Topic: Is my CPS (crankshaft position sensor) BAD? It still runs.... but not too good

[carcollector]

1997 TJ 2.5 147k:
 - threw a p0320 code for cranksensor (no speed signal to distrubutor, or something), but it will start and idle. Sometimes it is hard to start (like a gas problem) but idles good and for long periods. I have noticed a little fluctuation in rpms at idle and when holding pedal at any rpm range.
It just will not accelerate properly. I can ease the rpms up to 4000 and hold it, but to try it normally it will want to stall. Sometimes when trying to re-accelerate it has minor backfires through the intake before wanting to stall out - BUT, it runs good down the road at steady speeds if I baby the gas. It is just very hard to take off; must tach it to around 3000 and ride clutch or it will stall, but when it is cold sometime it is normal until it heats up.

I have changed distributor that has a camsensor in it, but the code came right back. I swapped TPS, but admit I didn't disconnect battery and let computer reset before returning the part. Every post I have read about CPS states will not start or there is intermittent loss of all power.

It acts more like starving for fuel, but fuel pump was replaced by prior owner that I inherited the Jeep and the problem from. There was a fuel pump box in the Jeep to confirm what he said, but he dosen't know if install was done done properly by local "shade-tree" mechanic.

I believe that "MAYBE" the minor backfires are from uncalculated drop in RPM due to loss of fuel pressure, and the distributor timing is advanced based on the input from the TPS, camsensor and CPS since the ECM is constantly trying to anticipate timing/airmixture/injectors, and that is why I got a CPS code, and it threw a TPS code once, and multiple misfire codes - but I may be wrong

It is not the cat I am pretty sure and no O2 codes

But what i really want to know is: Will the Jeep even run if the CPS is bad

If it will run with a bad CPS, will it run like I described mine does?

[sharpxmen]

your ignition timing is controlled by the PCM based on the CPS input, the sensor in the distributor (called the cam sensor) is used for fuel delivery and for PCM sync with the crank sensor - you are correct, the advance is adjusted based on engine temp, tps, IAT but the main ignition timing map (table, not the map sensor) is based on intake pressure (vacuum) given by the MAP sensor vs. RPM and sequenced off the CPS.

If you had a crank sensor code just replace it, the PCM probably detects misses or low signal levels and that's why it throws the code, it will run even if it misses a beat or 2, but like you describe will not start easy and run like in 3 cylinders at times (when it misses signals off the CPS). Could also stall at times if the cam and crank go out of sync before it can regain it, the PCM will go in error and stop controlling the fuel and ignition.

[carcollector]

OK, I popped in a used CPS from a cash for clunker cars in the junk yars, and it does the same thing!  I have noticed some black soot and moisture dripping from the tailpipe, but I think that is from all the rpms I have been giving it.

I am going to drop the tank and look at the fuel filter - it runs good in the upper rpms, but have to ease into gas from idle or it will stall.

could it be the tps, I changed it once with a new one, but I didn't unhook the battery for 30 seconds or anything.

ALSO: I have a clicking/popping noise coming from inside the valve cover - could something in there be causing a problem.  Never heard anything like it, I thought it was the exhaust manifold making the noise. I only hear it after the engine is shut off, and it last for up to 5 minutes.... I am hoping it is just a lifter bleeding down.

[sharpxmen]

OK, I popped in a used CPS from a cash for clunker cars in the junk yars, and it does the same thing!  I have noticed some black soot and moisture dripping from the tailpipe, but I think that is from all the rpms I have been giving it.

I am going to drop the tank and look at the fuel filter - it runs good in the upper rpms, but have to ease into gas from idle or it will stall.

could it be the tps, I changed it once with a new one, but I didn't unhook the battery for 30 seconds or anything.

ALSO: I have a clicking/popping noise coming from inside the valve cover - could something in there be causing a problem.  Never heard anything like it, I thought it was the exhaust manifold making the noise. I only hear it after the engine is shut off, and it last for up to 5 minutes.... I am hoping it is just a lifter bleeding down.

could be fuel related, i would do some diagnostics before throwing out more money on it

1. check the fuel pressure
2. do a compression test of all the cylinders cold and warm engine

tps can cause something similar so i would also suggest testing the output on it and see if you get faulty readings (but then again, this is from what i understand based on your description, there is nothing really concrete that i can relate anything to other than the behavior so it's all speculation in the end).

i have no idea what the popping sound can be under the valve cover (maybe someone else here had that experience before or maybe is the exhaust cooling down which is common sometimes) - but i would maybe take the cover off while it does that (get everything ready for that, maybe take the cover off and inspect it when cold and then put it back together just with a few screws to be able to pop it off quickly  - don't drive it like that, just warm up the engine and then listen and if it does it take it off to see or hear better what is happening there)

unless you have a seized lifter or rocker or in the worst case scenario a bent valve that is seized in the guide and it goes back into place slowly while cooling - but that would come out in the compression test though, so i would start with those 2 first and take it from there.

i don't think a lifter bleeding out would make that noise as it's full of oil and even if it would bleed would be slowly and not making popping sounds unless it's dry already

any issues with oil pressure, voltage, any other codes? does it run strong in high rpm? does it idle fine?

