MG TF 135 starts and runs on 2 cylinders but not 4

Hi,

I recently inherited my late father's MG TF 135.

After 2 years of sitting in a garage in Spain it would not start. The garage changed the fuel pump, performed a general service and took it to be tested for the Spanish version of an MOT which it passed sin defectos.

When driving it to the ferry port to bring it back to the UK last week it performed beautifully with plenty of power for the first 4 hours then stopped without warning on a motorway. It was about 40 degrees C that day and I may have noticed the water and oil temperatures rise slightly above where they had been sitting up until that point but there were no other obvious signs of overheating. The car completed its journey on a lorry and it hasn't started since.

After a weekend of poking around I have found the following:
- on turning over the engine will occasionally cough and maybe turn over once or twice under its own power but never start
- no connectors obviously disconnected or wires damaged
- a cheapo ODB reader shows no fault codes. I have yet to buy a Pscan.
- Fuel reaching the rail but whether the rail is at 3.5 bar is yet to be proven
- to test for spark I removed spark plugs 2 and 3 (which you all know share a coil) but left them and the coil connected so I could see the spark. The engine started immediately, idled perfectly and revved.
- I replaced 2 and 3 and removed 1 and 4 and kept the plugs and coil connected in the same manner. Again the engine started immediately.
- With all spark plugs and coils replaced - back to the beginning with the engine not even trying to start.

I have replaced the coils, leads and plugs but that changed nothing. 

So this one really has me scratching my head. As it appears to me, the fact that the engine starts and runs fine on each pair of cylinders indicates that there is a correctly timed spark and fuel and no compression issue. Have I missed something obvious? I am convinced this will be a simple fix once I determine the problem.

I shall be grateful for any suggestions anyone may have.

Thanks!

Morning ,have you done a compression test .It sounds as though the head gasket has gone .They should of course be nearly all the same reading ,I think thats the first step to take before going any further  ,I believe its between 125 and 175 ,It may be down a little on one or two,but a big drop in pressure is a giveaway . Len

Even though they replaced the fuel pump, I would still have my suspicions about it, NEVER rule out something just because it is new. ALWAYS suspect the new part!
If the car had any water in the fuel tank or lines then it wouldn't take long to kill the new pump.
When the pumps on these things start failing they can do so intermittently making the hard to diagnose, and MG/Rover in their infinite wisdom didn't see fit to monitor the fuel pump Via the OBD system.
So check you have power to the pump, do a fuel pressure test, flow rate test. and checked that the fuel isn't stale.
Are all the injectors getting the signal to squirt? have they been bench tested for flow rate and spray pattern?
Once you're satisfied that the engine is getting sufficient rations of motion lotion,  you should move on to checking all the connections and earthing of the ignition system.
Test the resistance of  the HT leads,
Do a compression test.
Once you've gone through that lot get back to us and we can go through further possibilities with you.

 

Thank you both for your quick responses. I shall follow your suggestions. A compression tester is on order.

The fuel pump works - I get fuel flowing out of the fuel rail no problem when I disconnect the return pipe from the pressure regulator. 

Would you agree that the fact that the engine fires up and runs on 2 cylinders (and on the other 2) indicates that the injectors are delivering fuel and the spark plugs are providing a correctly timed spark? Even if not the precise quantity of fuel and the most perfectly timed spark should the engine not run on 4 cylinders if it runs fine on 2?

Here is a fundamental question 
Is the battery new?
Are you getting full power to each plug ?

Thanks for the reply.

The battery is not new and has been discharged a few times but I have been keeping it fully charged since the problem arose.

The sparks appeared strong to me.

Is it possible a discharged battery is the culprit even if it has sufficient power to turn over the engine?

Thanks again 

Have you tried leaving the 2 plugs which are under the coils in place and removing the other pair of plugs which have the leads ?

Incidentally do you know how long ago the cambelt was changed ?  It would be worth checking the tensioner and to check the cam and crank timing marks line up as they should in case there may have been some belt slippage.

 

I wouldnt blow the cash on a new one until I had checked the volts on the old one.
I suppose my thoughts are, is it man enough to do all the things necessary on start up?

If the battery is man enough to turn the engine over with vigour, there’ll be enough puff to drive the electronics. The output devices which drive the coils should crack the coils, again with sufficient vigour to create a spark man enough to ignite the fuel/air mix.
What you are experiencing is odd.
Have you had all the plugs out & placed them in such a way as they are earthed, you should be able to see how fat the sparks are.
M

Carrying on from that. The system is wasted spark, in other words there are only two pulses instead of the usual four.
I seem to recall (I’m away again so away from my notes!) that 1 & 4 are paired 2 & 3 are also paired.
If 1 is firing so also is 4, but as 4 is at bottom dead centre that spark is wasted.
That probably won’t help sort your problem but it’s interesting.
M

It has been said by some engineers the when a wasted spark system fires at the bottom of the stroke it can help with emissions by igniting any unburned fuel.....as such it is not wasted.... but if your a cynical old bastard like me, you call it a load of bollocks for the engineers to put a positive spin on cost cutting. Less components = less cost.
If they were really concerned about burning any fuel left unburned in the combustion process they would employ a twin spark ignition system which has a doubled up ignition system (2 spark plugs per cyl) this works by igniting the mixture at two places in the combustion chamber simultaneously, this can allow the flame front to travel more quickly thereby burning the air/fuel mixture more completely and producing more power!, this system is seldom used due to cost and added complexity.

I can see that working & never considered it. I wander it I can use that as an excuse if I have emissions problems at my next MOT. Probably not.
M