Stubborn misfire
Posted: Thu Nov 28, 2019 10:03 pm
Hi
I'm having some problems with an annoying misfire. When I reassembled the engine I took the braided earth off the coil bracket and capacitor fixing and used it to provide an alternative ground path from the chassis to the engine. The bracket and capacitor (assumed to be for radio suppression) got a new ground wire that runs direct to the chassis bolt.
My car has what looks like an Aldon LU142A ignition module in the distributor. It uses a hall effect sensor to detect the rotor arm position. This is connected to the + and - side of the coil respectively. The coil appears to be a gold anodised unit, like the Lucas DLB105 sport high output coil. It has no ballast resistor fitted, which jibes with what is said here: https://www.autoelectricalspares.co.uk/ ... -100-p.asp - the DLB110 is for Lotuses but there's a comment saying use the DLB105 if no ballast resistor is in place.
During diagnosis of the misfire I have checked timing, carb balance and idle mixture. It's all spot on. I noticed some arcing between the coil output (HT plug) and the + / - terminals, only visible in the dark. I know it shouldn't do this and I have cleaned the top of the coil and the rubber cap for the HT lead, to little avail. Also tried to put extra insulation around the cap, by way of a dry section of water hose, slit along its length and slid over the HT connection to the coil, such that the rubber is between the HT plug and the coil terminals. Still have the misfire.
It all worked fine before I took it apart. What else can I check?
I have suspicions:
Does anyone have any suggestions as to how to further diagnose it? I'm not keen on shelling out on a new coil, HT leads, dizzy etc unless I know there is a fault in the parts being replaced. It's expensive doing this with trial and error.
I'm having some problems with an annoying misfire. When I reassembled the engine I took the braided earth off the coil bracket and capacitor fixing and used it to provide an alternative ground path from the chassis to the engine. The bracket and capacitor (assumed to be for radio suppression) got a new ground wire that runs direct to the chassis bolt.
My car has what looks like an Aldon LU142A ignition module in the distributor. It uses a hall effect sensor to detect the rotor arm position. This is connected to the + and - side of the coil respectively. The coil appears to be a gold anodised unit, like the Lucas DLB105 sport high output coil. It has no ballast resistor fitted, which jibes with what is said here: https://www.autoelectricalspares.co.uk/ ... -100-p.asp - the DLB110 is for Lotuses but there's a comment saying use the DLB105 if no ballast resistor is in place.
During diagnosis of the misfire I have checked timing, carb balance and idle mixture. It's all spot on. I noticed some arcing between the coil output (HT plug) and the + / - terminals, only visible in the dark. I know it shouldn't do this and I have cleaned the top of the coil and the rubber cap for the HT lead, to little avail. Also tried to put extra insulation around the cap, by way of a dry section of water hose, slit along its length and slid over the HT connection to the coil, such that the rubber is between the HT plug and the coil terminals. Still have the misfire.
It all worked fine before I took it apart. What else can I check?
I have suspicions:
- There may be a crack in the coil's insulated neck, where the HT lead plugs in. Can't see one. Have attempted to fit the plug with silicone inside its rubber cup, then a spray with WD40 to displace any water but it hasn't helped.
- It might need a ballast resistor? Although it didn't have one before and ran fine.
- Removing the braid has affected it in some alchemical mystical way, despite an alternative earth being put in there.
Does anyone have any suggestions as to how to further diagnose it? I'm not keen on shelling out on a new coil, HT leads, dizzy etc unless I know there is a fault in the parts being replaced. It's expensive doing this with trial and error.