[carcollector]

idles real good and forever if I let it - good voltage, clean terminals, awesome oil pressure, recent tune-up - Replaced the tps but did not reset computer and run just as bad - changed distributor and cps and still runs bad (was a code for that) - runs strong in higher rpms and can rev and tach it back up as long as I keep the rpms high - lower rpms it bogs/stalls out like it is getting too much air or not enough gas.

Anyways - I dropped the tank, see the new fuel pump inside, but pickup screen was floating in the gas tank ( has new screens/o-rings ) it is an autozone "master" pump.
I really am not sure if I knocked the screen off trying to remove the module or not - but before I did it I drove it around the neighborhood and noticed after corners, hard stops, or bumps it wanted to stall out no matter what I did (like it was low on gas)  I have not put much gas in it anticipating having to drop the tank, BUT

would a module without a pickup screen act like that if the gas level was low?

The biggest thing that worries me is the inability to acclerate normally without it falling on its face from a low rpm -
going around a corner and losing power is definitely from low gas level, but the acceleration thing is driving me nut and I am afraid to drive it in traffic

I mean, you really have to feather the gas and not over accel until you are in a higher rpm
could it be as easy as the pick up screen, or did maybe the pump pick up some trash and is poooping out?

Sincerely,
No Fuel Pump Pressure tester on hand guy

[sharpxmen]

idles real good and forever if I let it - good voltage, clean terminals, awesome oil pressure, recent tune-up - Replaced the tps but did not reset computer and run just as bad - changed distributor and cps and still runs bad (was a code for that) - runs strong in higher rpms and can rev and tach it back up as long as I keep the rpms high - lower rpms it bogs/stalls out like it is getting too much air or not enough gas.

Anyways - I dropped the tank, see the new fuel pump inside, but pickup screen was floating in the gas tank ( has new screens/o-rings ) it is an autozone "master" pump.
I really am not sure if I knocked the screen off trying to remove the module or not - but before I did it I drove it around the neighborhood and noticed after corners, hard stops, or bumps it wanted to stall out no matter what I did (like it was low on gas)  I have not put much gas in it anticipating having to drop the tank, BUT

would a module without a pickup screen act like that if the gas level was low?

The biggest thing that worries me is the inability to acclerate normally without it falling on its face from a low rpm -
going around a corner and losing power is definitely from low gas level, but the acceleration thing is driving me nut and I am afraid to drive it in traffic

I mean, you really have to feather the gas and not over accel until you are in a higher rpm
could it be as easy as the pick up screen, or did maybe the pump pick up some trash and is poooping out?

Sincerely,
No Fuel Pump Pressure tester on hand guy

check the fuel pressure, also would be a good idea to replace the fuel filter and yes, you might have had some dirt going in the pump so that should come up on you fuel pressure test if it's the case (you'll need to monitor it when it has the issue so plan for something that can be looked at while driving). if all of that checks out i would also check the fuel injectors. if there are no codes you'll have to eliminate possible causes one at a time or keep trying to replace parts until you hit the jackpot but in this case it is more like gambling unless you know for sure what the cause is.

[carcollector]

well , acouple of days ago it had misfire codes and p0320 (speed signal to distributor)/  I replaced the distributor (has a cam sensor in it), re-ran the codes and got a TPS and P0320 code again.  re-placed the Tps, started it and the same, but did reset computer if that really matters, and returned the part immediately.  Cleaned the Cps and connector, and was the same - replaced Cps and the same ------------

Would fuel pressure dropping off in hard acceleration cause it to trip those codes and back fire through the intake a second later?  I mean the cPS/TPS/Dist/O2 send signals to PCM to advance the timing in that situation and if there was no fuel and the rPMS weren't what they should be, wouldn't the computer have the timing advanced too much?  I do admit it "might" be running a little better, or it is more driveable "mabye" since I cleaned the CPS Harness, but the hesitation/stall/bog on acceleration really sucks

[sharpxmen]

well , acouple of days ago it had misfire codes and p0320 (speed signal to distributor)/  I replaced the distributor (has a cam sensor in it), re-ran the codes and got a TPS and P0320 code again.  re-placed the Tps, started it and the same, but did reset computer if that really matters, and returned the part immediately.  Cleaned the Cps and connector, and was the same - replaced Cps and the same ------------

Would fuel pressure dropping off in hard acceleration cause it to trip those codes and back fire through the intake a second later?  I mean the cPS/TPS/Dist/O2 send signals to PCM to advance the timing in that situation and if there was no fuel and the rPMS weren't what they should be, wouldn't the computer have the timing advanced too much?  I do admit it "might" be running a little better, or it is more driveable "mabye" since I cleaned the CPS Harness, but the hesitation/stall/bog on acceleration really sucks

misfire code wouldn't have anything to do with the cam sensor though. I have to admit that sounds like mine when i had the tps issue, but since you replaced it and was doing the same thing it's hard to think that you got a bad one. one thing i'm thinking is did you at any time had the new crank sensor and the new tps installed on the Jeep - just thinking that it could be the odd 1 in a million case of 2 bad sensors at the same time.

the distributor has no input on the ignition advance, it only distributes the spark to the corresponding cylinder spark plugs. O2 won't influence the ignition advance either (at least from what i know).

