Just got my new setup in the car and I'm having some problems. The motor is a forged 347 with a TH400 trans. The motor ran great at first, I went out driving to put some miles on the new motor and it started to miss and breakup in the 3000-4000 range so I stopped got some gas and it didn't want to go anywhere. The missing and breaking up went down low in the rpms the tach in the dash stop working. So I towed it home. My HPtuners was showing a P0336 - Crankshaft position {CKP} senser performance code. I replaced the senser and plugs, the motor came back alive and was running great. Took it out and 5 miles later the same thing happened again. I don't know what to do I checked all the wiring over and over again the grounds are good. I put a third one in and same thing sitting in my drive way, it seems like when ever the motor get to a nice operating temp the CKP goes out but when I let the motor cool all the way down it starts working again and the motor runs great. What do you guys think I'm stumped??????????????????????

 

did you do the relearn procedure? you might have to take it to a shop with the software that can do it. im not sure if HPTuners can do it.
also, pull the CKP out and look at the reluctor ring while some one turns the motor over BY HAND!!!!! the ring might be fucked up. also check the sensor itself for metal shaving and/or damage

 

I did the relearn, HP tuners can do it. The sensor is clean when I pull it out. And as far as veiwing the reluctor ring it's to tight to see in the hole. I don't know, it runs so good intill it gets hot then it throw the code sumbles and misses all over the place. Still stumped?

 

how big is the hole for the sensor? are you able to stick your finger in there and feel the ring?

 

Yes but I haven't had a second person to turn the motor over while i feel it. If the reluctor ring was bad why does it run so good at first?

 

I will move this over to internal engine. I think that there might be additional info to be picked up over there.

 

If it runs crappy when it gets hot I would start to think the PCM going into closed loop is the problem. Then again, it might be a PCM ground or something like that. Could also be a bad primary ground from the battery to the frame and so forth.

 

I can't be a ground problem, I added 2 ground straps to the motor and one to the frame. As far as the PCM goes I've tried a different pcm and it does the same thing. Both pcms metered the same way for voltage going to the crank position sensor.

 

The crank position sensors are going bad. Some of them will start working for a short time when the motor cools down, but after it goes out a few times, it dies for good.

 

Is can I check the sensor with a multi meter? I checked the voltage going to the sensor with my computer in, then I put a different computer in and it metered the same.

 

Ok, you have a 12V feed going into the sensor. Pin B on the sensor should be a ground (actually a low reference but it's basically a ground). Also, something just came to mind being you have a new motor. Sometimes the Crank sensor has to be shimmed out alittle on the older SBCs with SFI injection. I imagine an LS1 can have the same problem. Has the sensor been chewed up any??? If so you need to shim it out. If not it might be sitting too far off and when the block gets hot from the engine running it pushes the tolerances out because aluminum expands. I highly doubt this is the problem but it seems possible. If it is indeed a sensor mounting boss problem then I would talk to the motor manufacture about it. The sensor puts out a digital square waveform for tach ignition ect ect. I'd make for certain sure all your wires and connections are good. If not then I'd start looking at the motor itself. Is the block of the motor new or is a rebuilt core motor???

 

The sensors have no damage to them at all and I tried shimming it out alittle just to try and it made it not start at all. The block and crank are OEM. I just had some forged parts put in.

 

It seems that it's not the sensors but a heat problem every time the motor get hot it throws the crank sensor performace code. When the motor cools down it runs great again. What do you think? I replaced the wires going from the ECU to the crank sensor, I use 16ga wire. Still the same thing.

 

Ok, let me ask this then. Has this particular block ever run correctly in your vehicle prior to the forged component installation? If there is too much meat on the mounting bosses for the CPS then when the aluminum block grows from the heat of it running then this could happen.

 

This is the OEM block it ran great for over 100,000 miles. Nothing has changed between the block and the crank. Both are OEM. I just had pistons, rods, cam, and heads put in.

 

Ok, if it isn't that then it's perhaps the crank reluctor wheel. Can't think of anything else if you've covered grounds, sensors, PCM, and the wiring.

 

But why would the car run so good if the crank reluctor wheel was off?

 

Man I feel your pain...talk about a f'ed up problem to be dealing with...if you find the answer I'd love to hear it..

 

Ya it really suck this is 3 weeks I've been fighting this problem. Nobody knows what to say when I tell them whats going on.

 

• The following conditions may cause this DTC to set:

- Poor connections: Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

- Crankshaft reluctor wheel damage or improper installation.

- The sensor coming in contact with the reluctor wheel.

- The engine running out of fuel.

- If the crankshaft rotates backwards, this DTC will set. This condition is only with vehicles equipped with a manual transmission. This condition can occur when a vehicle is on an incline and the clutch is released and an engine stall occurs.

• Excess crankshaft end play causes the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. This could result in any one of the following:

- A no start

- A start and stall

- Erratic performance

• Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.