short the heater wire to lambda output, this puts 12v on the ECU input, that will make the ECU think the mixture is rich, but in this case both the short term and long term trim is stuck at 100% removing fuel in RoverGauge. If the short term trim is moving, the probes are working. One thing I will say is loss of fuel pressure or lean running under load wont cause hunting RPM or a misfire at low RPM when the fuel requirement is low, I don't want you to chase faults that may not be there, as the results are so inconsistent. If you think you have a misfire, just try melting a cable tie onto each exhaust header on a warm engine, as its less likely to melt on a cylinder thats not firing correctly.

Right next installment. I have checked the fuel pressure when driving it is fine drops a little on over run but is 36 psi on acceleration.
The Voltage to the lambda sensors drops to zero after 3300rpm app.

As can be seen at,
rpm 5248.
Lambda STD "0"
MAF 78%
Throttle 59%
Temp 80C
Fuel pressure 36PSI
The engine feels like I have hit the rev limiter.
By the way this was in 3rd gear. Or I would be totally illegal.
Info from other screens.
RG RPM is very similar the the cars RPM.
RG 5248 rpm (misfire or running out of power) rpm 4752 matrix segment DE.
RG MPH reading always seems to max out at 40MPH and starts about 30 as soon as you are moving.

[blitzracing]

The lambda readings in Rover Gauge are fuel trim values, not the voltage that comes out of the probe. It will drop to zero in RoverGauge as the ECU stops monitoring the lambda probes at 3400 rpm as its not longer under emission control. What we need is the actual voltage from the probe with a test meter, as this will still be there even when RoverGauge is ignoring them- so this is where you need 1.2 volts or so under full load with a test meter. Fuel pressure tests really need to be done at full load, peak RPM, not just the acceleration phase as the fuel demand wont be at peak until l 5400 rpm but that's likely to be at around 100 mph in third gear from memory in my car (TVR may have different gearing), so its not that easy to do without getting noticed - Mind you something as simple as a failing HT coil will cause a nasty misfire as the RPM rises and the spark potential demand is at its greatest, and the dwell period at its shortest The readings you have there seem OK, but its only what the ECU sensors see and the ECU is not that smart .

Edited by blitzracing on Sunday 12th January 17:17

[QBee]

blitzracing said:

The lambda readings in Rover Gauge are fuel trim values, not the voltage that comes out of the probe. It will drop to zero in RoverGauge as the ECU stops monitoring the lambda probes at 3400 rpm as its not longer under emission control. What we need is the actual voltage from the probe with a test meter, as this will still be there even when RoverGauge is ignoring them- so this is where you need 1.2 volts or so under full load with a test meter. Fuel pressure tests really need to be done at full load, peak RPM, not just the acceleration phase as the fuel demand wont be at peak until l 5400 rpm but that's likely to be at around 100 mph in third gear from memory in my car (TVR may have different gearing), so its not that easy to do without getting noticed - Mind you something as simple as a failing HT coil will cause a nasty misfire as the RPM rises and the spark potential demand is at its greatest, and the dwell period at its shortest The readings you have there seem OK, but its only what the ECU sensors see and the ECU is not that smart .

Edited by blitzracing on Sunday 12th January 17:17

In my Chimaera 6000 rpm is around 90 in 3rd, 125 in 4th etc
So 5400 rpm will be just over 80 in 3rd, or around 55 in 2nd.
Shirley this is a job to be done on the rolling road?

[spitfire4v8]

All rovergauge is telling you is that the stuff that can be read by rovergauge is looking fine. What rovergauge can't tell you is why your engine hits a brick wall at higher revs if it's not something rovergauge is capable of measuring directly. You need good old fashioned diagnostic techniques for that, and because as a home mechanic you are limited what you can change/test in a repeatable way, you are much better at this stage handing it over to someone who can do the testing for you.
It could be any number of reasons for the reluctance to rev .. bosch ignition coils are a favourite (I see lots of cars with new bosch coils which wont rev over 5000rpm) .. or a weak mixture (as I said, your fuel map looks very odd for a chim 450) .
Fuel pump/pressure issues are incredibly rare but can happen.
You are going to waste days chasing this by looking at rovergauge, there's nothing on there that points to your cause. The only thing you could do is see what the lambda output is doing as the revs rise as blitz says .. that will at least tell you if the mixture trend is weakening or richening. Weak mixes very quickly make the engine hit a brick wall, it would have to be incredibly rich to achieve the same effect (lots of black smoke out the back).

