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Discussion Starter · #1 ·
2001 S10 S10 LS Extended Cab 2.2 w/ 5 Spd. w/ 179,300 miles.

The truck started to stall or quit. Can quit at anytime; at the light or at highway speed. Was thinking fuel pump or ignition.

Replaced most of the ignition components: plugs, wires, coils, ignition module.

Problem remains.

Hooked up the laptop, and though there was no engine light, I got a DCT: P1632

From what I gather the PCM is killing the fuel supply. Anything specific to the S10 that might cause a problem in this area?

Thanks,
Ken T.
 

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GM vehicles are famous for defective ignition switches. Millions have been recalled.


"ENGINE STARTS AND RUNS NORMALLY, BUT SUDDENLY DIES WHILE DRIVING
This is one of the most common symptoms of a worn ignition switch. Worn contacts inside the switch may cause a momentarily loss of voltage as a result of heat or vibration (as when driving on a rough road or hitting a bump). Any loss of power through the ignition switch will cause the engine to stumble, misfire or die."
Quoted from: http://www.aa1car.com/library/ignition_switch.htm w/o permission but at least I gave them the credit.
Might be worth looking into since switches are a lot less expensive than BCM's or PCM's. Unless you are lucky and get a new switch with the same resistance as your old one you will have to do the 30 minute re-learn. Steps 3 and 4 on the link in the previous post.
 

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Discussion Starter · #4 ·
Thank you for the responses. I carry two sets of keys in my pockets (in case I lock the keys in the truck once or twice a year...). I can't recall which set I was using, but I always start the morning with the same set (has the house key on it), and never had an issue on the way into work.

When the truck started dying yesterday, I noticed that the key has to be cycled to OFF then a restart can be attempted. Sometimes this has to be done twice, but in every case, it restarted as if nothing had happened. Normal power and normal drivability.

Any clues on the best way to troubleshoot this? I have to replace the steering wheel anyway, so I am not to particularly worried about getting into the column. But, I wonder about the BCM and PCM. Is there a check for these?

Thanks,
Ken T.
 

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Discussion Starter · #5 ·
Drove it home from work, died twice with the the same key I used in the morning.

When I got home took my dead blow hammer (that I usually use to wake up the fuel pump on some mornings...) and started tapping around the steering column. After a while I was able to cause the engine to stumble and idle poorly. Turned the engine OFF, then restarted it, and it idled normally.

The ignition switch is on the way. I ordered an AC Delco one from RockAuto. Here's hoping it's been improved over the years!

Ken T.
 

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After you install the new switch there is 6.667% chance it will fire right up. Since the switches come with 1 of 15 possible chips with somewhere between 2k and 5k ohms resistance, you will more likely have to do the re-learn mentioned above. The truck will try to start, but will die within 1-2 seconds if the Passlock chip doesn't match the value that the BCM originally learned on it's first start up years ago. There are ways to measure the resistance and bypass Passlock, but I wouldn't recommend it since it will take longer than the re-learn and requires butchering the anti-theft wiring. Not to mention making your truck easier to steal. If you are IN Houston that might be a consideration. If you're outside the city I imagine theft isn't much of a problem since rural Texans have been known to have a gun or 2.
 

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Discussion Starter · #7 ·
After you install the new switch there is 6.667% chance it will fire right up. Since the switches come with 1 of 15 possible chips with somewhere between 2k and 5k ohms resistance, you will more likely have to do the re-learn mentioned above. The truck will try to start, but will die within 1-2 seconds if the Passlock chip doesn't match the value that the BCM originally learned on it's first start up years ago. There are ways to measure the resistance and bypass Passlock, but I wouldn't recommend it since it will take longer than the re-learn and requires butchering the anti-theft wiring. Not to mention making your truck easier to steal. If you are IN Houston that might be a consideration. If you're outside the city I imagine theft isn't much of a problem since rural Texans have been known to have a gun or 2.
This is interesting. I've seen what a Passlock key looks like; you can see the resistor in the middle of the key. However, my key doesn't look like a passkey. It's just a piece of brass.

Am I missing something?

Ken T.
 

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Passlock has the chip in the cylinder. The thinking is that if someone slide hammers out the lock it won't start.
Passkey has it in the key. Makes replacement keys expensive.
 

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Discussion Starter · #10 ·
Well, that didn't work...

