89 K1500 starts then stalls

[jswordy6763]

OK, this truck has been down a year and a half with this problem, so there is a long description ahead. Appreciate all help with this!

When we started out working on it last spring, here is what we had:

It's my neighbor's truck, has the 5.7 Vortec. He is laid off, and I am trying to get it going for him. He does not have a lot of money to throw at unneeded parts (or a pro mechanic), so here's what we have for symptoms and have done...

The truck will start and run briefly, but then seems to run out of fuel. Spark is present. I understand these trucks use a timed fuel pump circuit for startup, then the firing engine should produce 15 psi oil pressure, which closes the sending unit switch to restart the fuel pump for run status. (This truck has an oil gauge, not a light.)

The pump does run and shut off when key is turned, engine fires off a little but then dies, seems fuel starved. Replaced filter. Initial fuel pressure at manifold plenum port is 65 psi -- perfectly in-spec.

The truck ran great on a trip to town, then he came home and shut it off, and it would not restart and run. No prior troubles, except the fuel pump was replaced about a year ago. We have replaced the throttle positon sensor, the fuel filter and the oil pressure sensor.

With the new oil pressure switch in, engine has the same problem, so we know it was not that.

Here is the sequence: Insert key and turn to ON, fuel pump runs and shuts off. Pressure at the port is 65 psi at that point (in spec). Turn key to start, engine will fire on that pressure buildup and run for a moment. Pressure steadily drops to around 55 psi (which is below the minimum spec of 61 to fire the injectors). It runs out of fuel after initial firing and then if you keep the key at start you are just cranking it. The fuel pump never comes back on for the run phase (which is what we hoped the new oil pressure sensor would remedy).

Just for grins, I checked the operation of the pump relay. It works perfectly, and the contacts are making contact internally. If you pump up the pressure and leave the truck sit for an hour on a run to town (a 14-mile round trip for each run, mind you), it will still hold pressure when you get back, so it is not the in-tank check valve. All fuses are good, and as I said the Throttle Position Sensor has been replaced already and is brand new, as is the fuel filter.

We pretty much can be satisfied from this sequence that the ignition system is fine and that the fuel injection system is working, except the pump at run. If the fuel pump would come back on after initial start, the engine should run fine. I have confirmed by listening in the filler neck as the procedure above was carried out that the pump is not coming back on.

OK, so while we are in town we get a loaner scanner. Hook it up, just to be sure. No codes are stored, because the battery has been disconnected at some point. We cuss.

Now it widens way out as to what it could be. We know the well-defined parameters of the problem, all we need is to be pointed to the cause, and that is the sticking point. We are at the place where parts prices start at $75 quickly rise past $150 a part from there.

I have heard from a tech that the Engine Control Module (ECM) has to see an ignition pulse train from the igniton system in either crank or run to keep the fuel pump coil energized. He says it does this as a safety so that if the motor stops running with the key on, you don't continue pumping fuel. He thinks this pulse train is not getting to the ECM, so it never re-energizes the fuel pump relay. This pulse train should run thru the electrical ignition switch, he says. Says he has seen this problem on several GM's, and in these cases it was a burnt ignition switch. If I can get a wiring diagram, he says to check this signal for integrity back to the ECM (he thinks its the yellow wire...anybody know for sure??). He says I can also get an inspection mirror and look at the switch, it probably has a charred plastic body.

And here's what we have done down to now:

Here are the exact symptoms, with data we have found:

1.) Key turned to first position (ON), fuel pump runs (confirmed), gauge at plenum port shows 65 psi. (This pressure will hold as long as a starting attempt is not made, so check valve is fine.)

2. Turn key to START, engine starts up and immediately dies, rail pressure falls to nothing. Fuel pump does NOT run (confirmed).

So what I am saying is that the fuel pump runs for the initial phase, but does not continue to run after that. This may sound like I am beating a dead horse to state the obvious, but guys at other forums have not been able to pick up on this. This is the problem, the pump will not run past initial pressurization.

What we have tried:

1. Tested spark. Hot and blue. No probs there.

2. Replaced fuel filter.

3. Bench-tested relay. It works (and if it didn't the pump would not start for initial pressurization).

3. Replaced oil pressure sending unit. (You can crank the engine and it does show fine oil pressure on the gauge inside the cab on that initial short startup.)

4. Plugged up a borrowed Chevy dealer test ignition switch, same start and die symptoms. Probably not the switch.

I have had people at GM headquarters tell me it is the security system, serviceable only by a dealer. If it is that, I will find a way to hotwire around it. Other mechanics have said the ignition switches fail to send a confirmation signal to the ECM. Using the replacement tester would seem to have eliminated that.

