I just bought a 98 blazer that had a cold start issue. I replaced the fuel pump and it started right up but was running rich and I could smell gas in the oil. I removed the throttle body and could see that the left bank was clean so I repalced the injection. Now it runs great until I shut it off. For about 10 minutes it will start back up run fine. after that it wont start for another 10-15 minutes. During that time fuel pressure is 65 psi and spark is good but it has no injector pulse. Then it starts back up and runs great. I changed the ignition module and it does the same thing. Could the crank or cam sensor cause no injector pulse but still have spark? Any help would be greatly apreciated.

 

Does the SES light come on, and then go off, when you initially turn the ignition on?
Does the SES light come on or stay on while trying to start or when driving the vehicle?
Have you checked for DTC's, (Diagnostic Trouble Codes)? If so, what are they?

The camshaft position sensor will not affect the problem you're having. DO NOT replace the crankshaft position sensor unless there is a DTC indicating a problem with it, AND following the flow chart specifically instructs you to replace it.

 

Captain Hook, the SES light comes on when I turn on the ignition and goes off when cranking. The only code it has had was a p0507. I found a vacum leak and the code hasn't come back.

 

When the engine is cold, check fuel pressure and leakdown. When you initially turn the ignition to the RUN position, the fuel pump is activated for ~2 seconds and then deactivates. Fuel pressure must be checked during the 2 second time frame when the pump is running. Key ON, engine OFF, fuel pump running: Pressure must be 60psi to 66psi and must remain above 55psi for at least 10 minutes after the pump shuts off. Post your results. BTW, how did you check for injector pulse?

 

Fuel pressure is 65 psi and holds for 15 minutes at least. (Didn't check it after that). I used a noid light to check the pulse.

 

You checked for pulse on all 6 injector circuits?

 

Just one. I waited for a no start condition, pulled the trottle body and checked #1.

 

Something is screwy here. If there is no injector pulse, (on one or multiple cylinders), there will be a DTC in memory and the SES light will be on. If the SES light works, as you say it does, and it's not on while the engine is running, and no DTC's are in memory, that means something that is not monitored by the PCM is causing the problem. Fuel pressure is not monitored so it can't set a DTC if there's something wrong with it. Recheck fuel pressure and leakdown when the engine is cold, post #4 explains how to check it. Post the results. BTW, why would you pull the throttle body to check for injector pulse?

 

I played with it all day and it started every time. I got a new fuel pressure gauge, mine was 20 years old and I didn't trust it. The new gauge shows 90 psi (100 running) and stays above 80 for 30 minutes. I didn't trust that reading so I borrowed another gauge and it reads the same. I tested the noid light I was using and it's bad so I'm not sure if I have a pulse or not. I'm going to drive it to work tommorow and there will be frequent short stops. I'll leave the gauge on it so I can see if there's a fuel pressure problem if it won't start. The weather was much cooler today (high of 67) so that may have something to do with it starting all day. Do you think the high pressure could be the problem? It doesn't act flooded. Also, the dtc p0507 came back and I found another vacum leak. So far it hasn't come back.

 

If you had it running, rest assured that you have injector pulse Fuel pressure is definitely a problem! As for your 90psi reading... Did you check fuel pressure exactly as described in post #4? If key on, engine off pressure is in fact 90psi, anything above 75psi can/will rupture the diaphragm in the fuel pressure regulator. Do not replace the regulator until the cause of the excess pressure is located and repaired. After it's repaired, check regulated pressure to make sure the regulator is functioning properly.

The 100psi reading, (engine running) is a huge problem. Maximum fuel pump output pressure is typically between 73psi and 108psi. Yours is very close to that indicating there's probably a restriction in the fuel return line. Check the fuel return line for a restriction somewhere between the regulator and the fuel tank. It might be kinked, or it may have been mistakenly connected to the vapor fitting, (instead of the return fitting) on the fuel pump module. If you disconnect the return line at the rear of the plenum, you should be able to blow into it very easily, (back to the tank) if not, find and fix the restriction.

High fuel pressure could explain most, if not all, of the problems you're experiencing.