Hi all,

i recently picked up a new Z car project and I am having a difficult time trying to get it running. I will try to organize the info i have as best as possible.

From a high level, the car will not start when cranked. Occasionally if you hold the throttle open you can get it to light off but it will barely chug along on a couple of cylinders before cutting back out. If you pull the plugs after cranking they are soaked.

Another odd thing i have noticed, the fuel pump runs any time that the key is in the run position. Fuel pressure is good at 38psi, return line to the tank is clear as well. I took the CSV out of the circuit and put a fuel pressure gauge on the soft line where it used to connect.

I also put an oscilloscope on the back of the #6 injector plug and measured a pulse width of about 6ms when i grounded the negative side of the coil to make the injectors fire.

With the plugs out laying on the valve cover all 6 cylinders appear to have good spark.

previous owner was chasing the same thing so it has a lot of new parts:

Fuel pump

Fuel filter

Cap/rotor/plugs/wires

CHTS along with new harness plug

Reman AFM

All new injector connectors



I have the FSM and I have worked thru the following tests in the EF section (ambient temp is about 50*F for tests below):



Throttle Valve Switch Test

#1 - passed

#2 - passed

#3 - passed



AFM Tests

#1 - 200 ohm

#2 - 310 ohm

#3 - 70 ohm

#4 - no shorts to ground on pins 32/33/34/35

#5 - good, moves without resistance



Air temp sensor tests

#1 - 3.7k ohm

#2 - no short to ground



Cylinder head temp sensor test

3.3k ohm



Exhaust gas sensor test

0 ohm



Thermotime switch tests (i have the CSV unhooked and the fuel line blocked)

#1 - passed

#2 - 60 ohm



Control unit ground circuit tests

Passed, all have 0 ohm resistance to ground



Any ideas? i am stumped....

 

Additional info

i got it to start by pinching off the fuel supply line and shooting some ether in the intake, then unclamping the fuel line after it started.

it was only running on two cylinders based on what the plugs looked like but I did get another oscilloscope trace off the injector and the pulse width at 3k rpm was very similar to what I saw at cranking (6ms pulse width)

is the ecu fried?

 

If you have fuel, spark, and compression it should run. If all the injectors are working and all 6 spark plugs are firing, something is off. L28s are not knows for bad head gaskets or cracks, they're extremely sturdy engines. I have put a couple through hell and they still ran halfway decently even in the worst condition.
Mechanically is everything in order? The fact that you said it's only running on 2 cylinders makes me think it's probably not timing related. Are you sure all your valves are operating properly? They need to be adjusted regularly under normal use, if neglected for long enough the adjustment can back off completely rendering the valve inoperable- I have even seen rockers fall off before.

As far as the ECU goes, I'm not much help on electronic stuff. Your first post was gibberish to me lol. I'm currently chasing an electronic issue on an '83. Try tossing another ECU in there and see what happens. 79-82 n/a computers are cheap and relatively universal, it's the 83 only ECU that's hard to come by

 

Update - ECU was the culprit, I got another used one off eBay and it runs pretty well now. I will try to get another scope trace during cranking and post it up for posterity if anyone else is dealing with this in the future.