No Injector Pulse?

[barno68]

This is an issue with a '95 LT1. Engine won't start (new rebuild), it has spark (new opti and coil) but I do not think the injectors are firing. Here is what I have tested and the results:
-All the injectors read about 12.8 ohms
-12V to the pink injector wire
- each ground wire is good
- ran a test light between the two terminals on multiple injectors and cranked the engine for 10-15 seconds and the light did not flash
- ran the same test between injector ground and battery +, no flashing light



I think that narrows it down to pulse, but how to fix? This is a swap and I am running a new engine harness and the ECU has VATS disabled. I chose to go with the fuel relay on my existing painless harness rather than the one on the new engine harness, would this have any effect?

One last thing, I have never used a high torque starter and this thing is loud as heck and does not turn the engine over very fast (new battery)... just throwing that one out there.

[Badley]

If the starter is having a "issue" you may not have the starter and motor grounded good enough. Grounds are a big thing on these FI motors.

The relay could be a problem, but fairly hard to tell with out seeing diagrams for the two harnesses. Can you hear the fuel pump kick on when you turn the key on?

[barno68]

If the starter is having a "issue" you may not have the starter and motor grounded good enough. Grounds are a big thing on these FI motors.

The relay could be a problem, but fairly hard to tell with out seeing diagrams for the two harnesses. Can you hear the fuel pump kick on when you turn the key on?

Can't miss the sound of the fuel flow- I have #42psi at the rails.

I am running several large braided ground wires, but you never know. I will try the old jumper cables to the engine block and see what happens. Thanks.

[xx_ED_xx]

Without seeing what you did hard to tell. As long as you are using the signal wire which i think is ground to operate the relay and the other side has keyed power then you should be good. I know I was playing with an mefi setup in my truck and one of the grounds for the ignition circuit wasnt hooked up which also affected the injector pulse.

[barno68]

I have not had a chance to try and turn the engine over again, but did do a resistance check on both the starter and ECM ground to battery ground.
ECM was 6 ohms, seems ok considering it is on the opposite side of the engine from the battery but I will run a jumper and see what happens. The starter was .1 ohms, definitely no issues there.

Any other suggestions on the injector signal issue? Thanks.

[MrQuick]

Since everything goes through the opti spark I'd look to that. How did it install? any forcing or mis alignment issues? What is your TPS reading at cranking?

If you can borrow a set of niod lights to test injector pulse as a test light could cause damage to electronic parts and connections. Also the ground is real fast and a light might not catch it.

here's an excellent LT1 reference site. http://shbox.com/1/how_tos.html
vince

[Rhino]

Also the ground is real fast and a light might not catch it.

x2. When helping a friend with an EFI swap we thought we had injector issues as well. A standard test light wouldn't even flicker. The injector is only open milliseconds at a time.
a noid is the only way to go.

In a pinch, you could probably use an LED wired in the proper polarity. Most LED's light up at 1.2v, which the injector connector can easily supply. It wouldn't totally light up, but you should at least see a flicker.

[megaladon6]

did you have the VATS system disabled?
what does the LT use for cam or crank signal? did you check those?

[79PonchoUK]

You'll soon know if your injectors are working. Just put a screw driver between your ear and the injector (sharp side not in your ear lol) and you'll definitely hear them if they're clicking.

[barno68]

x2. When helping a friend with an EFI swap we thought we had injector issues as well. A standard test light wouldn't even flicker. The injector is only open milliseconds at a time.
a noid is the only way to go.

In a pinch, you could probably use an LED wired in the proper polarity. Most LED's light up at 1.2v, which the injector connector can easily supply. It wouldn't totally light up, but you should at least see a flicker.

Thanks for the noid light suggestion, the injector signal is present. So one more thing to check off on the "why the engine will not start" list! Thanks for the help all.

[79PonchoUK]

Thanks for the noid light suggestion, the injector signal is present. So one more thing to check off on the "why the engine will not start" list! Thanks for the help all.

Still listen for the injectors though...if you can't hear them then they aren't working. Even if some signal is present.

It's not unheard of for injector drivers to go weak, it's very unlikely...but I've had it happen. for the sake of 20 seconds minutes listening....

[megaladon6]

double check your ignition timing also.

[barno68]

double check your ignition timing also.

That is what I am avoiding- it is an LT1, so the only issue with timing would be the timing chain placement. I am pretty sure it is correct as I spent a fair amount of time trying to get the dots to line up when installing it. The last thing I really want to do is drain the coolant again and pull the front of the engine again.

[BK2LIFE]

if your timing was that far off, youd know. motor would run, or at least try to fire/backfire, as long as you got the dots lined up, your good to go, worse thing could be your off a tooth, which would advance/retard the cam, but it would still run, just moves the power band up or down a bit. if your so far off it wont run, your valves would hit the pistons..

what computer are you running? have you tried checkin the codes depending on how your system is set up?

and how about the old days? have you sprayed any carb cleaner down the t-blades to see if at least your plugs are working/firing? this way the motor would at least fire if the injectors aren't spraying fuel.