January 10

2001 Chevy Suburban Intermittent No-Start

Chevy Trucks GM Trucks, Podcast


Mark: Hi, it's Mark Bossert here with Mr. Bernie Pawlik, Pawlik Automotive in Vancouver. 19-time winners of Best Auto Repair in Vancouver, as voted by their customers. We're talking this morning about a truck, a 2001 Chevy Suburban, that had an intermittent no-start problem. How are you doing this morning, Bernie?

Bernie: Doing very well.

Mark: What was going on with this rather large, rotund, boat anchor? SUV?

Bernie: Well, I add in, actually, this happened to be my own personal vehicle. What was happening is about a month and a half, two months ago, it developed this interesting no-start issue. I pulled into a store, got something, walked out, cranked the engine over. Cranked over fine, but it wouldn’t start.

I go, oh, that's weird. It's never done that before. I was a little flustered, and after trying it for a couple of minutes it started up, ran great, and I drove home going, oh, that's kind of weird, and it never gave me a problem for another couple of weeks.

I Mentioned it to my wife. She goes, “Yeah, it's done that once before, too.”

So, never gave it much of a problem, and because I'm busy, it's like the classic thing of the shoemaker's kids having their bad shoes. Sometimes, unfortunately, my cars get treated like that. In the case of this vehicle, it kind of went like that. It took about a month and a half, or so before we finally got to the final diagnosis and repair, which we're sharing on this podcast.

What happened in between is it just got slowly worse, but it seemed to always be consistent. If the engine was hot and you leave it for a few minutes, it would be hard to start. But, if you left it for a little longer, it would start just fine.

That was basically the issue, and it boiled down to being a bad fuel pump, at the end of the day, which was surprising because I'd replaced the fuel pump about three or four years ago with a high-quality pump that wasn't dead.

But, I figured, hey, let's get on top of this thing because the vehicle's got pretty high mileage. Let's make sure the pump's good, because they're one of the things that quit on these vehicles, and you don't want to be stranded somewhere. So, finally, eventually, this replacement unit quit, probably a lot sooner than I expected it would.

Mark: How did you diagnose that it was the fuel pump, and then how did you verify that the pump was the problem?

Bernie: Right. Well, initially, I didn't really ... I figured it was a fuel issue because ... Just by the way that the vehicle was operating. But, it didn't seem, initially, like a fuel pump, because, normally, when a pump dies, it'll do what we just did there. Maybe you might bang the gas tank, or something, to get it going. It doesn't usually restart after a couple of clicks of the key, so I figured maybe there's some kind of weird electronic or electrical glitch with the vehicle. A sensor, perhaps.

First step was of course to hook a scan tool up. Scanned it for codes. There was nothing relevant in any sort of way to a no-start issue. Tested some of the sensors like the crank sensor, which is a pretty important input, in terms of starting the engine. It was fine. Figured, possibly, again, because it was an intermittent issue and not happening consistently, I figured maybe there was an issue with the Passlock key.

There's a security system on these GM vehicles, and they have to send a signal. When you insert the key and turn it, it sends a signal to the computer to start it or not. It'll do exactly this. It'll crank over, but it won't start. It'll disable the fuel. So, tested out that system pretty thoroughly. It was all good.

Again, just kind of in life, it got busy and then, eventually, the vehicle got worse and finally died. Finally, the final straw was banging ... I had an emergency, I had to bang the gas tank with a hammer. It started up. So, okay, that's pretty much a guaranteed diagnosis right there.

Mark: Bringing back, flashing back to memories of crawling under this old Volvo I had, that I had to pound on the fuel pump to get it to go.

Bernie: Yeah, yeah. Yeah. The reason that works, by the way, if anyone's wondering, is that the pump, it has motor with a ... It's called a commutator. It's got little brushes and eight spots on the motor. When one of them wears, the pump can't turn, but if you bang it ... And it doesn't always work. Sometimes the pump's so dead it won't work. But, sometimes, if you bang it, it just jolts the pump enough to move that little millimetre, or quarter of a millimetre enough, to just get the electricity to flow, and then the pump starts running.

Mark: Did you do something else to check that?

Bernie: Yeah. The other interesting bit of diagnosis, because I was ... The other one that I use is a lab scope, to look at the actual current ... It's called a current ramp test of the fuel pump. Just to see what was happening with it, because, as I said, I was surprised because the pump wasn't that ... I mean it was like three, four years old. It really shouldn't have died at this early of an age. So, I wanted to see exactly what this looks like, because this is a test we can do sometimes to test people's fuel pumps. And, you know, if someone's got an intermittent issue like this, it's a good way to see, hey, is the fuel pump actually the problem?

So, I'll just share some pictures here. We did this with a lab scope.

2001 Chevy Suburban Intermittent No-Start
2001 Chevy Suburban Intermittent No-Start

 Mark: What is a lab scope?

