"checking spark" you want to be able to jump about 4" of free air to be enough for a plug, try swapping leads and look for cross shorting

4" (100mm) of spark seems a long way.... would that be the same on any petrol car??

rob

HI all...

Just after some advice on the following;

No.4 cyclinder seems to have problem.... The engine seems to have a miss and when I remove No.4 lead, there is no change in engine idle but with the other cylinders there is a change in idle when lead is removed. I've swapped plugs with no changes & I've checked for a spark on No.4 lead... aok.
I've just done a compression test with the following readings:
(Dry Test)
No.1 - 120
No.2 - 125
No.3 - 125
No.4 - 125

(Wet Test)
No.1 - 125
No.2 - 130
No.3 - 130
No.4 - 130

The engine has a engine knocking noise upon startup (seems to be coming more from top of engine) & as the motor warms up the engine knock slowly seems to dissappear....
The motor does blow smoke (blue I think...) when u rev it and is fumey...

Any ideas from the more experienced people out there......

cheers....

rob

Did you do the compression test correctly?

Those readings are very low. Standard compression should be 199 psi, with a service limit of 170 psi. Are the valves adjusted properly? Maybe they are a bit tight.

Damo... I believe so..... I removed all plugs & inserted the tester into the sparkplug slot & turned the key over for the motor to wind over 5/6 times... is that correct??

I just measured the resistance of the leads as follows:
No.1 - 3.15k ohms or 3150ohms (longest lead)
No.2 - 3.11k ohms or 3110ohms (2nd longest lead)
No.3 - 2.62k ohms or 2620ohms (3rd longest lead)
No.4 - 2.72k ohms or 2720ohms (4th longest lead)
Coil lead - 1.53k ohms or 1530ohms (shortest lead)

I assume that the resistance should get less the shorter the lead gets??

Are these readings about right??

Anymore than about 12k ohm for a lead and it's time to bin, so those readings look ok. Those compression readings are low, but are consistant, so you may want to check you valve clearances. When you pull number 4 plug out what does it look like?? Is it wet/dry/black/gunked up? Swap the plug with another cylinder and see if that makes the other cylinder miss or if the miss is still in number 4. Check for a vacuum leaks as well, particularly around #4 cylinder. I think the brake booster probably feeds off #4, so check that and also the vacuum hose to the manifold from the booster.
Hope this is of some help. Keep us posted.

Elio

From memory resistance should be 1k ohm per 100mm.... someone correct if I'm wrong.

Swap 2 leads and see if the miss changes to that cylinder that no4 lead went onto, simplest way to check the lead

jesse

check ya plugs to see what color the electrode is after a drive. this will help determine whats stopping the spark. If its black and covered in sludge then ya have an oil fouling issue from either rings or stem seals.

Holding the throttle open allows unrestricted airflow into the chambers. If the throttle is left closed then there is vacuum created in the intake. Sometimes the throttle doesn't affect the reading, sometimes it can give you lower readings.

What did you do different for the 'wet' test? Did you use oil?

Holding the throttle open allows unrestricted airflow into the chambers. If the throttle is left closed then there is vacuum created in the intake. Sometimes the throttle doesn't affect the reading, sometimes it can give you lower readings.