1997 C1500 hydrolocked after MPFI

[Tataocb]

I bought a 97 C1500 with a 305 with 160k miles a couple months ago. It had a code for running rich and multiple misfires. I replaced O2 sensors, plugs, wires, dist rotor and cap and still got the code. The truck would stumble a bit when idling and have a hard time starting when hot, but was driveable. For example if I drove 15 min to the store, went in, came back out 10 min later, it would take a bit of cranking before it started. I would get the multiple misfire code and at one point got a cyl 5 misfire code.
I plugged in a Bluetooth odb2 scanner and looked at fuel trim on my iPad and short term was at -30 on both banks. Long term was about -17. So I decided to replace the injectors with an MPFI system. When I took off the upper intake it looked like the regulator was bad because the runner right below it looked clean while the rest had carbon buildup. I installed the new MPFI spider, reinstalled everything and it fired up fine. I had it running for a couple of min and went inside to get the iPad. When I came out the engine had shut off on its own.
I tried cranking but it would not crank. I spun the engine manually and it was a bit hard to turn, but got it turning. Then tried to start again and it cranked for 2 seconds, then came to a stop and would not crank anymore so I thought it was hydrolocked.
I took out all the spark plugs and spun the engine by hand and fuel came pouring out of cyl 5. The spark plug was wet as well. I then primed the system a few times, turned by hand again and got the same result, fuel poured out of the cyl.
I then unplugged the master injector connector (big single plug that goes to the spider) to check if any of the wiring was going to ground, but it seems that is not the case. I removed the fuel pump relay and turned the switch to On when I did the test. Each injector connector has two pins, for each pair, only one pin lights up the test light which is connected to battery +. So that leads me to believe the signal it gets from the ECM is correct.
With the master injector connector still unplugged, I put the fuel relay back in and primed the system a few times. I spun the engine by hand and fuel poured out again.
That leads me to believe the new injector is stuck open because with the big connector unplugged, it is not getting a signal from the ECM, and yet when I prime the system, it still dumps the fuel into the cylinder.
I was pretty set on thinking it was a bad ECM or bad wiring going to cyl 5 since even with the old/stock injectors, it threw a cyl 5 misfire code. I thought maybe the amount of fuel it dumped was just not enough to hydrolock the engine, because I was still able to drive the truck. But the fact that it dumps fuel with the master injector plug disconnected seems to point to a bad injector.
I wanted to get some opinions before going back and removing the upper intake again since it is a bit time consuming. Are there any other tests I should run to confirm/diagnose?

 

[someotherguy]

Sounds like time to pull the upper intake and swap #5 with another one to see if the problem follows it or not.

Richard

 

[stutaeng]

It does seem like the injectior is stuck open.

Only way to test is do a injector balance test...

Have you hooked up a fuel pressure gauge? I would imagine all the pressure gest lost if the faulty injector is stuck open. I would do this before even doing the injector balance test, since you kinda already found the bad injector...but wouldn't hurt.

I would probably open the plenum to do a visual.

Careful on cranking a hydrolocked engine. You can bend a rod because fluids don't compress.

 

[Tataocb]

Thanks for the suggestions. It sounds like there is not much testing left to be done without removing the upper intake.

@stutaeng - I did not know there was a risk of bending a rod. Now I am worried since I was not there when the engine shut off. I don’t know if it made a weird sound or anything. I apparently was able to manually spin the engine past the position where it was getting stuck apparently. It got really hard to turn the ratchet, but it did go through. I still can’t explain how that could have happened u less the fuel was pushed back through the injector or it got past the rings. Is there a way to check for a bent rod or I’d have to wait until I fix it and get it running and listen for strange noises?

 

[stutaeng]

Not an expert by any means on this...but maybe you can remove all the spark plugs and try spinning by hand. Without the plugs the engine should spin freely,by hand or by cranking via the starter.

I suppose you can stick the little blade for determining depth on a dial calipers and see if you get consistent readings to TDC for each cylinder? Actually, just compare the one with the fuel in it to the adjacent one. That's probably all you need. That shouldn't take too much, especially since you will be removing the upper plenum on the intake.

 

[TheRabbitChaser]

