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02-07-2011
Engine will run and suddenly die without warning
Engine will not or not easily restart
Tachometer may drop to zero but the car will continue to run
it has all of the symptoms of a CPS failure, except i DONT lose spark, and the tcs light doesnt come on. and my CPS was replaced not too long ago.
02-07-2011
Originally Posted by bumpingtp
That sounds like the some of the problems I'm starting to have. Mine started with just a random stutter at low RPM's and progressed to stopping all together at low RPM, especially when I'm decelerating or making my way through a parking lot. It'll start back up instantly (for now).
02-10-2011
today, i took the time to do almost exactly as agentbluescreen advised, minus the fan wiring. i took used 6 3/4" x 3/4" pieces of micarta, approx. 3/16" thick, to hopefully reduce heat transfer. i also put some foil tape on one edge of each piece, as advised above. i'll update in a week or so and let everyone know how it's working.
02-10-2011
I had to space my ICM to fit my belt after installing my intercooler.
Just used some bolts and nuts.
02-11-2011
didnt work. car stalled yesterday. it's kinda weird, when i leave it in gear i can put the gas pedal to the floor and it slowly bogs and dies, but if i put it in neutral i can rev it freely, but it backfires when i let off the gas. im open for new suggestions!
02-11-2011
this issue was mostly found in the dead of summer. not winter.
02-12-2011
it does it year round. CPS was replaced, along with the harness
05-03-2011
My 98 GTP is doing this and it also hiccups time to time. I went to autozone they said MAF. I cleaned the MAF and it is completely fine. I took my car to NTB they said MAP sensor so I repleaced the map sensor put in all new plugs and wires and still have the same issue. My car runs fine the first couple of minutes until the engine wars up and then it seems to run like crap. I checked and all of the recall stuff was taked car of back in 09 when I had them originally addressed. I also had the coils tested and stuff before the tune up. I also installed anew PCV valve. Any suggestions on what I am dealing with and how to fix them? Some mechanic said I probably need to get my injectors cleaned out but that makes no sense if the car runs fine when its cold and crappy when hot
05-13-2011
I presume you are talking about the temperature of the weather outdoors not the temperature of the lower engine block. This is important, because your engine temperature gauge only tells you what the temperature of the coolant is at the transmission side of the upper engine block (where the coolant exit hose is), not the temperature of the lower crankcase or the much hotter temperature of the cylinder heads. (heat rises)
Due to the tach readings I would strongly suspect that the tiny magnet of your "CPS" Crankcase Position Sensor is fouled and malfunctioning.
The CPS is a transistor Hall Effect magnetic sensor on/behind the large lower pulley on the bottom left side (passenger front wheel) of the engine. It can be replaced but you need a special puller to yank the pulley off (through the passenger wheel well) the crankshaft to get at it.
Unfortunately, what happens, over time (mileage like 180k) to these otherwise very reliable electronic solid state "timing points" replacements (that also provide the rpm tach signal) is that the magnet in it attracts metal filings from the brake discs. In other words, there is nothing wrong with the sensor it just looses sensitivity because small metal brake rotor filings (steel dust) somehow gets sucked into it and sticks to it's exciter magnet, enlarging and miss shaping the magnetic field that the slots in the pulley vanes are supposed to open/block for timing/rpm/index signals. It's not just from your own rotors, big trucks and other cars in front of you also stir up road dust containing metal filings that end up in your engine compartment.
The small tip of this sensor has a permanent magnet on a post between two transistors like so:
Sensor| gap |Magnet| gap |Sensor
The back of the main crankshaft (indexed by a slot-key) steel pulley has two cylindrical sets of notched-metal vanes, one that registers a full rotation (one notch for RPM that is also the fire order index point) and the others that register the six TDC cylinder/crank position timings (six notches for sequential timings). Without this sensor's two signals the tach and/or ECM/sparks cannot function, and a limp (lost tach-index count reference) will eventually lead to a backfire.
What happens to the sensor is these foreign metal filings (shown here as >==<) get stuck to the magnet, progressively and randomly fouling, weakening the (apparent) strength of the modestly strong tiny embedded-in-plastic (alnico?) magnet and corrupting the (apparent) size of the magnetic gap like so:
_ _ _ _ _ _ >>======<<
Sensor| gap>|Magnet|<gap |Sensor
_ _ _ _ _ _ >>======<<
Like anything electronic, the Hall Effect Transistors lose sensitivity as they get warmer so once the lower engine block warms up a bit (especially in city driving or at a stop/light where there's suddenly way less cooling air flow at the bottom of the engine) they no longer produce a strong enough signal and the system suddenly fails. More importantly the 6X timing signals can become inaccurate/erratic causing rough engine run, degraded fuel economy and higher pollution. The engine computer, thus being fooled by these erratic (chronically delayed and/or erratic) mis-timing signals will falsely (and consistently) assume that these rotational timing aberrations are happening because your coils (or wires or plugs) are at fault. Depending how big a metal filing is on what side of the magnet it can affect either the just the tach or just the ignition system firings or both.
