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Discussion Starter · #1 ·
The truck in question is my 2000 Chevy S10 ZR2 4.3 L V6 5 speed Manual. This is a bit of a story to explain, intermittent issues are weird. But I’m hoping to help other people in the future, please bear with me and give me your insight, this is a niche issue and I would really appreciate your help.

About a month ago, I was driving home to visit my family on break from college (from California to Colorado). The truck started doing slight stutters at 70 mph or so, where the truck would buck back (think how the speed governor feels, it feels exactly like that), during this time the throttle pedal would be completely dead, at which point I would downshift into 4th gear, press the gas and the truck would regain composure completely.

Sometimes the stutters would be more dramatic, causing the truck to be completely without power for several seconds, going from fine at 70 mph to barely catching itself down at 40 or so, and the strangest part is, it would run completely fine at that point. For the whole 3 weeks I was home in Colorado, the problem persisted, but it wasn’t as bad, and in this time I was replacing parts I BELIEVED to be the culprit, and the truck quit giving me trouble. Said replaced components include a new MAF sensor, a throttle position sensor, 3 new O2 sensors and a K&N air filter.

Needless to say the problem popped back up, and it waited until I was on the 1,000 mile drive back to LA to do it. The truck would buck on me, and I would do my usual downshift into 4th and then step on the gas some. The problem continued to get worse this time, until eventually it was really bad. I was going through Vegas where the truck suddenly did the buck, I downshift and step on it— nothing. Drop it into 3rd gear. Nothing, no gas no power at all. Rapidly losing speed in a huge crowd of traffic who is going 60 mph. Finally I drop into 2nd gear, panicked. Nothing. I pulled over, the truck died. I waited about 5 minutes where I was making rescue phone calls, and I wanted to get the truck off of the busy highway so I tried to start the truck. Oddly enough, it fired right up. I drove it up the very close by off ramp, where the truck then died and refused to start, I had a tow truck take it to the dealership.

Stick with me here because this is where it gets really weird. So, the dealership diagnosed the issue as a bad Catalytic Converter, which is strange because I just threw a new one on it a year ago. That cat was an aftermarket one though, and I can see it potentially failing for no deeper reason. They told me they pulled off the old cat and ran the truck without it, they said it fixed the issue, and they were actually correct here, the cat was bad, the tech shook it for me and it rattled with a heavy clunk, so yea great we thought we fixed it. Well, with the new cat on it, the techs were struggling to get the truck to start, it would crank but not start. They let me take it for a spin to try and figure it out, I drove it, it ran amazing for the first 5 minutes - that cat was bad for sure (likely a separate issue) 0 - but then the truck just randomly died again in the test drive. Then it bucked some, then it bucked a lot, then it died.

The next morning the techs tested the MAF sensor and found it to be reading a ton of airflow even if the truck was not running, the MAF was completely shot (yes, the one I bought from AutoZone 3 weeks prior) so they unplugged the MAF sensor and wow, we all thought THAT was the issue for sure.

The dealer didnt have a MAF, so I just ordered a factory one and decided to drive the remaining few hours back home to California with the MAF unplugged. Well, I was driving really happy that we figured it out, and about 20 miles from Vegas there it goes again, I felt a stutter. It was subtle enough I could have blamed it on a bump I didn’t notice, so I carried on. Then, about over 100 miles from Vegas, the truck does the exact same thing it did when it first broke down, it bucks, stutters, backfires some, loses all power and dies, from 80 mph one second to 0mph the next. I got the truck towed to another Chevy Dealership, this one only an hour from my house. When we unloaded my truck off of the flatbed, it actually started again just fine, and I drove it into a parking spot, and it died, so I let it be.

Now you are all caught up. Again, I know this is a really long story, but it is very very strange and I want to figure this out and help anybody else who hits this wall to find this in the future. Real quick another thing worth mentioning, I have worked on cars for years, and my dad was a mechanic for over 7 years and works on cars and trucks allll the time, him and I have worked on this Chevy together and here is a list of everything we have already replaced, though after that MAF less than a month old took a dump on me, maybe something I’ve already replaced is the culprit.

Already Replaced:
Coil Pack
Ignition Wires
Cap and Distributor
Fuel Pump
Fuel Filter
Throttle Position Sensor
Air Filter
Rebuilt Transmission (Brand new everything, less than 6,000 miles ago)
Accessory Belt
Alternator
Battery

My hunch is that this issue is fuel related, or electrical related. I don’t THINK it is the fuel pressure regulator, but maybe I’m wrong? Again, I REALLY appreciate any help.
 

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Going to sound like a really wacky though, had a shop truck not too long ago doing the same. Turned out to be the vent for the tank was plugged. Behaved almost as you describe. The problem was figured out when the gas cap was not put back on after one of those rescue calls in traffic. Letting the truck set always fixed the problem as it would eventually suck air into the tank to let fuel flow, other wise it was like sucking on a water bottle until all the air was out.
 

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That's one possibility. Problem is there are a lot of possible causes. Have you read the codes to see if they tell you anything? Have you tested the fuel pressure? First 2 things you should always do.
 

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Discussion Starter · #4 ·
That's one possibility. Problem is there are a lot of possible causes. Have you read the codes to see if they tell you anything? Have you tested the fuel pressure? First 2 things you should always do.
The check engine light was reading me a P0420 before I threw the new cat on it, now that it has the new cat it's gone, the P0420 code is the 'Bank one catalyst system below efficiency' or something like that. The fuel pressure is reading normally, or at least it seems to be, I'm not sure if a possible fuel pressure regulator malfunction would cause stuff to change. Thanks for the suggestion though!
 

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Discussion Starter · #5 ·
Going to sound like a really wacky though, had a shop truck not too long ago doing the same. Turned out to be the vent for the tank was plugged. Behaved almost as you describe. The problem was figured out when the gas cap was not put back on after one of those rescue calls in traffic. Letting the truck set always fixed the problem as it would eventually suck air into the tank to let fuel flow, other wise it was like sucking on a water bottle until all the air was out.
That's really strange, wow. I never would have thought that could happen. I'm going to look further into this, sounds like a valid point. I really appreciate the insight, like I said since it is a strange problem, strange solutions are more than welcome.
 
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