Help Diag, Crank no start post Headgasket repair.

2010 Toyota Tacoma I4 2.7 RWD

Hello all, I'm new here and don't personally drive the truck in question often, it's a company vehicle that has been very well loved, as in driven a LOT with minimal maintenance.

To begin, the backstory is that the truck has 200,000 or so miles, and would have a terrible misfire on startup for ~30 seconds. Attempts to fix this involved new NGK spark plugs, new coils, and a new battery. There was a misfire code present, (along with the ever present ABS and TCM light which I cannot seem to clear, even after installing some new wheel speed sensors and trying a relearn procedure.)

Seeing how much coolant the truck was consuming, along with the state of the coolant overflow reservoir, along with several posts on this forum that described the exact same issue I decided it was most likely a head gasket issue, with a slow leak filling one cylinder partially.

A coworker and I did the head gasket job, with the use of a lot of RockAuto parts, we replaced the timing chain, as well as the exhaust cam sprocket, the drive sprocket for both timing and balance chains, as well as all associated chain guides. The infamous coolant bypass tube was replaced at this time as well with a Toyota factory stainless steel alternative. The head was sent to a machine shop, decked and the valves were all checked for sealing. It came back without needing the valves done. Reinstalling the head we used new head bolts as well. The water pump, thermostat and various gaskets were all replaced while the front cover was off as well.

Since the truck has been put back together in its entirety however, I cannot get it to start. It will crank healthily, and build oil pressure but not send fuel. The fuel pump works, and with the relay removed and the two wires jumped with a paperclip we were able to get the fuel pump to prime the system. Even with the fuel pump jumped in such a way the truck would not start.

I have not tested for spark yet, as I believe it is not sparking, as the fuel pump and ignition would kick on together. (I believe.)

Currently for troubleshooting I have checked all fuses and relays both in cab and in engine bay. I have checked and reconnected nearly all of the sensors in the engine bay. I believe they are all connected properly, as the harness makes it very easy to tell what goes where exactly.

My current thoughts are that something is wrong in the wiring such that the ECU doesn't see the crank sensor activating and therefore is not priming the fuel pump. I have tested the 3 wire lead to the crank sensor and found some interesting results. From research it should have a common ground, a 12v power supply and the third wire would be a signal wire. In testing I've found that with IGN on the 12v and the signal are both getting 8v, and the ground loses it's ground connection. with ign off, I have found that the 12v and ground are continuous, which is absolutely baffling me. When the ECU is unplugged the continuity disappears.

Does this signal a fault in my ECU? the battery was the very first thing to be removed in the head gasket job and I've not arced or done any questionable wiring.

Thank you for reading through this huge post.

 

Not sure where the voltage is coming from (I don't believe there's a bias voltage, at least the 4.0L doesn't have a bias voltage on them), both the crank and cam sensors on the 2.7L are variable reluctance type and generate their own signal.

The ground (Pin 3 Brown) is wrapped around the signal wires and is just there for shielding/noise reduction, Pin 2 (Green) is the Cam & Crank signal ground (NE-) and Pin 3 (Red) (NE+) is the Crank sensor signal.
On the Cam Sensor Pin 2 (Green) is the signal ground and Pin 2 (Blue) is the Cams Sensor signal.

A scope is required to see the actual signals but are you sure you didn't swap a connector somewhere?
Did you get the Crankshaft reluctor wheel installed properly?
Do you have any codes?
Do you have RPM on the scanner while cranking?

Image is what the signals should look like, top line is cam bottom line is crank.

 

Hello, Sorry for the late response. The very first thing I checked was to pull the AC bracket, and pull out the crankshaft sensor, to make sure that the wiring was intact. I also used an inspection camera to look inside the front cover and verify that the crank reluctor wheel was in place. Both of those appear to be fine.

I just went out to the truck. I haven't reinstalled the AC or the Crank sensor yet, so the crank sensor is not even plugged in. When the Truck is cranked the Tachometer spikes to 5,000 RPM.

EDIT: I did some more testing.

I reinstalled the crank sensor, and cranked again, same results, bouncing between 4-6,000 RPM

I also just pulled and tested the camshaft sensor. It appears to be in good working order.

