4AGZE AE86 - very intermittent spark and fuel

[Jim621]

Hi All,
Ive bought an 86 with a 4AGZE conversion, and am struggling to get it started - although it has run in the past.
The GZE has CAS for spark and is the MAP sensor version.

There isn't any spark while cranking using a timing light on the spark plug leads, or when removing one spark plug. And the fuel pump doesn't run when cranking.
I have got the car to fire and run a few times now, so I know it all works...but its just intermittent.

So far I have checked:
The fuel pump(s) run when connected to a different 12 volt battery. (note that there are 2 pumps installed in parallel (well electrically parallel), the low pressure lift pump and high pressure bosch 044).
There is 'some' voltage getting to the fuel pumps when cranking - a voltage test light illuminates, and the multimeter reads around 10 volts.
Battery voltage is fine at rest (12.5volts), and ok when cranking (11.5 volts).
Fuel pump relay is working (the relay will operate when 12volts is applied to the blue/yellow signal terminal).
The COR clicks when cranking (I haven't gone any further with this yet).

Im getting frustrated and want to know what to check next.
My thought is either there is a bad earth, or a relay is partly faulty and not passing enough current to power the fuel pump, spark and ECU while cranking.

Do you guys have any suggestions on what to check next? (and how to check would be good too
Thankks, Steve

[NIZLAH]

one possibility that it could be out of a number of things is that the key barrel is worn enough that it it doesn't make enough contact to supply 12v to the coil while cranking.... this was one thing that I thought could have been an issue on my smallport... ended up been something else though.. test at the coil with volt meter and see what it reads while cranking..

just an idea...

[Hen may possibly be a nut]

10V at the fuel pumps while cranking sounds a bit low (maybe fatter wiring would help), but not dangerously so. It should still start if everything else was working. One simple way to check the fuel system is to run the return line from the fuel pressure regulator to a bottle/bucket (if you have a surge tank you may also need to put the other end of the return line into the bottle too). When cranking you should get fuel coming past the regulator and out the return line. Just be careful not to douse your engine bay in petrol and set it on fire.

Sounds like a bit of time with a multimeter is in order. Check that the coil is getting power when ignition is on, and the ignitor, and the ECU. I think (other can surely confirm) that if you pull the CAS out and turn the ignition on then spinning the CAS shaft should make the motor spark. Just be sure to mount the CAS correctly afterwards.

Another thing to check is error codes out of the ECU. These may point you in the direction of something dodgy.

[Matt]

Earth out the main loom properly... it is a clump of brown wires that bolts to the inlet manifold on a bigport.

That is the most common cause of no spark on the 4ages. Measure the voltage at the ecu, by using the e1 pin and the B, B+ as well.

[Jim621]

Nizlah - The key barrel does seem very loose, and the key can be removed when its at the accessories position. So ill check that out for sure.
So inside the key barrel, is there two different sets of contacts for the cranking position (one for starter motor and one for electronic systems ie spark, fuel and ECU)? The car cranks fine, so i would presume its getting enough current/voltage to start - and the COR relay clicks when you are cranking so would assume the key is giving the COR relay 12volts??

Hen - 10V at the fuel pump is low - the fuel pumps have a fat wire from the firewall through to the pump, but i cant trace the wire in the engine bay. Being a bosch 044 pump its quite loud, so i can hear it when its running. When i connect 12volts from the battery to the fuel pump wire near the drivers footwell the pumps start and run fine, even when cranking - so there is an issue somewhere between the battery, key barrel, fuel pump relay or something with the ECU crank signal.
Ill try the CAS trick, and check the 12Volts at the coil with ignition on.

Thinking about it now ill try disconnecting the starter motor solenoid wire and check the circuits when the key is in the crank position - this should rule out low battery voltage when cranking.

cheers for the input guys.
Steve.

[Jim621]

All, an update on my issue.
The battery was on its way out so have swapped it for a fresher battery. cranking speed has improved and fuel pumps work now every time.

I still don't have spark though.

Does anyone know how to diagnose if the 4AGZE ignitor is working correctly??

Pulling the CAS out from the engine and spinning it by hand with ignition on I get a spark....it doesn't look healthy though, so I suspect maybe im not getting a spark when the spark is trying to jump under compression of the engine. my timing light doesn't show any spark when cranking, but it does when spinning the CAS by hand.

Also, testing the coils I get ~2 ohms across the primary coil, but don't get any reading across the secondary coils - how should you test these coils? I have checked the secondary coil (ie across the two spark plug connections), from one side of the coil to the primary and to earth....there doesn't seem to be any connection.

cheers, steve

[Nikkojoe]

Check the ignitor is earthed nicely. I once bolted mine to the rocker cover thinking it would earth (initial checks seemed like it was earthed), but it would just cough and splutter when cranking. Ran a new earth directly to the ignitor it fired up first go.