[chardrc]

ALSO: I have a clicking/popping noise coming from inside the valve cover - could something in there be causing a problem.  Never heard anything like it, I thought it was the exhaust manifold making the noise. I only hear it after the engine is shut off, and it last for up to 5 minutes.... I am hoping it is just a lifter bleeding down.

i think my jeep does this also.. i always thought it was the exhaust cooling, but when i installed my electric fan i had the jeep in low range 1st gear and when i took the wrench to take off the fan it turned over the engine.. after a few revolutions and stopping i got the same sound as after i turn off the motor and since turning over by hand doesn't create hot exhaust it can't be the exhaust cooling.. but im not being very useful since i haven't found out exactly what it is and how to fix it.

[MYSTANGT]

I HAVE THE SAME ISSUE

mine wont stall but its hard to start, idles a little funny and does drop in rpm after hard stops.

I have replaced the CPS as i had a code for it...NOTHING changed.

I also found out that my throttle body and intake manifold have gasoline all over them!

I ordered injectors and will be replacing them within a day or two and will post the results.

PLEASE keep us updated on your progress. I am MOST concerned if your issue will be resolved after a new pump/filter and fuel pressure regulator.

I decided I will replace all of that if the injectors dont fix up my issue.

WE HAVE TO WORK AGAINST THESE GREMLINS TOGETHER. Keep posting reults and findings & good luck 

[tommy69z]

I have a similar issue with my 97 TJ 2.5 that I just bought...I cleaned the TB and IAC and it cranks and idles better, but I still get an occasional pop back in the intake while slightly accellerating, also, while at cruising speed, it feels as if a cylinder is dropping out losing power, doesn't feel like a miss, just a power loss, if I get on the gas to bring the rpms up it clears up, no engine light has come on yet?

[dwtaylorpdx]

Mine did that all the time when the exhaust manifold was cracked.

Dave

[Eucalypta]

A cracked manifold might be the gremlin we are all looking for; I have the same problem and even though I dont see a leak and due to the fan blowing, cannot feel it either, I do smell some exhaust under the hood.
At cold engine the car runs fine; when warmer and under load (acceleration or climbing a hill) the problem occurs. The engine hicks up, lacks power, seems to be starving and when pushing the throttle it backfires. Idling is ok.
The car ran great, just before a spring lift with skidplate lowering. This might have put some stress on the manifold, making the 16 yo thing to crack.

I also exchanged fuel filter, eliminated the TPS, injectors, etc.
Only fault code I got was the O2 sensor; which would made some sense; it could pick up wrong measurement because the crack is just a few inches before the O2 sensor. So it would not be the cause but the result of the problem.

A friend of mine owns a 4.0 YJ and seems to have similar problem; we exchanged EVERY sensor, tested the fuel pressure, exchanged vacuumlines etc. No sollution.
He also has a minor manifold leak.....

Has anyone had this problem and exchanged the manifold? Did it cure the problem ?

[sharpxmen]

A cracked manifold might be the gremlin we are all looking for; I have the same problem and even though I dont see a leak and due to the fan blowing, cannot feel it either, I do smell some exhaust under the hood.
At cold engine the car runs fine; when warmer and under load (acceleration or climbing a hill) the problem occurs. The engine hicks up, lacks power, seems to be starving and when pushing the throttle it backfires. Idling is ok.
The car ran great, just before a spring lift with skidplate lowering. This might have put some stress on the manifold, making the 16 yo thing to crack.

I also exchanged fuel filter, eliminated the TPS, injectors, etc.
Only fault code I got was the O2 sensor; which would made some sense; it could pick up wrong measurement because the crack is just a few inches before the O2 sensor. So it would not be the cause but the result of the problem.

A friend of mine owns a 4.0 YJ and seems to have similar problem; we exchanged EVERY sensor, tested the fuel pressure, exchanged vacuumlines etc. No sollution.
He also has a minor manifold leak.....

Has anyone had this problem and exchanged the manifold? Did it cure the problem ?

a cracked manifold would give you higher idle unless the crack is close or on the MAP line vac fitting so the reading is inaccurate. In your case it's more likely the cat converter, i replied in your other thread but you didn't mention the exhaust fumes under the hood, but now that you did it makes more sense that you have a plugged cat.