Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Severe misfiring on 3.7 V6 Roadster

Below is Roadster throttle schematic I referred to and showing two potentiometer's on throttle pedal sensor. Could second be a backup?

Dunno, we need an ECU genius

I understand FBW aircraft have three sensors on the control column which are continuously compared. In the unlikely scenario of one disagreeing the other two provide the control input.

What do you think about the idea of starting the search with the parts that don't give any information to the ECU? Because one thing is known, you can't read out an error. For example, a broken lambda sensor, a broken MAF sensor or a broken accelerator pedal will give you information to the ECU. But does a coil pack, for example, or ignition cables do that too?
You've probably been browsing US Mustang forums? There are hundreds of users with all kinds of electrical problems.

I had a similar problem, although not as intermittent, on another engine. Someone suggested plug wires, which I resisted because they looked fine and were less than 3 years old. Finally I relented and instant fix! Apparently, modern OEM plug wires can have a relatively rapid internal break down due to the fact that have to be easily recyclable ( this is what I have been told). Might as well start with the easy things first!

I agree. Do the simple things first. Even a new set of cheap leads will sort it out. If successful then you can always upgrade to better leads later. Just because the leads look ok doesn’t mean the internals are ok.

Thanks for suggestions but 3.7 V6 uses coilpacks. Will leave as is now after ECU relay swap, re-seating fuses, cleaning MAF sensor and re-seating throttle pedal connector. Issue seems to be a very intermittent minor one and resets after engine stop/start. Might take it for a run with OBD2 connected to phone and see if anything shows up.

So far have found throttle position starting cold at 17% and dropping within a few seconds after engine start to 14% whilst idling at 800 rpm. Probably lower at idle with fully warmed engine. Full pedal reads exactly 75% engine off so guessing this is an PCM coded setting.

34 mile round shopping trip yesterday provided some interesting results following above checks and changes. Engine started and ran fine but had my OBD2 dongle connected and bluetoothed to OBD Torque app on my phone.


Should have taken a screenshot before app shut down, but these are figures I noted from the customised dial setup I have which record max and min in many cases and are quoted below:

Max speed xxx kph
Max revs used 4700 rpm (wasn't rushing)
Max coolant temp 98°C (normal)
Load 100% max
Throttle 75% max
MAF max 173 grams/sec
Intake temp range 22 - 36°C
Ambient temp range 22 - 25°C

I was a little surprised the throttle butterfly only reached 75% (same as with engine off) since I know I floored it for a few seconds, until I discovered a thread on a Lotus forum that is, where the same figure had been found. Discounting the usual BS that such produce the best answers concluded the throttle spindle itself causes some restriction such that the final 25% of movement makes little or no difference, hence the PCM controlled limit to allow quicker throttle response.

I was very pleased to see such a high MAF peak though showing excellent volumetric efficiency despite only 4700 rpm being used. A rough guide for normally aspirated engines is engine capacity in litres x 40 to give a max MAF in grams/second, i.e. 149 for my 3.7 V6.

Max intake temperature seemed high until I remembered being stationary at idle for some time at level crossings. Pleasing bit are the minimums recorded though showing that my air intake mods seem to be working fine keeping temp the same as ambient once on the move.

Next week a few of us have a dyno session booked near Royston. I will be up against a Brooklands Roadster with the factory ECU upgrade and an Earls tuned +8. Watch this space

May the best car win Richard
Interesting about the 75% open position. I guess the sizing means going to 100% is't needed & maybe if closing form 100% the force of the incoming air makes it dificlut to close.

Could be John but my own view shared by others, is that it's quicker to close the throttle from 75% given it's all that's needed, than from 100%.

Would be interested to see what yours opens to when you have a moment. It can be checked without starting engine just put pedal to metal with ignition on and Bluetooth hookup. The instrument to configure is shown in Torque app under Settings/Add Display/Dials as "Throttle Position (Manifold)".