Edited by spitfire4v8 on Tuesday 14th January 07:46

[blitzracing]

QBee said:

In my Chimaera 6000 rpm is around 90 in 3rd, 125 in 4th etc
So 5400 rpm will be just over 80 in 3rd, or around 55 in 2nd.
Shirley this is a job to be done on the rolling road?

I wont argue with that, I just remember it s not easy to hold the engine at peak fuel requirements for more than a second or two what ever my diff ratios may be compared to a TVR.

[LenChim]

blitzracing said:

The lambda readings in Rover Gauge are fuel trim values, not the voltage that comes out of the probe. It will drop to zero in RoverGauge as the ECU stops monitoring the lambda probes at 3400 rpm as its not longer under emission control. What we need is the actual voltage from the probe with a test meter, as this will still be there even when RoverGauge is ignoring them- so this is where you need 1.2 volts or so under full load with a test meter. Fuel pressure tests really need to be done at full load, peak RPM, not just the acceleration phase as the fuel demand wont be at peak until l 5400 rpm but that's likely to be at around 100 mph in third gear from memory in my car (TVR may have different gearing), so its not that easy to do without getting noticed - Mind you something as simple as a failing HT coil will cause a nasty misfire as the RPM rises and the spark potential demand is at its greatest, and the dwell period at its shortest The readings you have there seem OK, but its only what the ECU sensors see and the ECU is not that smart .

Edited by blitzracing on Sunday 12th January 17:17

I tested the voltage on both the lambda's with a voltage meter set at 3 volts fsd, both cycled well until 3300 rpm approx then they both dropped to zero volts, me driving and passenger watching the volt meters and RG. He was also watching the 40 psi pressure gauge plumed in the the injector manifold, and yes we were under full load two up and 90 plus mph when when we ran out of rev's at about 5400 rpm. They was the results that I posted earlier.
I have a couple of spare HT coils so I will switch out the current one and road test when the weather is a bit better.
Many thanks guys for sticking with it.

[TV8]

Hi Len, I had a couple of people contact me about the AfM but checking you have ruled that out as ok? I had running problems and that was temperature dependant and caused by the AfM. Can you hear the stepper motor resetting when you switch the car off?

[spitfire4v8]

I would be surprised if what you are experiencing is ignition related, that would usually be accompanied by a very distinct misfire.
My money is still on a weak mixture* .. the lambdas going immediately zero volts as soon as it comes out of lambda control, plus the hitting a brick wall in power, are both weak mixture issues, rather than ignition issues showing the symptoms of a weak mixture, iyswim.
Also, if it is indeed that, although the rv8 is very hardy in respect of tolerating weak mixes for long times, I'd get that sorted.

Case in point .. my v8S in its original 4 litre form struggled one time to better 90mph on the straight at Snetterton. I did the whole track day but when I got home I got it put on the rollers. it made 125hp and was very very weak. Correcting the mixture gained me 70hp!
On the track day there were no misfires, just a really poorly performing car which completely ran out of steam at 90mph.
The cause was the fuel pressure regulator, but that's an incredibly rare fault, they're normally bulletproof, and you say yours seems stable anyway under load and is a sensible number (2.5bar x 15psi = 37.5psi)

• best guess obviously based on the evidence, there's no substitute for actual proper diagnosing on the car.

Edited by spitfire4v8 on Tuesday 14th January 07:53

[LenChim]

TV8 said:

Hi Len, I had a couple of people contact me about the AfM but checking you have ruled that out as ok? I had running problems and that was temperature dependant and caused by the AfM. Can you hear the stepper motor resetting when you switch the car off?

