Help! 3.9 efi not starting

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e4yob

New Member
Posts
54
Location
Weston-Super-Mare
I have just fitted a 3.9 efi into my 90 which was originaly a 2.5td, I'm 99.9% that I have wired it up correctly and I'm now at the point of getting it to turn over but not fire up.
I think I have more or less narrowed it down to the injectors not getting a signal from the coil to fire them, although I am getting a sprk from the plugs.
I have read somewhere that this could be a non bosch coil drawing to much current.
i have done many tests from the haynes manual which is showing that I am getting 12v from the coil negative terminal with the ignition off but the book says I should be getting 0v, Could this be down to the ignition amplifier on the dizzy not working correctly.
I know the fuel relay and injectors are working as I have earthed them at the ECU plug and they operate.
So is my diagnosis is its eithere the non bosch coil or ignition amp or could it be my ECU itself.
I have also checked all my earths and connections which seem ok.
I should say that the engine has been outside under a tarpolin for nearly 4 years.
hopefully someone has expirenced shuch a problem and can shed some light as I don't want to chuck money at things it isn't likely to be.

Karl
 
my plugs are dry when I crank it over, Ive tested the injector plugs and I get 12v at both sides which drop to about 8-9v when cranked. I know my fuel pump is working fine and so are the relays although the fuel relay isn't geting a signal from the ecu to energise it (pin 85 on relay), however if I earth pins 16, 11 and 13 0n the ecu plug the fuel relay energises and the injectors wil fire.
What I do know is the ecu relies on the trigger pulse from the -ve side of the coil which is the same trigger pulse for the spark of which i'm getting.
 
O.K. lets start with LT checks. Ignition ON, engine stationary

Get your volt meter and check battery volts; hopefully you have over 12v.

Next - Check Battery -ive to coil +ive should read Max -1v of battery volts.

Next - Check Battery -ive to coil -ive should read MAX 1v below battery volts.

Last - check between Ground and one of the mounting screws on the ignition amplifier; this should read 0v to Max 0.1v

To check the ignition amplifier, start with ignition OFF. Check between battery +ive and coil - ive. Reading should be 0v.

Then switch ignition ON you should still see 0v. Then get an assistant to cracnk the engine, voltage should increase when cranking. If no increase you need to check pick up coil resistance - Remove ignition amplifier from side of dizzy, measure resistance across the two pins in the side of the dizzy, should be 2k ohms and 5k ohms.

The other thing I would ask is if you have disturbed the base plate in the dizzy? Have you checked the pick up air gap? This must be correct or it won't work.
 
ive done all of the LT checks all ok apart from the the ignition amplifier check,
start with ignition OFF. Check between battery +ive and coil - ive. Reading should be 0v.
instead of getting 0v I'm getting battery voltage and no change when the engine is cranked.
i've not yet checked the pick up coil resistance as i didn't want to disturb the dizzy.
I haven't touched the dizzy or checked the pick up air gap.
The engine is how i bought it and was assured it was a runner when removed
 
just another thought, in the wiring diagram it shows a capacitor comining from the +ve side of the coil going to earth. looking at mine I don't seem to have this unless its deep within the loom somewhere. Would this have an impact on things
 
get the ecu tested went to a customers to wire it in and found it had a faulty ecu and then the injecotr rail was full of rust and caused the injectors to fail replaced four after cleaning and it had bore washed the engine took 1 hour of pooring oil into the plugs holes and cranking over to get compression back!!!
 
vougese39 said:
get the ecu tested went to a customers to wire it in and found it had a faulty ecu and then the injecotr rail was full of rust and caused the injectors to fail replaced four after cleaning and it had bore washed the engine took 1 hour of pooring oil into the plugs holes and cranking over to get compression back!!!
Click to expand...

Sounds like a nightmare!!

A word of warning about ecu testing - I had a duff ecu, it was tested "no faults found". It would not run right. I was subsequently told the ecu wasn't reading the AFM. Replaced ecu; never looked back.
 
Last edited:
i've just ordered myself a new dizzy from flee bay to eliminate that side of things, in the mean time is it possible to take the ecu somewhere to be tested and are the bench tests conclusive.
 
e4yob said:
i've just ordered myself a new dizzy from flee bay to eliminate that side of things, in the mean time is it possible to take the ecu somewhere to be tested and are the bench tests conclusive.
Click to expand...

If you know somebody with a known good ecu see if you can borrow it and hook it up and see if yours runs any better. If not you need to test/check the various inputs to your ecu:

Air flow meter, throttle potentiometer, coolant thermistor, fuel thermistor, engine speed (from wire off coil). I think that covers the main bits.

BTW is your battery and alternator in good shape.
 
unfortunately I don't know anyone with the same engine to try another ecu,
the engine came from a 93 l reg classic and it has got cats which are all connected.
Ive tested the tune select ressistor and get a reading of about 3900 ohms.
The battery probably could do with being changed as it will only charge to about 12.5v
I'll spend a few more hours on it tomorrow and re check all the wirirng and other inputs to the ecu.
If anyone has a 14cux ecu or knows anyone in the w-s-m area that I could try out give me a shout.
 
well i've re checked all my wiring and earths, all good, I think I'm just going to wait till I get my new dizzy, if that doesn't work then I'll go down the ECU route.
Your right by saying the injectors are on a switched earth, as when i earthed the injector pins on the ecu plug the injectors worked. I know the trigger pulse is reaching the ECU from the coil and i have 12v at the injectors.
 
e4yob said:
well i've re checked all my wiring and earths, all good, I think I'm just going to wait till I get my new dizzy, if that doesn't work then I'll go down the ECU route.
Your right by saying the injectors are on a switched earth, as when i earthed the injector pins on the ecu plug the injectors worked. I know the trigger pulse is reaching the ECU from the coil and i have 12v at the injectors.
Click to expand...

Sustitute your ecu, I suspect a replacement dizzy is going to be a waste of time, effort and cash. BTW have you checked the pick up air gap and made sure the ignition amplifier is working?
 
well a new dizzy fitted made no difference as you stated but at least i know ive got a spare lol so i'm now going to have to try and source another ecu and just hope that it is a good one. I have just read that the starter inhibit switch can cause problems,. I've yet to wire mine up as i was wating until I got the thing running before I tided every thing up. So i will now try wiring it up and see if that makes a difference.
 
Yep not a blind bit of difference lol So now its down to the ecu, so i've got to weigh up the option of going for a second hand unit and hope I don't get conned by buying a duff unit or get mine checked and then have it repaired. As i don't know anyone with another unit to try. I think by the time I get this thing running I could have bought a complete running car to do the swap and then made some money back selling the left over bits. But thats just me trying to save a few quid lol Still I wont be beaten!
 
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