I Have a 1994 Cadillac STS that I had to swap an engine in. I found an engine out of a 97 elderodo. I thought it would be just a simple swap of the intake, but once I had the engine all bolted up I found out that the heads were different. So my old intake would not work!. So I swapped the throttle bodys and made the new intake work with minor modifacations to the wireing, Really not that big of a deal. Long story short I got it running but at first It would crank but no injector pulse or spark. Then I unpluged one of the crank sensors and it cranked for like five seconds and fired up. Now I can unplug one sensor and and it will run. Plug the other sensor in, it will not run. Unplug the other sensor it will run also. So that means each sensor works fine, but they wont work together. My question, What would cause it to run on one sensor, but not both? Any support would be helpful and much appreciated. Thank You!

 

Car is designed to run off both sensors, you may just have bad sensor. Transfer sensor from to new to you engine and see what happens. If you still have old engine or it has a core and still have it save all the sensors you can as spare/ test parts.

 

I have replaced both sensors from the old engine, and same thing happens. Why would one sensor cancel the other one. If I plug them both in, it is a no start. I have been driving it to see which codes come up. There is a lot. so here's the list.... P013,P017 which are O2's not ready. The two that come on as soon as I clear them are P038 Crankshaft to ignition module failure (because one is unplugged I presume), and P132 Knock sensor connection problem. The others are P047 IPC- pcm data problem, p023 electronic spark timing signal problem, P107 PCM-BCM data link problem, p137 loss of TCS data. Then there is I032, and I052, and I037 which are loss of data codes..., T072 serial data link fault. So my computers aren't talking to eachother. Why would that be.....? My blower motor doesn't work either, could that be somehow connected- I have power and ground at the motor itself, but no signal from the grey and black wire... My guess is all this is why the engine blew up in the first place. The people I bought the car from kept driving it when it was pinging and broke the piston and through a rod. So no mater what I need to resolve this problem!. I don't know when to even begin to start looking. I need to get the computers talking to eachother somehow and I hope I can plug the other sensor back in. It starts hard when its cold like its not getting an injector pulse at first. Thanks for the input!

 

I suggest to check engine grounds. Does it matter which sensor is plugged in?

 

No it is one or the other. but I am starting to think that the instument cluster is going heywire with all the data loss codes. my blower motor works intermittently, and i can plug in the sensor while it is running and it wont die but as soon as you shut it off and try to start again there is no rpm signal.

 

I can only find three grounds and they are all good. at least they ohm out fine. there is one down by the transmission on right side of engine. There's one on the other side by egr. and the battery grounds. Do you know of any more. my Haynes service manual is worthless when it comes to pcm diagrams or engine diagrams. they are none existant.

 

There is one on thetransmission below water pump.Grounds are better checked with Voltmeter or a 12v miniture bulb and socket fab.ed in to a test light. Most 12v test lights sold use 6v bulbs which dont "load" circuit enough to test some circuits. how was engine swapped out the top or bottom?

 

I did it out the top of the car.

 

When codes are cleared, what comes codes reset?...All modules.

 

the crank sensor and the knock sensor come back right away, you have to drive it a ways to have serial data codes.