98 K2500 Suburban won't stay running.

[AyWoSch Motors]

Hello. Back again with yet another suburban question, from yet a different burb.
Got a 1998 K2500 suburban with a vortec 454 recently. I did a little tinkering to it to see if it would fire up. Put in a new battery with new leads, an alternator, ac pump, belt and tensioner, a new key, and fixed some wiring. Got it to crank over and fire right up, but wouldn't stay running more than a few seconds. I figured it must be old stale gas from it sitting around. So I unhooked the fill neck, stuck a hose down it, and with a 12v electric pump, sucked about 8 gallons of gas out until it started sucking air. Took out the fuel filter and cycled the key a few times to get the old out of the lines. Then I put 5 gallons of fresh in.
Still wont stay running, its doing the same thing as before.

I will start right up on a dime, and either just pop and spudder, or roar to life for about 3 to 4 seconds and aound great, then die again.
If I bottle feed it, itll stay running. Just a squirt for start up, and then the tiniest dribble to keep it idling. Sounds great, really nice and smooth, but wont stay running by itself.
I can hear the pump coming on, and when I cycle the key back and forth, I hear it come on, build pressure, and stop.

What could it be? Thanks

 

[someotherguy]

Check fuel pressure to begin with. The Vortec 7.4 isn't nearly as sensitive to fuel pressure issues as the small blocks, because the 7.4 uses real injectors instead of the poppet valve setup the small blocks use. The 7.4 will actually run at half the pressure spec, just won't have any power. Throw a gauge on it and if it's not somewhere around 55-60 then suspect a fuel issue.

Richard

 

[AyWoSch Motors]

Check fuel pressure to begin with. The Vortec 7.4 isn't nearly as sensitive to fuel pressure issues as the small blocks, because the 7.4 uses real injectors instead of the poppet valve setup the small blocks use. The 7.4 will actually run at half the pressure spec, just won't have any power. Throw a gauge on it and if it's not somewhere around 55-60 then suspect a fuel issue.

Richard

Okay, that sounds right.

I have no way of checking fuel pressure. I guess I'll have to buy a gauge or something. Now where would I check the pressure? Anywhere inline, or at back of the block where the lines come it?

And what would low pressure indicate? Would that be a bad fuel pump or leak in the lines somewhere, or bad injectors?

I ask because I have a bunch of parts trucks and I collect stuff like filters and pumps and such, so itd probabaly be easier for me to just change out a part I already have laying around than to have to buy a tool I dont have.

 

[someotherguy]

Handy pressure test port right at the front of the intake just under the plenum, should have a cap on top that looks remarkably like an A/C service port cap. Once you rule out clogged filter, low pressure is usually a bad pump. Regulator can be bad too, but you won't like it - you have to pull the upper intake to get to it because it's at the rear of the fuel rail, underneath the rear of the intake, retained by a snap ring. The short piece of vacuum line attached to it can rot and cause problems, too.

Richard

 

[mattillac]

....Got a 1998 K2500 suburban.......
....a new key, and fixed some wiring.......
....wouldn't stay running more than a few seconds......

....I will start right up on a dime....
....roar to life for about 3 to 4 seconds .....
....then die again.....
....If I bottle feed it, itll stay running.....

Just going off of the above, it sounds like it could be passlock (1998 and later models got GM's anti-theft feature).

For that, the symptoms should typically be "starts fine then abruptly stalls after 2 to 3 seconds", and the "SECURITY" light in the upper right hand corner of the instrument cluster should be flashing or solid (if passlock is preventing the vehicle from running).

If / when passlock activates, it is the injectors that are being disabled (so it should continue to run on starting fluid and/or other alternative methods of feeding it fuel).

I do believe there should be a "bulb check" when the key is rotated, so the "SECURITY" light should illuminate momentarily under normal circumstances.

Should also be a fuse there in the IP fuse panel, IIRC its position should be labeled "security".

Below is the relearn procedure (for when replacing related parts etc).

---

PASSLOCK REPROGRAMMING AUTO LEARN


IMPORTANT: If a new vehicle/powertrain control module (VCM/PCM) is being installed for the first the manufacturing enable bit will be set and the auto learn procedure may not be necessary.


The following procedure allows for anyone to reprogram the EVO/PASSLOCK module learned data code with any tools, other than the scan tool, when any of the following parts are replaced:


The EVO/PASSLOCK module
The PASSLOCK sensor
The VCM/PCM


The EVO/PASSLOCK module will set the DTC B3031 in the learn mode when entering the reprogramming procedure.


IMPORTANT: Erase the PASSLOCK related Diagnostic Trouble Codes (DTCs) that are stored in the VCM/PCM.


The following is the Auto Learn Procedure:


1. Insure the ignition key is in the ON position.
2. Clear all EVO/PASSLOCK module and VCM/PCM DTCs.
3. Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT key OFF in the process).
4. Wait 10 minutes . Observe the SECURITY indicator. Refer to the following list for the appropriate responses:


-If the PASSLOCK sensor was replaced the SECURITY indicator will flash for the 10 minutes duration.
-If the EVO/PASSLOCK module was replaced, the SECURITY indicator will flash for a few seconds and then remain ON for the remainder of the 10 minutes duration.