So basically you have to replace a perfectly good sensor, simply because it's center magnet is covered with steel (iron) brake rotor filings, there is really nothing else actually wrong with it. When you remove it and examine it closely you will clearly see these small steel brake rotor filings all built-up on it's center-pole "exciter' magnet. Larger filings are an even bigger problem, and time/mileage on the road need not be a factor if you have recently done the front brakes.
If you either replace it with a new, unfouled one or just use a more powerful magnet to remove the filings in/from it (and put it back in) all will be well again, save it will inevitably happen again, especially if you are a big (city driving) brake user or upgrade to metallic pads.
The permanent cure for this is to obtain several EXTREMELY powerful flat quarter-arc Samarium Cobalt or Neodymium (NdFeB) Magnets from an old computer hard disk drive head-arm actuator (thus totally destroying it before you throw it out, they all have two of them inside) and stick them (three or four of them) to the engine block close as possible to/around the base-back air space-slot of/behind the crankshaft pulley!
These incredibly powerful Neodymium or Samarium Cobalt hard disk arm-motor permanent magnets will quickly and easily capture almost all of the brake rotor dust from the dusty road-air around the area of the block behind the pulley, preventing air turbulence created by the spinning crankshaft pulley vanes from inducting metal filings along with other harmless dirt and dust into the engine's all-important CPS sensor forevermore.
GM provides a cheap plastic "foreign object guard" on the engine block around the back of the pulley to minimize air flow back there but it has no effect on brake (and bumper to bumper metallic rush hour road) dust, you need powerful magnetic "traps" to capture this sort of dusty-metal air-turbulence pollution before it ever gets close enough to the pulley gap to get sucked-in there. This will hopefully be the last of your engine's annoying CPS sensor problems, for a long long time.
TIP: Similar single-element Hall sensors are also used (one each) on the two front axles behind the brake rotors to provide the TCS/ABS control with front wheel RPM detection, and must likewise be cleaned of filings/rotor dust regularly during brake or front end bearing axle repairs or the TCS/ABS will similarly, eventually also appear to fail or go intermittent.
Last edited by agentbluescreen; 05-19-2011 at 05:14 PM.
05-13-2011
This is a photo of a fouled CPS center-magnet. Note all the "hair" of metal filings on the middle magnet. This both weakens and 'spreads out or shifts" the center polar point.
This is what it should/will look like if "new" or after it's just cleaned off with a damp rag, the magnet is very weak, you don't even have to remove it to do this.
I apologize for the blurry pic, but you get the idea... it can't/won't work properly with all those metal filings stuck on the magnet. On the inner 6X side of the sensor, wind from the rotating vane causes the spark to advance (on the highway) but as this wind diminishes (lower RPM) the magnetic "hairs" (along magnetic field lines) straighten up and the filings across the top and sides rejoin with one-another, weakening the overall magnetic field. This ironically results in almost the same ignition problems as pitted points and a bad distributor cap do, now easier to remedy but much harder to get at.
Last edited by agentbluescreen; 05-19-2011 at 05:26 PM.
05-15-2011
If you are short of cash (removing the 7" main crankshaft pulley to service or replace the $35 CPS sensor at a shop will cost you at least 2 hours -$75 labor) one other possible way to clean the filings off the rather weak magnet of the CPS sensor is to squirt high pressure water into the crack between the pulley and the engine block from the top/front (forward) edge of the back of the crankshaft pulley-engine block crack downwards, hopefully flushing the filings out.
The CPS and wiring is completely encapsulated and fairly waterproof, but the plastic foreign object protector may make this method of water-flushing to clean the magnet off (without pulley removal) not work at all or not work too well. If the problem is really severe this emergency quick fix may reduce it or buy you a bit of time, in any event the water down there behind the pulley in the crankshaft bearing area will drain out quickly and can't do much harm to anything down there. (psst - the crankshaft pulley is like a centrifuge, it will quickly suck-blow the water out like a spin dry cycle)
This method of flush cleaning the Hall Magnet works on the wheel hubs for the ABS/TCS sensor magnets. The stationary ABS/TCS sensor is on the lower part of (each front) axle block. People usually just replace the whole axle block/bearing/hub and sensor as a single unit, but it is also only "foreign object protected" in the hub/block gap allowing ferrous dust to get in there and foul the sensor's magnet, which cannot be accessed, cleaned, removed or replaced.