I replaced the ignition switch on Saturday. Wasn't that bad of a repair actually, and I drove the truck Sunday, and on Monday put nearly 80 miles on it....and almost made it home. I was ready to put it all behind me when the engine just quit.

By this time, it was definitely old-hat, so I calmly threw in the clutch, turned the ignition to OFF, then restarted the engine and drove home. I pulled up in the drive way, left the motor running, and went to get the laptop out of the house. As I was getting the laptop unpacked, the motor started to stumble and run poorly....and I just couldn't get the laptop booted up and ready in time before the engine died. When I restarted it, it ran perfectly of course. I could not replicate the issue with my mallet. :(

Afte rI made the repair on Saturday, it was late, so neglected resetting the P1632 code. So, when I brought up the I went ahead and cleared. I'm going to go ahead and drive it tomorrow to work (~40 miles round trip). When it stalls, I'll see if the code comes back.

If it does...suggestions? BCM, PCM. I would hesitate to call wiring because the the truck was just sitting there when it started to run bad.

If it doesn't, does that leave me back to fuel delivery? Fuel pump, or maybe some debris in the fuel line?

Thanks,
Ken T.
 

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Discussion Starter · #11 ·
The weirdness continues!

I drove home fully expecting the truck to die, which it did half a from home ( of a 19.5 mile commute most of which is 50-60 mph).

I plugged in the computer to see if the P1632 had returned. It did not, and so I reasoned that maybe the replacement of the ignition switch was an incidental repair. The software has a button to "scan for enhanced DTCs" I believe these are those GM only codes. The P1632 is an "enhanced DTC" as it reads code type "EDTC."

So, scanned for EDTC, and the result was....

B2600 DAYTIME RUNNING LMP Control #1 CKT MALF

So, now this is really getting strange. I am wondering if the ECM or BCM has gone bad. In every instance of the engine dying, there's been the extended run time and always in the afternoon (hotter outside). This has never occurred on the way into work, only on the way home.

Anyone have any thoughts on this?

Thanks,
Ken T.
 

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These are hard to diagnose without the right tools. Possible problem areas are the lock cylinder, the wiring out of the cylinder, wiring over to the BCM, or the BCM itself.

I'd locate the BCM (someone here may be able to tell were exactly it is located, but Alldata says it is located somewhere to the right of the gas pedal on the heater box) and remove the covers on the steering column. Get the truck running and see if wiggling any of the wiring out of the key cylinder, the wiring over to the BCM and connectors and cables into the BCM cause it to shut the engine down. Pull the connectors off and see if you see any corrosion. If you're lucky you'll be able to locate a bad wire or connector pin that causes the problem. Sorry I can't offer more help, but that's a place to start.
 

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Discussion Starter · #13 ·
These are hard to diagnose without the right tools. Possible problem areas are the lock cylinder, the wiring out of the cylinder, wiring over to the BCM, or the BCM itself.

I'd locate the BCM (someone here may be able to tell were exactly it is located, but Alldata says it is located somewhere to the right of the gas pedal on the heater box) and remove the covers on the steering column. Get the truck running and see if wiggling any of the wiring out of the key cylinder, the wiring over to the BCM and connectors and cables into the BCM cause it to shut the engine down. Pull the connectors off and see if you see any corrosion. If you're lucky you'll be able to locate a bad wire or connector pin that causes the problem. Sorry I can't offer more help, but that's a place to start.
Thanks for your thoughts Rimara!

I am headed that direction. I have the FSMs for the truck, so I should be able to track down the BCM. There is a pattern so far, afternoons only (hotter outside), and after four kills yesterday, it's showing the same code. The P1632 has not returned.

I'm not saying it's not wiring, but on two occasions it just acted up in the driveway. And, it's not a clean kill. I'm more patient now (I don't panic anymore when it happens), so I take more time with it. It actually starts running really bad as I initially reported in "yet another fuel pump thread."

Another thing I thought about while sitting in the driveway with the laptop hooked in, the alternator seemed a bit loud with the whine. The computer and the gauge both say 13.7 V fully loaded with all accessories on. But, I was wondering about that one; this alternator maybe be closing in on 100k. I don't know if I have a ripple that making things ugly for the BCM/PCM.

So, today, I'll be strapping in the laptop to ride shotgun with the data logging. When that thing goes south, hopefully I can see what's up. Thing is, I can't monitor all 120 sensors, so I'll have to pick 5 or 6, and see how it goes.

Ken T.
 