-If the VCM/PCM was replaced with a new programmed VCM/PCM and connected to the vehicle for the first time, the vehicle will start and this procedure may not be necessary.
-If the replacement VCM/PCM was connected to any vehicle at any other time, even momentarily, the SECURITY indicator will flash for a few seconds and then remain ON for the 10 minutes duration.


5. The SECURITY indicator will transition from flashing to ON briefly to OFF after 10 minutes if remaining in the ignition ON position.
6. Turn the ignition switch to the OFF position and wait for 10 seconds .
7. Repeat steps 3-6 two more times. The new security code is ready to be communicated among the PASSLOCK sensor, EVO/PASSLOCK module and VCM/PCM. The new password is learned on the next ignition lock cylinder cycle from OFF to CRANK to ON (start attempt).

---

FWIW there isn't a "chip" in the ignition key, the sensor is located in the lock cylinder/housing etc. For 1998 and later its probably a good idea to have keys made by VIN# (instead of duplicating already worn keys).

Food for thought.

And sorry about chopping up your OP.

 

[AyWoSch Motors]

Just going off of the above, it sounds like it could be passlock (1998 and later models got GM's anti-theft feature).

For that, the symptoms should typically be "starts fine then abruptly stalls after 2 to 3 seconds", and the "SECURITY" light in the upper right hand corner of the instrument cluster should be flashing or solid (if passlock is preventing the vehicle from running).

If / when passlock activates, it is the injectors that are being disabled (so it should continue to run on starting fluid and/or other alternative methods of feeding it fuel).

I do believe there should be a "bulb check" when the key is rotated, so the "SECURITY" light should illuminate momentarily under normal circumstances.

Should also be a fuse there in the IP fuse panel, IIRC its position should be labeled "security".

Below is the relearn procedure (for when replacing related parts etc).

---

PASSLOCK REPROGRAMMING AUTO LEARN


IMPORTANT: If a new vehicle/powertrain control module (VCM/PCM) is being installed for the first the manufacturing enable bit will be set and the auto learn procedure may not be necessary.


The following procedure allows for anyone to reprogram the EVO/PASSLOCK module learned data code with any tools, other than the scan tool, when any of the following parts are replaced:


The EVO/PASSLOCK module
The PASSLOCK sensor
The VCM/PCM


The EVO/PASSLOCK module will set the DTC B3031 in the learn mode when entering the reprogramming procedure.


IMPORTANT: Erase the PASSLOCK related Diagnostic Trouble Codes (DTCs) that are stored in the VCM/PCM.


The following is the Auto Learn Procedure:


1. Insure the ignition key is in the ON position.
2. Clear all EVO/PASSLOCK module and VCM/PCM DTCs.
3. Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT key OFF in the process).
4. Wait 10 minutes . Observe the SECURITY indicator. Refer to the following list for the appropriate responses:


-If the PASSLOCK sensor was replaced the SECURITY indicator will flash for the 10 minutes duration.
-If the EVO/PASSLOCK module was replaced, the SECURITY indicator will flash for a few seconds and then remain ON for the remainder of the 10 minutes duration.

-If the VCM/PCM was replaced with a new programmed VCM/PCM and connected to the vehicle for the first time, the vehicle will start and this procedure may not be necessary.
-If the replacement VCM/PCM was connected to any vehicle at any other time, even momentarily, the SECURITY indicator will flash for a few seconds and then remain ON for the 10 minutes duration.


5. The SECURITY indicator will transition from flashing to ON briefly to OFF after 10 minutes if remaining in the ignition ON position.
6. Turn the ignition switch to the OFF position and wait for 10 seconds .
7. Repeat steps 3-6 two more times. The new security code is ready to be communicated among the PASSLOCK sensor, EVO/PASSLOCK module and VCM/PCM. The new password is learned on the next ignition lock cylinder cycle from OFF to CRANK to ON (start attempt).

---

FWIW there isn't a "chip" in the ignition key, the sensor is located in the lock cylinder/housing etc. For 1998 and later its probably a good idea to have keys made by VIN# (instead of duplicating already worn keys).

Food for thought.

And sorry about chopping up your OP.

That sounds like exactly it. And there is a security light that stays on. I'll look into that more. That sounds like a pain though. Thanks

 

[someotherguy]

The light should be flashing if Passlock is what shut you down. In my experience the engine will stall almost immediately, every time. YMMV

Richard

 

[BeXtreme]

That sounds like exactly it. And there is a security light that stays on. I'll look into that more. That sounds like a pain though. Thanks

Its also worth noting that the fuel pressure check valve is right on the front near the oil fill tube and is the exact correct size to fit a tire pressure gauge on it. I've used a cheapo $0.99 tire pressure gauge from autozone and had it work perfectly fine in a pinch.

 

[618 Syndicate]

In my experience the engine will stall almost immediately, every time. YMMV

Richard

Based on his description that's what I thought it was doing.

 

[someotherguy]

Based on his description that's what I thought it was doing.

Maybe. Sometimes tough to tell from how people state it. I can see how one might read his post either way. Sounded to me like it's not as consistent behavior as I'd expect Passlock to be. Either way he's armed with next steps in troubleshooting.

Richard