3.5 V8 hotwire, not starting

[v8hotwire]

Engine
1977 3500 V8
Hotwire fuel injection
Car has been running perfectly in this setup since 2008

Symptoms,
Starter turns well
Fuel pressure is good; pump starts, and pressure reads 38psi before cracking.
Spark exists at plugs; held plugs to earthing point around the car
Petrol is in the cylinder; not a huge smell coming through the exhaust though, so perhaps injector related

I have got Rovergauge up and running. Throttle is registering perfectly, temp gauges registering. no revs though when I turn the engine over. No fault codes being picked up.

Any pointers on where I should look next? I bet it's a loose lead somewhere. Anything I can check with a voltmeter?

Jim

[350zwelgje]

On flapper versions there is a wire from the ignition amplifier to the ECU to tell it the engine is running. There is a bullet connector in this wire in the area of the airflow meter that can become disconnected. Without this signal, it won't fire the injectors and when it happened to me, your symptoms were just like you describe.

Rob

[blitzracing]

The ECU is fed from the switched side of the coil, so it gets 4 trigger pulses per engine revolution. You can do a really simple test to check if the ignition is getting to the ECU. Disconnect the king lead from the top of the distributor, and strap its connector near the chassis to make a spark gap. Remove the rotor and rotate the engine until one of the trigger lobes aligns with the pickup (as if you where going to measure the air gap). Then turn on the ignition and tap a screwdriver tip across the air gap to complete the magnetic loop. You should get a sharp crack as the coil fires the king lead, and the fuel pump should kick in to life if the ECU is getting a signal for about 3 seconds- it just needs a single pulse to do this. Its the same timed pulse you get when the ignition is switched on. If there is no pulse, you need to check the loom connections for the 6.8 k resistor that is in the loom between the coil and ECU.

Shown here half way down the page:

http://www.britishv8.org/Articles/Rover-14CUX-EFI....

[eliot]

v8hotwire said:

no revs though when I turn the engine over. No fault codes being picked up.

So the ECU doesn't know when the engine is turning over and therefore wouldn't register a fault code.
If you are getting a spark, then you need to trace the wiring that runs from the negative side of the coil to the ECU (Black with white stripe possibly...not had a rover for over 10 years)

If you are not getting a spark, then just the basics - rather than anything to do with the ECU (ECU has nothing to do with sparks, it meerly monitors the dizzy to get an rpm signal)

[v8hotwire]

Thanks folks, makes good sense. I'll concentrate on the negative wire from coil to ecu next then.

Jim

[v8hotwire]

blitzracing said:

The ECU is fed from the switched side of the coil, so it gets 4 trigger pulses per engine revolution. You can do a really simple test to check if the ignition is getting to the ECU. Disconnect the king lead from the top of the distributor, and strap its connector near the chassis to make a spark gap. Remove the rotor and rotate the engine until one of the trigger lobes aligns with the pickup (as if you where going to measure the air gap). Then turn on the ignition and tap a screwdriver tip across the air gap to complete the magnetic loop. You should get a sharp crack as the coil fires the king lead, and the fuel pump should kick in to life if the ECU is getting a signal for about 3 seconds- it just needs a single pulse to do this. Its the same timed pulse you get when the ignition is switched on. If there is no pulse, you need to check the loom connections for the 6.8 k resistor that is in the loom between the coil and ECU.

Shown here half way down the page:

http://www.britishv8.org/Articles/Rover-14CUX-EFI....

I don't get continuation through the 6.8k resistor. But, I have a spare, and same. Is that cos the resistance is so high? One measures 7.2k ohms, the other 6.2k ohms (on my old voltmeter).

Jim

[v8hotwire]

Don't worry. I bridged the resistor, but still no revs registering. The white/black wire has continuation though, and there is spark. Hmmmm. One of my checks must be wrong.

[eliot]

I assume the ECU is actually powering up - i.e. it is registering temperature etc.

[Mr2Mike]

v8hotwire said:

I don't get continuation through the 6.8k resistor. But, I have a spare, and same. Is that cos the resistance is so high? One measures 7.2k ohms, the other 6.2k ohms (on my old voltmeter).

Jim

The word is "continuity". Continuity tests are to determine if something is either open circuit (or high resistance) or closed circuit (low resistance), they are not suitable for testing resistors. Since the resistor in this case is a fairly high resistance, a continuity tester will see this as an open circuit, which is exactly what it has reported. Use a continuity test when you are testing wires, connectors and fuses etc. not electronic components.

The very fact that you have measured the resistance and it's within the expected range suggests the resistors are fine. Bridging the resistor is not likely to be a great idea, it's clearly there for a reason.

[v8hotwire]

Thanks.

Yep, the ecu is powering up as it is registering throttle pot, temp etc on Rovergauge.

[eliot]

So you need to check that you have continuity all the way back to the ecu connector for that wire next.

[v8hotwire]

Yep, all the way from coil to ecu connector, I've got continuity.

Hmmm.....

[blitzracing]

Time to try another ECU then, but dont try the bridging of the resistor again, there's a lot more than 12 volts on that connection to the coil as the coil discharges, so the resistor is there for a reason.

[eliot]

blitzracing said:

Time to try another ECU then, but dont try the bridging of the resistor again, there's a lot more than 12 volts on that connection to the coil as the coil discharges, so the resistor is there for a reason.

Yes agreed on both points.

[v8hotwire]

Just tried new ecu, nothing.

Will try some easy start into the plugs, see what happens,

[eliot]

Can anyone else with the ECU software confirm they see around 300rpm during cranking (my megasquirt does).

Also check that your sensor readings (tps/air temp) are still present during cranking - as there is a "live" that goes dead during cranking phase - maybe the ECU is miswired on this line.

[v8hotwire]

Thanks mate.

Not done the EasyStart yet. But just had a thought. I noticed that the fuel pump kicks in when I'm cranking, so I am guessing injectors are firing, and am therefore thinking the ecu knows the car is cranking.

So, probably time to go back to checking the spark? Damn. I've already seen spark from each plug. I will check again.

[eliot]

ok - so are the spark plugs wet? - if so, they are firing.

[v8hotwire]

Right, just replaced all plugs. Old ones stink of petrol. :-)

But, battery is dead now, lol! On charge.

[eliot]

Check the state of your engine oil, as you may of been pumping petrol into the engine. The oil could be contaminated which can trash the bearings.