Square Peg Round Hole

I get a call from a shop that uses me regularly. He has this 2002 Jeep Liberty with 127,629 miles with a 3.7 Liter motor. He just swapped a salvaged motor in it and now it doesn't start. This shop does a lot of motor swapping. Every time I go to this shop there seems to be some type of motor being swung in and out. I arrive at the shop and do a quick visual on the installation. I crank the vehicle over and it doesn't start at all. Not even an attempt. Where to start.

I decide to start with making sure we have the right PCM in the vehicle. This is a shot of the module info with the DRB-3 scan tool.  Looks good so far. Notice that this is a JTEC controller. This will be important later on. I also looked at my scanned KOEO values and all looked normal. I checked my scanned crank sensor and cam sensor values while cranking and they were erratic. I really don't trust scanned values for crank and cam signals. I want to see them in real time.

I quickly identify the correct pins at the PCM for crank and cam sensors with my service information and setup my scope. I give it a crank.

Here we have crank sensor in yellow and cam sensor in green. We have nice clean transitions on both sensors. But, something seems odd to me. Let me zoom out a bit.

Hmm. I have seen this waveform many times but not a 2002 vehicle. This is where having a known good waveform library comes in handy. I know that I have a known good waveform from a 2002 Jeep Liberty 3.7 Liter in my library. Let's pull it up.

Here again crank sensor in yellow and cam sensor in green. This pattern differs greatly on both crank and cam of my no start Jeep. I am starting to realize what happened here. The pattern I am getting from my no start Jeep is a NGC controller pattern not a JTEC controller pattern. Lets look at them together.

Top pattern is our no start and bottom is my library pattern. NGC controllers didn't come out until 2004 for the most part. So now I ask the hard question. Hey, what year vehicle did this salvage motor come out of? There are a lot of blank looks at this point. Apparently, the salvage yard sold him a later model motor. Well can't we just swap some parts?

Well it is not that easy. The crank trigger wheel is bolted to the crankshaft and then we have the camshaft trigger wheel also to deal with as well. The salvage yard probably had good intentions in selling the shop a later model motor. However, in the long run it was the wrong decision. A correct year motor is the proper answer here.

I will be featuring some more "Frankenstein" vehicles as I like to call them in upcoming posts. I have a ton of them.

I will also be featuring some Pico scope and scope in general posts as well. My buddy Carlos at Aeswave gave me that suggestion and I am only too happy to oblige. Again, I can never say enough about Aeswave.com. They are excellent.

Since purchasing a Pico scope and becoming an "Autonerd" I have to say I have had some great customer support and the techs on the Autonerdz forums have been inviting and top notch. You can never have too many people in this business to bounce ideas off, blow off some steam, or to just chat. No one tech knows it all. We all learn something every day. Some of my lessons I would like to forget.

Remember, if anyone has any suggestions or something you would like to see drop me a line.