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No injector pulse/can't pull codes? Fried ECU?

1K views 9 replies 4 participants last post by  indy2000 
#1 ·
1993 GT with fresh 393w build, A9L w/moates quaterhorse. Dropped the motor in about a month ago car ran real strong, put about 100mi. on it and started to get tach jumping and high rpm miss/breaking up.
While trying to diagnose got up to 4k, started running rough and died had to get a tow home.
Couldn't get car to start so I started going through Joel5.0s no start EFI check list and this is what I found.
Spark is good.
Fuel pressure/pump is good.
12vdc at red wire on injectors.
NO injector pulse, used a test light jumpered between harness pins.
I also can NOT retrieve any KOEO codes.
I'm thinking my ECU may be fried, I opened it but nothing seems obvious, suggestions appreciated.
 
#2 ·
you are no where near able to call the ecm, with the tests you listed.

verify 5v ref circuit

verify power and grounds at the ecm

need to verify a PIP pulse to the ecm, its the rpm signal to fire injectors

all above tests need to be on energized circuits, and you perform a voltage drop test......no ohm or continuity tests.

OR

just swaptronics the ecm, and cross your fingers.
 
#5 ·
O.K. found some time to do a few more tests this afternoon.
Verified power and ground to ECM=ok
Tested STI ground to battery ground=ok
Removed ECM and tested rest. between pin 46 and pins 40,60=ok
When I had computer removed I opened case again for another look and this has me concerned but not sure if it would contribute to my no start issue.
Those are three different points on the board.
 

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#6 ·
I see you checked between the injector terminals
did you check them while hooked to the battery to narrow down if you have no pulse or no 12v?
hook to negative terminal and see if you get 12v and hook test light to positive to see if you get a pulse.
its easier to look for a problem in 1 circuit instead of 2
 
#7 ·
I got 12v at red wire on injector harness with key on.
I checked for pulse by using Joel5.0s method, Key on, remove pip plug and jumper test light between two terminals, loosen and rotate dizzy, I could hear pump prime but test light would never light, tried multiple times.
According to Joel's diag procedure this would indicate no injector pulse.
How to Solve an EFI No Start
 
#8 ·
what was your ground voltage at the ecm? power on.

What PIP plug are you referring to?

to check for inj pulse, disconnect one injector, test light to battery positive and the ground side of the injector harness, the wire that is the different color compared to other injectors......crank and check for flashing of the test light.
 
#9 ·
I guess I should have said spout connector, the small rectangular plug near the dizzy, the one you pull when you set timing.

Indy since your diag skills on theses ecm systems is much better than mine what would be the best way to test ecm ground voltage? I'm no sure if I'm doing it correctly.
 
#10 ·
to test the voltage drop on ANY conductor, all you do is have one lead on one end and the other lead on the opposite end, while the circuit is energized.

So you backprobe the ECM grounds on the ecm , that is one end

then using the other lead, you go to battery negative, and record the voltage drop, that is all a volt meter reads, is the potential, or difference.

The spout is SPARK OUTPUT, is a 0-10volt square wave sent by the ECM to the ICM

It is NOT a rpm signal

the rpm signal comes from the PIP at the ICM and goes to the ECM.

to see these signals you really need a scope, or realize you volt meter will give you an average voltage when cranking.

therefore backprobe the PIP at ECM,,,,,,,,,if you see 4-5 volts during crank you have the signal.

if NOT, you need to go to the ICM, at test it.
 
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