Repeated stalls

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Tex03Tahoe

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2003 Chevy Tahoe LT, 5.3 L, 8 cylinder, C-15706, original owner

311,000 miles. Following is fairly long and detailed…..trying to provide data that might help solve the problem.

Generally followed changing oil/fluids, may get a low oil message and have to add a quart of oil before the next 5000 mile synthetic oil change. Generally, gone to same mechanic for the last 15 years.

Original engine, installed rebuilt transmission a couple of years ago. Replaced alternator a couple of years ago. Replaced A/C compressor sometime in past. Replaced struts. Replaced various electronic components/modules like rear A/C, passenger front door switch, rear window motor. In cold weather, radio may not work until it has warmed up. In wet/rainy weather, seat heater may occasionally come on by itself. Replaced a couple of burnt out light bulbs in its life, windshield wiper blades, etc.


Recent history/events/issues stalls

Approx a month ago. Engine oil was down approx 1/2 quart. Added one quart. Later in day, drove it, entered onto highway, accelerated to approx 65 mph, a message came on that said “low engine power” and car slowed down while pressing accelerator, eventually coasted to stop and died. Attempted to restart. Engine cranked. After trying several times, it did restart. Drove it home. Took it to have oil changed a couple of days later since I thought maybe I put too much oil in which might have created an unintended consequence. Part of decision was because a friend also said he had gotten a similar message one time on his Chevy truck for a similar issue….maybe a simple coincidence….I don’t know. Tahoe ran fine for several weeks.

A week and a half ago, was driving stop/go on a Houston feeder road. Engine lost power again and rpm’s dropped even when pushing on accelerator. Coasted into parking lot, vehicle stopped running, and message displayed said something like “time to change oil”. I thought maybe the mechanics forgot to reset the code so I reset it myself. I checked the engine oil after several minutes and it was fine. Restarted and drove it five miles.

Later that afternoon, restarted and had driven approx 10 miles and it was doing well. Then I was accelerating to get on faster highway and getting up to approx. 55-60 mph. Again engine rpm’s dropped and had to coast to the side of the road. No “engine problem light” nor any message at all. Tried restarting car in neutral and park and wouldn’t. After several minutes of turning switch off, removing key, putting key back in, cycling transmission through N, R, D, and back to Park, it eventually restarted.

Drove another 10 miles, engine was doing well. Was driving speed of traffic 55-70 mph. Then again lost power and coasted to stop on side of highway. No message nor “engine problem light”. Went through a similar sequence of putting in neutral, park. Wouldn’t restart at first. Sat there for a few minutes. Cycled through N, P, R, D. After several minutes was able to restart.

Drove another 5 miles, at lower speeds through streets/feeder road approx 35-45 mph. Came to stop at red light. After change to green, proceeded to 25-30 mph for quarter mile and turned into neighborhood. RPM’s dropped again and stalled. No message nor “engine problem light”. Went through a similar sequence as above, restarted and arrived at home.

Called mechanic. On way to shop approx 2 miles away, had to come to stop in school zone because of children crossing. Lost rpm’s and car stalled again. Was able to restart car and drove to mechanic. Rediscussed previous events. There were no computer codes available even with all the previous happenings. Mechanic suspected that the problem might be the throttle body valve and module but no conclusive data. Replaced with OEM throttle body valve and module parts. Started up and drove intermittently for approximately a week. Various speeds in neighborhoods and on highway….probably for a total of hundred miles. Ran well. Noticed that engine had a little higher rpm’s when coming to a stop and had to apply brakes a little more but it would slow to idle when stopped for a few seconds.

A week later, I was driving to local store. When pulling onto one of the streets, I noticed the transmission didn’t quite “shift normally” when accelerating. Went 1/8 mile and stopped at red light. When it turned green, rpm’s had fallen slightly and car wouldn’t accelerate when I put my foot on the accelerator. It limped into parking lot, wouldn’t accelerate, and then stalled. Let car set for several minutes. Again cycled lever through P, N, R, and D a few times. Put back in park. Removed/inserted key a couple of times. Restarted car and it seemed to run fine. Drove it home. Turned off engine. Restarted a couple of time in driveway.


In the above cases, I have never noticed any problems with the gauges(oil pressure, charging amps, fuel tank, etc) and the readings have been in a normal range….except for when rpm’s would drop low as mentioned above.

Any suggestions, thoughts, ideas as to the potential problems? Spark, oxygen/air, fuel, computers/controls, transmission/interactions, etc. Thank you.
 
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Donal

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Sounds like some the electrical devices are loosing power during operation. Maybe get someone to verify and confirm the condition and capacity of electical conductors, connectors and wiring. Such as battery cables, connections and load test. Plug in connectors, ground connections and crimps, wiring conditions, especially at places where cables are rubbing and can be damaged. do the pull and wiggle tests on harnesses while the engine is running. Keep it simple and execute the fundamentals.
 
