lets discuss Crank Position Sensors for a moment

I have a starting issue I have been chasing for over a year. Sadly it has come down to one of two issues. God forbid, Vapor Lock or Crank Position sensor. Please take my word that the issue is not high current electrical at this point. I have replaced EVERYTHING from starter to battery, cables. ground straps and trust me. Sadly its not that simple. I have a slow/ to no crank when hot. It always "tries" but then the computer shuts of the starter after hearing a 1/2 hearted crank. So I pulled the crank position sensor. At 70*F the sensor reads 910 ohms. (in tolerance according to a friend of mine that works for a dealer) So I put the sensor in the oven and brought it up to 220*F and the resistance goes to 1200.... Now I Don't think this would give me the issue. Because when the car cranks resistance should go down on this sensor not up and I am not getting any CEL codes. So if the senor starts out high, it would think the car isn't turning....... I don't know.. Im so out of ideas at this point. when I pulled the sensor it was caked full of crap and shavings. Sensors are pushing $300.00 I don't want to just "try one" I want to approach this with a little more knowledge. Thanks for your input.

The computer does not shut off the starter. As long as power is supplied through the ignition switch, clutch switch, etc to the starter, the starter should keep spinning. The DME will shut down the fuel pump if it doesnt like the crank sensor signal but it wont shut down the starter. Is the issue a slow spinning starter or normal spinning but then cut off or wont fire?

Btw, the resistance test of the sensor may not be conclusive. To fully test it, you need to use a scope to check its waveform, per the service manual. E.g., if one of the teeth of the flywheel is bent slightly, that will throw off the sensor. If your starter is "cut off" during cranking, I still highly suspect it's an electrical issue. What does you voltmeter in the instrument cluster show when cranking. It should not drop below 9v.

I'm sorry to argue with you. But yes, when the car starts, no matter if you hold the key in the start position or not, the starter shuts off when it see the engine is running. It does tell this by the CPS.

First not arguing. More like discussing. Just trying to help here. You verified when the engine is hot, you can hand rotate it and all the other accessaries and pulleys?

Whenever someone posts something like this: "Please take my word that the issue is not high current electrical at this point." I strongly suspect the problem is related to exactly what the poster believes it is not related to. My info is the engine will crank with a defective/non-functioning crankshaft position sensor but the DME will not trigger the fuel injectors or spark plugs as it does not know when to trigger these. Clean the crankshaft position sensor and be sure you install it with the proper gap/clearance and the sensor is secure. Then look elsewhere for the source of the problem. Where to look? Well....something in the high current electrical system would be my WAG. Oh to comment on your most recent post I can't confirm what you say is true regarding the DME shutting off the starter once the engine begins to run, but if it is true then look at this circuit from the DME to whatever the DME talks to (electrically) to turn off the starter when the engine spins up from a start. A relay perhaps is failing and mimicking a premature "shut off the starter" signal.

I know nothing about electronics, but perhaps buying and installing a used CPS might at least allow you to rule it out, no? If it's still an issue, you can just resell it and only lose the cost of shipping.

i do not think vapor lock is an issue here. a dvom at the starter when it quits cranking will tell you if you have voltage at the starter .does this type of starter have a solenoid on it ? cranking voltage testing,starter draw [amps] ,battery load tested ?

-I thank everyone for their inputs. -I've replaced the starter -I've replaced the battery -I've removed the new starter and took it an had it tested -I've replaced the cable that goes from the alt to starter to jump post -I've cleaned the orig ground strap -I added a ground strap -I cleaned the ground connections at the battery -When I shut the car off an then hit the starter RIGHT AWAY. It starts, lazy but starts If I wait 15 seconds it gives a 1/2 hearted crank and stops -I pulled the CPS cleaned and re installed. -I have to start to look at other possibilities. Again open to all input I've also noticed I'm running warmer than I used to according to the dash gauge. Again thanks for input cause I'm out of ideas.

I will do a hand crank test later tonight.

Quotes source post: 10608071

When you wait the 15 seconds and then the engine gives a 1/2 hearted crank then stops how long do you have to wait before the engine starts normally? Also, about the dash gage reading... do you have an OBD2 scan tool that you can use to view say intake air temp, coolant temp, fuel trims, etc. at engine start? I'd also be interested in having a voltmeter and seeing what the voltage does and amperage too as the car manifests this behavior.

