Rebuilt engine installed truck wont start

My shop put in a rebuilt engine from a well known rebuilder who I will not mention. After getting everything installed the engine will not fire. The scanner reveals that I have no crank signal. No RPM during cranking.

I checked the crank sensor 5 volt reference is there from the ECM. I have a good ground and I hooked up a scope and graphed the crank sensor while cranking at the ECM. I have a good crank signal saw tooth pattern on the scope.

I was told to replace the ECM. Replaced and reprogrammed, no crank signal. Replaced crank sensor, engine harness, and ignition module. Still no crank sensor.

Isuzu is not much help in the situation. They feel that the replacement engine is the problem. They feel that the reluctor wheel that the crank sensor reads is either incorrect or in the wrong position and the ECM cannot interpret the sensor signal.

Anyone have any ideas???

2000 trooper 3.5liter

Maybe the timing belt is out of alignment?

Doubtful.

I dont think the computer cares if the timing belt is aligned correctly or not. The computer is getting a crank signal to the ECM but is not recognizing it.

Isuzu as well as other Isuzu techs that I have spoke with feel that the problem is with the aftermarket engine. I looked in the parts catalog and there is only one crank for the 3.5 liter engine but there are several for the 3.2. Since the 3.2 and 3.5 are identical except for the stroke length it is possible that the incorrect crankshaft was installed by the rebuilder.

Its not what I want to hear either but....

At any rate, whatever I find out I will let you all know so that no one else runs into a similar situation.

to clarify: are you saying the engine is cranking, i.e. turning over, or are you saying the engine is not cranking, i.e. engine is not turning over?


//bc

Cranking meaning turning over.

I have a good sawtooth pattern coming from the crank sensor at the ECM using a scope.

I was told that the cam sensor does not have to be functioning for the vehicle to start and run, it will just set an MIL.

I believe the vehicle would run without it but may not restart. I tried to graph the Cam sensor yesterday and am not getting a signal. Perhaps I have a bad cam sensor. I have had them short and rob the 5 volt reference from the crank sensor causing a no start condition but nothing like this.

I found out the problem in case anyone was interested. The engine that I was sent for this application is incorrect. The crankshaft in this engine does not have the correct number of teeth on the reluctor wheel for the crankshaft sensor to see.

The ECM counts the number of teeth to determine #1 and cannot do this due to the fact that there are not enough teeth.

Isuzu states that they have seen this problem frequently.

I was going to mention that but there is no need now it has happened to me

thanks for the followup...
so did isuzu say: is there anyway to check this before installing?
2eye: how do you check it?


thanks //bc

Here is how I found out we have a crank issue.

I pulled the crank sensor out of the block and left it connected to the wiring. Then I unplugged all the coils, I wasnt sure how or if this would even work without catastrophic consequences.

I took my air drill and grounded it to the battery with a jumper wire, not sure if this would matter or not but it made sense to me and this isnt exactly scientific.

I installed a NOID light to one of the injectors and then ran the drill at varying speeds while holding the crank sensor close to the drill chuck. The chuck breaks up the magnetic field and causes the ECM to think the engine is cranking. The NOID light would light and then off. It was difficult to get it to do this frequently because I am holding the drill in one hand and the crank in the other and trying to bring the two as close to each other as possible without actually touching.

I also watch the Ms of the injectors to make sure the injectors were indeed firing.

We determined that either the wheel has the incorrect number of teeth, is damaged or the crank sensor is not close enough to the wheel on the crank.

I attempted to shave the mounting of the crank sensor to bring it closer to the crank. I did a few thousandths at a time. At one point I had a crank signal on the scanner and then it went away, I thought I was getting close. I also grounf the paint off the block but I did not want to push it for fear of damaging something further.

I WILL NOT be using aftermarket engines ever again. This is my second bad exp. with the same company, not to say that there product is not what it should be, I dont know but I have not had good luck with them. Maybe they need to work on QC. Maybe I need a horseshoe over the toolbox.

thanks for the followup...
so did isuzu say: is there anyway to check this before installing?
2eye: how do you check it?


thanks //bc

I dont believe there is a way to check it. My understanding is one crank design had 6 large teeth the other had 58 small teeth. I suppose you could look in the crank hole and turn the engine and count the teeth, that maybe difficult with 58 teeth to count and no way to mark where you started especially with it already in the vehicle.

I was unable to find a crank sensor to reluctor gap spec in service manuals, I am sure the engineers would know this, but I did not think to ask them.