81cuttysupreme

I'm fresh out of ideas as to why i can not get my motor to stay running, or usually run at all. I swapped an LS1 into a G body, oldsmobile. Problem is it will only start about 1 out of 10 times, run for a few seconds and then die. I have had the VATS checked on the ecm twice, it is turned off. I have a constant 58psi at the fuel rail, I have spark at all of the plugs. The injectors were flow tested and worked fine. I beleive the injectors are not getting the trigger signal after the initial start signal. When i hooked up a light to the injectors they would flash a couple of times and then quit. They all have the 12 volt constant going to them. I have replaced the cam sensor and crank sensor, and the map sensor. The ecm is set up for mass air flow and the maf is pointing in the right direction.

I have a basic scanner that for a little while said the map sensor circuit had low output, that was when i changed the map sensor and checked for 5 volts at the plug. The scanner now is not reading any codes, but the motor isntn doing anything different than when it had the codes. I have checked the grounds with a vom and they show no resistance to the firewall.

I did try spraying starter fluid into the throttle body and the motor was able to stay running. To me that further points to a lack of fuel being the reason for the motor not running.


At this point I'm really out of ideas. I desperately need some help. So please bring on the help!

therabidweasel

iTrader: (5)

Have you pulled a plug after cranking to see if it is wet or dry? Are you using the same pcm and injectors from a donor car or is this an all new setup?

Checked the grounds to the firewall? Do you have grounds connected to both heads, 3 on drivers and 2 on passengers? That assumes a late model f body harness, I don't know about anything else.

81cuttysupreme

The harness is a reworked 99' fbody harness. It only had two ground wires on the back of the driver side head. Most of the setup is new. 60lb injectors, rebuilt engine, ls6 top end the new sensors mentioned above. I have checked the grounds and they appear to be good. I checked with a vom. I did pull a plug too, it was dry. Which makes sense with no injector pulse. I just don't know why I'm not getting them to pulse correctly?

gMAG

iTrader: (1)

Is it possible that you have battery in 'start', but not in the 'run' position?

81cuttysupreme

I checked batt supply for ecm it has 12v in run position. So does ignition. ???

Redbull87

iTrader: (3)

Was the ecm reflashed for this setup?

81cuttysupreme

ya ecm was re flashed. and i'm not pulling any codes.

LS1MCSS

iTrader: (18)

There should be three ground wires if it's a reworked stock harness. See if one of the ring connectors has two wires going into it. If not, that could be the problem.

gMAG

iTrader: (1)

What I would try next, is to pull the fuse for the fuel pump.
Then, with a noid light on any one of the injector harnesses, crank the engine and see if the inj fuel sig is regular. Then, try an inj on the other bank for the same signal.
The injectors are individually fired by supplying ground from the ECM, to each individual injector, in turn.
Also, verify that the ECM has a good ground. Check between the ECM case & chassis.
Edit:Forgot to mention...my reworked harness had two broken/partially open wires, which I had to troubleshoot. One of the wires was the crank signal. In my case, I had zero fuel pulse sig.

81cuttysupreme

In order to check the pulse to the injectors i unplugged all the the injector plugs. Then I tested them with the noid light. I tested a couple on each bank. All of them flashed two quick times when i hit the starter and then nothing even though i continued to hold down the starter. One of them flashed again after about 10 seconds of holding the starter down. I wasnt willing to hold the starter down for that long time after time. It is possible other ones may flash after a long time also. How can I check the crank signal pulse? Can I probe one of the crank signal wires while the motor is turning over? The sensor should get a constant 12V right? Is there a measureable voltage that should be coming back to the ecm?

are you saying by checking the case is grounded that if i touch the outside of the ecm with a probe of the vom and the body with the other I should get a closed loop? no resistance? i have not checked that.

gMAG

iTrader: (1)

In order for the pulsing to take place, there must be a ground from the ECM to each of the injectors.
I'm not exactly sure WHICH main grnd is responsible for the individual grounds @ the ECM.
The pulsing should take place indefinitely, as long as you crank.
The crank sensor should have 12v/grnd/sig lead. So, there should be 12v (or so) @ the crank sensor, from the ECM. There should be a grnd @ the crank sensor, and there should be low voltage spikes from the crank sensor. This can also be verified with an ocilloscope. In my case, the yellow wire is the CKP sig lead.
One thing I'm gonna say, is that bec you do have noid operation, and that the noid operates relatively the same for each cylinder, that there is nothing wrong with the sensor, & nothing wrong with grnds to the ECM.
You might try retightening your main grounds at the back of the cylinder head, then verifying a solid ground by checking the ends of the ground leads at their termination points.
Did you check for battery to each of the inj harnesses? It should be there, full time/key on.

81cuttysupreme

I did check for 12v at each of the injectors and it checked good for all of them. Like you said the ecm has the capability to pulse the injectors but for some rason it will only pulse them for the first couple seconds. I can recheck thhe grounds. Maybe one of the connectors had two wires going into it and I didn't notice. I will look to make sure there are 3 ground wires. If the harness\ecm had a bad ground would the 12v power supply to the ecm show any fluctuation?

gMAG

iTrader: (1)

To check 12v, I think that you'd be better to remove the fuel pump fuse, remove one inj harness, then crank, while holding the VOM probe onto the battery lead, at the open harness. If batt remains while cranking, then it would have to be a fault at the ground side.
Short of testing the crank sensor for an ongoing, proper firing trigger, you could try what I did. I left the crank sensor > ECM harness connected, then bypassed the 3 wires by bridging jumpers at the correct ECM pins, & also at the sensor wires, as close to the sensor plug, as possible.
There could be an intermittant open, but I doubt it, because you seem to have the same result, no matter the inj being tested.
One other thing...if you can locate the ECM pin for common ground, which eventually is switched to each inj ground, you can verify that your ground is good at least to the ECM.
I've read of issues like this, where the VATS did show as disabled, but it actually was not disabled.
Sorry I can't be more exact. As you know, these issues involve old-school shooting.

gMAG

iTrader: (1)

I recalled this thread, after noticing that you had your ECM reflashed.
Just another idea, after you finish checking the obvious...post 22 & 23.
https://ls1tech.com/forums/conversio...art-issue.html

crainholio

iTrader: (2)

Sounds like a VATS glitch, didn't get disabled in the PCM. And whip out your fuel pressure gauge and report back w/ fuel pressure reading at the rail during cranking.

81cuttysupreme

I have check fuel pressure a few times. It holds right around 58 during the prime the start and during the idle if the motor starts up and after it dies. No problem with pressure. The injectors have been tested too and they worked fine on the test bench.

gMAG

iTrader: (1)

You can buy a cheap VATS sig generator off ebay. They cost $25, or so.

LS1MCSS

iTrader: (18)

When the engine does start, how long will it run?

81cuttysupreme

If the engine does start it only runs for a few seconds. But it has actually been a while since it has started. I would say it hasnt started in the last 10 start attempts. I did check the positive side of the injector plugs tonight, one on each side. The voltage did drop down into the 10's during the start, but I would imagine this is normal.

I also checked the harness grounds again. There are 3 of them connected to the driver side head, and my vom shows a closed loop to the firewall, 0.3ohms.

So i feel like i'm still trying to find out why the injectors quit pulsing. Is it possible to back probe the wires at the ecm? Do the plastic covers pull off? Can you check the crank signal with a VOM? or is it too fast of a pulse?

poloaa009

The harness is a reworked 99' fbody harness. It only had two ground wires on the back of the driver side head. Most of the setup is new.