Engine hiccup: help appreciated

**honkbox** · 03-11-2012

I have a 2000 gtp with 157000 miles on it. While driving down the highway even with the cruise set the engine shuts off for a millisecond and the tach stops working. Car continues on its way with no issues except that he tach is not working. Once I can stop and restart the car the tach works again and everything is fine. Usually on the way home the same thing happens and the process is repeated.

The other issue I have is the abs light and traction control light is on. I know this is a faulty speed sensor but how can you tell which side needs to be replaced. Don't want to replace both.

Any help with these issues would be greatly appreciated. Thanks.

**honkbox** · 03-11-2012

Seems like the cps may be my problem after a little research on this site. Problem is when I go to the write up on how to replace it, the post isn't available anymore. Says some thing about an error. Can anyone steer me to where I can get ahold of this write up. Thanks.

**agentbluescreen** · 03-11-2012

The crankshaft position sensor is a two-channel hall (magnetic blocking) effect center magnet/dual-transistor affair that detects two signals about the crankshaft's current position by reading (being blocked by) two sets of vanes on the backside of the main harmonic balancer (largest pulley at the bottom of the engine, accessible through the front passenger wheel-well).

There are two circular rows of metal "vanes" on the back of the balancer pulley, one with a single vane that functions as index position/tach signal and the other with six (x4) vanes that (more finely) indicate the precise timing of each of the six cylinders. A separate camshaft position sensor (facing into the sealed engine) picks up any lag or lead in the valve operations. This CPS sensor and pulley-vane affair replaces points and a distributor, directly reading the crankshaft with no gearing between it and the truth.

While they should and do last forever, the problem with the magnet and it's two Hall effect transistors is that the magnet is exposed to metallic brake dust and road grime through the thin air-gap between the plastic "foreign object shield" on the engine block and the back of the spinning (air sucking and blowing) balancer pulley, way down there right over the dusty road!

What happens is that over time, metal filings from brake rotors (and other people's brake rotors) find their way in there and lodge themselves on the center magnet, resulting in a magnetic filing shunt that greatly weakens the power of the magnet causing the Hall-effect transistors to be progressively more unable to get a good magnetic pulse. This problem gets far, far worse when the transistors are hotter, such as when the engine gets hot in summer, you use low octane fuel, the A/C or are in city driving. Occasionally wind conditions on the highway themselves can cause momentary failures as well. Hall effect transistors don't like heat and their sensitivity (even when new) drops markedly at high temperatures, so there is really nothing wrong with them - there's simply no more/enough "magnet" once it's covered in metal filings!

To add insult to injury these metal filings on the CPS center-magnet both blow (due to wind) and "move themselves" around (due to the movements of the metal vanes) causing it's magnetic field to seem to "move erratically" to the sensors, a set of conditions that result in a lot of erroneous ECM codes relating to bad ignition coil, bad ICM or bad spark plug/wiring codes where no problem actually exists. the computer has no way of knowing that it's own base-index and base-timing references are inaccurate, so it just assumes something further up the line is the issue.

In most cases the CPS simply needs to be removed and cleaned of metal filings on it's center magnet and all will be well again, but replacing it is also a good option, just keep your old one and clean it off for next time.

A good, more permanent solution (I have used and recommend) is to place a few very, very strong magnets (such as those rare earth neodymium or samarium cobalt magnets found in old hard drives) in a circle around the harmonic balancer on the outside of the lower engine block around it to trap brake dust before it gets into the pulley's back air gap. It's not a 100% solution but neither is the cheap plastic "foreign object shield" that lets this junk get sucked in there in the first place! Like the magnets that clean your ATF of metal bits in the tranny, it's simply an added layer of protection that will greatly increase your future mean-time between failures.

Keeping these four (or more) strong rare earth "air cleaner" magnets well-cleaned by wiping them off with a damp rag now and then will, likewise, maintain their ability to trap metal filings and dust before it gets sucked into the balancer-pulley's air gap, as a regular maintenance item.

**FordMan77** · 03-11-2012

This is from memory so bear with me.

To replace the crank sensor you need to disconnect the neg. batt. cable, remove the pass. side tire, the splash gaurd around the crank balancer, the sepentine belt, then remove the harmonic balancer. The sensor is to the right side of the balancer and is held on w/ 2 bolts. There should be a plastic shield around it as well. Disconnect the electrical harness from it, remove the 2 bolts and there you go.

In order to remove the crank bolt, remove the inspection cover from the trans so you can see the bottom of the flywheel and clamp a vice grip on the flywheel. Then when you spin the motor backwards it will catch on the vicegrip and the bolt will come out. Be warned- that bolt probably has orange loctite on it from the factory and is torqued to 110 ft/lb. so it may fight you. Best bet would be a good impact wrench, or a long cheater bar. You will also need some small 4" long bolts in the correct pitch/thread to remove the balancer as most on the market do not come with the proper ones. I got mine at True Value.

When you go to reinstall the balancer be 100% sure that the KEY ON THE CRANKSHAFT IS LINED UP WITH THE SLOT IN THE BALANCER!!! If you don't you will screw up the woodruff key and possibly the crank slot. I reused my stock crank bolt even though technically it is a torque to yield bolt and should be replaced. Your call there. Dealer has it if you want a new one. Make sure it is properly torqued after install. Then remove the vicegrips from the flywheel and reinstall the cover. The rest should be pretty straight forward.

