97 S10 Blazer Hard Cold Start Problem


Pilot423
10-14-2009, 11:48 AM
Two major problems with my 1997 S10 Blazer 4.3. It has become increasingly difficult to start cold. If I give up and wait 5-10 minutes it will grudgingly start. I replaced the temp sensor with no joy.

Also, once warm, the transmission will not downshift, and starts from 3rd gear at a standing stop. If I shut the truck off, wait a few minutes, it will start out in first gear a couple of times, and then go back to taking off in 3rd. gear again. I'm getting the P0785 OBD code, but a lot of forum members seem to think it's the ignition swith or the ECM. How can I narrow it down? I hate to invest too much in this truck. But other than those two problems, it's in great shape and runs well with almost 140,000 miles.

MT-2500
10-14-2009, 03:01 PM
Two major problems with my 1997 S10 Blazer 4.3. It has become increasingly difficult to start cold. If I give up and wait 5-10 minutes it will grudgingly start. I replaced the temp sensor with no joy.

Also, once warm, the transmission will not downshift, and starts from 3rd gear at a standing stop. If I shut the truck off, wait a few minutes, it will start out in first gear a couple of times, and then go back to taking off in 3rd. gear again. I'm getting the P0785 OBD code, but a lot of forum members seem to think it's the ignition swith or the ECM. How can I narrow it down? I hate to invest too much in this truck. But other than those two problems, it's in great shape and runs well with almost 140,000 miles.

Code P0785 is for the 3-2 shift solenoid electrical problem.
Check plug in and wiring to it.
Check for 12 volts to it key on.
If voltage to it and wires are good replace solenoid.

On the hard to start cold run a fuel pressure check.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

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