27 replies to this topic

[Dave the Rave]

My mini has always struggled starting when left for a period of time but starts first time if left for an hour or so. All i could think is that the spark is really quite poor.

Engine is 1330cc, stage 3 head, fast road cam, aldon fast road distributor with magnetronic electronic ignition module and ballast resistor. I have wired the black wire from the module to the negative side of the coil and the red wire to just before the ballast resistor.

Does this make any sense:-

Resistance across coil 4 Ohms
Voltage across coil 5 Volts
Voltage across coil, starter cranking 2.5 Volts
Voltage across coil, engine running 3.8 Volts

All i can think is that there is some sort of wiring problem that i need to look for because those measurements look a bit pants.

[theoldtartspimp]

is it taking a long time to start or is it not turning over properly ??

if its taking a long time to start my engine used to do this try starting without the choke when it fire then pull the choke out or put your foot on the pedal to lift the revs worked a treat on mine

[Dave the Rave]

It has no trouble turning over, just won't fire.

I've tried loads of combinations of choke to no avail, all i could think was the poor spark isn't enough to start it when it's been left overnight.

[theoldtartspimp]

might sound stupid but spray some wd40 on the dizzy cap could be moisture causing a problem

[Retro_10s]

No, Don't spray WD40 under the cap, it does seem to help a bit but For the cap to function correctly it needs to be Dry! not wet!

On my old 1098 I put a small bead of silicone round the base of the dizzy wear the cap seats, let it set and then when you put the cap on it createsa seal, it worked great, never got condesation and didn't break the seal down for about a year!

Dry electrics are happy electrics, electrics doused in WD40 are bodged electrics.

Degrease the cap inards with white spirit, then I made sure it was all dry inside the dizzy with a light hairdrying lol, lightly oil moving parts with 3-1 and then replace cap.

[Dave the Rave]

Excellent tips guys, cheers but i think it's a bit more terminal than that. Everything on the car is tip-top and all i keep thinking about is that this poor spark that's stopping it from firing when cold. Been through the whole new battery, new plugs, leads, dizzy cap and rotor arm route. What's wrong with the old girl

[minidaves]

sounds like a compresstion problem to me

dave

[Dave the Rave]

Compression is fine minidaves. Engine is pretty healthy. Any other ideas, gonna have to get this sorted before it gets really cold!

[theoldtartspimp]

No, Don't spray WD40 under the cap, it does seem to help a bit but For the cap to function correctly it needs to be Dry! not wet!

as retro 10's don't spray it inside the cap it can cause problems i should have said on the outside

last month when it was really peeing it down the car started to misfire the dizzy was that wet it was arching on the outside of the cap put a pastic bag on it after 10 mins she was alright but she didn't want to start in the morning sparyed some wd40 and it started almost straight away


have you had the car rolling roaded still sounds like my problem with the choke might be over fueling at low revs

ps what plugs, leads etc are you using

Edited by theoldtartspimp, 06 November 2006 - 12:28 PM.

[Dave the Rave]

Yeah car has been set up on rolling road. The operator never said anything about rich mixture at idle but who knows. Checked it quickly with a colourtune and it doesn't seem that rich. Plugs are NGK BPR6EVG, reasonably new leads, cap and rotor arm from Minispares. I normally run my distributor with a bag round it to stop it getting soaking wet 2.

[dklawson]

Dave, moving away from the WD-40 discussion and back to your measurements....

"Engine is 1330cc, stage 3 head, fast road cam, aldon fast road distributor with magnetronic electronic ignition module and ballast resistor. I have wired the black wire from the module to the negative side of the coil and the red wire to just before the ballast resistor"

Repeat your voltage measurement tests if they were not performed as follows.
1) At the coil, mark and disconnect the low tension wires.
2) Use ohm-meter across the bare low tension terminals on the coil.
3) With the low tension wires still disconnected (and loose ends not touching anything) measure across the ballast resistor.
Attempting resistance measurements with wire connected to a circuit will introduce errors as other elements are adding to the equation.

