1998 Pontiac Firebird SERPENTINE BELT TENSIONER FAILURE

Tiny
DARKKNIGHT98
  • MEMBER
  • 1998 PONTIAC FIREBIRD
  • 5.7L
  • V8
  • RWD
  • AUTOMATIC
  • 144,000 MILES
I have had to replace the serpentine belt tensioner 3 times in the last 3 months ever since I installed a new alternator form Car Quest Auto Parts. If I run my car hard from a stop or a slow roll at about 4,000 rpm the lights start to dim and the voltmeter takes a dive to the left. When the engine rpm drops below 4,000 rpm the lights brighten back up and the voltmeter move to the right of 13 volts where it should be. I have seen the tensioner position move closer to the marks on the housing and I can push on the belt with one finger and make the tensioner move towards the marks on the housing. When I replace the tensioner, I can't make it move with one finger and it position is to the left of all the marks on the housing. I install a new one today and took my buddy for a ride in my car and when the engine rpm got to 4,000 the voltmeter took a dive to the left in both 1st gear and in 2nd gear. It returned to its normal position once the engine rpm dropped below 4,000. We checked the tensioner when we got home and its position is now to the right of the first line on the housing. Do you have any idea why these tensioners are going bad so quickly? Could this alternator be generating an unusually large amount of resistance above 4,000 rpm and damaging these tensioners?
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Sunday, February 22nd, 2015 AT 4:59 PM

9 Replies

Tiny
DR LOOT
  • EXPERT
From personal experience I can tell you the alternators from Car-quest are garbage, 3/5 fail lets start by returning the alternator to Car-quest and get another one. You should've went to Napa, all of Car-quest alternators are rebuilt in China
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Sunday, February 22nd, 2015 AT 7:04 PM
Tiny
CARADIODOC
  • EXPERT
That might be a little extreme. If any parts supplier knew they had something with an unusually high failure rate, you can be sure they would address it. They aren't going to sell a product knowing they are likely to have to replace it under warranty. They don't want that publicity or reputation.

Well, there is an exception though and that is GM. They had, in my opinion, the world's second best generator design up through 1986, but they redesigned them for the '87 model year and turned it into the worst pile ever. There are plenty of perfectly fine parts that come from China, Japan, Korea, Mexico, and many other countries. At issue with this U.S. Design is their tendency to develop huge voltage spikes. It is real common to go through four to six replacement generators in the life of the vehicle, and it has nothing to do with the rebuilder or where they're located. If you suspect a failing generator, talk with the engineers at GM.

To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. That is the key component in damping and absorbing those harmful voltage spikes, but as they age, they lose their ability to do that.

I'm not sure why you're running at 4,000 rpm that often or why you're watching the gauges instead of the road, but you have to consider that to have the problem only show up at higher engine speeds, it has to be due to centrifugal force or an electrical issue. I suspect we can rule out centrifugal force because that wouldn't affect multiple generators. When they're rebuilt, the only rotating part, the field winding, is not replaced. It's an original part and it obviously didn't fail earlier. Also, it wouldn't expand and hit the stator winding without causing permanent damage.

The voltage spike issue has to do with exactly the same thing that takes place in an ignition coil. The voltage regulator turns field current on and off 400 times per second, and it varies the percentage of off-time to on-time to vary the current output. When current flow is turned on, it takes some time for the magnetic field to slowly build up. When current is turned off, that magnetic field has no choice but to collapse instantly, and that is what induces a huge voltage spike. That's desirable in an ignition coil to fire a spark plug, but in the generator, those spikes can damage one of the six diodes or the voltage regulator, and it can interfere with computer sensor signals. In fact, GM generators are often responsible for elusive engine running problems that defy diagnosis.

The first thing to do when you have a GM generator failure is look at the battery. If yours is over two years old, don't blame Carquest or any other parts supplier. Blame the engineers at GM who have no interest in improving the design of their generators.

The next thing to look at is if there are external controls for your generator. If you look at Chrysler's design, the voltage regulator lives inside the Engine Computer, and thus it can take advantage of everything the computer knows. AC generators can easily take over five horsepower to run when under high load. When you're trying to pass a freight train, while going up a steep hill, and when pulling a trailer, that five horsepower might come in handy, so the Engine Computer can command the voltage regulator to turn the generator off under certain conditions. That can include wide-open-throttle, engine cranking, engine running too hot, and things like that.