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Discussion Starter · #14 ·
UPDATE:

Was able to spend some time with the truck today with the data logger. The results were interesting, but I still have questions.

Here's what I know:

1. It take time for the truck to die. Never dies on the drive into work, but always dies on the way home when it's warmer outside (about 20 degrees warmer, more traffic).

2. The engine doesn't actually die, it tries to die. 3 times upon arriving home, I just sat and waited parked in my driveway. In 5 or 10 minutes the engine starts to stumble barely able to idle.

3. Vibration isn't a factor.

4. The engine will not restart immediately if the engine dies. You have to wait a couple of seconds, and you don't have to cycle the ignition as I claimed before.

Here's a chart of the what happens to the engine when it starts to stumble:



Here we have the truck sitting in the driveway. Vehicle speed = 0. The truck had died earlier while I was driving, so I came home to wait for the truck to die again.

I have voltage, engine RPM, and Fuel Trim represented here. I was tracking about 20 different items, including misfires. This was the most useful, and of course the computer doesn't know anything about fuel pressure. Looks like to me that the computer is trying to add fuel when the RPM starts to fall. You can see after the stumbling, it recovered a bit, but the line isn't smooth, and neither is the idle. It never idles well again until the engine is restarted.

I tried to locate the schrader valve for the fuel pressure gauge, but all I could find was the evap port up atop the motor. Anyone got a pic? This is a Flex motor.

I'm thinking fuel pump again, but without a scope or a way to get the fuel pressure, I just don't know what to think at this point. I have $300 in parts in the truck now. I don't want to blindly blow another $300 on a pump without something solid. The only thing I have supporting the idea is that the fuel trim is apparently maxed out. But why would this be a problem only when the truck is driven for an extended time while it is warmer.

Thoughts anyone.

Ken T.
 

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So it's not throwing the p1632 anymore?

Here's a couple of things to check:

1. Check the pump ground lug that is located back near the bumper on the driver's side...on the C-frame.
2. Check the ground lugs located on the engine above the oil filter. Best to get to them thru the wheel well.
 

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Discussion Starter · #16 ·
I wasn't able to edit my message, but I had this to add:

One last thing, after making the truck run in the driveway for several minutes stumbling and idling poorly, it did set a P0171 (Fuel Trim System Lean).

Thanks,
Ken T.
 

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Discussion Starter · #17 ·
So it's not throwing the p1632 anymore?

Here's a couple of things to check:

1. Check the pump ground lug that is located back near the bumper on the driver's side...on the C-frame.
2. Check the ground lugs located on the engine above the oil filter. Best to get to them thru the wheel well.
Will do. Thanks Rimara! I'll get back and let you know what I have.

Ken T.
 

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Looking at the charts, it looks like fuel delivery. The low volts is probably because of low RPM which in turn is because of the lean condition indicated by the trim. At this point, it doesn't look like the security cutoff is the problem because the p1632 is not present, which would just cut the fuel completely.

When was the pump replaced? What brand? Was a new connector installed to the harness? Were the connections soldered, or just a crimp connection?

Does the o2 sensor switch between .1 & .8 volts when it's running smoothly?
 

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Discussion Starter · #19 ·
Looking at the charts, it looks like fuel delivery. The low volts is probably because of low RPM which in turn is because of the lean condition indicated by the trim. At this point, it doesn't look like the security cutoff is the problem because the p1632 is not present, which would just cut the fuel completely.

When was the pump replaced? What brand? Was a new connector installed to the harness? Were the connections soldered, or just a crimp connection?

Does the o2 sensor switch between .1 & .8 volts when it's running smoothly?
The fuel pump was replaced, twice by the dealer when the truck wasn't yet a year a old, and it's been on the same pump now for nearly 16 years.

The O2 sensor wave form looks good, oscillating between .1 and .8 volts. The thing just gets aggravated, and it never recovers until the engine dies and is restarted.

It never can restart though, unless you wait about 2 or 3 seconds, then hit the starter. I have discovered that you don't even have to turn off the ignition (contrary to what I reported before). Is it because the fuel pump needs the pressure to bleed down?

I plan on checking those grounds. I'd like to wire in a LED on the fuel pump circuit, so I can see in the cab if the fuel pump is energized the next time it goes to pieces. If I could find the schrader valve, I'd hook in a fuel gauge, but I don't see it anywhere.

Ken T.
 

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The schrader should be at the back of the fuel rail...at least it is on mine.
 
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