On the other hand, to measure voltage drops you want all the normal wiring connected. In this case, with the low tension wires hooked to the coil, place your meter in volts mode across the low tension terminals. For voltage drop measurements you must have current flowing. To insure this, temporarily connect a jumper wire from coil (-) to chassis ground and switch on the ignition. Your meter will now show the voltage drop across the coil. You can't get an accurate measurement of this voltage with the engine running.... the current is turning on and off each time a cylinder fires. With the jumper wire in place you're forcing a continuous current flow and you should measure a voltage drop across the coil close to 6V.

My first take on your numbers above is that you might have the ballast resistor connected incorrectly. In addition to the ballast resistor connection on coil (+), there should also be a wire going off to an extra terminal on the starter solenoid. The intent here is that you "bypass" the ballast resistor so the coil gets more power/voltage while you're cranking the engine. Your 2.5V value seems WAY too low.

[Dave the Rave]

Cheers for the reply dk, i see from searching previous posts you've answered a lot of leccy probs before.

I carried out the checks before as you said, as well as the additional one; so to re-itterate, we have:-

Resistance across coil, terminals disconnected 4.4 Ohms
Resistance across ballast resistor, terminals disconnected 4 Ohms
Voltage across coil, terminals connected 5.3 Volts
Voltage across coil, jumper wire between coil-and ground 5.8 Volts

I agree that the 2.5 Volts whilst cranking sounds well pants, any ideas? Maybe it's a case of bad wiring somewhere?

[dklawson]

I'm at a loss. The values you recorded for the coil and ballast resistance seem way too high to me. Out of curiosity... did you confirm that your meter is reading correctly? Short its two leads together and confirm you get a reading close to zero ohms. Then, buy a resistor around 100 ohms and check it with your meter. Resistors have stated tolerance ranges (+/- 1%, 5%, 10%...) so your reading should be within the tolerance of whatever the resistor is. I don't mean to beat a dead horse or suggest anything is wrong with your test equipment but the readings are high. Also... meters need good, working batteries to make resistance measurements. Make sure the meter's batteries are new.

Now I admit I've never worked on Magnetronic... so they could be unique installations... but I've never seen a coil or a ballast resistor that measure close to 4 ohms. As I think I mentioned earlier, a typical ballast resistor will be close to 1.5 ohms and the ballast coil to go with it will also be somewhere between 1 to 2 ohms.

Your measurement of the coil voltage with the jumper in place sounds about right since you're measuring 4 ohms on the ballast and 4.4 ohms on the coil. Doing the math based on your numbers, your battery may only be at 11 volts. (I won't bore you with the details here). A battery in good order will typically show around 12.5 to 13 volts with no loads attached. Be sure to check your battery voltage before going too much further.

You didn't mention if you have the wire between the solenoid and the Coil (+) terminal.

[maph2]

have you made sure that the plug leads are completely isolated from the head lamp loom. particulalry in damp weather, the spark can arc from the plug leads to the nearest electrical cable (which is usually the headlamp loom running in the slam panel. the splash guard is good for this.

[Dave the Rave]

Hi dk, you make a very good point about checking the multi-meter which i didn't even think of (silly me just assuming it was right) :blush: . The resistance between the meter leads is 2.8 Ohms (maybe because of the fuses in the leads), which would make the resistance readings somewhat more beliveable. I also checked a resistor at work with another meter, which checked out ok and mine, again measured the 2.8 additional Ohms.

Proper readings are as follows:-

Resistance across coil, terminals disconnected 1.6 Ohms
Resistance across ballast resistor, terminals disconnected 1.2 Ohms
Voltage across coil, terminals connected 5.3 Volts
Voltage across coil, jumper wire between coil-and ground 5.8 Volts

If any light could be shed now it would be a great help, would love to get this sorted!