Backround:

I am adding a tbi to my 78 MGB with a 1.8L 4cyl. I had it running with stock dist and fuel only. I want to control timing with ecm so I took an old dist and added a relutor and coil pickup/ 8pin icm.

Problem:

I have it timed and can get it to fire with starter fluid. I checked fuel pressure. tried new icm. But I am not getting injector pulse. Double checked wiring and assume injector is good since it ran before.

So in a fuel only system does the VATS have any affect?

I have no ideas what to check next. I want to make sure it is not the ecm before I install my EBL flash.

 

Was thinking, I had to cut the magnet on the coil pickup. Is it possible that it is strong enough to fire the coil but not to send signal to the ecm?

Also when it was fuel only I ran the tach straight to the ecm without a filter. It seemed to work but maybe I pushed it and fried the ecm. Just odd that it worked before I swapped the dist. I am thinking this might be the issue. When I first got it running I had error code 42 and 43. Then it went to the code for vss which I was told would do that if reved high in neutral. Now I just have 12 code.

Any ideas?
I am going to try a heavy magnet on the back side of the pickup. And I might try run it with the bypass wire unplugged.

 

The ICM may still be bad. If it doesn't send a distributor reference pulse (DRP) to the ECM, the ECM won't fire the injectors. It can also be that the ECM was damaged by the high voltage spikes from the previous set up.

VATs will disable the injectors. The '8062 truck ECM doesn't have it.

RBob.

 

Will a bad ecm damage the EBL Flash? I don't want to spend the time and money to find out the hard way. lol

 

Sure, don't want to install an EBL system into a bad ECM anyway.

For testing the distributor can either measure the voltage from it or use an LED and 470 ohm resistor.

The reference pulses low is to ECM pin B3 (this is ground at the distributor)
The reference pulses high is to ECM pin B5

Remove the distributor from the engine and using a jumper clip/lead ground the body of the distributor to the engine. Connect all of the connectors to the distributor and ICM.

Key-on, engine-off, and spin the distributor by giving it a quick twirl of the drive gear. Should have spark and should have a 5 volt square wave on the DRP wires. This is where the LED/resistor or DVM come into play.

If the fuel pump is wired as GM did it, it should run for 2-seconds every time the ECM gets a DRP.

RBob.

 

Just had a thought. Will not having the est/knock sensor connected or the wire connected to anything, make any impact on the injector firing?

 

no

 

Like rbob said if you don't get a tach signal from the correct icm to B5 of the ecm the injectors won't pulse.

 

cool. thanks. Will try and do some tests tonight.

 

highest voltage i got was 2.9. since it sees some signal but not a strong enough one leads me to think my ethnic engineered pickup is not strong enough. makes sense, half the magnet = half the signal. Unless the icm has some impact on this?

 

This may be OK. Recall I said a 5V square wave signal. I should have elaborated. If you measure a 5V square wave signal with a 50% duty cycle, a DVM will/should show about 2.5V

That is because half of the time it is at 0 volts, and the other half of the time it is at 5 volts.

Note that the ICM buffers the pickup coil, and sends an ICM derived signal to the ECM.

Try spinning the distributor slower, and see if the DVM shows spikes in the voltage. Those spikes are the DRPs. Again (more of the 'Note'?!), a slow spin may not produce enough of a magnetic signal to the ICM to trigger it.

RBob.

 

The 2.9 was a max reading not an average. so it was sending the drps but not up to 5v. Not sure what the usable level is, +/- 0.5?

Going to pick up a new pickup tomorrow and give it a go. New ecm and icm will have to wait till payday. The living paycheck to paycheck strategy to wealth seems to be a gimmick.

Oh and an interesting result to my tests... I placed a magnet on the side of the pickup. This must have cancelled the installed magnet because the max volt dropped to 1.8.