Someone else suggested the crank position sensor. Does that have anything to do with the fuel pump not starting on a Chevy after initial pressurization? It doesn't on the other stuff I have worked on, but I want to be sure here.

And then this, just last week...

We now have a new problem, apparently. Neighbor called me to say he now can only get 14 psi now out of the fuel pump when it initially runs. The truck has been sitting a few months, so who knows what has happened in that time. Looks like a new fuel pump is first before we can start on the other problems.

I have not seen the wiring to the pump yet. If there are only two wires to it, like every other brand I have seen, we're screwed as far as maybe having a new pump solve all the problems. But if there are 3 or more, we have a chance that the pump is actually the culprit, even though it ran in the first portion of the start sequence. The pump was replaced a year before this problem cropped up. I doubt a new one will solve it all. Every other electric pump I have ever seen, when it fails, it is cooked. There is no partial operation.

OK, so I now know this, too, after going throught eh extensive Passlock thread on this site and trying to recode it...

1.) There are 7 wires going to the pump, with two plugs. If I got the colors right: One plug has a gray, a brown with white stripe, and 2 blacks. The other has a gray, a green and a black. Anybody know where these go?

I would like to be able to test them if possible to make sure they work correctly before putting in a new pump.

2.) In trying to recode the passlock, the security light comes on and stays on. It never goes out. We let it sit as long as 15 minutes, it did not go out. I ran through three 11-minute cycles as the relearn says, but the light never did go out. Wazzup with that?

I sure was happy to see all those wires. The other makes I have worked on have 2 wires to the pump, so it either works or not. Having 7 means the pump could indeed be part-dead.


So this is where we are right now. Where to go from here? I'd like to test those wires to the pump, if I could. Might be replacing the pump will fix everything. We kind of doubt that, but with 14 psi, looks like we have to replace it. Do the pumps partially go out on these? Every other vehicle I have worked on fuel injection had just two wires to the pump.

Appreciate all help and suggestions. It is in my shop now, and it needs to run and get out of there!

Thanks in advance!

[MT-2500]

89 TBI fuel pressure specs are 9-13 lbs.

The fuel piump relay should power fuel pump gray woire key on engine prime up for 2 seconds and then on engine cranking and engine running.

Check ther gray fuel pump wire for 12 volts engine cranking and engine running.

If not jumper gray wire and see if fuel pump runs and engine runs.


The oil pressure switch only powers fuel pump engiune running if relay fails.

Post back what you find.

[jswordy6763]

Originally Posted by MT-2500

89 TBI fuel pressure specs are 9-13 lbs.

The fuel piump relay should power fuel pump gray woire key on engine prime up for 2 seconds and then on engine cranking and engine running.

Check ther gray fuel pump wire for 12 volts engine cranking and engine running.

If not jumper gray wire and see if fuel pump runs and engine runs.


The oil pressure switch only powers fuel pump engiune running if relay fails.

Post back what you find.

I APOLOGIZE! Typo on my part. This is a 1998, the prime spec is 60+ psi, cuz it has the poppet injectors and they will not work below 58 psi. The pump is currently delivering only 14 psi max to the port up at the intake plenum.

Pretty sure we need another pump first, but then there is the issue of it running on prime but not running for the RUN portion of the sequence. We replaced the oil pressure sender because it must close to complete the RUN loop. That did not fix the trouble. I plan to jumper the pump to the battery and see what happens. Probably need a new pump first, though, as I said.

Pretty sure the issue is with passlock. I get a steady SECURITY light on the dash. It never goes out. I have heard that is a sign of a wiring fault in that system, and the most likely fault area is in the column where the wire meet the lock cylinder. True? If I can ever get the thing to run, I plan to install the toggle switch cutoff for passlock described in the exhaustive passlock thread here. Got to get it to run first, though.

Any other cuases of a steady SECURITY light I should check?

If we must, I will permanently hardwire the pump to the battery, with either a toggle switch on dash or utilizing a switched wire off the ignition switch. That is a last resort, though.

So we are dealing with two different problems at the same time. Thanks in advance for any and all help, suggestions, etc.

[Bob B]

Hi,
This should be the same as your 98,
On my 97, there is a pigtail wire just behind the fuse box on the left side of the engine compartment. You jumper this to 12v which is inches away in the fuse box and the pump will continue to run for further testing purposes.
I drove with it jumpered one time when the relay failed.

Bob B

[777stickman]

On the SECURITY light issue. The only real way to diagnose this system is with a high end scan tool that can access the PASSLOCK module and check for DTC's. Most over the counter/loaner code readers cannot do this. With the light staying on says that there is most likely a DTC stored in the PASSLOCK module.

