Hi All,
I just did an engine swap with a newish (64kmi) f23a1 engine from a salvage yard to replace my old f23a1 engine (140Kmi) that unfortunately and surprisingly had poor compression in one of the cylinders.

After the install, I started the engine and it cranked and perpetually fired on the first twist of the key. The engine continued to idle like normal. Upon inspection of the gauge cluster, I noticed the CEL was on. When I played with the throttle it was in some limp mode and limited the revs to about 2950 RPMs. I then drove the limping car 30 miles and stopped at an auto parts store and had the codes checked.

I found P1361 only. I then cleared the code and restarted the engine. The CEL came right on. Upon checking the codes again, I got a P1361 again. I drove again another 60 miles and checked the codes. Again I only got P1361. When I got home, I did some research and found that P1361 is caused by intermittent or absent or noisy top dead center (TDC) sensor signal.

I also checked the timing with a timing light and it was pretty much right on.

So I did some more research on the net and found a diagnostic test for P1361, http://www.justanswer.com/questions/...c-sensor-noise
I did this test and found the TDC sensor to have 2.2KOhms at the 4 prong terminal and also 2.2KOhms at the terminal that connects to the ECM. I also checked for ground shorts per those instructions and none were found.
I wiggled and disconnected and reconnected the terminals something like 5 times. Between each test, I reset the CEL by pulling fuse 13, then restarted the engine, but immediately the CEL would come on (I'm assuming it's the same P1361, I dont have a diagnostic OBD2 tool). I also cleaned the terminals using brake part cleaner to dislodge any non-conductive contaminants but still no luck.

The last thing in that test is to replace the ECM with a known good one and try again.

Since I know this code was not set prior to removal of the original engine, which leads me to believe that the ECM is not bad, and being that I don't want to speed $50 on a replacement ECM that I can't get a refund on (should the code persist), I'm not quite sure what else to do.

Short of replacing the ECM, can anyone suggest another cause for P1361 that I can test and maybe repair?

I don't own a factory (Helm) repair manual and the Chilton I have is practically useless, not to mention I'm running low on cash as it is (losing my job in a few months due to cut backs). I'm savvy with tech stuff (I'm a mechanical engineer and straight up gear head) so I'd appreciate any help I can get.

Thanks for reading my long and hopefully detailed enough rambling...

regards,
Krishna

 

How clean is the front of that engine? TDC sensor is at crank/oilpump, so check if that area is cruddy or maybe metal shavings near the magnetic sensor??

Everybody says the resistance checks for that sensor should ID a bad sensor, but I've always wondered if the sensor can get flaky but still pass the simple resistance checks. Any way to get your hands on an oscilloscope?

 

JimBlake,
Thanks for the reply.

The front of the engine is quite clean. The engine looked prestine when I got it so I doubt that might be a factor. Plus the timing cover was intact w/o any damage.

Since the TDC sensor is only used for start up (right?), do you think this sensor is a hall-effect sensor and not a powered proximity sensor? Hall effect sensors are not powered as opposed to proximity sensors so it might make sense to just use a hall-effect sensor... But if it's a proximity sensor, then it's powered and I would need to test for power, correct?

Does anyone know if the TDC sensor is powered? If so, how do I test it for power?

Jim, my other next thought was to get an oscilloscope. I don't have one, but I'll see if I can borrow one from work (probably not likely to happen). That should tell me if I'm getting a signal when the car is running.

In that link I provided, the ECM connector 31, pin 8, what does that do? Where does it go?

Thanks again.

 

I don't think it's hall-effect. I think it's magnetic proximity. But I don't know what the signal SHOULD look like. Perhaps it generates a low-V signal as the toothed-wheel passes by the sensor. Got a meter that can respond fast? Analog meter needle might wobble, but cheap-ish digital DMM probably can't respond fast enough.

The writing style & the pictures in that link look like they're taken right out of the Helm book. I don't have the '98 Helm book any more (sold it after I sold that car). Somewhere I might have the ECU pin-outs, but not here & now. I'll try to remember to look. The notation "31P" just means it's a 31-pin connector. It's the ECU plug "C" so that wire would be called "C-8" in most pin-out charts.

 

D'oh... it says what it is right there...

CKPP = CKP sensor (crank position) positive signal

 

Ok. so by that reasoning, TDCP = top dead center positive, right?...
So If the engine is running and i measure the voltage between this pin (TDCP) and the ground, I should get a 5 or 10v square wave right? Or does positive signal just mean that's the power supplied to the sensor?

What is TDCM? M=? Or is the this where the supplied voltage comes in?

And the sensor is grounded in the engine via the bolt?

 

Not sure about that stuff. It might not be a very clean square wave, it might just be looking for zero-crossings.

TDCM I don't know what the "M" stands for. That was never clear in the Helm book, but I always assumed it was the ground side of that sensor. I suspect it's not grounded thu it's mounting bolt, but has a ground leg in the wiring harness.

Try to back-probe those plugs. Be careful before you strip any wires (to measure in-place). I think some of those sensor wires are shielded.

 

I want to close this thread out since I resolved the problem.

The resistance of the TDC sensor is in spec. The next thing to replace was the ECU. However, I resisted following the troubleshooting guide and followed my gut feeling and replaced the TDC sensor since I had one lying around and the only thing I had to lose was time spent working as opposed to buying and ECU and getting it programmed.

So, after 3 hours of working, I replaced the TDC sensor, reset the codes by pulling fuse 13. Drove the car for 60 miles, no codes so far!!! The broken sensor that I removed looked brand new and clean!!! What a surprise!

Moral of the story: troubleshooting guides aren't always right. And the ECU rarely goes bad. Just because the sensor passes the ohm test, doesn't mean that it's working. I also doubt that some dirt covering it will cause it to fail unless it is covered in ferrous/magnetic particles.

On a side note, I didn't get ahold an an oscilloscope until today, after the repair, but as some engineering tech feedback, I'll update you guys on what the signal should look like in case someone else wants to know.

Thanks for the help Jim.

 

I'll be interested to know what those signals look like. I feel kinda vindicated in my belief that a bad sensor can pass the resistance check. Maybe low probability, but it IS possible.

ABS wheel sensors are similar too, and THOSE can probably gather iron dust from brake rotors.

We appreciate you coming back with information after you get your car fixed. That helps the next guy who finds this thread.