That capability of temporarily reducing output and load on the engine is built into GM's voltage regulators but it isn't used very often. If it is on your car, that can explain why the output is being reduced at higher speeds. The simple fact that output is restored when engine speed comes back down to normal proves no catastrophic failure is occurring.

The other thing related to generators is you need three things to make them work. That's a magnet, (electromagnet in this case), a coil of wire, and most importantly, movement between them. That's why we have to spin the field winding with a belt-driven pulley. The faster it spins, the more voltage spikes are being generated. Those spikes could overwhelm the voltage regulator and send it into a momentary shutdown to protect it.

A less-common problem has to do with what the engineers did to get higher output current capability out of a small package. They did that in part by decreasing the distance between the stationary stator winding and the spinning field winding. You were lucky to get 65 amps out of the old design. The current design is much smaller but 140 amps is not unrealistic. The first problem is when just a little play develops in the bearings. That lets the core hit the stator frame. In real bad cases it locks up. I've seen two where the generator stalled the engine, and people cut the belt to allow it to be restarted. Even when they don't lock up, you have to consider how an expanding core will change how the magnetic field interacts with the stator. Reducing the magnetic field is exactly what the voltage regulator does when it is desirable to reduce output current and voltage. Reducing the output due to a disturbed magnetic field is not intentional but it isn't a permanent failure either.

If you still think there's a problem, have the generator tested, but always do that with it on the engine. Since movement is a factor in determining maximum output, testing for maximum current is always done at 2,000 rpm. That is more than fast enough to provide the full rated current. You should be able to get close to 100 amps. If the most you can get is 35 amps, there is a shorted diode, and the common suspect is the battery and the resulting excessive voltage spikes.
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Sunday, February 22nd, 2015 AT 8:50 PM
Tiny
DARKKNIGHT98
  • MEMBER
Thanks for the excellent lesson on how car alternators work. But you didn't really answer my question. Do you think the alternator could be generating a large enough resistance above 4,000 rpm to over stress the tensioner and cause it to fail? Last night I ordered one built by ACDELCO that appears to have a slightly different design. That is cheaper and changing it out is faster and easier than having my OEM alternator rebuilt(which I do still have in a box) and spending 2hrs laying underneath the car to install it.

I bought the current alternator from Car Quest because in the past they sold very reliable parts. The sales manager said it was made in the U.S. But it had a "made in China" label on it. I was quite skeptical about it but mine stopped charging late on a Sunday afternoon and that car is my everyday transportation and I got to the store 5 mins before closing so I bought it.

I am quite disappointed to see how so many of our auto parts stores are replacing electrical parts made in the U.S. Canada with parts imported from Asia. I would have either ordered a BOSCH alternator or had my OEM one rebuilt locally if I could have afforded the car to be down for several days.
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Monday, February 23rd, 2015 AT 6:35 AM
Tiny
CARADIODOC
  • EXPERT
I don't have a good answer about the stress related to speed, but I should add another chapter to my sad story that might give you some insight. First of all, in an attempt to use correct terminology, I'm calling this an AC generator as that is the term the industry chose recently to standardize many things. The alternator was developed by Chrysler and first used in 1960, and they copyrighted that term. Regardless, everyone will know what you're referring to when you say "alternator".

The first important point to understand is that unlike the older DC generators from the fifties and before, AC generators are physically incapable of generating more than the maximum current they are designed for. To build one that is capable of producing more current than the other one, you simply have to add another loop of wire to each stator winding, and use diodes that can handle that much current. (A diode is a one-way valve for electrical current).

The next and more important detail for your problem is the voltage regulator is going to command the generator to deliver exactly the amount of current needed to run the electrical system and recharge the battery, and no more. System voltage is an indicator of the system's needs and is what the regulator uses. Notice that engine speed is not a factor in determining the generator's output.

If it helps, think of the engine's oil pump. If you double engine speed, you double what the pump can deliver in terms of volume, but not pressure. The pressure relief valve dumps the excess oil right back into the oil pan, so system pressure stays the same, the resistance to oil flow stays the same, and therefore oil flow to the engine stays the same, regardless of speed.