 

It's hard to say, are you 100% sure you have everything connected properly and don't have a connector swapped or grounds missed somewhere?

If that's all good without scoping the signals it's probably gona be a bear to find.

 

I know nothing but does the horn work?

 

I have checked all the connections several times, but I may have to get in the engine bay tomorrow and confirm that those pesky grounds on the back of the head are securely fastened. Thankfully the way Toyota made this harness it doesn't appear I could have swapped a connection.

I can test with a basic multimeter to insure that everything is well grounded, which I believe it is.

Do you know from which sensor the vehicle reads engine RPM?

EDIT: Yes the horn does work. Is this relevant?

 

Most engines use the crank sensor, I'm not sure about Toyota. I believe it needs both to start but I could be wrong, I don't have a 2.7l to experiment on mines a V6.

 

So if I am getting the same Tachometer results with the crankshaft sensor installed and uninstalled I believe that this would point to either crankshaft sensor failure, reluctor failure, or some issue with the harness wiring between the sensor and ECU?

 

With the repairs that were done my suspicion would be a pinched harness or something that wasn't connected properly but without seeing it myself it's a hard one to guess at.
What if you unplug both the cam and crank sensors does the tach still act goofy?

 

I just tested. Both crankshaft and camshaft sensor unplugged, and the tachometer moves just the same.

 

Have you verified with a scanner that the engine RPM in scan data matches what the tach is doing?

If it does I would have to believe something isn't connected properly somewhere, a harness is pinched or broken, or a ground got left off or is broken somewhere.
Without putting my hands on it that's all I got.

 

I just tried my basic Bluetooth code reader Torque app tool, I wasn't to get codes with a semi-professional 0bd2 scanner earlier, and was not able to get information with the Bluetooth obd2 reader. What is interesting is that with the key in the ignition switched to ON, they RPMs would occasionally fluctuate up to 2,000 or so and back down without any inputs.

EDIT: The buzzing sound is coming from the EFI relay in the fusebox.

 

That really sounds like a main ground or power is not connected.
Here's the location of all the ground points in the engine bay. Triangles are grounds, rectangles are harness connectors.
Also check your main block and body grounds from the battery.

 

Thank you very much for the diagrams and direction. Will print this out and proceed. Hopefully the rain can stay away for a few more days.

EDIT: I just used a jumper cable attached the battery ground to try to add a large amount of extra grounding, - no change.

Could you possibly show me a zoomed in picture of what connector EF1 is? I don't see something that corresponds to that one in the bay.

 

I don’t know if this will help.
But it’s all I got as for what it looks like.

 

Anymore Input anyone? I am at an impasse. I have tested and everything appears to be well grounded. Any off the wall ideas?

 

I have a 2005 and I admire you for attacking a head gasket problem.
I expect mine to give it up, in that I have 140K on the truck and that is the mileage that it has been know to fail in that years model.
I have done much work on cars and trucks and have gotten into the engine on many, but the head gasket job on these things is daunting.
It would cost about 3K for the dealer to do it, but they told me they have done it before with good results. At the cost of new or used trucks today, I would probably opt to have it done at the expense of my ego.
Good luck in finding your problem.

 

Have you checked powers and grounds at the ECM?

Key on ECM plugged in.
Powers:
E8 Pin 1 (Black)
E8 Pin 3 (Blue)
E8 Pin 7 (Light Green)
E8 Pin 9 (Beige)

Grounds:
E4 Pin 3 (Brown)
E4 Pin 6 (White/Black)
E4 Pin 7 (White Black)
E4 Pin 28 (Brown)
E5 Pin 3 (White/Black)
E5 Pin 4 (White/Black)
E5 Pin 7 (White/Black)
E5 Pin 22 (White/Black)

 

ECU's rarely fail.

This is likely error somewhere along the line.

Is it possible the crank tone ring is installed backwards or forgotten?

We don't have many 2.7s up in Canada so I have limited experience with them.

Checking for spark will show if the ECU is getting a crank/cam signal.

 

I thought this too at first but then the OP posted this little detail and I started suspecting a power, ground, or shorted wire issue.