[MT-2500]

Originally Posted by jswordy6763

I APOLOGIZE! Typo on my part. This is a 1998, the prime spec is 60+ psi, cuz it has the poppet injectors and they will not work below 58 psi. The pump is currently delivering only 14 psi max to the port up at the intake plenum.

Pretty sure we need another pump first, but then there is the issue of it running on prime but not running for the RUN portion of the sequence. We replaced the oil pressure sender because it must close to complete the RUN loop. That did not fix the trouble. I plan to jumper the pump to the battery and see what happens. Probably need a new pump first, though, as I said.

Pretty sure the issue is with passlock. I get a steady SECURITY light on the dash. It never goes out. I have heard that is a sign of a wiring fault in that system, and the most likely fault area is in the column where the wire meet the lock cylinder. True? If I can ever get the thing to run, I plan to install the toggle switch cutoff for passlock described in the exhaustive passlock thread here. Got to get it to run first, though.

Any other cuases of a steady SECURITY light I should check?

If we must, I will permanently hardwire the pump to the battery, with either a toggle switch on dash or utilizing a switched wire off the ignition switch. That is a last resort, though.

So we are dealing with two different problems at the same time. Thanks in advance for any and all help, suggestions, etc.

No problem.
You are welcome.
If Bad security system.
The security system shuts down injector pulse after the 2 second run.
But should not turn off fuel pump.
There is a relearn or bypass to security.
The key on 10 minutes untill light goes out for 3 times and the see if it will start.
Also Jumper the pump and see what it does.
Specs are 60/66 and you need 63-64 lbs lbs to squirt injectors on cold start.
For testing fuel pump.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[jswordy6763]

Originally Posted by MT-2500

No problem.
You are welcome.
If Bad security system.
The security system shuts down injector pulse after the 2 second run.
But should not turn off fuel pump.
There is a relearn or bypass to security.
The key on 10 minutes untill light goes out for 3 times and the see if it will start.
Also Jumper the pump and see what it does.
Specs are 60/66 and you need 63-64 lbs lbs to squirt injectors on cold start.
For testing fuel pump.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

1.) We did the relearn process, twice. The SECURITY light never goes out. Never. So we timed it 11 minutes a cycle, and shut it off even if the light was still lit. No diff whatsoever.

2.) Recap of trouble: 5 months ago, it would start and run a second, then shut down. We had pump run at initial prime, no pump run on RUN. Pump held 65 psi pressure at the plenum port. (The specs I have on it says it must hit at least 58 psi to fire the poppet injectors. 60-65 is spec on prime pressure.) Once started the pressure fell off cuz the pump no longer ran.

Truck has sat 5 months since that time because no one can figure it out. He has had 4 guys look at it, myself included. Everybody BUT me says it is the fuel pump. I say new pump will not solve it all.

OK, so LAST WEEKEND we move it next door to my shop and pull the bed back so we have access to fuel pump top. Now we just get 11-14 psi initial prime pressure, and the pump still does not run after initial prime times out. SECURITY light stays on steady, does not turn off. I am saying we need a new pump cuz of the low prime pressure, but I do not think that will solve the pump not running at RUN.

3.) OK, so you are saying the security system will not shut off the pump on RUN. But that contradicts everything else I have seen on it, including the lengthy passlock thread here. They all say starts up, then shuts off...which is our symptoms, before the pressure issue arose.

4.) I will run the checks you suggest on the regulator, etc. tonight. Good point on that. Thanks for those.

Other ideas? It's a tough one!

[MT-2500]

To test fuel pump jumper the gray fuel pump feed wire.
The security systems just shut off fuel injector pulse.
As in the 2 second start and run and shut down.
Light staying on and not going off after 10 minutes is a bad problem on anti theft.
Has any one insatalled a remote start or add on anti theft system.

[jswordy6763]

Originally Posted by MT-2500

To test fuel pump jumper the gray fuel pump feed wire.
The security systems just shut off fuel injector pulse.
As in the 2 second start and run and shut down.
Light staying on and not going off after 10 minutes is a bad problem on anti theft.
Has any one insatalled a remote start or add on anti theft system.

Truck is stock. No remote start, no add ons.

What yer saying here is, even if I hotwire the pump to run, the truck likely won't run as long as the security system is haywire. Looks like GM is gradually boxing us into the high-dollar dealer service hole here. Maybe I could do the MFI spider swap and hotwire the pump and get it to run, but that's a $500-1,000 fix there, doing it myself, and it is still not right. I am concerned this will be a high-dollar fix for my neighbor, who is laid off and has never been a rich man. Let's see what we find out tonight.