Other things you have to consider and yet I do not believe you have are the relays. For instance the DME relay, the ignition relay and the fuel pump relay. That the engine stops cranking vs. just cranks and doesn't fire suggests to me the DME relay or the ignition relay should be at the top of the list of things to be considered.

If the engine is slow to spin, then its either the starting system is fhe issue or the engine is siezing up. It's one or the other. Fist step is to check the engine. Try to turn it with a breaker bar, while the seprentine belt is on and then when it's off. Then report back.

I'm posting from my phone please excuse typos: Ok, how long do I have to Wait: it's getting longer and longer, I'd say at this point 1/2 hour. I did the hand crank test, the engine is about the same to turn over by hand no matter cold or hot. So that puts me back to electrical. I have to be missing a connection point somewhere. Some other posts talk about a point somewhere above the transmission. Any one know where this one is and if it is on my car? Very early 99 c2

One quick test. When it cranks slow, jump start it with another car idling at the engine jump start terminal and the airfilter bolt. If it starts fine, your problem is electrical between the battery and the starter (since you already eliminated the ground strap with a jumper cable before. Very difficult to believe the engine is running fine then seize tge next second after it stopped. You hand crank test just verified that.

Btw, cleaning the cable contacts are not enough. Those cables can look fine but when you peel back the insulation, the copper is all GREEN, heavily corroded inside. I did voltage drop test on that y starter/alternator cable and able to detect I almost lost 0.5v on that 3 feet cable. Decided to change it out and sure enough, the cable was heavily corroded at the crimp point.

I've got a used CPS that should be good.... I'll loan it to you if you want to troubleshoot with it? http://forums.pelicanparts.com/porsc...000-996-a.html

Quotes source post: 10608806

+1 thou I would connect the - cable to the engine. This would rule out the ground cable.

I'll do the jumper test from the jump points.

When I was putting the engine back in, don't remember seeing any ground points in the transmissiom tunnel.

Quotes source post: 10609700

He is not looking at ground points on the engine. He is looking for #18/34 that connect 19 and 17. Anyone knows? He has already replaced 21/22 and cleaned the contacts on 29. image.jpg

Quotes source post: 10609245

Agree. Thought about that but will need to find a safe place away from the rotating parts of the engine. Maybe on the engine brace or exhaust clamps under the car.

Clamp it to the sump plate.

Quotes source post: 10609762

Not too sure since it's aluminum which may have surface oxide that's an insulator. It may work though. I prefer steel if available hence the suggestion of engine brace or exhaust clamps.

here is a video of the issue: 996 start issue - YouTube

Quotes source post: 10609728

I Have not cleaned 34 or 6. Going to do that this afternoon.

Quotes source post: 10609922

Weird that your tach doesn't register for several seconds after engine is started.... I vote Crankshaft position sensor. Again, I've got an extra used good one... Can loan and if it proves to be your solution, I'm sure we can figure it out.

Well, I'm no expert but that behavior still looks to be voltage related. The first restart after the engine was warm I believe I spotted the voltage meter needle dropping to 0v. It does not look to be a crankshaft position sensor related problem but if you want, if you can, borrow one and see. I may be wrong. But I would not recommend you buy one unless you are comfortable with the risk that you may end up with a spare CPS to go with the perfectly good one that came out of the car. I am glad to hear the voltage is 13.8V. That's a very good number. But I wonder what it is at the end of the trip? One possible issue is the alternator starts out working just fine but it stops after some time. The engine manages to run ok for a while but back at the garage the battery can't restart the engine. After sitting a while the battery recovers -- though how long it can keep this up is a good question -- then the car restarts just fine. And the alternator is ok. For a while. I encountered this once indirectly at a dealer service department. The tech had a car in his bay on the lift -- I can't recall the model of car now but I know it was a very new model year -- and out of curiosity I asked him what's the issue? He said the alternator. The symptom was the engine would start and run just fine idle just fine but after a few minutes the dash warning lights would come on the engine would begin to run poorly then the engine would die. After turning off the key and letting the vehicle sit a few minutes the engine would fire right up and then do the same thing all over again. The tech traced the problem to an alternator that was not able to supply the electrical needs of the engine/vehicle. Due to the battery's excellent condition it was able to supply sufficient power to start the engine and run the vehicle, for a while. Oh, I might mention that my VW Golf TDi once lost its V-belt and among other things alternator power thus the vehicle was running solely on battery power. The car ran just fine for 15 or more miles as I drove into Albuquerque and stopped at a car parts store to pick up an alternator and belt and other things. The only sign something was amiss was a dash warning light was on. (That and the power steering and brakes were no longer power assisted.) My point is a car can run some miles without any apparent problems with no alternator power. As an aside, and I do not necessarily think there is any connection, have you used a scan tool to view the engine coolant temperature, to put a number on it vs. just going by what the dash coolant temperature gage "reads"? If the temperature really is elevated this bears looking into.