Bernie: So, what is a lab scope? This is basically ... I'll just share the picture here, we can see it. Basically, a lab scope, it's an oscilloscope that attaches either to ... It either takes a voltage or an amperage signal. In this case, we use a current probe, and we actually take a sweep of the actual current that's being drawn through the fuel pump.

So, this is with the new fuel. This is the engine running, and this is the current flowing through the fuel pump. So, on one side, we have the voltage being used, and on other side we time-frame. So, you can see, this is 100 milliseconds across here. This is a hundred one-thousandths of a second. So, this is ten one-thousands of a second.

So, you can actually calculate the speed that the pump's turning. I'm not going to get into that. It requires a little bit of math, but not a lot.

You can see little pumps here. One, two, three, four, five, six ... This is basically a healthy fuel pump. It's got a little bit of a dip. The reason it has these different little pulses is this is where the commutator, which is where the brushes run inside the motor ... This is where they contact. So, there's a change in current flow every time it goes past.

Now, this is a good pump. Let's have a look at what a bad pump looks like, the old one. Very hashy. There's some distinct rises here, but there's also very distinct drops. Now, this is a bit unusual for a fuel pump, too, because a lot of current problems with fuel pumps ... You'll often find, if you have a bad fuel pump, the pattern'll actually look like this, except it'll have one or two missing peaks here.

That often indicates, oh, there's a commutator that's actually worn off. Whatever was going on in this fuel pump caused a pretty radical spike in voltage. Interestingly enough, when the engine was running, it ran perfectly. But, I think, because these big spikes here required a lot of power to get the pump turning, that's why it wouldn't start. When you're cranking the engine over, the voltage is lower. So, it just didn't quite have enough juice to turn. But, once it was moving, it worked fine.

So, that's what we can see with a lab scope. There's many things we test with lab scopes. It can take a little extra time to hook it up, but often it'll verify things. I had someone some in with this concern, and said, hey, I got this intermittent problem, but it only happens once in a blue moon. This is the test we could of done that didn't take a lot of time, that could of verified, you know what, your fuel pump pattern's bad, we should change it.

Mark: So, after you replaced the fuel pump, everything ran well?

Bernie: Yeah, it started fine, ran well. Perfect. Yeah, really nice.

Mark: This is quite an old-

Bernie: We're giving life to the vehicle again.

Mark: This is an 18 year-old vehicle now, and it's yours. How does it run overall, and is it worth still keeping it going on the road?

Bernie: Yeah, it's really good. I've taken really good care of it, and the engine actually wore out at about 300,000 kilometres, so I replaced it. I put a 6.0L, so it's a slightly larger engine than the 5.3L that came in it. I put a nice, used 6.0L engine in it. It runs great. As I said, I've kept up all the maintenance and repairs on it. When you drive it, it just drives like a brand new truck still.

Even the shock absorbers, which surprisingly, they're still original, and I've towed a trailer with it. It's built well. The ride is perfect. It's smooth. The only thing I can complain about, the fuel economy is not great because it's a big beast, but other than that, it's a good vehicle.

I'll keep it for a few more years. It's worth doing, but again, the key is to fix things as they wear out, as opposed to leaving a big pile of things, and all of a sudden, it's like a multi-thousand dollar bill, and you go, no, that's not worth it, I'll just junk it. But, a replacement for a Suburban is a lot of money, even a good used one.

Mark: Yeah, instead of ... It's a heck of a lot cheaper to spend a few thousand a year than $80,000 or more on a brand new one.

Bernie: Well, actually, a hundred. The equivalent of this model, I've seen them in dealerships, it's over $100,000. That's a lot of money for a truck.

Mark: Yeah.

Bernie: But, if you keep it 20 years and you amortize it out, then that's only $5,000 a year, but you still need the $100,000. It's a lot of monthly payments, or a lot of cash upfront. Whichever way you go. So, a good used one works well.

Mark: So, I take back it's a boat anchor. It's just a good used vehicle that's fulfilling its purpose.

Bernie: Yeah, yeah. It's not a boat anchor yet. It still works and runs, and it's a good boat hauler.

Mark: So, there you go. If you have a boat hauler or trailer hauler, or a people mover, that's huge and needs some maintenance, the guys to see in Vancouver are Pawlik Automotive. You can reach them at 604-327-7112 to book your appointment. You have to book ahead, they're busy. Or, check out their website, PawlikAutomotive.com. There's tons of information on there as well. There's the YouTube channel, Pawlik Auto Repair. Hundreds, literally ... Over 400 videos on there of all makes, models and years of cars and types of repairs and maintenance as well. Thank you so much for listening to our podcast. We appreciate it, thanks Bernie.

Bernie: Thanks Mark. Thanks for watching and listening. We love having you as an audience member. Thanks.

About the author 

Bernie Pawlik

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