And to find out what hub is having the issue and needs to be replaced, have it scanned on either a GM Tech II scanner, or something that can read ABS codes as most generic parts store scanners will not read these. Dealer may want $50-$100 for a scan. Once you find out which one it is try disconnecting the harness behind that wheel and cleaning it out as they can get corroded and cause an ABS light. If this doesn't work then get a TIMKIN hub from Rock Auto and call it good.

**FordMan77** · 03-11-2012

I just found this as well from Bill. Should help you out and even gives you the size of the bolts needed to remove the balancer.

Jack and support passenger side front of car.
Remove tire
Remove plastic splash shield in front of harmonic balancer
Untension belts
Remove crank bolt (24mm)
Using a balancer puller and m6 x 1.00 pitch bolts about 60-75mm in length pull the balancer

Disconnect crank sensor electrical

Remove plastic crank sensor shield

Remove crank sensor (2 x 13mm bolts and wiggle it)

Reverse for installation.

Tip, when reinstalling the plastic crank sensor shield. Ensure each of the three nubs have clicked on the bolt ends.

**agentbluescreen** · 03-11-2012

Replacing it involves having a hoist or good floor-jack and stands, removing the front passenger tire, wheel-well shrouds and both drive belts, locating the access port under the flywheel and installing a powerful vice grip to lock the crankshaft/flywheel. Then you unbolt the balancer with a big socket and breaker-bar. After that you need a specific GM puller to pull the balancer off it's taper fit, most standard ones will not work.

Once the balancer pulley is off you remove the plastic "foreign object shield" and then the two screws that hold the (now fully exposed) CPS Sensor with the big gob of iron filings stuck to it's center magnet and replace it, or just leave it (shield and sensor) together and wipe the magnet off with a damp rag until it is cleaned of filings.

For the overall standard shop labor cost, (around $200) the extra $40 for a new sensor is a small added expense, but believe me you really are no/little further ahead with a "new" one. The sensor itself is seldom the problem, the metal filings on it's magnet are.

**agentbluescreen** · 03-11-2012

If you examine the second and fourth pictures above, that rusty-brownish spot on top and two little "lumps" (on sides) of crud on the center magnet are brake metal filings that "short-out" (shunt) the two poles of the magnet in the center of the sensor assembly. This crud (usually a lot worse) can be just wiped off to restore the plastic-embedded magnet to "as new" condition again. These metal filings stuck to the plastic magnet housing make the magnet both weaker and wider than it's supposed to be (to it's two sensors). Longer (also weakly magnetized) filings that "move around" often come off with the balancer (and fall away unnoticed) when it is pulled, but the hard core build up of fine magnetized dust remains stuck there unless/until they are cleaned off and removed.

**honkbox** · 03-11-2012

Thanks guys. Once again this site has come to my rescue. I have enough info to get started. Let you know how it turns out. By the way if there is anyone in the Tacoma WA area who knows where a good place to get that scan is it would be great if you could message me. Thanks

**FordMan77** · 03-11-2012

For a 2K GTP with 157K on it I'd rather not take the chance of wiping the sensor off and having it fail again shortly thereafter, thus leaving me stranded somewhere and adding a huge towing bill to the mix. These are known failure parts on these motors. For the amount of work that goes into getting to it I'd spend the $40 on a new sensor for piece of mind alone. I've never heard of just wiping it off and having it work again, but then again new things everyday, right?

BTW, the CKPS on my 95 Bonne didn't have anything on it when it failed. It was as clean as the day it was installed yet died just the same. The only reason I noticed this is because it was strange how clean that area was compared to the rest of the motor. Electronics are great, when they work, lol...

And as far as getting it scanned, maybe a Dobbs or the like can do this for you. I know the dealer can, but like I said they will want to charge their diagnostics fee, which around here is about $80.

**agentbluescreen** · 03-11-2012

I agree it's a big messy job to get at it, so a new one definitely can't hurt, but avoid any non-Delco aftermarket (generic) ones, as they may be a problem too.

Most of the OEM ones I've seen/tested just (very obviously) had the filings build-up issue. The engine pictured above is not a 3800SC Series II it is missing the second little harness plug and cam sensor on the upper left side of the crank.

BTW the ABS/ATC light is part of the same problem, with no rpm the wheels shouldn't be turning, so the computer wisely "deduces" that the power brakes can't/won't work.

When mine failed (hot engine stall) it was just the (outer) timing side of the sensor that was failing, the tach always worked, when the engine cooled down it would always work fine again. But many others have reported the link between the two if the tach side is malfunctioning as well.

**FordMan77** · 03-11-2012

Yes, most definetly go w/ a Delco unit. I got mine for the Bonne from the dealer and the price wasn't too far off from Rock Auto's pricing, and since I needed it "now" and not in 3-5 days it worked out just fine.

**BillBoost37** · 03-12-2012

FWIW I've typically replaced with standard auto parts store.

The job is big and messy? I might be spoiled with the air gun. Total is usually about 30 minutes.

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