ChevWagons88

I have a 1997 7.4L 454 Chevrolet and it's not starting. It cranks but doesn't fire. It was only starting after a good 15-30sec and would run great! It had been doing this ever since I got it 2 years ago. It was throwing a code P1345. So, I bought a new Crankshaft Position Sensor. I put it in and cleared the code and tried starting it and now it just cranks but never fires. So, I put in the old Crank Sensor to check and now it won't even start with that! Not even after the 15-30 sec. I'm at a loss because I haven't done anything else other than swap out the sensors. Any ideas? Did I fry the computer clearing the code before starting? Is there a learning process for the sensor? Any ideas would be helpful. Thanks guys!

EinST

Welcome to the forum. You may be looking at multiple problems with a vehicle that old. Extended cranking time is usually caused by insufficient fuel pressure. P1345 is not the lack of signal from the CKP sensor (the reason you tried replacing it?) but the correlation between the CKP and CMP sensor signals, often caused by worn distributor gear. Check the fuel pressure, check for actual spark at plugs, and check the distributor, more or less in that order.

oldchevy

When mine cranked for 30 seconds or so, it was the check valve in the fuel pump losing pressure when not running. Rather than change the fuel pump that was running good, I put a check valove in the fuel line. That worked great. Maybe since yours won't start at all now, the fuel pump gave out. I agree the first step would be to check the fuel pressure.

ChevWagons88

Thanks so much for the reply guys. Did some more checking. Not getting spark at plug when cranking and Checked fuel pressure too and it was at 20-30 which seems low - does anyone know what recommended fuel pressure is for a 7.4 engine? Think I'm going to go ahead and drop tank and put in a new fuel sending unit and pump and go ahead and put in a new filter too. Is there any way to check the distributer w/out pulling it?

shamrock246

The pressure should be 56-62psi,the pressure regulator might be an easier thing to try,the no spark could be a bad coil or ICM on the back of the upper intake manifold