Discussion
My engine's not running properly. So as today is nice and sunny I would like to try my hand at fixing it myself. Then I can go for a nice drive...
Here are the symptoms:
- starts ok (as usual)
- idle is fine
- rev from idle = large flat spot and then rough sounding (like not firing on all cylinders)
- when driving it sounds a bit like a big lawn mower and is under powered
- ocassionally at low revs it 'lurches' as if suddenly it's firing properly
I've eliminated throttle pot as when disconnected the engine gives the same problem.
I've also checked that the leads are all connected and that the distributor is not damp inside.
Someone must have had similar before...
Any suggestions?
Here are the symptoms:
- starts ok (as usual)
- idle is fine
- rev from idle = large flat spot and then rough sounding (like not firing on all cylinders)
- when driving it sounds a bit like a big lawn mower and is under powered
- ocassionally at low revs it 'lurches' as if suddenly it's firing properly
I've eliminated throttle pot as when disconnected the engine gives the same problem.
I've also checked that the leads are all connected and that the distributor is not damp inside.
Someone must have had similar before...
Any suggestions?
Sounds like a metering problem. Do you have air flow meters? Otherwise possibly the throttle pot. (Same symptoms when disconnected does not prove it is OK.)
It would be worth sticking a passive strobe in the king lead to confirm you have a healthy spark, that would rule out an ignition problem.
It would be worth sticking a passive strobe in the king lead to confirm you have a healthy spark, that would rule out an ignition problem.
GreenV8S said:
Sounds like a metering problem. Do you have air flow meters? Otherwise possibly the throttle pot. (Same symptoms when disconnected does not prove it is OK.)
It would be worth sticking a passive strobe in the king lead to confirm you have a healthy spark, that would rule out an ignition problem.
Not too sure about air flow meters (and I've lost my copy of the Bible - it's been 'tidied up' somewhere).
So, disconnecting the TP is not really a valid test then?
Was the rotor arm okay?
Any symptoms when revving the engine in neutral or is it only happening while driving?
More than likely a fuel starvation problem I'd have thought... The symptoms you have described may be due to any of the following:
a) lambda sensor(s),
b) faulty temperature sensor(s) and thermotime switche(s)
c) throttle potentiometer
d) fuel injector(s)
Any symptoms when revving the engine in neutral or is it only happening while driving?
More than likely a fuel starvation problem I'd have thought... The symptoms you have described may be due to any of the following:
a) lambda sensor(s),
b) faulty temperature sensor(s) and thermotime switche(s)
c) throttle potentiometer
d) fuel injector(s)
Thanks for the replies so far!
rotor looked ok - I renewed it about 9 months ago
Symptoms are apparent when revving in neutral. Problem seems to disappear when revving hard whilst driving.
Think I'll do more testing on the TP as it's let me down before. It's a Cerbera one on there at the moment.
Fuel injectors were cleaned last summer.
Not too sure how to check the sensors.
NickP_S2 said:
Was the rotor arm okay?
rotor looked ok - I renewed it about 9 months ago
NickP_S2 said:
Any symptoms when revving the engine in neutral or is it only happening while driving?
Symptoms are apparent when revving in neutral. Problem seems to disappear when revving hard whilst driving.
NickP_S2 said:
More than likely a fuel starvation problem I'd have thought... The symptoms you have described may be due to any of the following:
a) lambda sensor(s),
b) faulty temperature sensor(s) and thermotime switche(s)
c) throttle potentiometer
d) fuel injector(s)
Think I'll do more testing on the TP as it's let me down before. It's a Cerbera one on there at the moment.
Fuel injectors were cleaned last summer.
Not too sure how to check the sensors.
NickP_S2 said:
More than likely a fuel starvation problem I'd have thought...
Well done! On a whim I stopped at a garage to fill up and, whilst paying, saw some of that injector cleaning petrol additive stuff on the shelf.
After a short drive with it in the tank and me revving hard the problem has disappeared.
I'm happy again. Thanks for the tip!
Hi Paul,
Sorry I have missed this post until now, thought it worth mentioning that there is apparently a fuel filter in the tank and this can starve the pump of fuel if it becomes clogged and can lead to pump failure if not dealt with.
I discovered this from somebody else and then had the same problem on mine and had to replace my pump as it packed up after a while but leading up to that I had all the same symptoms as yourself.
Listen out for an irregular noise from your pump as you start your engine.
Sorry I have missed this post until now, thought it worth mentioning that there is apparently a fuel filter in the tank and this can starve the pump of fuel if it becomes clogged and can lead to pump failure if not dealt with.
I discovered this from somebody else and then had the same problem on mine and had to replace my pump as it packed up after a while but leading up to that I had all the same symptoms as yourself.
Listen out for an irregular noise from your pump as you start your engine.
I had very similar symptoms a few months ago, just after I had washed the car. When I took it out, it was running very rough, was OK at idle, but would not accelerate without lurching about. I made it back home and left the car for a while, when I went back out 30 mins later it had cleared completely!
I am convinced it was water that had got in somewhere, possibly the TP? Something to watch for though, I am VERY careful now when washing the car
I am convinced it was water that had got in somewhere, possibly the TP? Something to watch for though, I am VERY careful now when washing the car
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