96 Tahoe dies while driving and won't start

[east302]

- there is 12V on each injector


September, 17:


Installed test light on each injector circuit:

Ignition on: light is lightly on
Cranking: light flickers
diconnecting VCM (red an blue): light is off

It's flickering while cranking and constantly on by ignition on.

Revisiting the above, did you say that when you jumper the voltage and ground connection for each injector the test lamp is on with ignition on?

For example, if you test between voltage 'K' and ground 'J' at injector 8 with ignition on (not cranking) do you get voltage?

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You should get voltage on the pink wires (circuit 439) at each injector when grounding elsewhere. But, if you get voltage on all injectors at all times when jumping the voltage supplies to the ground feeds from the VCM, then that would seem to point to a VCM grounding issue.

It only grounds each injector when it is meant to supply fuel to that cylinder, so I would think that you'd only have constant voltage if there's a short to ground between the injector and, or within, the VCM.

It looks like the VCM itself is grounded at pins 17 and 18 in connector C3 to grounds 103 and 104.

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[Nightflyer]

Good morning eysi, east302 and the other...

I'll testing every connector on sunday.

@east302: you said: "
Revisiting the above, did you say that when you jumper the voltage and ground connection for each injector the test lamp is on with ignition on?

For example, if you test between voltage 'K' and ground 'J' at injector 8 with ignition on (not cranking) do you get voltage?"

Yes: there where power ~12V

Best regards

 

[Nightflyer]

And what about the misfiring..? Timing looks good. Only the cap and rotor? The spark plug wires are ok...

 

[V_Kint]

And what about the misfiring..? Timing looks good. Only the cap and rotor? The spark plug wires are ok...

Looking at the steps you've taken so far - on the fuel side you replaced the injectors and were still getting no fuel. Fuel pressure was low, so you replaced the fuel pump. Now the plugs are wet, but no start and it acts as the timing is off. It might be worth checking to see if the new injectors were plugged into the correct ports.

 

[east302]

Good morning eysi, east302 and the other...

I'll testing every connector on sunday.

@east302: you said: "
Revisiting the above, did you say that when you jumper the voltage and ground connection for each injector the test lamp is on with ignition on?

For example, if you test between voltage 'K' and ground 'J' at injector 8 with ignition on (not cranking) do you get voltage?"

Yes: there where power ~12V

Best regards

Question for the group:

Should he be getting a constant ground when testing between each injector's voltage supply and its ground feed from VCM with ignition on and not cranking?

I would think that he shouldn't. If they always have a complete circuit, then the injector would always be open.


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[eyesi]

ok, lets start again,
I'm Matthias from Bamberg, Germany. I've an 96 Tahoe (350 Vortec TBI) and a real big problem:
do you have TBI or CSFI,? i have been considering CSFI,
CSFI http://www.fourwheeler.com/how-to/1012or-csfi-to-mpfi-vortec-engine-fueling-fix/


if it is TBI, fuel pressure would be 9-13 psi

if it is CSFI 60-66 psi and range very critical

if MPFI, same as CSFI, although big fluctuations are not concern for a no start condition


If you have TBI, and 60 psi in the system, so oo... voila!

 

[Nightflyer]

I've done the cpfi to mpfi conversion. And the injectors are on their right place in the intake....

 

[Nightflyer]

I've fuel at every spark plug......I think the misfiring is the problem. Could low pressure be the reason for the misfire??

Tomorrow i'll check the timing again....there's help from a good friend.

 

[east302]

Maybe someone will know for sure, but if your VCM is providing a constant ground to each injector (instead of momentary when needed to fire) then that seems like it would be your issue.


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[eyesi]

I've fuel at every spark plug......I think the misfiring is the problem. Could low pressure be the reason for the misfire??

Tomorrow i'll check the timing again....there's help from a good friend.

I've fuel at every spark plug......I think the misfiring is the problem. Could low pressure be the reason for the misfire??

Tomorrow i'll check the timing again....there's help from a good friend.

Nightflyer, have non sense "assume" that you have or have not injection pulse at injectors, and/or spark at each spark plug, it is necessary verify at each injector and spark plug, one by one. For testing injector pulse i use an extra injector plugingit at each injector harness conector, feeling it or hearing it while cranking the engine. About misfire, it takes place when the engine is running and one or more cilynders are not contributing power, and is not exclusive from spark fail, just in case... ( i use a ford 90-00 injector without the plastic bottom cover for "feel" the tip of injector pulsing)