Vs V8 Berlina No Injector Pulse

[TEMPA]

Hi all,
Hoping someone can help with problem on my 1995 VS 5.0 V8 auto Berlina. It has an intermittent fault which results in there being no fuel injector pulse and therefore no start. After a period of time it will then start. I do not have to do anything to make it start, it just starts when it is ready.

I have spark, fuel at the fuel rail and it will crank over with no problems, just will not pulse the injectors.

I have tried a new throttle position sensor, new ignition module and the ECU and Memcal have been workbench tested but as the fault is intermittent his may not mean a lot. I have just about pulled all my hair out.... Any ideas would be appreciated.

 

[vkberlina]

Guess what I have just been experiencing the same problem with my 5L I have just put into my VK. Grrrrrr, tricky problem

I have bench tested pretty much everything and it all checks out, next thing im checking this week when I get a change is for a bad earth. Particularly around the EFI relay in the engine bay fuse box. I have found if I disconnect the battery wait a while and try again it works, but I dont know how accurate this is as I may disturb something as I sart working on other things while I wait.

Also I have found I am getting 12V + to both terminals of the injector while the issue occurs, I also have tested the relay for the EFI. I ran out of time today to diagnose the problem further.

Next im going to check the earth on the EFI relay, I know my Injector harness earth is spot on.

If you come up with anything id appreciate any info, same will be returned.

cheers
Scott

 

[Doctor Bob]

12 volts on both sides of the injector is correct when not firing, this should stay untill the pcm grounds it to open the injectors.
Try another distributor.
Cheers Rob

 

[jdd]

If there’s spark, I don’t see the point in trying another dizzy to solve this problem.
12V on both sides of the injectors is normal, the PCM pulses one side of the injectors to ground while the other side has 12V applied to it via the EFI relay.
There’s not many things that could cause such a problem although diagnosing it may required some patience.
Since there’s spark, it’s unlikely to be anything associated with the EFI relay or associated wiring.
It’s possibly going to be something like a high resistance connection in the injector harness or in the PCM earthing.
There’s a remote possibility that it could be a faulty injector. Since all injectors are connected in parallel, it only takes one with a faulty coil (shorted turn) to exceed the current source capabilities of the PCM. It might be worth disconnecting one injector at a time to test for this.

 

[vkberlina]

I had a 10min look at mine tonight and it started 1st go, 2nd go fine. After that it wouldnt start, I unplugged #1 Injector and it started fine. I then started to go through the rest of the injectors one at a time whilst number 1 was in it wouldnt start.
But after my testing i went back to #1 unplugged and it still wouldnt start.

I think I have a short or wiring problem in the injector harness, over the next few days im going to unpick the harness and see if i can find my fault.

any ideas?

cheers
Scott

 

[TEMPA]

Hi,

waiting for somemore ideas to appear so I can try them as I am now at my wits end. Havedn't had a chance to try unplugging the injectors one by one yet but will be giving it a go as so far it seems the most probable. Any other suggestions most appreciated.

 

[TEMPA]

Have tried unplugging the fuel injectors one by one when the car is in no start mood but makes no difference unfortunately. Have checked resistance/voltage on injector end of looms and all is normal as well when the car will not start. Definitely has spark and 12V to both wires of injectors just will not switch them to earth to cause them to pulse. Has signal in to ECU from ignition control module, have tested it and also been proven to be correct as there is spark. Believe it is picked up from same signal. Any one have any other ideas? PLEASE !!!!

 

[Doctor Bob]

I have seen a VS with a similar problem, the transistor in the hall effect in the distributor was faulty, signal is a square wave 5-0v, the faulty one still had a square wave signeal but it was 5-2.5v, it still made spark as the ignition module sees this as a good cranking signal, but the PCM wouldnt fire the injectors as the signal was incorrect for it.
NOTE: for those not so technically minded the dissy could be stuffed

Cheers Rob

 

[vkberlina]

Thanks for that info, I will test it tomorrow, if so im in luck my dizzy is under warranty
What the funny thing with mine is it starts but once I shut it down it wont, almost like an auto reset circuit breaker has tripped. I disconnect the battery come back a while later and away it goes.
But it could make sence once the dizzy starts warming up the problem occurs.

At least I know what direction to have a play with tomorrow

cheers
Scott

 

[vkberlina]

I have done some testing today,

I picked up anther dizzy for the engine, put it in, put multimeter on the hall effect out put, turned the ign on and it read 4.65v thats 2v higher than what I was getting out of my last dizzy, when I crank the car over I find it drops to 2.75v

Im still not getting any injector pulse so im wondering if the computer is stuff or is there something i have missed?

A couple of questions,

Does Timing affect the output?
Any way to test for a dead computer?

cheers
Scott