Again the sensor and magnet are completely plastic encapsulated, (though the backs of GM harness connectors just have rubber grommets and aren't too water resistant) so water in this area (not on wire-entry backs of connectors) is not much of an issue. YMMV
Always do your utmost to avoid getting water into the back wire-entry points of GM (and all) automotive electrical connectors, at that location they are merely rubber grommet "splash resistant" not "waterproof".
Last edited by agentbluescreen; 05-15-2011 at 02:49 PM.
05-15-2011
Another note about the left front (passenger) ABS/TCS sensor wiring on GTP's with the chronic warped front plastic manifold cover oil leak (they tried to just get away with putting a fatter gasket ROFL) is that this oil crud leaks down onto the top of the passenger side axle/control arm/rail. This is also where a second ABS/TCS sensor extension-cable wire from the passenger front sensor connection to the main engine harness lays.
Over time oil accumulation there will cause corrosive salt and brake rotor grindings to adhere to the connector and wires and thus, with moisture, to eventually get into the back of both of the connector's (rather leaky and loose) rubber-grommet splash-seals. This will cause leakage in the insulation values and may make the passenger-wheel sensor signal drop off, the easiest solution is to clean it with high pressure water. It's just down below the passenger side radiator plumbing connections 10" towards the center, laying on the rail.
Again get your dealer to fix the fire hazard SC recall repair again and/or get under the car and clean the extension connector-backs off (use brake cleaner) and then seal them good with some silicone to prevent oil/salt/water penetration.
Last edited by agentbluescreen; 05-15-2011 at 02:38 PM.
05-28-2011
agentbluescreen,
Thanks so much for all of your posts. They're very helpful to all of us - and our mechanics! - who are having the same woes.
This is such a simple question I'm a bit afraid to ask it, but here goes: since the cars having these elusive problems typically have many K miles on them, and since you say gunk and corrosion are major culprits, would having the engine compartment steam-cleaned solve part of the problem, apart from the high-heat issue? I'm just thinking that these cars ran fabulously for sooo long, even with all of the high heat, so I'm wondering what has developed, and, since so many of us have replaced parts 'til our wallets are blue in the face, it doesn't seem old, worn-out parts are the whole problem....
Also, it's been 1.5 weeks since your last post - - how's it going with your car now - - is it still stall- and non-start-free? If so, you seem to be the only one who has conquered this gnarly beast!
05-28-2011
P.S. My 98 Grand Prix 3.8 V6 SE, with 205K miles, does the stall thing (on and off the highway) & the not-start thing (for varying amounts of wait-time), for the last four months. It of course seems to be, like agentbluescreen's, after short stops (like going to lunch) and when the weather is warmer - and during the later evening after a warm day.
The dash lights I have on are: ABS, Non-Trac and intermittently (like on one week, off the next) the Service Engine Light (That light has been doing that for literally years, with the car running beautifully).
We've replaced: CPS, wiring harness, fuel filter, fuel relay, fuel pump, ICM, plugs and the 2009 Recall wire "channel" or whatever it's called.
We've checked: plug wires/boots, battery connectors, MAF and EGR.
The codes have repeatedly been checked and cleared, and currently there's only CPS "A" and EGR. The first is new, the second was examined and OK.
That's my story an' I'm stickin' to it.
05-28-2011
Oh - and tach needle dropping to zero & staying there 'til next start - and this still happens, even though we just replaced the ICM - and it usually happens soon before either a stall or a non-(re)start.
'Interesting thing: The car usually does better when the gas tank is full... maybe something to do with the gas staying cooler and so keeping other things relatively cooler?
05-28-2011
Man, I keep thinking of more things to say!...
I have also smelled the strong smell of gas after a stall with non-(re)start. We haven't replaced the fuel pressure regulator yet, but we've already spent over $2K without success, and replacing parts doesn't seem to be doing it, and others have replaced that part & the problem remained....
05-28-2011
OK, another thing:
agentbluescreen also mentioned vacuum leaks, and I know there's a crack at the back of my manifold cover (I don't get how this works, but my mechanic replaced the part of it -?- that fixed a crack at the front, that was letting major exhaust into the cab; there's still some coming in now when I'm sitting in my driveway idling, but when I get moving it blows away behind the car).
Could a small crack in the manifold cover be the stalling/not-starting culprit?
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