[MT-2500]

Has the passlock module or ign switck/key or VCM been replaced?
If so it may need to be reprogramed with a GM tech 2 scanner.
Light on steady indicates the antifieft system is locked up someplace.
Needs to be put on a anti theft capable scanner and checked out and for codes.
If you can get any codes post back code no.

But it only shuts off injector pulse after 2 second start.
You should still be getting the 2 second run before shut down if everything else is ok.

[jswordy6763]

Here again is a recap of the basic conditions: 1998 K1500 4WD pickup. Key to ON, pump runs for initial prime. Key to START, pump does not run for RUN segment. The engine would start for a second, use up available fuel from the prime, and die.

When we first started working on it months ago, pump would prime to 65 psi and hold that pressure. It now will prime to just 10 psi.

We now have a steady SECURITY light. Never shuts off.

I also noted last night something I had not seen before, and this happens repeatedly. Key ON, pump primes and shuts off. Key turned from ON to OFF, pump runs again and shuts off. Is that correct? Owner says it has always done this; I never noticed it prior to last night. Bad ignition switch, maybe?

-----

OK, last night's test results, using the Shrader valve test port at the plenum (which is straight off the fuel line):

1.) Key to ON, pump runs and shuts off. 10 psi. Falls slowly.

2.) R line pinched off at pump, key to ON: 10 psi, falls slowly.

3.) Gray wire tapped, direct wired to battery, pump runs constantly: 10 psi.

4.) Electrical test, gray wire to black wire on a digital meter, key ON: 11.34 initial volts, falling back to 0.

5.) Electrical test, brown wire w/white stripe to black wire (this should be the fuel sending unit): 5.34 steady volts.

If you are thinking fuel filter, it was replaced when we first started working on the truck. I think the fuel pump is toast, or maybe the screen is plugged. As mentioned before, the fuel gauge needle oscillates slightly at its reading point, and owner says it has done so since pump was replaced about 3 years ago. He only got abbout a year and a half out of new AC/Delco pump before this trouble.

Now, on to the security system. The only test performed that may have coded it was several months ago, when a certified GM tech at a dealership gave me a test ignition switch/harness and told me to plug it in to the connector and use a screwdriver to operate it, as a test to see if the switch in the truck had burned up. That could have been read as a theft attempt.

But there are many reasons the SECURITY light could stay on, including broken wires in the column at the tumbler. I want to check all that out before giving it up to the dealer.

It would appear that our next action is to replace the fuel pump, then start worrying about the other issues. What do you think?

I've been working on cars and trucks for 32 years, and this thing is the most wacked FI/security system I have seen. Thanks!

[MT-2500]

Has the passlock module or ign switck/key or VCM been replaced?
If so it may need to be reprogramed with a GM tech 2 scanner.


Get the fuel pump pressure up to specs first.

Then work on security system.

[jswordy6763]

Originally Posted by MT-2500

Has the passlock module or ign switck/key or VCM been replaced?
If so it may need to be reprogramed with a GM tech 2 scanner.

As I wrote above:

Now, on to the security system. The only test performed that may have coded it was several months ago, when a certified GM tech at a dealership gave me a test ignition switch/harness and told me to plug it in to the connector and use a screwdriver to operate it, as a test to see if the switch in the truck had burned up. That could have been read as a theft attempt.

Nothing else has been done or replaced.

[jswordy6763]

Pulled the fuel pump last night. There is some black debris and water in the tank. Tonight, we will pull the tank to clean it, drain fuel line, and install new fuel pump. Then I have a couple other things to do that will take me away from it. Sometime this weekend, we should know where we stand. There are still mechanic friends saying replacing the pump will fix it all. I doubt it -- but wouldn't that be nice?

I hear elsewhere a gimpy crank position sensor could be it. No signal from it shuts off the fuel pump, as a safety feature in case of a wreck. Think so? Is there a way to test it with a VOM? It has 3 terminals.

I'll check in later; post back for sure on Monday. Thanks!

[MT-2500]

Volt meter only checks the voltage to it.

It takes a lab scope to test signal for proper signal.
They can fail or get weak hot or cold and sometimes the plug in does not make good connection.
I had one on a ford one time that would quit and you could unplug it/and or tap on it and it would run another 30-60 days and quit again.
And one on a cavilar that would run 90 days and quit on road.
Let it sit 30 minutes and it woulkd go another 90 days. not 89 or 91 right on 90 days.
Never did figure that one out untill iy finaly quit all together.
Your crank sensor Should be setting a code for it if very bad.

Black stuff in tank can be from a failing fuel pump.
Did you run a full pressure test on it before removing it?