Quotes source post: 10610040

Good point. In first hot start the volt gauge goes slowly to 10v (bottom). When engine run's, the v-gauge show's only 13v. And when you try to start it last time, v-gauge drops below 10v fast. Try to jump the car from the battery, this way you can be sure that all the cables are ok. If the car starts normally, I'd say that Macster's suggestion is spot on.

I took a v read at battery and at engine compartment jump point today when hot, while running, I had 13.7X I cleaned the connection where the + batt lead connects at the fire wall. No change. I'm going to clean the other one that has to be somewhere under the car After it cools off a bit. I really think its a starter issue. And yes McMaster, the voltage may very well drop to zero if I stall the stater motor. An electric motor is pretty much a short if its stalled.

Glide, thank you but I no longer feel this is the problem.

At 24s cold start, the voltmeter reads 11v, you need a new battery. I can hear it cranks slower than normal too even when cold. Since you get 14v after the engine starts, I think your alternator is most likely fine but there are tests to verufy that. Now hot start, you turned the key really quickly but I think I saw the same 11v right before you crank it. That means your battery is not charging properly during drive. Corrosion may contrbute but when the engine is not running, the voltmeter will show the full battery voltage even with corrosion. So I think your battery is weak. i expect a full powerful hot start if you jump from the engine bay. If yes, do what Speed suggested to jump start from the frunk to eliminate the cables. You could have a parasitic draw that's draining your battery over night.

I can't find my damn jumper cables.

Quotes source post: 10610204

Please use 6 gauge or fatter if you could. Those wimpy 10 gauge may lead you down some false diagnostic paths.

Maybe someone else can weigh in on whether they have ever seen this with P-cars, but I know some other makes have experienced this behavior when the starter heats up due to proximity to the motor, and the starter tolerances are so close that the resulting expansion causes the starter to bind It will not show up on a bench test because the starter is cold at the time.

Quotes source post: 10610684

Exactly! I found the + connection up under the transmission, it shows promise of being an issue. But will take to long to try to remove. So Tomorrow I will go buy what I need to bypass this cable. If the problem persists after this, I will remove the starter again and find a shop that can heat it to 270* before they test it. And then I think the problem will show up.

I had this happen on my old Trans Am, during changing of the starter, I was too lazy to pu the starter heat shield back on and had the same exact issues that you have now. Ths starter would heat up from the aftermarket headers and do exactly what you have in the video. Therefore, I'm agreeing that your issue is probably a starter that acts up when it's heat soaked.

after watching your video i think my car had kinda similar attitude 2 years ago, so, i simply went to autozone and bought biggest battery i could fit into frunk, you have to undo a bolt in the stock battery holder to fit bigger longer unit in there. it is heavier than a stock one, indeed, and it sux to haul more dead weight in the sports car but after that i never had issues with slow cranks and car can sit in a garage way longer now with no issues. if you have good pro grade multimeter you can try to measure actual voltage drop at the battery terminals during fast cranks and during slow cranks, you will need an assistant for that. you can always use an external battery and when car is shut off with key off apply voltage to starter directly when car is hot and off on neutral gear to check if you get mechanical issue with some bearings or starter itself.

Quotes source post: 10611188

I thought you already rebuilt it and had same problem with previous starter. Anyway, just to be safe, if you jump start, only jump with a known good battery and with the other car engine OFF to prevent damaging the other car's alternator.

I had the CPS go out in my 1999. I would be driving along & the motor would just quit. Have to wait several hours for it to start up & then it would not start at all.

