I changed the fuel pressure regulator yesterday in my 2001 Blazer LS 4.3 4WD. When I started it up it idled about 2500 rpm. I let it run a few seconds and shut it off. I then restarted it and got the same thing with the service engine light now on. I let it run about 2 min thinking it may settle down, but no luck. When I turned the key off it kind of shook a few times like it was still trying to run. When I checked the code it was P122 TPS low voltage. When I checked the connector I hadn't plugged that one back in. After plugging it in I got in and turned the key and got a "Thunk". I pulled 2 plugs I could get to and they were bone dry. I had a friend with a lift change them for me last time but before I pay to tow it there I was wondering if it may have hydrolocked when it ran a bit after turning it off last time? Edit: I was just wondering if it could have sucked excess fuel into the cylinders when it was still chugging after I turned the key off. Should I try to manually crank the engine with some of the plugs still in ? Due to arthritis and back problems I just can't get to some of the plugs here in my driveway. Could running the engine with The Throttle Position Sensor unplugged damage something ?

 

After you addressed the cause of the P122, did the "thunk" set a new DTC code (such as "random misfire") and turn on the service engine light again? I'm going for the diagnostic approach.

 

I could not start the engine again to get any codes. It acts like it is locked up. When i turn the key there is one clunk sound but no spin. I did put my code reader on with the key in on position, but there were no codes stored since I had cleared the last one.

 

I experienced hydrolock on my 1996 Blazer LS, 2WD, 4.3 L. I am hoping my experience might help you decide if you want to turn the engine manually. In my case the fuel pressure regulator leaked fuel into the intake manifold for cylinder 5 and locked that cylinder. When I tried to start it, it went "clunk". Here are my notes: "Removing spark plugs to turn crankcase by hand. With all plugs in it is very hard to turn the crank case pulley, but I could move it just a little. After removing plugs 2, 4 and 6, it is no easier to turn. When I took out #5 plug, the gas poured out of the spark plug hole. After #5 plug was out I could turn the crank with moderate force and even more gas came out."

So without removing any spark plugs, you could likely make a definitive test of whether your vehicle is hydrolocked by how hard it is to turn the crank pulley manually and decide what to do on that basis. If you have to put so much torque on the crankcase pulley that it gets scary (like 90 ft. lb. lug nut torque) to move it very little, I would conclude it is hydrolocked. If it turns through the cylinders with moderate force, then it is not hydrolocked.

 

I went out and pulled plug 5 and gas came out and motor turned. It's to dark tonight but I'll try to get to others tomorrow if I can and leave a followup. Thanks cal_redwood.

 

Just FYI to help you out; if #3 plug is going to be pulled, best trick is to unbolt the steering shaft from the coupler, push/pull the steering shaft towards the steering wheel just enough to be able to move the shaft out of the way of #3 plug.

The steering shaft only bolts one way so no problem with doing this.

 

LannyL81, I am very glad to know this since I have dealt with plug #3 several times the hard way.

 

Okay ,so I pulled all the plugs but 1 and 3. 6 had a little fuel in it but not as much as 5. 2 and 4 were dry. I could turn the motor by hand. I left the plugs out for about an hour to maybe help evaporate any fuel in there. I changed the oil and filter then reinstalled plugs after checking the gap. I turned the key about 3 seconds it spun over fine but didn't fire. I pushed pedal to floor in case it was flooded. It spun over but didn't fire. I tried a third time and got a "clunk". Now it's locked up again.

 

Checking fuel pressure and leakdown will tell you if there are any leaks in the fuel lines in the plenum, fuel injectors, fuel pressure regulator, or poppet valves. You'll need to check it at the service port next to the distributor, and at the fuel filter outlet.

If crossfire inside the distributor cap is excessive, it's quite possible for the ignition to "fight" the engine and not allow it to turn over. To see if this is the problem: Disconnect the electrical connector at the ignition coil, (not the coil wire) and see if the starter will turn the engine over.

 

I second Captain Hook's diagnostic plan. More specifically, I suspect that your fuel pressure regulator, which you just installed, is leaking fuel into cylinders 5 and 6. If your 4.3 L engine is the same as mine, the intakes for these cylinders are on either side of the back of the engine right under the fuel pressure regulator, which is installed on the rear end of the SCFI spider injector. Did you remove the old tiny o-ring before putting in the new pressure regulator or did it come off when you pulled the old one out? Are you sure the fuel pressure regulator installation clip is facing the right direction (it is not reversible) and properly seated on the injector and regulator? If the new regulator came apart, did you put it back together in the correct order? Did you put clean engine oil on the new o-rings?

On my vehicle you can install the fuel tubes that go into the top of the injector before putting the plenum back on, turn on the fuel pump, and check for fuel pressure regulator leaks visually before putting the plenum back on.