Is this a weak spark?

[edwardbahaw]

I have a NAS spec 3.9 V8 fitted on a 110 defender and the problem is that it starts poorly. It takes about 5 attempts before it starts. It also runs quite rich as determined by the strong scent of the exhaust fumes.Today I have replaced the plugs with a set of clean used ones and took a video of the sparks from one of the plugs which I removed. See the you tube link below.

These sparks seem very weak to me. In case you are wondering the plug is earthed via a jumper lead.

Also, swapping the plugs has not rectified the starting problem nor the excessive fumes from the exhaust.

Previously in an attempt to solve this problem I have already changed the following using new parts.
Ignition coil
Rotor
Distributor cap
Ignition module/amplifier
HT Leads


Any thoughts or suggestions are highly appreciated.

[Josh NZ]

Are the replacement parts genuine LR or of comparable quality?

The sparks should be blue and fat. Your Ecu might be thinking that there is more air going in than is actually going in and injecting more fuel. Maybe your air flow metre is playing up?

I'm not overly knowledgeable on EFI systems but there are plenty on here who are!

HtH

Josh

[edwardbahaw]

Thanks for the reply Josh!

I reckon these sparks don't look blue and fat?

The replacement parts are OEM.

I actually have a Hawkeye pro 2.0 and the cable which connects to the diagnostic socket on the 14cux ECU which gives live data on: fuel injection pulse width, MAF voltage signal, TPS voltage, signal, coolant temperate etc

I'm gonna do some research now on the MAF voltage signal to see if mine is within range during tick over.

Does anyone know what is the required pulse width during cranking? Mines go up to around 6.8ms during cranking for fuel enrichment I figure to sync with the open air bypass valve compared to around 3.5ms at idle.

[Rangy35]

If the engine starts, the spark is not weak. You have something else causing the hard starting. You dont say how long you crank during this five attemps, have you done a compression test, do you have more than 12,2 volt at the coil when cranking?

[edwardbahaw]

Rangy

Thanks for your reply. I usually crank for 3 second intervals and it takes about 5 attempts. Also I need to press on the accelerator to get it to started otherwise it would not start period.

Can you remind me how to test the voltage on the coil when cranking?

Much appreciated.

Ed

[edwardbahaw]

Update: After alot of online research I just advanced the ignition timing a bit and it starts spot on now BUT when it is driven there is significant pinging.

Is this a stretch timing chain?

Ed

[edwardbahaw]

Hi all

Just an update to everyone on my findings and plan going forward.

If I advance the ignition timing by turning the distributor anti-clockwise by about 10 degrees it starts perfectly but if I test drive there is significant pinging.

To solve the pinging I gradually returned the distributor to its original position in 2 degree movements. Each time I fired it up and test drove and each time it became even harder to start. The pinging only goes away when the distributor has been returned to its original position at which point to get it started is extremely difficult. It cranks fine but it does not fire. I have to step on the accelerator and then it struggles to fire up until about 5 attempts with each attempt being about 2 to 3 seconds of cranking. With the ignition advanced its starts on the first attempt without having to step on the accelerator.

So my plan forward in the absence of a timing light and timing marks on the crank pulley I am going to remove all spark plugs except no. 1. Then with the distributor cap removal I am going to rotate the engine by hand using the 24 mm nut on the crank pulley. My aim is to see if i get full compression just at the point when the distributor rotor aligns with the no1 spark plug (5 o clock position) If it fails this test then my conclusion is the engine timing (valve, piston TDC and ignition) is off and I would have to strip the front and correct it.

Does this make sense or is there a better way?

Ed

[FridgeFreezer]

Hang on a sec here:

- Hard to start

- Strong smell of fuel

Being a NAS 3.9 I'm guessing that should be Hotwire EFI, in which case #1 suspect is coolant temperature sensor (the 2-pin one for the ECU, not the 1-pin one for the gauge on the dash), followed by checking in no particular order: airflow meter, fuel pressure, throttle position sensor, fuel temp sensor, air temp sensor (in airflow meter).

And of course it's a weak spark it's a Lucas ignition system!

[edwardbahaw]

Freezer

Thanks for your suggestions. I have checked all the mentioned sensors before. I even have a hawkeye pro 2 which interfaces with the ecu using a special cable and all sensors are good (most are new btw)

I already removed all the plugs which makes the engine easy to turn by hand and I discovered that I can move the crank about 4 degrees back and forth and without the distributor rotor moving.

This can be a worn distributor drive gear or a stretched timing chain.

Thoughts anyone before I strip out more parts?

[edwardbahaw]

Update:

I can now verify that the timing chain is stretched since I have removed the left hand rocker cover and I am able to turn the crank shaft pulley back and forth approximately 8 degrees before the push rods begin to move.

In addition with a probe fitted down in no. 1 cylinder as I turn the crankshaft pulley toward TDC on the compression stroke I can see that there is upward piston movement before the intake valve is fully closed which means less air and less compression leading to difficulty starting and rich running which is the symptom and the cause is a stretched timing chain.

So solution is to change timing chain and sprockets.

Am I right?

[Bowie69]

Well you are just saying your engine is a bit worn really.... V8's tend to start easily even when completely knackered, so I still think it is likely to be something external to the core of the engine.