Quotes source post: 10611574

I have thought about a higher crank amp battery, but to me that is a band aid and not really fixing the problem. I feel eventually your problem will resurface with no where else for you to go as what ever the true issue is continues to get worse.

Am having very same symptoms on my '99 996 C2 - at a DE this weekend. Tried jumping from my Highlander and from a portable battery pack at various moments and it didn't really help much - was jumping at the battery in the frunk - didn't occur to me to try the engine jump point - doh. Didn't have my DVM handy but will make sure I bring it next time. I have a Durametric - any real time data I should try to capture during cranking ? Anyways - subscribed - looking forward to hear when you do solve the issue.

Its either vapor lock or starter. I did the test with running a jumper cable from the Battery to the jump point in the rear of the car. Same exact situation. Maybe to night I will do it again and use a jump battery in the back.

I hate to ask this but........is the coolant level normal ?

Quotes source post: 10615362

It was slightly low a few weeks ago. But I found the burp valve open. Figured it just steamed out there. Been keeping my eye on it and its been stable.

1) I don't think the jump point is really your problem. I know I'm just adding to the confusion, but an amp meter reading on the fat cable to the starter (or right off the battery) would be really interesting. I bet it's going to show a huge current load going to your starter. Remember, each time you use the starter, it gets very hot. Therefore if it's already a little hot (after driving like you did in your video) and you use it twice in a row, I bet it's VERY hot. Lends credence to the expansion theory. 2) I think the high running temperature plays into this somehow. I can't think if it's a cause or effect yet...

Assuming the battery is good -the symptoms suggest a bad starter motor or the solenoid .Not sure how these were tested .The solenoid could partially work and appear ok until hot and under load .The jumper cable bypass test tend to rule out bad connections . Haven't looked thru the wiring diagrams but the clutch interlock may have a relay in the circuit that is flaky .

Quotes source post: 10615247

This was not what I (or Ahsai) suggested you to test. Take a nother car, or battery that is freshly charged and use that to jump the car. Like you would do when you have a empty battery in the car. Do this test from the battery and from the jump point at the engine bay. If the new battery starts the car in both places, problem is in your charging system. If it starts from the engine jump point, but not from the battery, it's the cables. If no start on both places, the problem is the starter. Simple as that.

Quotes source post: 10616628

Right and I think he still planned to do those tests. I think he has problems with the battery and/or charging system at least. In his clip 0:24s cold start, his battery is at only 11v before cranking. You could actually hear the cold start is slower than normal. Hot start at 2:40s shows 11v as well. At 11v, the battery will struggle at cold start and won't have a chance at hot start if his starter is acting up or has more resistance to turn when hot. His voltmeter reads 14v right after engine is started and seems to remain at 13.5v or higher throughout the drive so I think it's more likely the battery itself is not holding charge. Granted he may also have a problem with the starter especially with the hotter than normal engine.

I don't go by the dash gauag my meter tells me I have 12.6 with key on at the jump point cold, the crank is the fastest (cold) it has ever been. It has NEVER cranked as fast as it does since I have cleaned up every ground and pos cable connection in the car. I will get back to it tomorrow. Had to take some time off before I beat it to death.

it was getting heat soaked from the engine running hot due to the drivers side Rad fan not kicking in for stage one. Jumpered the stage 2 rad relay to kick in when stage one is activated for testing. Drove car will over an hour. Car now starts every time. Well that was simple

Quotes source post: 10624728

Glad to hear that you get it sorted out. That's an interesting case.

good that it is fixed and good for the report back

I'm having same issue - starter getting bogged down and won't start the engine when hot - all voltages are good - starts fine cold. Sure enough my drivers side radiator fan stage 1 is not coming on - opening up connector X1/1 in the frunk I can measure that the ballast is open but the stage 2 path looks OK. Now my car is a track-only car with AC removed - wondering if there is any reason not to permanently jumper stage 2 to stage 1 ? This would be a lot cheaper than a replacement ballast resistor ... Any reason why it would be bad to run the fans on high rather than low the bulk of the time ? As a separate question is it more likely that my engine compartment fan is nixed ? It seems strange to me that a stage 1 radiator fan would make a difference when the car is being driven at speed and as soon as the engine is turned off it would do nothing anyway ... I tend to not let the car idle for long even after a run. Is there any reason to expect a new or rebuilt starter would be less heat sensitive ?