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Tex03Tahoe

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Sounds like some the electrical devices are loosing power during operation. Maybe get someone to verify and confirm the condition and capacity of electical conductors, connectors and wiring. Such as battery cables, connections and load test. Plug in connectors, ground connections and crimps, wiring conditions, especially at places where cables are rubbing and can be damaged. do the pull and wiggle tests on harnesses while the engine is running. Keep it simple and execute the fundamentals.
Thank your for your comments and reply.
I am not familiar with all these electronic devices, connectors, and wires.
Is there something specific in my comments, ie a certain cause that would have lead to these stalls? Where would one actually start? Ie. Certain wires, connectors, components to start with first? Thank you for your expertise and comments.
 

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It might help if some of the wording would be more detailed. Instead of "wouldn't start" perhaps "no crank" or "would crank normally but took a long cranking time before firing up" would help to describe the situation.

Also "wouldn't accelerate," does that mean the engine would rev up in rpms but the truck didn't move any faster? Or ???

Need more direction on this; when the issue presents, what codes are found by the scanner?

Spitballing, I would recommend a careful inspection of the throttle body pigtail wires, back about 6-10" from the TB. They tend to break or be compromised under the insulation, and inspecting the wires by feel (instead of a simple visual) may find an issue.

Also, graphing and comparing the smoothness of the throttle position sensor and the pedal position sensor and comparing may show a dropout or flat spot in one or both; they work together to actuate the throttle body.
 
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Donal

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Thank your for your comments and reply.
I am not familiar with all these electronic devices, connectors, and wires.
Is there something specific in my comments, ie a certain cause that would have lead to these stalls? Where would one actually start? Ie. Certain wires, connectors, components to start with first? Thank you for your expertise and comments.
If you within a 100 miles or so, I can probably schedule a day or so to show you the items to check.
 

rockola1971

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OP wrote "“low engine power”...Did you mean reduced engine power? If so this is a clue and usually means you have the dreaded broken wires at the throttle body for the fly by wire. A wire breaks in that harness and you will get that reduced engine power along with just above idle max throttle. The throttle will NOT respond to you at all. A replacement plug with wiring pigtail is available and is a normally stocked item in most auto parts stores.
 
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Tex03Tahoe

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To add to the above suggestions. What is fuel pressure? Sounds like it could be a pump in the process of dying.
On Tuesday of this week, I took the Tahoe for a long drive out in the country away from congested areas in town and ran it at a variety of conditions. After aro 45 minutes, and doing some repeated fast accelerations in a safe setting, the Tahoe engine stalled repeatedly, rpm’s would drop, and it just stopped. I would give it some time and then restarted in neutral and it would run. I cautiously “babied“ the throttle/accelerator, ran it around 35 mph and got it back close to town. Got into an adjacent neighborhood and in driving to my house in my neighborhood with some stops/starts at stop sign, it stalled out again around 4 times.
Took it to the mechanic. Of course no computer codes to see so they had to road test and recreate the situation. The following day, they did a road test on it and for the first 30+ minutes on the interstate, it was fine. On their return home, it stalled for them six times. They would get out, knock on the fuel tank, would restart and drive. So they did check the fuel pump in the shop and it wasn’t delivering a large volume. They changed the fuel pump and the new one pumped a lot more volume they said.
I got the Tahoe back and noticed an improvement in acceleration and performance. I hope that it was the ultimate solution. I need to take an hour long trip or so to make sure that was the issue.

Thank you for the suggestions.
 
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Tex03Tahoe

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When
OP wrote "“low engine power”...Did you mean reduced engine power? If so this is a clue and usually means you have the dreaded broken wires at the throttle body for the fly by wire. A wire breaks in that harness and you will get that reduced engine power along with just above idle max throttle. The throttle will NOT respond to you at all. A replacement plug with wiring pigtail is available and is a normally stocked item in most auto parts st
OP wrote "“low engine power”...Did you mean reduced engine power? If so this is a clue and usually means you have the dreaded broken wires at the throttle body for the fly by wire. A wire breaks in that harness and you will get that reduced engine power along with just above idle max throttle. The throttle will NOT respond to you at all. A replacement plug with wiring pigtail is available and is a normally stocked item in most auto parts stores.
When they replaced the throttle body, it also had a new module to plug into and they checked the wires.
 

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rockola1971

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Thats the typical culprit...but that problem will produce a "reduced engine power" on the cluster and the engine RPM will default to around 1000rpm no matter what your throttle input is. If you were just having stalling problems then I would replace fuel filter AND the pump, esepcially when the volume test was low.
 

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