I bought a 97 C1500 with a 305 with 160k miles a couple months ago. It had a code for running rich and multiple misfires. I replaced O2 sensors, plugs, wires, dist rotor and cap and still got the code. The truck would stumble a bit when idling and have a hard time starting when hot, but was driveable. For example if I drove 15 min to the store, went in, came back out 10 min later, it would take a bit of cranking before it started. I would get the multiple misfire code and at one point got a cyl 5 misfire code.
I plugged in a Bluetooth odb2 scanner and looked at fuel trim on my iPad and short term was at -30 on both banks. Long term was about -17. So I decided to replace the injectors with an MPFI system. When I took off the upper intake it looked like the regulator was bad because the runner right below it looked clean while the rest had carbon buildup. I installed the new MPFI spider, reinstalled everything and it fired up fine. I had it running for a couple of min and went inside to get the iPad. When I came out the engine had shut off on its own.
I tried cranking but it would not crank. I spun the engine manually and it was a bit hard to turn, but got it turning. Then tried to start again and it cranked for 2 seconds, then came to a stop and would not crank anymore so I thought it was hydrolocked.
I took out all the spark plugs and spun the engine by hand and fuel came pouring out of cyl 5. The spark plug was wet as well. I then primed the system a few times, turned by hand again and got the same result, fuel poured out of the cyl.
I then unplugged the master injector connector (big single plug that goes to the spider) to check if any of the wiring was going to ground, but it seems that is not the case. I removed the fuel pump relay and turned the switch to On when I did the test. Each injector connector has two pins, for each pair, only one pin lights up the test light which is connected to battery +. So that leads me to believe the signal it gets from the ECM is correct.
With the master injector connector still unplugged, I put the fuel relay back in and primed the system a few times. I spun the engine by hand and fuel poured out again.
That leads me to believe the new injector is stuck open because with the big connector unplugged, it is not getting a signal from the ECM, and yet when I prime the system, it still dumps the fuel into the cylinder.
I was pretty set on thinking it was a bad ECM or bad wiring going to cyl 5 since even with the old/stock injectors, it threw a cyl 5 misfire code. I thought maybe the amount of fuel it dumped was just not enough to hydrolock the engine, because I was still able to drive the truck. But the fact that it dumps fuel with the master injector plug disconnected seems to point to a bad injector.
I wanted to get some opinions before going back and removing the upper intake again since it is a bit time consuming. Are there any other tests I should run to confirm/diagnose?

I would pull upper intake, unplug your coil an leave the fuel pump relay installed but have the fuel injector assembly disconnected at the main spider plug , take the injectors nozzles out of the lower plenum have a helper crank the engine with the key observe to see any of the injectors leak under pressure.

 

[Tataocb]

I pulled the upper intake again, reconnected the fuel lines to the spider assembly, turned the key to prime the system and it ended up being a bad pressure regulator on the new assembly. As soon as it primed it poured fuel out the regulator and directly to the runner below it which I assume goes to the number 5 cylinder. I turned the engine by hand to flush out the fuel.
I replaced the regulator, primed it again 3 or 4 times, nothing came out of the regulator, tinted the engine again by hand and nothing came out either so I assume I should be good to go.
I started putting everything back together but had to stop as it was getting dark and the truck is in my driveway. I will finish up putting it together and post my results.
I have attached a screenshot from a video I took of the regulator dumping the fuel when the system was being primed.

 

[GoToGuy]

What brand upgrade did get?

 

[stutaeng]

I pulled the upper intake again, reconnected the fuel lines to the spider assembly, turned the key to prime the system and it ended up being a bad pressure regulator on the new assembly. As soon as it primed it poured fuel out the regulator and directly to the runner below it which I assume goes to the number 5 cylinder. I turned the engine by hand to flush out the fuel.
I replaced the regulator, primed it again 3 or 4 times, nothing came out of the regulator, tinted the engine again by hand and nothing came out either so I assume I should be good to go.
I started putting everything back together but had to stop as it was getting dark and the truck is in my driveway. I will finish up putting it together and post my results.
I have attached a screenshot from a video I took of the regulator dumping the fuel when the system was being primed.

WOW! That's an epic failure!
All too often I see fuel pumps getting loaded as the first parts cannon, without even hooking up a pressure gauge! The injectors and FPR are not too often considered as culprits on these trucks... probably because they are hidden down there. Out of sight out of mind!

You did good diagnosis!

 

[someotherguy]

I pulled the upper intake again, reconnected the fuel lines to the spider assembly, turned the key to prime the system and it ended up being a bad pressure regulator on the new assembly. As soon as it primed it poured fuel out the regulator and directly to the runner below it which I assume goes to the number 5 cylinder. I turned the engine by hand to flush out the fuel.
I replaced the regulator, primed it again 3 or 4 times, nothing came out of the regulator, tinted the engine again by hand and nothing came out either so I assume I should be good to go.
I started putting everything back together but had to stop as it was getting dark and the truck is in my driveway. I will finish up putting it together and post my results.
I have attached a screenshot from a video I took of the regulator dumping the fuel when the system was being primed.

Good catch; sometimes you gotta just open it back up and see what's going on.

As they warned you earlier, that fuel in there can cause major problems. Not only bend rods, but also dilute the oil enough you'll cause some significant engine wear. So crank it with the plugs out AND coil disconnected from the power supply - you don't want any stray spark igniting the fuel blowing out of the cylinder; you'll want a fire extinguisher nearby anyway in case any ignition source (think - spark from the starter motor/solenoid) decides to set off the vapors. Once the cylinders are clear of any excess liquid fuel, change your oil!

Richard