I recently installed an Airdog lift pump (Airdog II 4G DF-100) and since then I’ve experienced varying crank times. Prior to the install, the truck would turn over for maybe 0.5 second before firing right up, every time, without fail. And it feels like half a second is generous on the long side. Since the install, crank times vary between the 0.5sec up to 2 seconds. The engine seems to run a bit smoother since the install and no indication of a misfire. The most noticeable impact of the install is varying cranking times. 
 

From what I’ve read the symptoms could be due to worn injectors or poor fuel pressure but would love to hear the collective thoughts of the crew here. I’m thinking maybe 1 or 2 injectors may be going bad. Could crank duration be affected by which piston is up next in the firing order when an injector is failing? I’m sitting at just over 140k miles and I believe I’m on stock injectors and believe in at the end of their life. Injectors are planed for when I do the quad soon. 
 

We did test the pump, which the newer air dog lift pumps are designed to build pressure and shut off until the engine is cranked. I know and have observed the pump cycling when the key is turned to on, just before cranking.  We tested flow when we installed it by observing the return flow line draining into a bucket while the engine is running, which I admit was weak but the documentation also states the original return line will continue to function as before so volume will be split between the two. The install has been in for some time now and no detectable leaks have been observed. 
 

I don’t have a set of gauges yet. My next upgrade is a quad with fuel pressure, trans temp and egt gauges but life keeps getting in the way of the truck budget.

I've got to ask does the wait to start light come on instantly? Being if the ECM isn't booted up completely and showing a wait to start light cranking times could be long being there is nothing to control the VP44 and make it start. If the ECM isn't booted up then there is no communication to turn on the fuel pump relay which turns on the power for the VP44, then without the ECM there is no communication on the CANBus link to the VP44. Kind of like asking to surf the internet without booting up the computer it doesn't work too good. 

 

Air in the fuel will also cause hard starting too. Suction side leak can draw in small bubbles of air that is compressible and might prevent the injectors from firing. This can come from a few different things like bad o-rings on the injectors, cross over tube o-rings, bad return lines (tee at the rear or banjo bolt seals. Even with modified fuel systems like AirDog with quick connect fittings may leak air at times too. This can be resolved by replacing with the old school JIC push lock connections. 

 

With a bad crank sensor it may or may not start. Most of the ECM and PCM system don't come online till there is valid crank signal. This is part of a safety system so if there was a accident then when the engine stops the pump and fuel supply is cut off for fire protection and safety reasons. The older series like yours where the crank sensor is in the block the sensor doesn't hold up because of temperature changes. As the sensor is heated and cooled it breaks down the HAL effect coil and the magnet inside the sensor till the signal is weak. This is why in the later series the cam sensor was ditch and then crank sensor was moved to the cam location. Less heat and the sensors last much longer without failure. 

Thanks for the info on the crank sensor. It's been a few days since the it was changed and I haven't noticed a delayed start since. When I experienced the cel last week, there was a momentary engine hesitation while driving and ran fine afterwards, which was a 10 min drive home. On the surface it seems the crank sensor could be the culprit of intermittent delayed starts if the sensor can take sometime to fully degrade rather than go out all at once. 

 

I haven't noticed a delayed wait to start light. I just walked out to check and it lights up immediately. I cycled the key several times with the same result. It was the first light to illuminate every time. I will keep an eye out for it, though. 

 

I was wondering the same regarding air in the system. It didn't quite seem to make sense, however, since the AirDog is supposed to significantly decrease the amount of air that reaches the VP44 and the entire system should be positively pressurized, resulting in fuel exiting the system rather than air entering the system. I imagine a damaged o-ring would show a pretty significant leak at these pressures if it were to allow air to enter the system when the engine is off. I could certainly be wrong though. I'm no expert in fluid dynamics. 

 

 

 

  On 10/10/2022 at 3:43 PM, DrJekyll86 said:

I was wondering the same regarding air in the system. It didn't quite seem to make sense, however, since the AirDog is supposed to significantly decrease the amount of air that reaches the VP44 and the entire system should be positively pressurized, resulting in fuel exiting the system rather than air entering the system. I imagine a damaged o-ring would show a pretty significant leak at these pressures if it were to allow air to enter the system when the engine is off. I could certainly be wrong though. I'm no expert in fluid dynamics. 

 

So the common problem is the suction side of the system. All the lines between the pump and the fuel tank can leak while running sucking air in and also while parked and draw air in and drain the fuel lines down. Crossover tubes can leak air in while parked and so can the return line plumbing like the banjo seals at the rear of the head and the tee fitting at the rear of the engine. Then my last one was what I had was bad o-rings on the injectors and it would weep air in and bleed the prime off. As for the suction side you can make sure it has running prime like after a drive and then using the blower side of a shop vacuum pressurize the fuel tank and then have a second person look for moist spots at joints in the suction side.

 

  On 10/10/2022 at 3:43 PM, DrJekyll86 said:

I haven't noticed a delayed wait to start light. I just walked out to check and it lights up immediately. I cycled the key several times with the same result. It was the first light to illuminate every time. I will keep an eye out for it, though. 

Good. The ECM and PCM are most likely fine then.

 

  On 10/10/2022 at 3:43 PM, DrJekyll86 said:

Thanks for the info on the crank sensor. It's been a few days since the it was changed and I haven't noticed a delayed start since. When I experienced the cel last week, there was a momentary engine hesitation while driving and ran fine afterwards, which was a 10 min drive home. On the surface it seems the crank sensor could be the culprit of intermittent delayed starts if the sensor can take sometime to fully degrade rather than go out all at once.

As for the crank sensor. In the basic sense the senor is a small barrel magnet wrapped with thin copper wire. How it functions as a metal tooth comes near the sensor it creates a frequency pulse. Ohm it out will just verify the winding is still good but cant measure the magnet flux and its strength. As metal passes by and the pulse is made the ECM counts the pulse (or frequency) and with a bit of math it can figure out engine RPM. This is why it would be optimal to have a oscilloscope for testing this. Now as for why the sensor fails. I've got to ask one dumb question. Q: How do you destroy a magnet? Well there is physically striking a magnet with a hammer which randomizes the flux in the magnet. The other way is heating and cooling. Most of the problems with the early 24V crank sensors I believe is from the heat cycles on the magnet and the pulses get to weak over time and then ECM calls out the error. This why the cam sensor was ditched and the crank sensor was moved to the gear case where its cooler.