Engine running lumpy
Discussion
Not long got my E-Type (1969 4.2) back from a year in a Body-shop and I finally got to ride the beast earlier today. Aside from a few other minor niggles the main problem I've encountered is the engine being lumpy with erratic tick-over and sounds like it's mis-firing and not running on all cylinders. Before it entered the Body-shop it ran fine. I'm no expert regarding these problems and I was wondering if anybody out there could shed some light as to what I could do to alleviate it.
If it's a regular steady miss fire under both idle and load then it indicates a cylinder(s) not firing.
Find which one it is by pulling the plug leads off one at a time with a insulated pair of pliers. The faulty cylinder will make no difference the the running of the engine when you remove the lead, a good cylinder will make the problem worse. Once you've located which cylinder(s) take out the plugs and check the gaps. Swap plugs and leads round to isolate the problem. If doing so makes no difference and the miss fire remains on the same cylinder with substituted plugs and leads have a careful look inside the distributor cap for evidence of damage, damp or arcing. Try another cap if you have one. Check the points for correct gap and see there's no or pitting on the contacts. Change the condenser - these cost pennies and cause no end of grief if they start to break down. Next do a compression check on all 6 cylinders and compare the readings. They should all be at least 100 and within 10% variation.
If none of this reveals the fault then move on to the fuel system.
A rough and erratic idle on an engine that runs well under high throttle openings AND load usually indicates a induction system air leak. Check all the fixings and bolts are tight. Check all the hoses and servo (if you have one) joints for perishing and listen round all the manifold and carburettor flanges with a piece of hose for hissing or whistling noises. If you find a leak dribble a little engine oil on the suspect area and see what happens.
The exact opposite - an engine that idles OK but is rough or down on power under load usually indicates fuel starvation. Clean or change the fuel filter, clean out the carburettor bowls and jets and try again. Water or rust in the fuel is common on old cars that have been standing and needs a through flush and clean of the entire fuel system to get rid of it. You may even need a replacement petrol tank if it's corroded inside. You may have a split diaphram or no oil in the carburettor dashpots. This will usually only cause temproary hesitation or flat spots when you accelerate and providing this is the only problem the engine will run well otherwise.
Once you are sattisfied there's none of the problems above then check the ignition timing. Then check all the carburettors are balanced correctly at idle. There is no point in trying to "tune out" a underlying engine problem - that's why you leave the timing and balance checks 'till last.
It's unlikley any of the mixture or ignition settings will have gone out while the car has been standing anyway - my money is on a simple fault like a perished plug lead, corroded contact or some crap in the fuel system.
Simples
Find which one it is by pulling the plug leads off one at a time with a insulated pair of pliers. The faulty cylinder will make no difference the the running of the engine when you remove the lead, a good cylinder will make the problem worse. Once you've located which cylinder(s) take out the plugs and check the gaps. Swap plugs and leads round to isolate the problem. If doing so makes no difference and the miss fire remains on the same cylinder with substituted plugs and leads have a careful look inside the distributor cap for evidence of damage, damp or arcing. Try another cap if you have one. Check the points for correct gap and see there's no or pitting on the contacts. Change the condenser - these cost pennies and cause no end of grief if they start to break down. Next do a compression check on all 6 cylinders and compare the readings. They should all be at least 100 and within 10% variation.
If none of this reveals the fault then move on to the fuel system.
A rough and erratic idle on an engine that runs well under high throttle openings AND load usually indicates a induction system air leak. Check all the fixings and bolts are tight. Check all the hoses and servo (if you have one) joints for perishing and listen round all the manifold and carburettor flanges with a piece of hose for hissing or whistling noises. If you find a leak dribble a little engine oil on the suspect area and see what happens.
The exact opposite - an engine that idles OK but is rough or down on power under load usually indicates fuel starvation. Clean or change the fuel filter, clean out the carburettor bowls and jets and try again. Water or rust in the fuel is common on old cars that have been standing and needs a through flush and clean of the entire fuel system to get rid of it. You may even need a replacement petrol tank if it's corroded inside. You may have a split diaphram or no oil in the carburettor dashpots. This will usually only cause temproary hesitation or flat spots when you accelerate and providing this is the only problem the engine will run well otherwise.
Once you are sattisfied there's none of the problems above then check the ignition timing. Then check all the carburettors are balanced correctly at idle. There is no point in trying to "tune out" a underlying engine problem - that's why you leave the timing and balance checks 'till last.
It's unlikley any of the mixture or ignition settings will have gone out while the car has been standing anyway - my money is on a simple fault like a perished plug lead, corroded contact or some crap in the fuel system.
Simples
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