Yes I can hear the stepper motor reset when I switch off.

[blitzracing]

LenChim said:

I tested the voltage on both the lambda's with a voltage meter set at 3 volts fsd, both cycled well until 3300 rpm approx then they both dropped to zero volts, me driving and passenger watching the volt meters and RG. He was also watching the 40 psi pressure gauge plumed in the the injector manifold, and yes we were under full load two up and 90 plus mph when when we ran out of rev's at about 5400 rpm. They was the results that I posted earlier.
I have a couple of spare HT coils so I will switch out the current one and road test when the weather is a bit better.
Many thanks guys for sticking with it.

So just checking you still have full fuel pressure on the injector rail at WOT (it will drop at less than full throttle) and you still have the lambda output dropping to zero? That would be a really odd combination, (assuming it not ignition) as basically the map data would have to be incorrect as you have full pressure behind the injectors, and the map controls the injector timing. What brought this fault on? Its not a second hand ECU or something silly from a Range Rover? Double checking what map is it? Its normally map 5 for cats.

[LenChim]

blitzracing said:

So just checking you still have full fuel pressure on the injector rail at WOT (it will drop at less than full throttle) and you still have the lambda output dropping to zero? That would be a really odd combination, (assuming it not ignition) as basically the map data would have to be incorrect as you have full pressure behind the injectors, and the map controls the injector timing. What brought this fault on? Its not a second hand ECU or something silly from a Range Rover? Double checking what map is it? Its normally map 5 for cats.

Just took the coil off and measured the resistances they are as the book, of course that does not mean it is not braking down under load. The ECU has been in the car since I got it and I have not noticed this problem in the past but as I have had all the other problem crop up maybe it was there all along so I have been testing the car's capabilities and now have found it. As to the map how do I check that?

[blitzracing]

It tells you the map number in the RoverGauge screen shot- just above the map table, I could not quite read it on the photo. Id drop the ECU out and split the case and check the chip then. It should have a label on it something like 4.5 cat if its TVR. I dont know the maps as well as Spitfire, but its worth checking if he does not recognise it as well. Also check your tune resistor- its poking out of the ECU loom in the footwell- its in a small clear plastic case, and should have white insulation wires on it (white tune). This should tie up with Map 5 shown in RoverGauge.

[LenChim]

blitzracing said:

It tells you the map number in the RoverGauge screen shot- just above the map table, I could not quite read it on the photo. Id drop the ECU out and split the case and check the chip then. It should have a label on it something like 4.5 cat if its TVR. I dont know the maps as well as Spitfire, but its worth checking if he does not recognise it as well. Also check your tune resistor- its poking out of the ECU loom in the footwell- its in a small clear plastic case, and should have white insulation wires on it (white tune). This should tie up with Map 5 shown in RoverGauge.

OK it seems as though we may have found some of the problem, The chip has a 4lt sticker on it. I can not find the resister as yet, I do not know how much of the loom I have to take apart to find it? Is it likely to be behind the battery box? As you can see from the pic I have undone some of the insulation from the loom.


As can be seen from the last pic:-
Current fuel map :-5
Multiplier:- 0x56CC
RPMLimit:
Row Scaler:- 0xB9

Right across the top of the screen it says:-
Tune No:-R2967
Tdent :-1A17
Check sum fixer :-FF
I Do not know what any of that means.

[LenChim]

It seems not to have liked two of the images I put up so lets try again:-

[LenChim]

And again:-

[blitzracing]

I cant see it in your loom, its not on all looms, as in the USA looms they dont want people changing maps, so the resistor is missing. It looks like this if you can find it, but as long as you are showing map 5 thats fine.




Im surprised the difference between 4 and 4.5 would kill the engine that badly, but I guess the 4.5 has much improved higher RPM breathing over the 4 ltr when it needs more fuel.

Maps here if you want to blow another chip or drop me a mail if you want me to do one for you.

http://www.remap-14cux.uk/bins/

[Penelope Stopit]

Here's an image from here https://www.pistonheads.com/gassing/topic.asp?h=0&...