The same is true of the generator. Lets say, for the sake of an explanation, at maximum output the generator takes five horsepower to spin and it develops 100 amps. If your electrical system needs 50 amps, the generator is going to take two and a half horsepower, but again, engine speed is not a factor. In theory the faster movement between the magnetic field and stator winding would result in more current being developed. More current getting pushed into the battery and circuits that use it will result in voltage, (electrical pressure), going up. The voltage regulator will see that higher voltage and reduce the small amount of field current going through the spinning field winding. That results in a weaker magnetic field which results in less current being developed in the output stator winding. That lower current will be, ... Tada, ... 50 amps, and two and a half horsepower.

To say it a different way, the generator puts the same load on the tensioner regardless of engine speed.

Now, there is another part to the story that I personally have not been involved in except to have two friends tell me about it, and that is that Chrysler is using a spring-loaded pulley on their alternators for quite a few years. I don't know what the problem was they found a solution for, but it's possible it had something to do with preventing vibration from the tensioner from transmitting to the alternator, and that will lower the stress on the belt. That's just a guess though.

You made reference to marks on the tensioner body. I'm not aware of any tensioner that has marks that are there for a useful purpose. Serpentine belts don't stretch, and they don't sink into the pulleys' grooves like the older V-belts did over time, so the tensioner arm shouldn't change position over time either. I think the clue you need to look at is that the tension is becoming real weak suddenly since you said you can push on the belt with just one finger. To me, THAT is what would point to a manufacturing problem since you said this happened more than once. The spring inside it didn't beak because then you'd have no tension at all. Rather, it sounds like one end of the spring popped off whatever it was hooked onto so not it doesn't have as much tension. You might consider comparing a new one at the parts store with one of the failed ones to see if you can tell if something happened to that spring.
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Monday, February 23rd, 2015 AT 11:35 AM
Tiny
DARKKNIGHT98
  • MEMBER
You can't see the spring on this tensioner unless you take it apart and I don't think the parts store will allow me to do that to one of their new ones. That is a very high tension spring and removing that cover might just allow it to unwind which could be very dangerous.

I just checked www. Gates. Com FAQ and saw where they answered a question about belts tensioners and they mentioned reference marks on the tensioner housing that indicate whether the tensioner is operating within its proper range. Those marks are machined into the housing right behind the belt pulley and are easily visible.

Thanks for your advice.

-James
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Monday, February 23rd, 2015 AT 3:14 PM
Tiny
CARADIODOC
  • EXPERT
Those marks make sense, but what would you do if they're off?
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Monday, February 23rd, 2015 AT 4:08 PM
Tiny
DARKKNIGHT98
  • MEMBER
Replace the tensioner, which I have done 3 times.

I sent my dilemma to Gates tech guys to see what they say about it.

Waiting to hear back from them.
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Monday, February 23rd, 2015 AT 6:21 PM
Tiny
SCHUELERAUTOSERVICE
  • MEMBER
If the belt doent squeal then your tensioner is more than likely fine, you should have 14volts at idle from the alternator with a decent amp load. Use ac delco in gm time is money. Drive it hard youll just need more parts sonner
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Monday, February 23rd, 2015 AT 7:59 PM
Tiny
DARKKNIGHT98
  • MEMBER
Yeah I am gonna try the ACDELCO tensioner. I never had this problem until I replaced the OEM part with the Gates parts.

I have been drag racing a 1970 chevelle for about 16 years so I am quite familiar with wearing out parts when you run cars hard. I started modifying this Firebird about 6 years ago and taught myself how to tune it thru the cars computer and it is now an 11 second daily driver. I live in Louisiana and this car has been to Texas 3 times and even to Atlanta once and never missed a beat on any of those trips. I buy good parts, do everything by the book and do all of the motor work myself.

The alternator charges fine as long as I am not manually shifting the car and spinning the rpm past 4,000 rpm.

I hope this GM tensioner solves this problem. There are plenty of cars out here with this same motor and the same pulley arrangement that get raced every weekend and they aren't having this problem.
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Monday, February 23rd, 2015 AT 8:17 PM

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